The incidence of lifestyle diseases such as inflammatory bowel diseases is increasing due to unhealthy eating habits and modern lifestyles, resulting in a growing demand for fermented foods worldwide due to their scientifically proven functional and nutritional attributes. Fermented foods are obtained by controlled microbial growth and enzymatic degradation of food constituents. These foods have a good amount of probiotic bacteria and bioactive peptides that benefit human health. Bioactive peptides are formed by either fermentation or enzymatic hydrolysis of food proteins. Fermented foods and beverages i.e., dahi, yogurt, kefir, kimchi, sourdough bread, pickles play a significant role in gut microbiota balance and mental health. Starter culture used in the fermentation of food products provide various health-promoting activities to fermented foods like anti-oxidant activity, anti-hypertensive activity, probiotic activity and improves protein digestibility. Several groups of lactic acid bacteria (LAB) strains produce Exopolysaccharides (EPS) such as a and b- glucans, galactans, fructans, and gluco- and fructo-oligosaccharides. EPS produced by LAB has a positive impact on gut health. In addition, probiotic bacteria have proven to be a beneficial ingredient for any gut disorder (inside or outside the GI tract). They regulate the level of immunoglobulins (IgA) and inflammatory cytokines and improve gut barrier activity. Symbiotic yogurt (made with bacterial strains of Lactobacillus acidophilus and Bifidobacterium longum) helps raise high-density lipoprotein (HDL) cholesterol and also changes the ratio of low-density lipoprotein (LDL) to HDL. Consumption of kefir inhibits the pathogen's action by the production of acids and bacteriocins. Isolation and pharmaceutical applications of health-promoting bioactive peptides from fermented foods have been emerging in dairy and food research areas.

Keywords: fermentation, high-density lipoprotein (hdl) cholesterol, gastrointestinal, health-benefits, probiotic bacteria, yoghurt, lactose intolerance

Fermented foods and beverages have been an integral part of the human diet, for centuries. Fermented foods or beverages are prepared through controlled microbial growth and enzymatic degradation of macro and micro constituents of food. The fermentation process of food can be categorized by the primary metabolites and micro-organisms such as yeast, Acetobacter, Lactic acid bacteria (i.e., Leuconostoc, Lactobacillus, and Streptococcus), propionic acid (produced by Propionibacterium freudenreichii), and ammonia and fatty acids. Fermentation is also defined based on food substrates viz. dairy, vegetables, fruits meat and fish, legumes crops (soybean), cereals, starchy roots, and fruits. Food that contains monosaccharides, disaccharides or oligosaccharides is fermented by yeast or lactic acid bacteria. Fermented milk and milk products have numerous health-promoting properties like hypertensive, hypocholesterolemic and anti-microbial effects¹ and their functional and microbial properties have recently been extensively studied.² Lactic acid bacteria retain the nutritional quality of dairy products and increase their shelf-life. Acidified conditions inhibit the proliferation of pathogens and microorganisms, which aids in preventing food spoilage by releasing anti-microbial bacteriocins.³ It can also have beneficial effects on gut health, i.e., modulation of gut microbiota and in the prevention and treatment of inflammatory bowel disease (IBD)⁴ in addition to anti-carcinogenic and hypo-cholesterolemic effects.⁵ Furthermore, lactose conversion to lactic acid occurs during lactic acid bacteria-induced milk fermentation.⁶ It also provides health benefits by alleviating abdominal pain and diarrhea in individuals with lactose intolerance.⁷ Fermented dairy products provide several health benefits, such as modulating gut microbiota and immune response, and lowering a person’s risk of hypertension, diabetes, and high cholesterol levels.⁸ Fermented dairy products contain tri-peptides, i.e., valyl-prolyl-proline (VPP) and isoleucyl-prolyl-proline (IPP) that are investigated for their possible health effects.⁹ Fermented milk products containing Lactobacillus sps. assist in treating moderate hypertension by producing ACE-inhibitory peptides and GABA (g -amino butyric acid).¹⁰ These tripeptides also exhibit anti-microbial, anti-inflammation, anti-mutagenic, anti-oxidant, and anti-haemolytic properties.¹¹

