Re: 콩 발효제품(된장, 미소, 나토, 청국장, 템페, 통림바이) 탐구!! 2022

[문형철]

Microorganisms

. 2022 Aug 9;10(8):1606. doi: 10.3390/microorganisms10081606

Fermented Soy Products and Their Potential Health Benefits: A Review

Fernanda Guilherme do Prado 1, Maria Giovana Binder Pagnoncelli 2, Gilberto Vinícius de Melo Pereira 1,*, Susan Grace Karp 1, Carlos Ricardo Soccol 1,*

Editors: Anna Reale, Andrea Osimani

• Author information
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PMCID: PMC9416513  PMID: 36014024

Abstract

In the growing search for therapeutic strategies, there is an interest in foods containing natural antioxidants and other bioactive compounds capable of preventing or reversing pathogenic processes associated with metabolic disease. Fermentation has been used as a potent way of improving the properties of soybean and their components. Microbial metabolism is responsible for producing the β-glucosidase enzyme that converts glycosidic isoflavones into aglycones with higher biological activity in fermented soy products, in addition to several end-metabolites associated with human health development, including peptides, phenolic acids, fatty acids, vitamins, flavonoids, minerals, and organic acids. Thus, several products have emerged from soybean fermentation by fungi, bacteria, or a combination of both. This review covers the key biological characteristics of soy and fermented soy products, including natto, miso, tofu, douchi, sufu, cheonggukjang, doenjang, kanjang, meju, tempeh, thua-nao, kinema, hawaijar, and tungrymbai. The inclusion of these foods in the diet has been associated with the reduction of chronic diseases, with potential anticancer, anti-obesity, antidiabetic, anticholesterol, anti-inflammatory, and neuroprotective effects. These biological activities and the recently studied potential of fermented soybean molecules against SARS-CoV-2 are discussed. Finally, a patent landscape is presented to provide the state-of-the-art of the transfer of knowledge from the scientific sphere to the industrial application.

치료 전략에 대한 연구가 활발히 진행되는 가운데, 

대사 질환과 관련된 병리적 과정을 예방하거나 역전시킬 수 있는 

천연 항산화 물질과 기타 생물활성 화합물을 함유한 식품에 대한 관심이 증가하고 있습니다. 

발효는 

대두 및 그 성분의 특성을 개선하는 강력한 방법으로 활용되어 왔습니다. 

미생물 대사 과정은 발효된 대두 제품에서 

글리코시드 이소플라본을 생물학적 활성이 높은 아글리콘으로 전환하는 β-글루코시다제 효소를 생성하며, 

인간 건강 발달과 관련된 여러 최종 대사산물(펩타이드, 페놀산, 지방산, 비타민, 플라보노이드, 미네랄, 유기산 등)도 

생성됩니다. 

peptides, phenolic acids, fatty acids, vitamins, flavonoids, minerals, and organic acids

따라서 

곰팡이, 세균, 또는 이들의 조합을 통해 

대두 발효로부터 다양한 제품이 개발되었습니다. 

이 리뷰는 대두와 발효 대두 제품의 주요 생물학적 특성을 포함하여 

나토, 미소, 두부, 두치, 수부, 청국장, 된장, 간장, 메주, 템페, 투아-나오, 키네마, 하와이저, 통림바이 등을 다룹니다. 

natto, miso, tofu, douchi, sufu, cheonggukjang, doenjang, kanjang, meju, tempeh, thua-nao, kinema, hawaijar, and tungrymbai.

tempeh

이 식품들의 식이 섭취는 만성 질환 감소와 연관되어 있으며, 

항암, 항비만, 항당뇨, 항콜레스테롤, 항염증, 신경 보호 효과 등 잠재적 효능이 보고되었습니다.

이러한 생물학적 활성과 최근 연구된

발효 대두 분자의 SARS-CoV-2에 대한 잠재적 효과도 논의됩니다.

마지막으로,

과학적 연구에서 산업적 응용으로의 지식 이전 현황을 파악하기 위해

특허 동향 분석이 제시됩니다.

Keywords: oxidative stress, fermented soybean foods, bioactive compounds, genistein, daidzein

1. Introduction

Oxidative stress (OS) is related to biologically harmful impacts of free radicals presenting itself as an imbalance between oxidants and antioxidants. During normal metabolic and oxidation processes, free radicals are released and, when excessive in the body, they cause oxidative damage to proteins, lipids, DNA, and RNA. Their deleterious effects include the attack on healthy cells leading to cell death and causing chronic diseases and premature aging. Continuous oxidative damage prevents the activity of a biological system, weakening the body’s defense mechanism [1,2]. Thus, the balance of the operating system in the body has a critical role in the beginning and/or development of various pathologies. Dietary factors with oxidants and antioxidants are reported to be responsible for altering the operating system in the body and improving the host’s antioxidant defense system [3].

Chronic diseases such as cancer [4], cardiovascular diseases [5], neurodegenerative disorders [6], metabolic syndrome [7], and inflammatory diseases [8], are associated with oxidative stress. The prevention or delay of these disorders can be related to the consumption of products with potent antioxidants. Fermented foods, green and red teas [9], grape seed [10], broccoli [11], soybean [12], goat milk [13], common bean [14], and others are examples of foods containing antioxidant components.

Correlated to a series of beneficial health effects, fermented foods appear as a promising alternative due to the presence of many compounds with bioactive properties including antioxidants. These promoting actions are credited to the metabolic and biotransformation activities carried out by microorganisms during the fermentation process [15]. Thus, the beneficial effects of eating fermented soybean foods on OS have been widely mentioned [16,17]. The main biological-associated components includes soybean isoflavones, flavonoids such as coumestans, non-flavonoids such as lignans, stilbenes, β-carotene, and anthocyanidins and polyphenols [18,19]. Compounds that have phytoestrogen and antioxidant functions. Several studies show the in vitro and in vivo antioxidant impacts of isoflavones, which directly suppress free radicals. The aglycone forms genistein and daidzein, found in greater quantities after fermentation, are mainly effective in suppressing reactive oxygen species (ROS) [17,20,21].

In addition to the antioxidant effects, other bioactive properties are conferred to fermented soy products, such as immunomodulatory, anticancer activity, prevention of cardiovascular diseases, the pathophysiology of Alzheimer’s disease, and cholesterol reduction [22,23,24,25]. The present review aims to provide an overview of the effect of soybean food fermentation and discuss its properties and performance of bioactive compounds.

1. 서론

산화 스트레스(OS)는

산화제와 항산화제의 불균형으로 나타나는

자유 라디칼의 생물학적 유해 영향과 관련이 있습니다.

정상적인 대사 및 산화 과정에서 자유 라디칼이 생성되며,

체내에서 과도하게 축적될 경우 단백질, 지질, DNA, RNA 등에 산화 손상을 입힙니다.

이들의 유해한 영향에는

건강한 세포에 대한 공격으로 세포 사멸을 유발하고

만성 질환 및 조기 노화를 초래하는 것이 포함됩니다.

지속적인 산화 손상은

생물학적 시스템의 활동을 방해하여 신체 방어 메커니즘을 약화시킵니다 [1,2].

따라서

신체 내 운영 시스템의 균형은 다양한 병리의 발생 및/또는 진행에 결정적인 역할을 합니다.

산화제와 항산화제를 포함한 식이 요인이

신체 내 운영 시스템을 변화시키고 호스트의 항산화 방어 시스템을 개선하는 데

기여한다는 보고가 있습니다 [3].

암 [4], 심혈관 질환 [5], 신경퇴행성 장애 [6], 대사증후군 [7], 염증성 질환 [8] 등 만성 질환은

산화 스트레스와 연관되어 있습니다.

이러한 질환의 예방 또는 지연은

강력한 항산화 성분을 함유한 제품의 섭취와 관련될 수 있습니다.

발효 식품,

녹차와 홍차 [9], 포도씨 [10], 브로콜리 [11],

콩 [12], 염소 우유 [13], 일반 콩 [14] 등은

항산화 성분을 함유한 식품의 예시입니다.

다양한 건강에 유익한 효과와 연관되어 발효 식품은

많은 생물활성 성분,

특히 항산화 성분을 함유하고 있어 유망한 대안으로 부상하고 있습니다.

이러한 촉진 작용은

발효 과정에서 미생물이 수행하는 대사 및 생물전환 활동에 기인합니다 [15].

따라서

발효 대두 식품 섭취가

산화 스트레스(OS)에 미치는 유익한 효과는 널리 언급되어 왔습니다 [16,17].

주요 생물학적 관련 성분에는

대두 이소플라본, 쿠메스탄과 같은 플라보노이드, 리간, 스틸벤, 베타-카로틴,

안토시아니딘 및 폴리페놀 [18,19]이 포함됩니다.

식물성 에스트로겐과 항산화 기능을 가진 화합물입니다.

여러 연구에서 이소플라본의 체외 및 체내 항산화 효과가 자유 라디칼을 직접 억제하는 것으로 나타났습니다.

