Functional Properties of Microorganisms in Fermented Foods

1Existing scientific data show many fermented foods have both nutritive and non-nutritive components in foods, which have the potential to modulate specific target functions in the body relevant to well-being and health of the consumers. However, 90% of naturally fermented foods and alcoholic beverages in different countries and regions of the world are still at home production under traditional conditions. Naturally fermented foods and beverages contain both functional and non-functional microorganisms. Functional microorganisms transform the chemical constituents of raw materials of plant/animal sources during food fermentation thereby enhancing the bio-availability of nutrients, enriching sensory quality of the food, imparting bio-preservative effects and improvement of food safety, degrading toxic components and anti-nutritive factors, producing antioxidant and antimicrobial compounds, stimulating the probiotic functions, and fortifying with some health-promoting bioactive compounds. Among bacteria associated with fermented foods and alcoholic beverages, lactic acid bacteria (LAB) mostly species of Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, Weissella, etc. are widely present in many fermented foods and beverages. Species of Bacillus are also present in legume-based fermented foods. Species of Bifidobacterium, Brachybacterium, Brevibacterium, and Propionibacterium are isolated from cheese, and species of Arthrobacter and Hafnia from fermented meat products. Several genera with hundred of species of yeasts have been isolated from fermented foods, alcoholic beverages and non-food mixed amylolytic starters which mostly include Candida, Debaryomyces, Geotrichum, Hansenula, Kluyveromyces, Pichia, Rhodotorula, Saccharomyces, Saccharomycopsis, Schizosaccharomyces, Torulopsis, Wickerhamomyces, and Zygosaccharomyces. Species of Actinomucor, Amylomyces, Aspergillus, Monascus, Mucor, Neurospora, Penicillium, Rhizopus, and Ustilago are reported for many fermented foods, Asian non-food amylolytic starters, and alcoholic beverages.

2Functional properties of microorganisms in fermented foods include probiotics properties, antimicrobial properties, antioxidant, peptide production, fibrinolytic activity, poly-glutamic acid, degradation of antinutritive compounds, etc. which may be important criteria for selection of starter culture(s) to be used in the manufacture of functional foods. Some genera and species of microorganisms are used as commercial starters in food fermentation (Table 1), and some of products are commercialized and marketed globally as functional foods, health foods, therapeutic foods and nutraceuticals foods. The present paper is aimed to review the information on some functional properties of the microorganisms associated with fermented foods and beverages, and their health-promoting benefits to consumers.

3Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. Probiotic organisms used in foods must have the ability to resist gastric juices, exposure to bile, and be able to proliferate and colonize the digestive tract. The beneficial effects of probiotic foods on human health and nutrition are constantly increasing, and probiotics are popularly using bio-ingredients in many functional fermented foods. The most commonly used probiotic bacteria belong to the heterogeneous group of LAB (Lactobacillus, Enterococcus) and to the genus Bifidobacterium, however, yeasts and other microbes have also been developed as potential probiotics during recent years. Some popular commercial probiotic cultures which are available in global markets include Bacillus coagulans BC30 marketed by Ganeden Biotech, Inc., Cleveland, OH, USA; Lactobacillus acidophilus NCFM, Lactobacillus rhamnosus HN001 (DR20) and Bifidobacterium lactis HN019 (DR10) marketed by Danisco (Madison, WI, USA), L. casei strain Shirota and B. breve strain Yakult marketed by Yakult (Tokyo, Japan), L. fermentum VRI003 (PCC) marketed by Probiomics (Eveleigh, NSW, Australia), L. rhamnosus R0011 marketed by Institut Rosell (Montreal, QC, Canada), Streptococcus oralis KJ3 marketed by Oragenics, Inc. (Alachua, FL, USA), and Saccharomyces cerevisiae (boulardii) marketed by Biocodex (Creswell, OR, USA; ).

4Products containing probiotic bacteria generally include foods and supplements. Fermented milk products are the most traditional source of probiotic strains of lactobacilli; however, commercial probiotic lactobacilli have also been added to meat products, snacks, fruit juice, etc.. Probiotic properties of Lactobacillus plantarum isolated from kimchi, Korean fermented vegetable product, has been reported, and is also found to prevent the growth of Helicobacter pylori. Probiotic strain L. acidophilus La-5 produces conjugated linoleic acid (CLA), an anti-carcinogenic agent. Pediococcus pentosaceus CIAL-86 isolated from wine shows anti-adhesion activity against Escherichia coli CIAL-153, indicating its probiotic potential in wine.