Cheese

Cheese can be fermented or unfermented. It is energy-dense food that contains a good amount of nutrients such as proteins, fats, minerals (i.e., Ca and Mg), and vitamins (i.e., Vitamin A, B2, and B12).⁶ During cheese production acidification of milk is done by starter culture that can be mesophilic or thermophilic bacteria. But nowadays several researchers are successfully using probiotic starter culture in cheese making. The enzyme used for cheese making, called rennet (obtained from calf stomach, or produced by microbial or plant source) is used for coagulation of milk protein (Casein, amino acid chain at 105 – 106 k-casein). Cheese has several bioactive peptides that exhibit different biological activities.¹² Biological active peptides, vitamins, and minerals together are responsible for the beneficial effects of cheese such as the management and treatment of several diseases.¹³ Kim et al.,¹⁴ reported that biometabolites produced in cheese from conjugated linoleic acids and sphingolipids played an important role in obesity management by modulating lipid and skeletal muscle metabolism.

Dahi

Dahi has a significant place in the Indian diet and is equal to the Western fermented product, yogurt. Dahi is the product obtained from boiled or pasteurized milk (90°C/5-10 minutes) followed by fermentation using lactic acid bacteria (in form of previous dahi, concentrate culture or freeze-dried culture). During fermentation, several changes occur in dahi making that possess positive effects on milk constituents such as protein, lactose, vitamin, and minerals. Dahi is prepared by inoculation of lactic acid bacteria that play a vital role in the production of nutraceuticals compound in fermented foods. Nowadays probiotic dahi attracts the attention of consumers due to its well-proven health benefits, ‘Probiotic’ bacteria are good or gut-friendly bacteria that maintain gut microbiota balance in the human intestine. In addition, LAB possesses several other positive effects in fermented products such as improved nutritional quality by producing vitamin B12.¹⁵

Yogurt

Yoghurt is a fermented milk product that is prepared by using certain starter culture strains (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus). Yogurt is a product that contains a good amount of macro and micro-nutrients such as fat, protein, vitamin B₂ and B_12, and milk minerals (Ca, Mg, Zn, and K).¹⁶ During the fermentation of yogurt, several changes occur, such as the production of health-promoting peptides from milk proteins, along with the synthesis of vitamin B₉, production of conjugated linoleic acid (CLA), improvement in calcium absorption and thereby improving the shelf-life of yogurt.¹⁷ Researchers reported that the human consumption of yogurt helps in the management of several intestinal and extra-intestinal diseases such as lactose intolerance, and infectious diarrhea. It also reduces the duration and incidence of respiratory infections and improves immune and anti-inflammatory responses.¹⁸

Koumiss

Koumiss or kumis is an ancient fermented milk drink also known as kumis, chige, airag and arrag (Mongolian language words). It is consumed in Central Asia and prepared by using raw mare’s milk. Kumis is prepared by using the back-slopping method, in which 30% previous batch of kumis (fermented) is added as inoculum in 70% raw mare’s milk.¹⁹ Zhang et al.,²⁰ reported that raw milk (Mare’s) kumis contains an abundant amount of LAB; i.e., Lactobacillus (L.) plantarum, L. helveticus, L. kefiranofaciens, and Lactococcus (Lc.) lactis. Kumis has a good amount of vitamins (i.e., C, A, E, B_2, B_12, and Pantothenic acid) and minerals (i.e., Ca and P). Kumis also contains essential fatty acids such as linolenic and linoleic acid. A higher amount of lactose in mare’s milk is suitable for lactic acid fermentation. Kumis reported several health-promoting properties i.e., regulates blood pressure, improves immune health, and has positive effects on the functioning of kidneys, liver, endocrine glands, gut system, nervous and vascular systems. Kumis is rich in microflora that plays a vital role in gut health and is helpful in the treatment of digestive diseases.²¹