발효 후 더 많은 양으로 발견되는

아글리콘 형태인 제니스틴과 다이제인은

반응성 산소 종(ROS) 억제에 주로 효과적입니다 [17,20,21].

항산화 효과 외에도 발효된 대두 제품에는

면역 조절, 항암 활동, 심혈관 질환 예방, 알츠하이머 병의 병리생리학, 콜레스테롤 감소 등

다른 생물학적 활성 특성이 부여됩니다 [22,23,24,25].

본 리뷰는

대두 식품 발효의 효과를 개괄하고

생물학적 활성 화합물의 특성 및 성능을 논의하는 것을 목적으로 합니다.

2. Soybean

Soybean (Glycine max) is one of the most widely grown oilseed crops in the world and one of the cheapest and most abundant sources of vegetable protein consumed as a food and dietary supplement [26]. The soybean has in its composition about 40% protein, 20% lipids, 35% carbohydrates, 5% minerals, and 10% moisture, in addition to other compounds such as fatty acids, vitamins, flavonoids, isoflavones, phenolic acids, and saponins [27,28].

In the context between global supply and demand for food, soy stands out for being a highly nutritious grain capable of providing a range of by-products for human consumption, in addition to attributing an important role in the production of animal protein (chicken, pork, and beef) [29]. Of the world oilseed production, 60% corresponds to soy and, of this total, only 6% is consumed in the form of whole grains, whole grains, and fermented products. The remaining 94% is processed industrially, being transformed into oil for human consumption, production of biodiesel, and development of chemicals, food, and cosmetics (18–20% of this total). The remainder crushed is usually transformed into protein-rich bran used for animal feed [30].

The world soybean production in the 2019/2020 harvest was estimated by the U.S. Department of Agriculture (USDA) at 337.298 million tons, in a total world area occupied by the cultivation of 122.647 million hectares, corresponding to the average productivity of 2.750 kg/ha [31]. The largest suppliers are Brazil (124.84 million tons), the United States (96.67 million tons), and Argentina (50 million tons), with a total planted area of 36.950, 30.33, and 17.1 million hectares, respectively. In Brazil, the average productivity was 3.379 kg/ha, while in the United States and Argentina the value was 3.187 kg/ha and 2.92 kg/ha, respectively (Figure 1) [31,32].

2. 대두

대두(Glycine max)는

세계에서 가장 널리 재배되는 기름씨 작물 중 하나이며,

식품 및 식이 보충제로 소비되는 가장 저렴하고 풍부한 식물성 단백질 원천 중 하나입니다 [26].

대두는 구성 성분으로

약 40%의 단백질, 20%의 지방, 35%의 탄수화물, 5%의 무기질, 10%의 수분,

그리고 지방산, 비타민, 플라보노이드, 이소플라본, 페놀산, 사포닌 등 기타 화합물을 포함합니다 [27,28].

전 세계 식품 공급과 수요의 맥락에서 대두는

인간 소비를 위한 다양한 부가 제품을 제공할 수 있는 고영양 곡물로 돋보이며,

동물 단백질 생산(닭고기, 돼지고기, 소고기)에 중요한 역할을 합니다 [29].

세계 유채 작물 생산량의 60%가 대두에 해당하며,

이 중 전체 곡물, 발효 제품 형태로 소비되는 비율은 6%에 불과합니다.

남은 94%는 산업적으로 가공되어

인간 소비용 오일, 바이오디젤 생산, 화학물질, 식품, 화장품 개발(이 중 18–20%)에 사용됩니다.

나머지 분쇄된 부분은 일반적으로 동물 사료로 사용되는

단백질 풍부한 껍질로 가공됩니다 [30].

2019/2020 수확기 세계 대두 생산량은 미국 농무부(USDA)에서 3억 3,729만 8,000톤으로 추정되었으며, 이는 전 세계 재배 면적 1억 2,264만 7,000헥타르에 해당되며, 평균 생산량은 2.750kg/ha입니다 [31]. 주요 공급국은 브라질(1억 2,484만 톤), 미국(9,667만 톤), 아르헨티나(5,000만 톤)로, 각각 3,695만, 3,033만, 1,710만 헥타르의 재배 면적을 차지합니다. 브라질의 평균 생산량은 3.379kg/ha였으며, 미국과 아르헨티나는 각각 3.187kg/ha와 2.92kg/ha였습니다 (그림 1) [31,32].

Figure 1.

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Production, productiveness, and total planted area in hectares of soybean in 2019/2020.

2020/2021 was considered the largest soy harvest in history, with an estimated world production of 362.85 million tons, which corresponds to an 8% increase compared to the previous harvest (Table 1). The projection still consists of an increase in exports, imports, animal, and domestic consumption. Thus, the estimated value of the final world stock fell by 2%, reaching 98.39 million tons [31].

Table 1.

Estimated global supply and demand for soybeans in the 2020/2021 harvest (in millions of tons).

Initial StockProductionExportImportAnimal ConsumptionDomestic ConsumptionFinal Stock

100.27	362.76	312.80	158.02	360.73	161.93	98.39
−11%	8%	4%	3%	4%	5%	−2%

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USDA projects the 2021/22 world soybean crop at 372.56 million tons. Brazil remains the world’s largest producer; however, the forecast was cut from 144 million, in the previous bulletin, to 139 million tons. Brazilian ending stocks of soy were also reduced from 28.25 to 23.55 million tons but estimates for Brazilian soy exports were maintained at 94 million tons. Argentina’s production was also projected to fall by 46.5 million tons, a cut of 3 million from the previous report. For the US, the USDA brought a slight increase from 120.45 to 120.7 million tons [33].

Asian countries are characterized by high grain consumption. In recent years, due to increased demand and domestic supply, China has become the largest importer of soybeans, accounting for more than 60% of world soy trading. It is because Chinese production accounts for only 20% of domestic demand and a large amount of soy is needed to supply pork feed. Compared to other crops, the application of soy resources is potentially greater, taking the efficiency of land use as follows: a soybean yield of 3000 kg/ha becomes a product to produce 343 kg of beef, 600 kg of swine, or 1200 kg of birds. In the absence of soybean meal, production dropped to 250 kg of beef [34,35].

In Europe, soybean cultivation is mainly in the southern and eastern regions, but still plays a minor role due to the higher latitudes with relatively cool conditions [36]. One important reason for expanding soybean cultivation into central and northern growing areas is the high demand for soy protein in Europe, which would require 9–12% of its arable land to be sown to soybeans [37].

In the 2020/2021 harvest, there is an estimate for Chinese imports of 96 million tons. Brazil also assumes the position of largest grain exporter, with more than 60% of the harvest destined for this purpose. Motivated by the high Chinese demand and the percentage, Brazilian exports are expected to reach 83 million tons. The global export forecast is 312.80 million tons, of which 55.8 million tons are from the United States and only 6.5 million tons from Argentina (Figure 2) [31].

미국 농무부(USDA)는 2021/22년 세계 대두 생산량을 3억 7,256만 톤으로 전망했습니다. 브라질은 여전히 세계 최대 생산국으로 유지되지만, 이전 보고서에서 1억 4,400만 톤으로 예상되었던 생산량은 1억 3,900만 톤으로 하향 조정되었습니다. 브라질의 대두 최종 재고량은 2,825만 톤에서 2,355만 톤으로 감소했지만, 브라질의 대두 수출 전망은 9,400만 톤으로 유지되었습니다. 아르헨티나의 생산량은 이전 보고서 대비 300만 톤 감소한 4,650만 톤으로 전망되었습니다. 미국에 대해서는 USDA가 120.45만 톤에서 120.7만 톤으로 소폭 증가시켰습니다 [

아시아 국가들은 높은 곡물 소비로 특징지어집니다. 최근 몇 년간 수요 증가와 국내 공급 확대로 중국은 세계 대두 무역의 60% 이상을 차지하는 최대 수입국이 되었습니다. 이는 중국 생산량이 국내 수요의 20%만을 충족시키며, 돼지 사료 공급을 위해 대규모 대두가 필요하기 때문입니다. 다른 작물과 비교할 때 대두 자원의 활용 잠재력은 더 크며, 토지 이용 효율성을 다음과 같이 고려할 수 있습니다: 1ha당 3,000kg의 대두 수확량은 343kg의 소고기, 600kg의 돼지고기, 또는 1,200kg의 가금류 제품을 생산할 수 있습니다. 대두 분말이 없는 경우 생산량은 250kg의 소고기로 감소합니다 [34,35].

유럽에서는 대두 재배가 주로 남부 및 동부 지역에서 이루어지지만, 상대적으로 차가운 기후 조건으로 인해 여전히 작은 역할을 합니다 [36]. 대두 재배를 중앙 및 북부 재배 지역으로 확장하는 주요 이유 중 하나는 유럽의 대두 단백질 수요 증가로, 이는 경작지의 9–12%를 대두 재배에 할당해야 할 것으로 추정됩니다 [37].