5Many species of LAB isolated from fermented vegetable and milk products have antimicrobial activities due to production of antimicrobial compounds such as bacteriocin and nisin. Many strains of LAB isolated from kimchi produce antimicrobial compounds such as bacteriocin by L. lactis BH5 and L. citreum GJ7, and pediocin by P. pentosaceus. Species of LAB isolated from kimchi show strong antimicrobial activity against Listeria monocytogenes, Staphylococcus aureus, E. coli, and Salmonella typhimurium. Weissella cibaria isolated from fermented cabbage product shows antimicrobial activity against Gram-positive and Gram-negative pathogens. Lactococcus lactis isolated from dahi, Indian curd, produces nisin Z that inhibits L. monocytogenes and S. aureus. Several LAB species isolated from Romanian traditional fermented fruits and vegetables have antimicrobial activity against L. monocytogenes, E. coli, Salmonella, and Bacillus. Microorganisms as protective cultures, e.g., bacteriocin producers, may have several advantages, as they can contribute to the flavor, texture and nutritional value of the product besides the production of bacteriocin.

6Antioxidant activities in fermented foods include 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity, 2,2′-azino-bis (3-ethylbenzo-thiazoline-6-sulfonic acid; ABTS) radical scavenging activity, total phenol content (TPC) estimation, and reducing power assay. Many Asian fermented soybean foods have antioxidant properties, e.g., natto, Bacillus-fermented soybean food of Japan, chungkokjang and jang, fermented soybean foods of Korea, douchi, a fermented soybean food of China, kinema, Bacillus-fermented soybean food of India and Nepal, bekang and tungrymbai, Bacillus-fermented soybean foods of India, thua nao, Bacillus-fermented soybean food of Thailand, and tempe mold-fermented soybean food of Indonesia. Antioxidant activities have also been observed in kimchi and yogurt.

7Bioactive peptides are formed during food fermentation by proteolytic microorganisms. In fermented foods peptides have some functional properties such as immunomodulatory, antithrombic, and antihypertensive properties. Species of Bacillus are involved in enzymatic hydrolysis of protein producing peptides and amino acids, which claim to have health benefits. Inhibitory properties of Angiotensin converting enzyme (ACE) have been studied in various fermented milk products such as kefir, koumiss, yogurt, fermented camel milk, cheese, and fermented fish products.

8Another important reason to ferment foods is to coax microorganisms into producing enzymes that also provide very useful services. During food fermentation microorganisms produce enzymes to break down complex compounds to simple bio-molecules for several biological activities such as proteinase, amylase, mannase, cellulase, and catalase in many Asian fermented soybean foods by Bacillus spp.. Common genera of mycelial fungi in fermented foods and beverages such as Actinomucor, Amylomyces, Aspergillus, Monascus, Mucor, Neurospora, and Rhizopus produce various carbohydrases such as α- amylase, amyloglucosidase, maltase, invertase, pectinase, ß-galactosidase, cellulase, hemi-cellulase; acid and alkaline proteases; and lipases. Taka-amylase A (TAA), an enzyme produced by Aspergillus oryzae in koji has many uses in industry. Dry, solid, cake-like mixed amylolytic starters used for alcohol production in the Himalayas have yeasts Saccharomycopsis fibuligera, S. capsularis and Pichia burtonii with high amylase activities.

9Bacillus subtilis subsp. natto in natto produces nattokinase showing fibrinolytic activity. Among bacteria isolated from fermented foods, B. subtilis and B. amyloliquefaciens, Vagococcus carniphilus, V. lutrae, Enterococcus faecalis, E. faecium, E. gallinarum, and P. acidilactici, and Virgibacillus halodenitrificans SK1-3-7 isolated from fish sauce fermentation produce fibrinolytic enzymes.

10Isoflavones are daidzein, genistein and glycitein, each of which exists in four chemical forms viz., aglycones, β-glucoside, acetylglucoside, and malonylglucoside in soybeans. Isoflavone glucosides are hydrolyzed into their corresponding aglycones during fermentation of some Asian fermented soybean foods such as sufu and douchi of China, miso and natto of Japan, chungkokjang and doenjang of Korea, tempe of Indonesia, and thua nao of Thailand. During tempe fermentation, isoflavone particularly Factor-II and aglycone contents are found to increase. Isoflavones in doenjang increase the activation of an LDL-C receptor, which is beneficial to prevent vascular diseases.