Kefir

Kefir is a very popular acid-alcoholic fermented dairy product in Europe (eastern part), Russia and Southwest Asia. It is traditionally prepared from kefir grains and the portion that remains after the separation of kefir grains. But nowadays commercial production of kefir uses freeze-dried kefir starter culture.²² Kefir has a slightly acidic taste and creamy consistency, and kefir grains used for kefir production are white to yellowish–white in colour, have a gelatinous texture, and size (diameter) of kefir grains varies from 0.3–3.5cm. Different microbial strains of kefir starter culture stick to a polysaccharide matrix of kefir grains, which contains LAB (10⁸ colonies forming unit (CFU)/g), yeast (10⁶–10⁷CFU/g), and acetic acid bacteria (10⁵CFU/g).²³ Kefir production can be done in three ways i.e, (1) the artisanal process, (2) the commercial process (by the Russian method), and (3) the commercial process (by using pure culture). Several researchers attempted kefir production by using non-animal milk such as soy milk, coconut milk, fruit juices, and sugar and molasses solutions.^24–26

Rosa et al.,²⁷ summarized the different health-promoting properties of kefir and reported that regular kefir consumption helps in the management of various gastrointestinal and allergenic diseases and conditions. Kefir consumption alleviates lactose intolerance and improves digestion. In, addition kefir also had health-promoting properties such as anti-hypertensive, anti-microbial, anti-inflammatory, antioxidant, anti-carcinogenic, anti-allergenic, and hypocholesterolemic effects.

Kimchi

Kimchi is a very popular ancient fermented food product, that originated in Korea. An ancient Korean book “Samkuksaki” (published in 1145 A.D.) and other ancient documents published literature about Kimchi and similar products. Presently kimchi is commonly consumed in the countries like China and Japan. As per ancient literature, kimchi is prepared by brine fermentation of vegetables in a stone jar. Raw materials needed for kimchi preparation are (1) Major raw materials (different types of vegetables such as Chinese cabbage, radish, cucumber, leaf mustard, sweet potato, etc.); (2) Spices such as black and red pepper, onion, mustard, cinnamon, garlic, and ginger; (3) Seasonings such includes salt, corn syrup, soybean sauce, sesame seed, and salt-pickled seafood; (4) Other optional ingredients varies according to geography, taste, and availability. These ingredients include mushrooms, seasonal vegetables, seafood, cereals, fruits, and meats.²⁸ During the fermentation of kimchi, several health-promoting compounds are generated such as phytochemicals, volatile compounds, organic acids, peptides, etc., which possess a wide range of functional properties. Scientific literature on kimchi shows that biological compounds generated during kimchi production had positive effects on immune health, and help in the management of cancers, metabolic syndrome, aging, and cardiovascular disease (CVD).²⁹ Kimchi has a high amount of salt content that will cause major health concerns of high blood pressure,³⁰ but studies show that raised sodium intake from kimchi consumption had no adverse health effects as higher potassium content of kimchi neutralized the effect on blood pressure.^14,31

Sauerkraut

Sauerkraut is a traditional fermented cabbage-based food product that is prepared by a natural fermentation process for thousands of years. It has low calorific value and contains good amounts of nutrients and Vitamin C, b-carotene, and folic acid content. In addition, sauerkraut has very pleasant organoleptic qualities. Sauerkraut is commonly consumed with fruit salad and added in soups, stews, and Caesseroles in Asia, Europe, and the United States. Saurkraut is prepared from shredded cabbage (0.7-2 mm thick strip) and anaerobic conditions are created by the addition of salt (0.7-2.0% sodium chloride). Several other ingredients such as spices, carrots, herbs, and wine are also added during the fermentation of cabbage to improve the flavour of sauerkraut. Fermentation of cabbage is done in anaerobic conditions (fermented in a container/jar and covered with a lid) for one week to months. Several scientific studies reported the health-promoting effects of sauerkraut on human health such as anti-oxidant, anti-inflammatory, anti-carcinogenic, and immunity booster.³²

Sourdough bread

Bread is a traditional food that is consumed since ancient times. Traditionally bread recipe contains flour (i.e., wheat or rye), water, salt (optional), and leavening agents (i.e., chemicals, baker’s yeast, sourdough). Sourdough is considered the oldest, natural starter and an alternative leavening agent for baker’s yeast and chemical. Sourdough bread’s popularity and consumption increased due to multiple health-promoting properties.³³ Fermentation of sourdough is naturally done by LAB and yeast. Natural sourdough fermentation helps in the management of gastrointestinal disorders, i.e., irritable bowel syndrome (IBS), and celiac disease i.e., gluten intolerance syndrome by changing the molecular structure of proteins and carbohydrates. Consumption of sourdough bread improves digestion and gut health as sourdough bread contains prebiotic compounds. In addition, sourdough has quality mineral and vitamin content.³⁴ Starter cultures used for the fermentation of different traditional fermented foods and beverages shows in Table 1.