2020/2021 수확기에는 중국 수입량이 96백만 톤으로 추정됩니다. 브라질도 최대 곡물 수출국으로 자리매김했으며, 수확량의 60% 이상이 수출용으로 공급됩니다. 중국 수요와 비중에 힘입어 브라질 수출량은 8300만 톤에 달할 것으로 예상됩니다. 전 세계 수출 전망은 3억 1280만 톤으로, 이 중 5580만 톤은 미국에서, 아르헨티나에서는 65만 톤만이 수출될 것으로 예상됩니다 (그림 2) [31].

Figure 2.

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Soybean production and export of largest producers and estimate for imports in the 119 2020/2021 harvest.

Plant genotype, location, climate, water, and maturity group are responsible for the quality characteristics of soy, e.g., protein, oil, fatty acids, soluble sugars, and isoflavones. The grain consists of 8% husks, 90% cotyledons, and 2% hypocotyls. The protein composition of the soybean grain on a dry basis is on average 40% (Table 2). The storage of proteins occurs in the intermediate layers of the grain, cotyledons, and hypocotyls. In the shell, the outer layer, there are greater amounts of carbohydrates cellulosic material [38,39].

2020/2021 수확기 최대 생산국의 대두 생산량 및 수출량과 수입량 추정.

콩의 품질 특성(예: 단백질, 기름, 지방산, 수용성 당분, 이소플라본)은 식물 유전자형, 재배 지역, 기후, 물, 성숙 그룹에 의해 결정됩니다. 콩 알갱이는 껍질 8%, 씨방 90%, hypocotyl 2%로 구성됩니다. 건조 기준 콩 종자의 단백질 함량은 평균 40%입니다(표 2). 단백질은 종자의 중간층, 엽고체, 및 hypocotyl에 저장됩니다. 껍질의 외층에는 탄수화물 셀룰로오스 물질이 더 많이 포함되어 있습니다[38,39].

Table 2.

Nutritional composition of soybean.

Components% GrainChemical Composition (% Dry Weight)ProteinsLipidsCarbohydratesOthers *

Husks	8	9	1	86	4.3
Hypocotyls	2	41	11	43	4.4
Cotyledons	90	43	23	29	5.0
Total	100	40	20	35	5.0

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* Minerals, vitamins, phytates, and isoflavones.

In addition to the high protein content, the soybean contains other bioactive and remarkably rich components, such as isoflavones, anthocyanins, and saponins. They are compounds known to have antioxidant capacity that is related to different health health benefits [40,41].

3. Fermented Soybean Products

The production and consumption of fermented soy are widespread in Asian countries. The main soybean products include natto, miso, tofuyo (Japan), douchi, sufu (China), cheonggukjang, doenjang, kanjang and meju (Korea), tempeh (Indonesia), thua-nao (Thailand), kinema, hawaijar, tungrymbai (India) (Figure 3), in addition to other widely consumed products, such as sauce, pasta, and soybean milk [42]. Records of some production methods were found in Cheminyoshul, a Chinese manuscript dating back to 530–550 dC, and others in the Korean manuscript Samkuksaki, dating from the 1392s, pointing to the consumption of fermented soybeans since the 12th century [43].

3. 발효 콩 제품

발효된 대두의 생산과 소비는 아시아 국가에서 널리 퍼져 있습니다.

주요 대두 제품에는

나토, 미소, 토후요(일본), 두치, 수푸(중국), 청국장, 된장, 간장, 메주(한국), 템페(인도네시아), 투아-나오(태국), 키네마, 하와이자르, 툭림바이(인도) (그림 3), 또한 소스, 파스타, 콩 우유 등 널리 소비되는 다른 제품들도 있습니다 [42].

일부 제조 방법은 530–550년경의 중국 문헌 《Cheminyoshul》과 1392년경의 한국 문헌 《Samkuksaki》에 기록되어 있으며, 이는 12세기부터 발효된 콩의 소비가 이루어졌음을 보여줍니다 [43].

Figure 3.

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Products fermented soy in Asian countries.

The large consumption of soybeans in Asian countries is related to the widespread adoption of grain cultivation. The variety of appropriate climates and geographic regions resulted in highly sizable crops, making soybean a staple in the region. With insufficient meat consumption, these fermented foods played a vital role as a source of protein in the Asian diet [44,45].

In ancient times, the basic idea behind soybean fermentation was the preservation of food. In the current perspective, the research is interested and directed to the application of fermentation to improve the bioactive components of soybean, responsible for health benefits, and reduce anti-nutritional factors [46,47].

The difference between fermented soybeans is based on several parameters, but mainly due to the microorganism used in the process. Thus, fermented soybean products are different in terms of aroma, texture, and therapeutic and nutraceutical values. Some fermentations occur only with bacteria, others using only filamentous fungi, and, in many cases, both these microbial groups are used. Some products are fermented only with Bacillus (natto, kinema, chungkookjang); some are fermented with fungi Aspergillus oryzae, Mucor spp. Rhizopus spp. and Fusarium spp. (douchi, tempeh, miso, tofu) and in some cases both microorganisms are used, as in the case of doenjang, where the bacteria involved in this process would be B. subtilis and fungi include Rhizopus spp., Mucor spp., Geotrichum spp., and Aspergillus spp. [42,48,49,50,51].

Soybean protein and isoflavones are the main functional constituents of fermented soybean foods. Soybean consists of one of the plant sources with the highest abundance of isoflavones. Because their chemical structure is similar and has an affinity for estrogen receptors, these compounds are usually called phytoestrogens [52,53].

The native forms of isoflavones have their bioavailability compromised because they are usually combined with sugars that minimize their absorption through the human intestinal tract. Isoflavones are categorized into two groups: glycosides and aglycone. The beneficial and functional effects of isoflavones on health are conferred to their aglycone forms, which are absorbed more quickly by the human body. In unfermented soybean, the presence of aglycone isoflavones is 2–3% of the total composition—this content being mainly corresponded to β-glucoside isoflavones [54,55,56].

Thus, the biotransformation of glycosidic forms into aglycones through fermentation is a desirable process to increase and produce more biologically active forms. In fermented soy products, the aglycone values vary from 40 to 100%. The conversion of the glycoside into isoflavone aglycones occurs through the action of β-glycosidase produced by microorganisms during the fermentation process. In addition to a higher absorption rate, aglycone forms have greater antioxidant activity than glycosidic forms. This explains the fact that the consumption of fermented soybean products in Asian countries is associated with the reduction of chronic diseases since the consumption of natural antioxidants is efficient in reducing the harmful impacts of reactive oxygen species (ROS) and in adjusting the body’s antioxidant load [57,58,59].

Soy protein fraction has many inhibitory enzymes, such as proteinase and trypsin, which make them less digestible. During fermentation, proteolytic enzymes generated by microbial populations hydrolyze proteins into peptides and free amino acids responsible for antioxidant activity and increasing the digestibility of soybean protein [60,61].

In addition to proteins and isoflavones, soybean is made up of numerous other functional and nutritional substances, such as fatty acids, vitamins, peptides, minerals, flavonoids, phenolic acids, and saponins [62].

Natto consists of a popular and traditional food in Japan that has been consumed since the 17th century and produced by fermenting soybeans cooked with strains of Bacillus subtilis var natto. It is known to have large amounts of peptides because, in the fermentation process, proteins are cleaved by extracellular proteases produced by the Bacillus strain, which increases the free amino acid content by 10% to 30%. Studies report that the proteins derived from this food consist of at least seventeen different amino acids, including glutamic acid, glutamine, aspartic acid, leucine, proline, serine, lysine, methionine, threonine, glycine, isoleucine, tyrosine, phenylalanine, histidine, arginine, alanine, and valine [63,64]. The consumption of natto has been shown to have an anti-aging effect, prolonging life expectancy, due to the metabolites found in natto extracts, for example, the enzyme nattokinase. Often, reduced life expectancy is caused by oxidative stress, and the relatively high antioxidant activities of natto are mentioned [65].

Miso is a fermented soybean paste, prepared from steamed soy, salt, and koji—cooked cereal or soy malted with Aspergillus oryzae. It is a traditional Japanese spice used to add flavor to soups and dishes consumed at breakfast by most Japanese families for over 1000 years. The process of maturation of the Miso takes from three to twenty-four months and involves different microorganisms, such as molds, yeasts and, lactic acid bacteria, which act by hydrolyzing the components of [66,67]. There are different types of miso, which vary according to local traditions and available ingredients; and this food can be classified according to the koji used: (1) rice miso, made by adding rice koji to soy; (2) barley miso with the addition of barley koji to soy and soy miso, made only with soybean. It is reported that during the miso ripening process, the peptides formed are made up of 3–20 amino acids and still include amino acids such as glutamic acid, aspartic acid, and proline [68,69].

Tofu is a Japanese fermented soy curd similar to cream cheese—a characteristic that results from the ripening or maturation process by proteases, carbohydrases, and other catabolic enzymes found in red koji (Monascus fungus) or koji yellow (Aspergillus oryzae), used in the preparation of this food together with tofu (vegetable cheese based on soybean) [50,70]. Its functional properties were investigated and associated with the presence of bioactive peptides. Thus, tofu came to be seen not only as a nutritional accompaniment but becoming a valuable source of protein [71,72].

Douchi is a popular product consumed for at least 2000 years by the Chinese, as a source of protein and flavoring ingredient. The preparation of the douchi is carried out in two stages: pre-fermentation, which consists of an aerobic process using several microorganisms as the starter culture (for example, Aspergillus oryzae, Zygosaccharomyces rouxii, Lactobacillus plantarum, Bacillus subtilis) and takes 12–15 days; and post-fermentation, where the addition and mixing of salt and other spices is carried out and left for 9 months in anaerobic fermentation, a process where the development of the special nutrients and flavor of the douchi occurs [73,74]. In recent years, douchi has attracted attention as a functional food source. Some studies have revealed the benefits of this food to health, including antioxidants, antihypertensive activity and even lowering blood pressure [75,76].

Mentioned as “Chinese cheese” due to its texture, sufu is a traditional fermented soy product that has been used as a flavor enhancer and appetizer. There are different types of sufu, which are produced by various processes in different locations in China through microbial fermentation, and based on the types of starter culture; sufu can be classified into fungi fermented sufu (inoculated with Actinomucor, Mucor or Rhizopus), sufu fermented by bacteria (inoculated with Bacillus or Micrococcus), and others (naturally inoculated) [77,78].

아시아 국가에서 발효된 콩 제품.

아시아 국가에서의 콩 소비량이 많은 것은 곡물 재배의 광범위한 확산과 관련이 있습니다. 다양한 기후 조건과 지리적 지역은 대규모 작물 생산을 가능하게 했으며, 이로 인해 콩은 해당 지역에서 주요 식량 작물로 자리 잡았습니다. 육류 소비가 부족한 상황에서 이러한 발효 식품은 아시아 식단에서 단백질 공급원으로 중요한 역할을 했습니다 [44,45].

고대에는 콩 발효의 기본 개념은 식품의 보존이었습니다. 현재의 관점에서 연구는 건강에 유익한 콩의 생리 활성 성분을 개선하고 영양 방해 요인을 줄이기 위해 발효를 적용하는 데 관심이 집중되어 있습니다 [46,47].

발효 콩의 차이는 여러 가지 요인에 따라 다르지만, 주로 발효 과정에 사용되는 미생물에 따라 달라집니다. 따라서 발효된 콩 제품은 향, 텍스처, 치료적 및 영양학적 가치 측면에서 차이가 있습니다. 일부 발효는 세균만 사용되며, 다른 일부는 필라멘트성 곰팡이만 사용되며, 많은 경우 두 미생물 그룹이 함께 사용됩니다. 일부 제품은 Bacillus (나토, 키네마, 충국장)만으로 발효되며, 일부는 Aspergillus oryzae, Mucor spp. Rhizopus spp. 및 Fusarium spp. (두치, 템페, 미소, 두부)와 같은 곰팡이와 함께 사용되며, 일부 경우 두 미생물이 함께 사용됩니다. 예를 들어, 된장에서는 이 과정에 관여하는 세균은 B. subtilis이며, 곰팡이에는 Rhizopus spp., Mucor spp., Geotrichum spp., 및 Aspergillus spp.가 포함됩니다. [42,48,49,50,51].

대두 단백질과 이소플라본은 발효 대두 식품의 주요 기능성 성분입니다. 대두는 이소플라본 함량이 가장 높은 식물 원료 중 하나입니다. 이 화합물은 화학 구조가 유사하고 에스트로겐 수용체와 친화성을 가지고 있어 일반적으로 식물성 에스트로겐으로 불립니다 [52,53].

이소플라본의 원형은 당분과 결합되어 인간 장관에서 흡수율이 저하되기 때문에 생체 이용률이 제한됩니다. 이소플라본은 글리코시드와 아글리콘 두 그룹으로 분류됩니다. 이소플라본의 건강에 대한 유익한 기능적 효과는 인간 몸에 더 빠르게 흡수되는 아글리콘 형태에 기인합니다. 발효되지 않은 대두에서는 아글리콘 이소플라본의 함량이 총 구성의 2–3%이며, 이 중 대부분은 β-글루코사이드 이소플라본에 해당됩니다 [54,55,56].

따라서 발효를 통해 글리코시드 형태가 아글리콘으로 전환되는 생물학적 변환 과정은 생물학적 활성이 높은 형태를 증가시키고 생산하는 데 바람직한 과정입니다. 발효된 대두 제품에서 아글리콘 함량은 40~100% 사이로 다양합니다. 글리코시드가 이소플라본 아글리콘으로 전환되는 과정은 발효 과정에서 미생물이 생성하는 β-글루코시다제의 작용에 의해 이루어집니다. 글리코시드 형태에 비해 아글리콘 형태는 흡수율이 더 높으며 항산화 활성도 더 강합니다. 이는 아시아 국가에서 발효 대두 제품의 섭취가 만성 질환 감소와 연관된 이유를 설명합니다. 자연 항산화제의 섭취는 활성 산소 종(ROS)의 유해한 영향을 줄이고 신체 항산화 부하를 조절하는 데 효율적이기 때문입니다 [57,58,59].

대두 단백질 분획은 프로테아제와 트립신과 같은 많은 억제 효소를 포함하여 소화율이 낮습니다. 발효 과정에서 미생물 군집에 의해 생성된 단백질 분해 효소는 단백질을 항산화 활성을 담당하고 대두 단백질의 소화율을 높이는 펩타이드와 자유 아미노산으로 가수분해합니다 [60,61].

단백질과 이소플라본 외에도 대두는 지방산, 비타민, 펩타이드, 미네랄, 플라보노이드, 페놀산, 사포닌 등 다양한 기능성 및 영양 성분을 함유하고 있습니다 [62].

나토는 17세기부터 일본에서 소비되어 온 전통적인 식품으로, Bacillus subtilis var natto 균주로 발효된 콩으로 만들어집니다. 발효 과정에서 Bacillus 균주가 생성하는 세포외 단백질 분해 효소에 의해 단백질이 분해되어 자유 아미노산 함량이 10%에서 30%까지 증가하기 때문에 펩타이드 함량이 높은 것으로 알려져 있습니다. 연구 결과, 이 식품에서 유래한 단백질은 글루탐산, 글루타민, 아스파르트산, 류신, 프로린, 세린, 라이신, 메티오닌, 트레오닌, 글리신, 이소류신, 티로신, 페닐알라닌, 히스티딘, 아르기닌, 알라닌, 발린 등 최소 17종의 다양한 아미노산으로 구성되어 있습니다 [63,64]. 나토의 섭취는 나토 추출물에서 발견되는 대사산물, 예를 들어 나토키나제 효소 때문에 노화 방지 효과와 수명 연장 효과가 있는 것으로 나타났습니다. 수명 단축은 종종 산화 스트레스에 의해 유발되며, 나토의 상대적으로 높은 항산화 활동이 언급됩니다 [65].

미소는 찐 콩, 소금, 그리고 아스페르길루스 오리자에 의해 발효된 곡물이나 콩 맥아로 만든 발효 콩 페이스트입니다. 이는 일본 전통 향신료로, 대부분의 일본 가정에서 아침 식사에 먹는 수프와 요리에 맛을 내기 위해 1000년 이상 사용되어 왔습니다. 미소의 숙성 과정은 3개월에서 24개월까지 소요되며, 곰팡이, 효모, 젖산균 등 다양한 미생물이 작용하여 성분을 가수분해합니다[66,67]. 미소는 지역 전통과 사용 가능한 재료에 따라 다양한 유형으로 나뉘며, 사용된 코지에 따라 다음과 같이 분류됩니다: (1) 쌀 미소: 콩에 쌀 코지를 추가하여 만들며, (2) 보리 미소: 콩에 보리 코지를 추가하여 만들며, 콩 미소는 콩만 사용하여 만듭니다. 미소 숙성 과정에서 형성되는 펩타이드(peptides)는 3~20개의 아미노산으로 구성되며, 글루탐산, 아스파르트산, 프로린과 같은 아미노산을 포함합니다[68,69].

두부는 일본식 발효 콩 커드로서 크림 치즈와 유사한 특성을 지니며, 이는 적색 코지(Monascus 균류) 또는 노란 코지(Aspergillus oryzae)에 함유된 프로테아제, 카르보히드라제 등 분해 효소에 의한 숙성 또는 성숙 과정으로 인해 발생합니다. 이 식품은 두부(콩을 원료로 한 식물성 치즈)와 함께 제조됩니다 [50,70]. 그 기능적 특성은 생물활성 펩타이드의 존재와 연관되어 조사되었으며, 이에 따라 두부는 단순히 영양 보충 식품으로만 인식되던 것에서 단백질의 귀중한 원천으로 자리매김하게 되었습니다 [71,72].