Hypocholesterolemic effects

Several scientific findings reported that regular consumption of selected probiotics (Lactobacillus acidophilus, Lactobacillus fermentum, Lactobacillus casei subsp. Casei, etc.) may help in the reduction of serum cholesterol (especially LD-L). Ali,³⁵ studied the Hypocholesterolemic effects of kishk (a fermented functional food product containing dried milk and whole wheat mixture) on a rat experimental model over a period of 8 months. Rats fed a diet supplemented with kishk significantly (p£0.05) decreased the body weight and the liver/body weight ratio (maximum decrease was 18.78% at 30% supplementation level). Administration of kishk supplemented diet increased several other body parameters such as high-density and low-density lipoprotein (HDL and LDL) cholesterol, triglyceride concentration, serum cholesterol and atherogenic indices. In addition, parameters of kidney functioning and enzymatic activities of liver enzymes, also elevated positive group (supplemented with kishk and a high-cholesterol diet).

Kobayashi et al.³⁶ investigated the hypocholesterolemic effects of fermented soymilk in rats. Male rats (Sprague-Dawley; age: 7 weeks) were fed with 1% cholesterol (Control diet); 1% cholesterol + 11.7% fermented soymilk (F-5); 1% cholesterol + 23.4% fermented soymilk (F-10) over the period of 5 weeks. The hepatic triglyceride, cholesterol level, liver weight and fat mass were reduced in rats fed with the fermented soymilk diet. A cholesterol synthesis-related gene expression (SREBP-2) decreased significantly (p<0.05) in the liver of the rats fed with the F-5 diet, while a cholesterol catabolism-related gene expression (CYP7a1) increased significantly (p<0.05).

Effects of fermented foods on gut health

The potential probiotic effect of the fermentation microorganisms is widely reported in modern research, several groups of starter cultures used for the fermentation of food products reported probiotic properties such as it to preserve the milk by producing lactic acid and other antimicrobial compounds; adding flavour to fermented foods by the production of flavour compound (such as acetaldehyde and other extracellular polysaccharides); improved nutritional quality by synthesis of vitamins and free amino acids. In, addition probiotics bacteria were also reported with therapeutic and prophylactic properties against cancer and control serum cholesterol levels.³⁷ Bekar et al.³⁸ conducted a preliminary trial (Randomized, double-blind study) of probiotics on infection of Helicobacter pylori and improves its eradication rate by triple therapy (Used antibiotics: Lansoprazole (30 mg, dose), Amoxicillin (1000 mg, dose), and Clarithromycin (500 mg, dose) with kefir 250 ml twice a day). The study revealed that kefir addition to triple therapy increased the eradication rates of H. pylori and decreased the adverse effects of triple therapy. The consumption of soybean and bean tempeh to improves the human microbiota compositions, an in-vitro gut simulator model shows that consumption of tempeh boosts the abundance of Bifidobacterium, Lactobacillus, Escherichia coli, and Enterococcus in the gut.³⁹ Sourdough bread fermented for 8 hours can be a good source for probiotic bacteria, as Costabile et al.⁴⁰ reported that consumption of sourdough bread significantly increased the level of bifidobacteria in the gut compared to non-fermented bread. Gastrointestinal health-promoting properties of different types of fermented food products are shown in Figure 1.

Figure 1 Gastrointestinal health-promoting properties of different types of fermented food products.

Probiotics bacteria role in gut health

Probiotic bacteria maintained the gut microbiota balance and add beneficial functions to gut microbial communities that prevent inflammation in the gut and other intestinal or systemic disease phenotypes. Probiotics have been extensively researched for their role in maintaining the intestinal barrier, which is act as the primary barrier against infections and food allergies entering the intestinal tract. The food matrix of fermented foods provides resistance to probiotic microorganisms in the GI tract in severe conditions such as highly acidic, bile salts and enzymes.⁴¹ Miqual et al.⁴² evaluated the anti-nociceptive of bacterial strain Faecalibacterium prausnitzii in rodent model and observed that F. prausnitzii significantly decrease colonic hypersensitivity in rats that were kept under neonatal maternal separation stress and partial restraint stress. The study also revealed that experimented bacterial strain exhibits anti-nociceptive properties and can be used for the treatment of abdominal pain in Irritable Bowel Syndrome (IBS) patients