두치는 중국에서 최소 2000년 이상 단백질과 향신료 원료로 소비되는 인기 있는 제품입니다. 두치의 제조는 두 단계로 진행됩니다: 첫 번째 단계는 여러 미생물(예: Aspergillus oryzae, Zygosaccharomyces rouxii, Lactobacillus plantarum, Bacillus subtilis)을 스타터 문화로 사용한 호기성 발효 과정인 사전 발효 단계 이 과정은 12~15일이 소요되며, 후발효 단계에서는 소금과 다른 향신료를 추가하고 혼합한 후 무산소 발효 상태에서 9개월 동안 숙성됩니다. 이 과정에서 두치의 특수 영양소와 특유의 풍미가 형성됩니다 [73,74]. 최근 몇 년간 두치는 기능성 식품 원료로 주목받고 있습니다. 일부 연구에서는 이 식품이 항산화, 항고혈압 작용, 심지어 혈압을 낮추는 등 건강에 유익한 효과가 있다는 것이 밝혀졌습니다 [75,76].

질감 때문에 “중국 치즈”라고 불리는 수푸는 전통적인 발효 콩 제품으로, 맛을 향상시키는 재료와 전채 요리로 사용되어 왔습니다. 수푸는 중국各地에서 미생물 발효를 통해 다양한 공정으로 생산되며, 스타터 문화의 종류에 따라 분류됩니다. 곰팡이 발효 수푸(Actinomucor, Mucor 또는 Rhizopus로 접종), 세균 발효 수푸(Bacillus 또는 Micrococcus로 접종), 기타(자연 접종)로 구분됩니다 [77,78].

4. Nutritional Changes in Fermented Soybean Products

Fermentation enriches the nutritional value of foods by increasing the content of vitamins, essential amino acids, or fatty acids, allowing detoxification and removal of anti-nutritional factors. In addition to proteins and isoflavones, soybean is made up of numerous other functional and nutritional substances, with increased fermentation process through microbial biotransformations. Microorganisms with abilities to produce specific hydrolytic enzymes, such as protease, amylase, and β-glucosidase, play a fundamental role in increasing functional properties [79,80,81].

The modification of isoflavones occurs through β-glucose enzymes, which degrade cellulose, hydrolyze the β-d-cellulose terminal non-reducing glucoside bond, and, consequently, release β-d-glucose. Thus, the amount of glycosides decreases by hydration by β-glucosidase, increasing the amount of isoflavones aglycones [82,83]. After ingesting the aglycone isoflavones, such as genistein and daidzein, they are absorbed by the blood vessels, hydrolyzed in the small and large intestine by intestinal hydrolytic enzymes and microbial glycosidases through deglycosylation, increasing their bioactive potential [84].

Some final characteristics of the fermented product, as well as the changes that occur during soy fermentation, are related to the type of microorganism used. In tempeh, for example, several amylases, lipases, and proteases are produced by fungi of the genus Rhizopus spp. These hydrolyze macronutrients into simpler, water-soluble compounds, resulting in the production of vitamins, phytochemicals, and antioxidant constituents [1]. The increased antioxidant effect of tempeh can still be attributed to the increased levels of polyphenols released by cell wall degradation by enzymes secreted by Rhizopus fungi during preparation in the boiling stage and through the course of fermentation [85].

Due to the metabolic activity of starter cultures, the levels of vitamin B complexes are also increased during fermentation. In tempeh, Rhizopus and the bacteria K. pneumoniae and C. freundii are the main producers of vitamin B12. In natto, Bacillus is the agent responsible for the increase of viitamin K2 [86,87]. The functionality of these vitamins is well known, being essential bioactive substances that act in the coordination of the nervous system and the development of the brain. Some studies still confirm‎ the significant increase in gamma-aminobutyric acid (GABA) in fermented soy products, responsible for the regulation of the central nervous system [88].

Microbial proteolytic enzymes involved in the fermentation hydrolyze protein content into peptides. The length of the chain and the composition and sequence of amino acids interfere with the biological activity of the peptide and, during enzymatic hydrolysis in fermentation and digestion, inactive bioactive peptides are released. Furthermore, the bioconversion of high molecular weight proteins into minors increases the solubility [89,90]. One of the main biochemical changes that occurs during fermentation is the hydrolysis of proteins by microbial proteases and the enrichment of nutritional effects depends on this reaction [91].

Angiotensin-converting enzyme (ACE) inhibitory peptides are generated by proteolytic degradation of glycinin and β-conglycinin, which consists of protein fractions from soybean. This enzyme acts in the conversion of angiotensin I into angiotensin II and inactivation of the bradykinin vasodilator, raising blood pressure and the risk of cardiovascular disease. Hydrophobic amino acids (Try, Phe, Trp, Ala, Ile, Val, and Met) or positively charged amino acids (Arg and Lys) show greater affinity with ACE. There are three classifications for ACE-inhibiting peptides, being (1) true inhibitor, unaffected by gastrointestinal digestion, (2) substrate, converted into other peptides with less activity in gastrointestinal digestion, and (3) prodrug, converted to true inhibitors by gastrointestinal digestion [92,93]. Still, several other nutritional changes are reported as a consequence of the soybean fermentation process, such as the increase in total soluble iron, the level of folic acid, the composition of tocopherol, with the levels of beta-, gamma- and delta-tocopherol being increased [40].

In summary, many metabolic activities and biotransformations take place during the soybean fermentation process. There are several beneficial health effects of the final fermented product, and its consumption is related to a series of bioactivities that will be mentioned below.

5. Potential Beneficial Health Effect of Soybean Fermented Product5.1. Antioxidant Effect

Many normal reactions in the body form by-products such as free radicals, which are species with unpaired electrons. If the antioxidant defense systems are not efficient, there is an increase in tissue damage and oxidative stress, associated with cell apoptosis and the appearance of several chronic diseases [61].

Due to the beneficial effects of the prevention of these diseases caused by cellular oxidative processes and reactive oxygen species, antioxidants, essential to prevent the formation and suppress the activities of reactive nitrogen and oxygen species, become the main compounds with benefits for health to be included in the diet [94].

Several fermented soybean foods have bioactive components, such as polyphenols, phenolic acid, saponins, sterol, and flavonoids, that protect against oxidative damage, with flavonoids and phenolics being fundamental compounds responsible for antioxidant activity [95].

Phytoestrogenic compounds and phenolic compounds are an important class of phytochemical antioxidants. In soybean and soybean products, aglycone forms are characterized by having greater estrogenic and antioxidant potential [96].

5.2. Anticancer Effect

Environmental factors, especially diet, are considered to play a key role in carcinogenesis. The incidence of cancer in the Asian population is relatively low, and Asians traditionally consume large amounts of soy-based foods, which are rich in isoflavones [97]. One of the first studies that linked cancer risk reduction and the consumption of fermented soy-based foods took place in Singapore in 1991, reporting that a soy-rich diet resulted in less breast cancer development in women in pre-menopause [98].

Soybean isoflavones are believed to have the potential to reduce cancer risk through their antioxidant activity and estrogen-like structure. Genistein presents estrogen binding affinity compared to estradiol (estrogen steroid hormone) receptors ER-α and ER-β of 4% and 87%, respectively. As a result, it binds to these receptors and plays an important role in preventing hormone-related cancers [99]. In addition, genistein is a known tyrosine kinase inhibitor and acts by preventing topoisomerase and angiogenesis. Through these functions, their effect is evident in the cascades of proliferation signals. Some bioactive peptides from soybean can also prevent the growth of tumor cells, such as lunasin and saponins, repelling the formation of the cell membrane and promoting cell apoptosis [100,101].

Several soybean products are mentioned for their anti-cancer potential. In Korea, fungi and Bacillus sp. are used in the fermentation process in Meju, a dry soybean block, which is used to produce other products such as Kanjang, Doenjang, and Gochuchang. The anti-cancer potential of Doenjang is associated with compounds, such as trypsin inhibitor, isoflavones, vitamin E, and an unsaturated fatty acid that contributes to the biological effect. In addition, Doenjang extracts invigorate glutathione S-transferase and increase the vitalization of natural killer cells [102].

Mostly, the anticancer effects of fermented soy products are associated with isoflavones. Some studies have shown that methylation-mediated epigenetic gene silencing can be reversed. Genistein is said to have a broad-spectrum anticancer effect on cancers of the breast, prostate, esophagus, pancreas, stomach, and colon, and metacarcinoma, lymphoma, and neuroblastoma. It also acts as a positive regulator of the mRNA expression‎ of several tumor suppressor genes, counteracting the function of growth-stimulating factors and inhibiting cell malignancy. Therefore, the consumption and inclusion of fermented soybean foods have stood out as a new therapy for the treatment of tumors [103,104].

5.3. Anti-Obesity and Antidiabetic Effect

Physiologically, obesity consists of an imbalance between energy intake and consumption that indicates an excessive accumulation of fat in the tissue and is considered a major health problem that is advancing significantly worldwide. Obesity is generally correlated with diabetes and metabolic syndromes leading to hyperinsulinemia and dyslipidemia [105].

As a result, interest in combating obesity and overweight is growing. Several studies show that a change in the diet prevents and alleviates a series of metabolic imbalances characterized by central obesity, dyslipidemia, and high fasting glucose. Some benefits are attributed to the physiologically active components of certain foods, therefore, they are used to prevent obesity and its complications [106,107].

The isoflavones daidzein and genistein found in high levels in fermented soybean foods are mentioned as having bioactivity, regulating the generation of lipids and thermogenesis in vivo. Through lipogenesis (synthesis of fatty acids and triglycerides), hyperlipidemia (high levels of fat particles in the blood), hyperglycemia (elevated blood glucose), and improved insulin resistance, aglycones and metabolites demonstrate their anti-obesity effects [108]. Some studies also associate these effects with the bioactive phytochemical content of fermented soybean foods as alpha-amylase and alpha-glucosidase inhibitors, protease inhibitors, hemagglutinin, and crude fibers, able to disturb normal metabolism and assist in the management of obesity and different metabolic disorders [109].

The consumption of isoflavones is also associated with an increase in HDL cholesterol and a reduction in total cholesterol, LDL, and triglycerides. In addition to isoflavones, soy proteins, as well as peptides, are active ingredients that lower the levels of LDL cholesterol and triacylglycerols [100].

There is an association between obesity and the transition from pre-menopause to post-menopause in women. This phase is correlated with the risk of several diseases due to the lack of hormonal regulation, including the accumulation of abdominal fat, hypertriglyceridemia, and high levels of low-density lipoprotein cholesterol (LDL-C), reduced high-density lipoprotein cholesterol (HDL-C), elevated blood pressure (BP), and impaired glucose tolerance/diabetes. Studies show that the consumption of fermented soybean foods rich in isoflavones has beneficial effects on the distribution of body fat and lipid profile in women during the menopause period, due to the structural similarity of these compounds with estrogen, their greater affinity for estrogen receptors and circulating concentration in the human body [110,111].

Clinical and experimental studies indicate that the population with obesity and overweight is more vulnerable to type 2 diabetes mellitus (DM2), with obesity dramatically increasing the likelihood of DM2. Individuals with type 2 diabetes mellitus are at increased risk of cardiovascular disease, even with aggressive control of glucose, cholesterol, and blood pressure [112,113].

Oxidative stress (OS) is closely associated with obesity and diabetes. Free fatty acids, which at high levels influence the production of reactive oxygen species (ROS) through mitochondrial electron transport chain complexes and enzymes in endothelial cells, decrease the bioactivity of nitric oxide, activate pro-inflammatory signaling pathways causing damage to cellular proteins and organelles. Damaged, more oxidizing mitochondrial enzymes enhance oxidative stress and cellular dysfunction. Chronic exposure to ROS negatively affects insulin signaling when stress pathways are activated. As a result, insulin resistance, glucose intolerance, β-cell, and mitochondrial dysfunctions are developed, advancing to a state of diabetes [114,115]. The consumption of foods rich in isoflavones is seen as a promising strategy in the treatment of diabetes and obesity. Genistein reduces the inflammatory state in obese people, decreases production, and neutralizes the effects of ROS, resulting in the relief of insulin resistance and, consequently, decreasing the risk of diabetes [116]. After ingestion, genistein enriches insulin resistance by increasing the production of insulin receptor substrate (IRS) 1, glucose transporter (GLUT) type 1, and N-terminal c-jun kinase, increasing the activity of superoxide dismutase, decreasing mitochondrial damage and lipid peroxidation. Daidzein, which is also found in soybeans, activates GLUT4 and IRS1 in adipocytes, adding insulin-stimulated glucose uptake [117].

Spermidine is a naturally occurring polyamine present in all living cells noted to play an important role in cellular functions and is found in different concentrations in fermented soy foods such as Chunjang (1.4–12.8 mg/kg), Doubanjiang (0.18 mg/kg), Douchi (74.92 mg/kg), and Sufu (1.3–32.87 mg/kg) [45,118].

Increased spermidine flux is associated with increased glucose and lipid metabolism. Many in vivo studies reveal that spermidine overexpression‎ protects against diet-induced obesity, and an epidemiological study shows that foods rich in polyamines, such as spermidine, are associated with a lower occurrence of cardiovascular disease (CVD), corroborating the theory that spermidine is beneficial in the treatment of obesity [119,120,121].

5.4. Anti-Inflammatory Effect

Inflammation is a natural biological mechanism in the human body in which the immune system protects against tissue damage due to physical trauma, harmful chemicals, and microbial agents. A wide range of progressive diseases is related to inflammation, resulting in (i) dysregulation of cell signaling, (ii) exaggerated appearance of cytokines, (iii) abrogation of the barrier function to inflammatory cells, and (iv) oxidative damage of tissues and organs. Thus, some studies suggest that the reduction or inhibition of chronic inflammatory mechanisms can prevent numerous diseases. Thus, a diet with anti-inflammatory components has beneficial biological activities [122,123].

In the inflammatory reaction, the macrophage produces nitric oxide (NO), which is usually detected as iNOS (inducible nitric oxide synthase) [124,125]. Isoflavones act as inhibitors of NO production and, consequently, cancel the production of IL-1β and TNF-α pro-inflammatory cytokines. After ingestion, these compounds inhibit the expression‎ of COX-2, production of pro-inflammatory cytokines, and activation of the nuclear transcription factor kappa-B (NF-κB). Thus, the expression‎ of several genes during inflammatory responses is controlled, and regulation of innate and adaptive immunity occurs. Isoflavones still affect the mechanisms of inflammation containing the inflammatory process through different intracellular signaling pathways triggered by AP-1, PPAR, Nrf2, MAPKs [123,126].

Epidemiological investigations show the associations between different soy foods and inflammatory markers, including highly sensitive C-reactive protein (hs-CRP), interleukin IL-6 and IL-18. The high levels of intake of these foods, including miso and soy sauce, are related to a reduction in the serum level of IL-6, a pro-inflammatory cytokine associated with several chronic diseases [127].

Above all, the anti-inflammatory effects of isoflavones are confirmed by the fact that they act in the elimination of reactive oxygen species (ROS), which are directly involved in inflammation.

5.5. Preventive Effect against Cardiovascular Disease

Some evidence reports the association between high soy consumption and the preventive effect against cardiovascular diseases (CVD), such as a lower risk of ischemic heart disease (IHD) or stroke. Soy protein and isoflavones are the constituents responsible for the lower risk of CVD, in addition to their beneficial effects such as lipid profile, arterial stiffness, blood pressure, and endothelial functions [128].

Nattokinase (NK) is an enzyme contained in the sticky component of natto, cheese-like food made from soybeans fermented with Bacillus subtilis, which can dissolve thrombi and fibrin. Because it is considered stable in the gastrointestinal tract, NK becomes an appropriate agent for oral thrombolytic therapy [129]. It is because NK acts directly degrading fibrin or activates other fibrinolytic enzymes, such as pro-urokinase and tissue plasminogen activator (t-PA). NK also inactivates plasminogen activator inhibitor-1 (PAI-1) in vitro, the primary inhibitor of t-PA, resulting in the enhancement of fibrinolysis [130,131].

The development of intravascular thrombi causes a variety of CVDs. Studies suggest that natto has broad thrombolytic efficacy and its ingestion has protective effects against CVD [132].

5.6. Neuroprotective Effect

The human brain is singularly vulnerable to oxidative damage and has high oxygen consumption, in addition to having a relatively high content of polyunsaturated fatty acids (PUFA), which are sensitive to oxidation. Otherwise, neurons are particularly sensitive to disturbances in the balance between antioxidants and the production of reactive oxygen species (ROS), since the levels of antioxidant defense in the brain are negligible. High content of active redox metals is found in the brain, which promotes the formation of ROS and is associated with the development of pathologies [133].

A possible therapeutic approach for the treatment of neurodegenerative diseases is to control microglial activation and reduce the number of pro-inflammatory factors since the overproduction of inflammatory mediators and cytokines causes chronic neuroinflammation, develops several neurodegenerative diseases, and can occasionally lead to neural cell death [134].

Studies show that isoflavones are protective against neuronal cell death, elevate existing neuronal function, and boost neuronal regeneration. Thus, interest in the consumption of fermented soybean foods rich in isoflavones is growing due to their supposed beneficial effects, such as the ability of genistein to inhibit the apoptotic signaling cascade in neurons [135].

5.7. Anti-Aging Effect

Aging is seen as an inevitable, universal, multifactorial, and complex progressive decline in the physiological functions of all living beings, affecting the condition of relative stability and making it susceptible to age-related injuries and diseases [136,137].