Fermented foods - Prevention against gastrointestinal disorders

Each year, gastrointestinal diseases account for a significant portion of morbidity and mortality worldwide. Since several decades ago, probiotics have been used to treat gastrointestinal diseases, but due to a lack of scientific evidence about safety and efficiency, this is not used for clinical procedures. There is a need to study the novel therapeutic attributes of these bacterial strains and fermented products. Improvements in cognitive function were seen in healthy older persons after receiving L. helveticus-fermented milk.⁴³ A probiotic preparation (VSL#3-6g/day) containing three Bifidobacterium species, four Lactobacillus strains, and one Streptococcus strain has shown promise in maintaining remission in ulcerative colitis and pouchitis, as well as preventing postoperative Crohn's disease recurrence.⁴⁴ An isolated yeast strain AKP1, that was added to the diet beforehand significantly reduced the cold-induced gastric lesion in the stomach.⁴⁵ Lactobacillus (Lactobacillus rhamnosus 19070-2 and L. reuteri DSM 12246) supplementation reduced the frequency of gastrointestinal symptoms significantly.⁴⁶

Fermented foods for anti-allergic reactions

Starter culture strain i.e., Lactobacillus is widely used in food applications due to its therapeutic properties and anti-allergic effects in foods.⁴⁷ In line, Yang et al.⁴⁸ examined the effects of Lactobacillus on soybean allergy alleviation. Studies revealed that Lactobacillus strains (Lactobacillus acidophilus, Lactobacillus plantarum subsp. Plantarum, Lactobacillus delbrueckii subsp. bulgaricus) alleviated the allergic symptoms in mice model, and reduced the IgE, IgG, and IgG1 level in serum, also up-regulated and down-regulated the level of interleukin (IL-2), IL-10, interferon-g, and IL-4, IL-6, IL-17A, respectively. In, addition, these bacterial strains promoted the proportion of regulatory T cells (Tregs) and suppressed the mast cell expressions. Similarly, studies by Won et al.⁴⁹ and Hong et al.⁵⁰ reported that probiotic starter culture strains (e.g., Lactobacillus and Lactobacillus kefiranofaciens M1) isolated from kimchi and kefir grains reported with anti-allergic properties.

Fermented foods alleviate lactose malabsorption

Lactose intolerance is a disease related to lactase deficiency in which a patient does not contain lactase (ß-D-galactosidase enzyme) for digestion of milk sugar (lactose), lactase deficiency leads to discomfort and abdominal pain, diarrhea, borborygmi and flatus on the consumption of lactose rich dairy products.⁵¹ Lactose intolerance can be genetic, damage of intestinal mucosa due to medication, surgery, radiation or disease, or congenital (it is an extremely rare condition in which lactase enzyme is completely absent). Fermented foods and dietary supplement with prebiotics, probiotics and synbiotics helps in lactose digestion by altering the composition of foods and the metabolism of colonic microbiota.⁵² Starter culture used in the manufacturing of yogurt, Streptococcus thermophilus, and Lactobacillus delbrueckii subsp. bulgaricus contain a limited amount of lactose degradation enzyme ß-D-galactosidase that helps in the malabsorption of lactose in lactose-intolerant peoples.^53–77

The utilization of fermented food products increases rapidly as they possess various nutritional and health properties, in addition to their preservation and sensory attributes. During the production of fermented foods, there are multiple bioactive peptides formed that have lots of potential health benefits against various diseases, e.g., Hypertension, obesity, hypocholesterolemic, lactose intolerance, inflammatory bowel diseases (IBD), etc. Fermentation of foods increases the level of the vitamins in the fermented products, i.e., vitamin B2 (Riboflavin), B9 (Folate), B12, and K. Fermented foods improve gastrointestinal health. There is a need for more studies, on the effects of different regional and traditional fermented foods on gut health and diseases and the identification and isolation of specific peptides for gut health for medical applications can be a new dimension of research.

None.

Author declares there is no conflict of interest in publishing the article.

None.

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