Therapies that help achieve healthy aging have become an efficient path to longevity in humans. In this search for the longevity of the body, antioxidant therapy has beneficial effects, pointing out the role of dietary antioxidants. The accumulation of oxidized molecules, such as lipid peroxides, proteins, and damaged DNA mediated by oxidative stress (OS), is the result of the aging process and the administration of antioxidants can prevent oxidation or exclude the production of free radicals, characterized by affecting the rate of aging [108,138,139].

Traditionally, fermented soybean food products are mentioned as having anti-aging properties. These effects are associated with the isoflavones aglycone genistein and daidzein [140]. Studies suggest the anti-aging effect of Tempeh in the pre and postmenopausal with the maintenance of the quality of the uterus, the improvement of skin quality, and bone strength [99,141]. It is because isoflavones act in the replacement of estrogen, improving the quality of life of postmenopausal women [142].

Some research show that neuroinflammation is related to low-grade systemic inflammation, common in aging. The cascade of neuroinflammation also correlated with systemic inflammation is one of the most widely accepted suspicions regarding Alzheimer’s disease (AD), one of the main common forms of age-related dementia. Antioxidant and anti-inflammatory nutrients are mentioned as agents that help to reduce or delay the development of AD [143].

Neuroinflammation in the brain can be reduced by the isoflavones present in fermented soy foods, known to have antioxidant activity. A promoter of proinflammatory activity, IL-1β, is decreased while a potent anti-inflammatory cytokine, IL-10, is increased. Moreover, the intake of isoflavones increases cognitive capacity and prevents oxidative damage in neurons. In AD neurodegeneration, the most damaging sequel is memory loss, with the first implicit mechanism being the deficit of cholinergic neurons, where the transmission of information is canceled due to the lack of neurotransmitters such as acetylcholine (ACh). Research suggests that isoflavones reverse amnesia by increasing acetylcholine and reducing levels of acetylcholinesterase [144,145,146].

After dietary supplementation with Chungkookjang, a fermented soybean paste from Korea cultivated by Bacillus sp., components, such as the isoflavonoids daidzein and genistein, elevated the activity of superoxide dismutase, an important free radical scavenging enzyme [147]. It has also been reported that, by improving memory functions and other neurological indications, gerbils induced by stroke are improved [148]. These, express cerebral ischemia after transitory artery occlusion, and afterward, have global neural cell death due to the addition of oxidative stress, and neuroinflammation [149,150].

Oxidative stress is the cause of reduced life expectancy. Some findings suggest that Natto significantly prolonged the life of nematodes, increased resilience to oxidative stress, and postponed the accumulation of lipofuscin, a characteristic of aging cells. This is cited for its anti-aging effect, relying on actions such as preventing heart attacks, stroke, osteoporosis, bowel disease, and improved cognitive function, especially with age [128,151].

The anti-aging effect of fermented soy foods can also be attributed to the high concentration of spermidine, bioactive polyamines found in high levels in foods such as natto and tempeh. Such a compound has several important functional and regulatory properties related to the physiology of cell aging, such as reversing memory loss, improving the blood lipid profile, and reducing cardiovascular risks, inducing autophagy in damaged cells [152].

6. SARS-CoV-2

A new strain of Coronavirus not previously identified in humans was reported in Wuhan, China in December 2019, being identified as a beta type of Coronavirus ß-CoV Group 2B. A total of seven human coronaviruses (HCoVs) have been identified before: HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, SARS-CoV—responsible for severe acute respiratory syndrome, MERS-COV—responsible for the Middle East respiratory syndrome, and recently the new coronavirus, called SARS-CoV-2—responsible for causing the new severe respiratory inflammatory disease, COVID-19 [153,154].

As of early May 2022, a total of 514,918,067 confirmed cases and 6,240,940 deaths caused by COVID-19 have been reported to the World Health Organization (WHO) [155]. SARS-CoV-2 enters the body using angiotensin-converting enzyme 2 (ACE2) and transmembrane protease, serine 2 (TMPRSS2), as target receptors to infect the cells. After affecting the epithelial cells of the human respiratory tract, the rapid replication of the virus leads to a storm of pro-inflammatory cytokines and chemokines. This hyperinflammatory state causes oxidative stress leading to damage to the alveolar and endothelial cells of the lung and chronic lung inflammation [156,157].

Given the pandemic scenario, numerous researchers investigate risk factors, clinical manifestations, and possible preventive and therapeutic actions. Health conditions such as obesity, diabetes, previous morbidities with risk of immunodeficiency, and chronic cardiovascular, renal, and respiratory diseases are also investigated for association and relationship to the high severity of COVID-19 [158]. Among the complications caused by the disease are ARDS, septic shock, coagulation dysfunction, metabolic acidosis, cardiac arrhythmia, kidney damage, liver dysfunction, heart failure, or secondary infection [159].

A therapeutic strategy for the control of SARS-CoV-2 consists of identifying anti-inflammatory agents to act on the reduction of uncontrolled inflammation in patients and the receptors for the ACE-2 enzyme since it is widely expressed by epithelial cells of the lung, kidney, heart, blood vessels, and intestine [160]. Flavonoid-derived bioactive compounds, such as isoflavones, are mentioned for their significant health benefits such as antibacterial, antioxidant, anticancer, anti-inflammatory, and immunomodulatory bioactivity [161].

There are a few studies related to dietary habits as a risk factor for COVID-19 instability. However, some differences in diet have been hypothesized to play a potential role in disease and fatality rate variability [162]. Based on mechanistic and clinical data, vitamins and folate, polysaccharides and dietary fiber, lipids, peptides, and natural polyphenols are known to be necessary for the body’s immune system against viruses [163].

For example, certain countries, such as Bulgaria, Greece, Romania, and Turkey, where there is high consumption of some types of fermented foods (cabbage and milk), are associated with lower mortality rates. The possible protective effects of antioxidants and angiotensin-converting enzyme (ACE) inhibiting peptides present in fermented foods may justify this hypothesis [164,165].

Adem et al. [166] performed a molecular docking study to identify the ability of 80 flavonoid compounds to bind to the 3-chymotrypsin-like protease (3CLpro), a known enzyme important for SARS-CoV replication. Other polyphenols and flavonoids, such as daidzein and genistein (found in fermented soy products), have been proposed as potential inhibitors of the main SARS-CoV-2 protease [167].

As already mentioned, bioactive peptides with therapeutic properties, including antihypertensive antioxidant, antitumor, and antidiabetic, are present in fermented soy products. Fermented soy peptides have previously demonstrated activity against several viruses, including the SARS-CoV responsible for the SARS outbreak in 2003 [168]. In the soybean fermentation process, the proteolytic degradation of the soy protein fractions (glycine and β-conglycinin) generates the ACE inhibitory peptides [169]. Studies have already mentioned the identification of ACE inhibitory and antihypertensive peptides in Natto and, also, two ACE inhibitory peptides isolated from tofu [71,170]. Other foods, such as douchi (fermented by A. egyptiacus) and sufu (a soybean fermented by the fungus), have peptides with ACE inhibitory activity [171,172].

Oba et al. [173] conducted a study with Natto to investigate the antiviral activities of this food against SARS-CoV-2. The results showed that Natto extract fully inhibited severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the cells. The protease activities of Natto extract were able to proteolytically degrade the British variant of the spike protein (receptor binding domain; RBD) of SARS-CoV-2, resulting in the inhibition of viral infections in cells.

A study conducted by Chourasia et al. [168] from soy cheese fermented with Lactobacillus delbrueckii WS4, identified and selected peptides for antiviral activity in silico. A total of twenty-three peptide sequences were examined for binding affinity to critical residues of the SARS-CoV-2 RBD protein and important catalytic residues of the SARS-CoV-2 pro-enzyme 3CL using molecular docking. The authors also showed in molecular docking studies of the selected peptides that they revealed a potential peptide “KFVPKQPNMIL”. This peptide showed a strong affinity for significant amino acid residues, for host cells (RBD) of the SARS-CoV-2 peak S1 glycoprotein that are responsible for binding the virus to the human ACE2 protein receptor and also an affinity for the important viral proteolytic enzyme 3CLpro. for viral replication.

Therefore, it can be concluded that fermented soy cheese could be explored as a prophylactic food for SARS-CoV-2 and related viruses. Furthermore, the multi-target inhibitor peptide, which effectively inhibited both viral proteins, could be used for in vitro and in vivo functions against SARS-CoV-2.

7. Bioactive Compounds in Soybean Fermented Product

Soy has long been consumed as a health food, and fermented soybean products are important components of traditional diets in Asian countries. The benefits of fermented soy are attributed to its phytochemical content and bioactive compounds, which confer numerous benefits to human health [174].

Many compounds are responsible for the bioactive properties of fermented foods mentioned in several studies. Isoflavones are compounds found in tempeh, which act as antioxidants and are also related to many chronic diseases [175]. Surya and Romulo showed that tempeh extracts protect HepG2 cells (human liver cancer cell line) against induced oxidative stress by reducing ROS generation, and eventually cell death [176].

Chungkookjang has compounds such as isoflavone aglycones, peptides, and dietary fiber, and is rich in poly-γ-glutamic acid (γ-PGA). Consumption of this food can act on memory impairment induced by Alzheimer’s disease and cerebral ischemia, so it prevents and alleviates neural cell survival, thus improving brain insulin sensitivity and neuroinflammation [147].

To investigate the hypothesis that chungkookjang consumption improves sensitivity and insulin secretion capacity, an animal model study reminiscent of the characteristics of type 2 diabetes in Asians was conducted. A high concentration of daidzein was observed and related to the anti-diabetic properties of chungkookjang, capable of improving glucose regulation by potentiating insulin secretion and reducing insulin resistance [177].

Recently, research in Japan has shown that higher consumption of natto and miso is associated with a lower risk of mortality [178]. These foods are sources of bioactive compounds such as nattokinase, bacillopeptidase F, vitamin K2, dipicolinic acid, γ-polyglutamic acid, isoflavones, vanillic acid and syringic acid, which have health-promoting effects [54].

Nattokinase is shown to be responsible for anti-thrombotic and anti-coagulative activities. The anti-thrombotic effect of NK can be used for the treatment of cardiovascular diseases, and such a compound also acts on amyloid degradation related to Alzheimer’s disease and on the suppression of atherosclerosis, heart attack, and stroke in sick patients [179,180]. The health benefits of miso are associated with the presence of isoflavones, such as 8-OH-daidzein, 8-OH-genistein, 6-OH-daidzein, which have strong antioxidant activity, this is related to a series of beneficial effects on human health [181].

Doenjang is an important food consumed in Korea, such food shows strong activities against several carcinogens/mutagenic agents, such as aflatoxin B1. Park et al. showed through studies that genistein and linoleic acid present in doenjang extracts have strong antimutagenic activities, being more effective among the other bioactive compounds found in this food, such as β-sitosterol, soy saponin, α-tocopherol, genistein, and phytic acid [182].

Fermented soy foods are composed of molecules, vitamins, and peptides that are found in greater availability after the fermentation process, which point to being a potential source of numerous health benefits. The bioactive compounds found in fermented soy products are associated with the microorganism used in the process as well as the traditional practice used in each region.

Several bioactive compounds are found in different fermented soy products, these and their health benefits are illustrated in Table 3.

Table 3.

Bioactive compounds of different fermented soy products and their health benefits.

Soybean ProductsBioactive CompoundsHealth BenefitsReferences

Tempeh	Isoflavone aglycone	Antioxidant properties	[183]
Tempeh	Isoflavone aglycone	Protection of HepG2 cells from oxidative stress	[176]
Tempeh	Genistein	Immunomodulatory Function	[184]
Tempeh	Trans-cinnamic acid	Antioxidant properties	[59]
Chungkookjang	Poly-γ-glutamic acid (γ-PGA)	Prevention of memory loss from Alzheimer’s and cerebral ischemia	[147]
Chungkookjang	Daidzein	Anti-diabetic property	[177]
Chungkookjang	Poly-γ-glutamic acid	Anti-obesity effect	[185]
Chungkookjang	Bacillomycin D and surfactin	Antimicrobial activity	[186]
Natto	Nattokinase (NK)	Anti-thrombotic and anti-coagulant activities	[179]
Natto	Vitamin K2	Reducing osteoporotic fracture risk	[187]
Natto	Bacillopeptidase F	Anti-thrombotic and blood pressure-lowering	[188]
Natto	Nattokinase (NK)	Fibrinolytic activity	[189]
Miso	Isoflavones aglycones	Anti-tumoral activity	[190]
Miso	Isoflavones aglycones	Protective effects against stroke	[191]
Miso	Isoflavones aglycones	Sympathetic nerve activity	[192]
Doenjang	Linoleic acid and Genistein	Antimutagenic active	[182]
Doenjang	Genistein	Antimutagenic and anticancer activities	[193]
Doenjang	Genistein	Anti-obesity effects	[194]
Kinema	Poly-γ-glutamic acid (γ-PGA)	Suppression of post prandial hyperglycemia	[195]
Kinema	Isoflavones aglycones	Antioxidant properties	[42]
Kinema	Group B saponins	Prevention of dietary hypercholesterolemia	[196]
Douchi	β-glucosidase and protease	Antioxidant activity	[197]
Sufu	Isoflavones aglycones	Enhancement of the physiological function	[198]

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8. Recent Patents and Innovations on Bioactive Compounds in Soybean Fermented Product

As presented throughout this review, the bioactive compounds present in fermented soy products are related to several beneficial activities for human health and well-being. Scientific studies confirm‎ this potential, and to complement this view, a patent search was conducted showing recent advances and innovations in the use of such compounds.

The patent search was conducted on the Derwent Innovations Index patent database, on 25 March 2022, performing one search for each bioactive compound in the field “Title”, namely *Linoleic acid*, *Daidzein*, *Genistein*, *Isoflavone aglycone*, *Nattokinase*, *Cinnamic acid*, and *Vitamin K2*, using the wildcard * to retrieve all documents containing the defined word roots. The keywords were combined with the International Patent Classification (IPC) A61P (Specific therapeutic activity of chemical compounds or medicinal preparations) using the Boolean operator AND. The IPCs A61P 003/04 (Anorexiants; Antiobesity agents), A61P 003/10 (Hyperglycaemia, e.g., antidiabetics), A61P 009/12 (Antihypertensives), and A61P 037/04 (Immunostimulants) were used to refine the search when necessary [199]. The time interval was the last five years, 2018 to 2022.

After analyzing the documents by reading the titles and abstracts, 334 documents were classified and analyzed using Microsoft Excel software, California, USA. Along these years it is possible to observe an increase in the number of registered patent documents related to the development and innovation of products made from substances obtained in the soybean fermentation process. The apparent decrease in the number of documents in 2022 is attributed to the date of search (March 2022) and to the secrecy period of usually 18 months before publication (Figure 4c). China (CN) and Japan (JP) were the countries that filed the most patents (Figure 4). China accounted for 169 registered patents, representing 50.6% of the total analyzed, while Japan registered 42 patents (12.57%) (Figure 4b).

Figure 4.

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Number of registered patents for the compounds of interest (a), countries (b), and years (c) of publications.

The substances generally most abundant in the fermented soybean product were nattokinase, genistein, and cinnamic acid because they are widely used in pharmaceutic formulations, for instance, in the prevention and treatment of chronic diseases. This was observed in terms of technology, because the highest number of documents was found for nattokinase (79), followed by genistein (69) and cinnamic acid (66) (Figure 4a).

The main company (assignee) that contributed to these patent filings was Hughes Biotechnology Co., Ltd.®, Taipei City, Taiwan, with 11.59% patent documents. This company is specialized in the development and manufacturing of plant-based nutraceuticals, focusing on the discovery and development of dietary ingredients that are based on the most current science, and reformulating existing ingredients to increase their potency. Other important assignees were Dongguan Anhao Pharm Co., Ltd.® Dongguan, China, with 10.6% documents, a skin health management company that integrates product technology research and development, sales, and service, and Kobayashi Pharmaceutical Co., Ltd.®, Osaka, Japan, with 7.5% documents, that develops ideas for pharmaceuticals and various other applications in daily life, such as dental hygiene skincare, and nutritional supplementation.

9. Conclusions

It can be concluded that the future of fermented foods is quite optimistic since consumer awareness of natural sources is growing with a health-promoting effect. In the interest of preventive and therapeutic strategies, it is worth considering the potential of fermented foods and their bioactive compounds capable of reversing or preventing the pathogenic processes associated with metabolic diseases. Natural antioxidants are found as one of the main components with beneficial effects in the prevention of many diseases caused by cellular oxidative processes and reactive oxygen species; oxidative stress (OS) is closely associated with a series of chronic diseases and metabolic imbalance. In this context, interest arises in fermented soy foods, which have bioactive compounds such as flavonoids, isoflavone, peptides, and soy proteins. Soy aglucone isoflavones are antioxidant compounds and their activities are associated with the ability to eliminate reactive oxygen species (ROS). The study carried out with fermented soy milk represents a new strategy for researching peptide-based therapeutics against SARS-CoV-2 and related viruses, investigating the inhibitory action of peptides derived from this product and other fermented soy products on responsible protein molecules by entry into the host cell and viral replication.

Author Contributions

Conceptualization, M.G.B.P., G.V.d.M.P., S.G.K. and C.R.S.; Investigation, F.G.d.P.; writing—original draft preparation, F.G.d.P.; writing—review and editing, M.G.B.P., G.V.d.M.P. and C.R.S.; visualization, F.G.d.P. and M.G.B.P.; supervision, G.V.d.M.P. and C.R.S.; project administration, G.V.d.M.P. and C.R.S.; funding acquisition, C.R.S. All authors have read and agreed to the published version of the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

Funding Statement

This work was funded by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and Conselho Nacional de Desenvolvimento Científico e Tecnológico do Brasil (CNPq).

Footnotes

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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