11Soybean saponins, which are oleanane triterpenoid glycosides, are again of two types viz., Group A and DDMP (2,3-dihydro-2,5-dihydroxy-6-metyl-4H-pyran-4-one; ). DDMP and their derivatives, Groups B and E saponins show health promoting benefits such as prevention of hypercholesterolemia, suppression of colon cancer cell proliferation, and anti-peroxidation of lipids. Saponin contents are increased in natto, which are generated by Bacillus natto. Kinema has high content of Group B saponin, which may indicate its health-promoting benefits to consumers.

12Poly-glutamic acid (PGA) is not synthesized by ribosomal proteins, but is produced by some strains of Bacillus spp. in fermented soybean foods of Asia. B. subtilis and B. licheniformis are widely used industrial producers of γ-PGA. It is safe eating the viscous materials of Asian fermented soybean foods since PGA is completely biodegradable and water-soluble and non-toxic to human.

13Some microorganisms present in fermented foods may degrade anti-nutritive substances and thereby convert the substrates into consumable products. Various steps employed during the processing of gari and fufu, fermented cassava products of Africa, such as peeling, washing, grating, fermentation, dewatering and roasting minimizes the residual cyanide contents of the product. Bitter varieties of cassava tubers contain the cyanogenic glycoside linamarin and lotaustralin, which are detoxified by species of Leuconostoc, Lactobacillus, and Streptococcus during traditional method to gari and fufu productions to yield hydrocyanic acid (HCN) which has low boiling point and escapes from the dewatered pulp during toasting rendering the product safe for human consumption. In tempe, Rhizopus oligosporus eliminates the flatulence causing indigestible oligosaccharides such as stachyose and verbascose into the absorbable monosaccharides and disaccharides. Degradation of anti-nutritive compounds by B. subtilis has been reported in kinema. Phytic acid is reduced during fermentation of idli and rabadi, a fermented cereal food of India.

14Ethnic foods have in-built systems both as foods and medicine to meet up hungry and also curative. The highest longevity observed among the people of Okinawa prefecture in Japan is mostly due to their traditional and cultural foods such as natto, miso, tofu, shoyu, fermented vegetables, cholesterol-free, low-fat, and high bioactive-compounded foods in addition to active physical activity, sound environment, happiness and other several factors. Korean kimchi has been claimed to possess health-promoting benefits. Kimchi has also anti-aging effect. Natto has several health benefits such as high contents of nattokinase, isoflavones, saponins, vitamin K, unsaturated fatty acids, probiotics and immunomodulating activities mostly produced by B. subtilis (natto;; ). Kinema has also some health promoting benefits. Indian popular fermented milk dahi has anti-carcinogenic property. Lactic acid produced in kimchi may prevent fat accumulation and to improve obesity-induced heart diseases. Anti-obesity effects have been reported in kimchi and in doenjang based on clinical trials. Red wine has anti-aging property due to presence of melatonin that regulates the body clock.

15Ethnic people have customary belief in medicinal values of some of their ethnic foods including fermented foods and beverages, however, clinical trials and validation of the health benefits claims of almost all naturally fermented foods and beverages of the world need to be studied. Some health benefits of fermented foods are listed in Table 2.

16Enrichment of substrates with vitamins, essential amino acids, and bioactive compounds occur during food fermentation. In tempe, mold-fermented soybean food of Indonesia, contents of folic acid, niacin, riboflavin, nicotinamide and pyridoxine are found to be increased by Rhizopus oligosporus, whereas vitamin B12 is synthesized by non-pathogenic strains of Klebsiella pneumoniae and Citrobacter freundii. Contents of thiamine, riboflavin and methionine in idli, a rice-legume based fermented food of India and Sri Lanka enhance during fermentation. Similarly, vitamins B complex and C, lysine and tryptophane, and iron contents have been found to increase during fermentation of pulque, an alcoholic drink of Mexico made from cactus plant. Riboflavin and niacin contents are increased in many Bacillus-fermented Asian fermented foods. Riboflavin and folic acid were found to be synthesized in kimchi by L. mesenteroides and L. sakei. Yeasts Saccharomyces cerevisiae, Candida tropicalis, Aureobasidium sp., and Pichia manschuria isolated from idli and jalebi, fermented cereal foods of India and Pakistan produce vitamin B12. Free amino acids are increased in fermented soybean foods.

17Antihypertensive properties of many fermented milk products have been validated using animal models and clinical trials. Consumption of fermented milks or probiotic bacteria and fermented soybean foods lowers the risk of heart diseases. Fermented whole grain foods can lower the serum LDL-cholesterol values, hypertriacylglycerolaemia, hypertension, coronary heart disease, insulin resistance, and hyperhomocysteinaemia. Consumption of some fermented foods reduces the cholesterol level in tempe, fermented soybean foods, and kefir. Calpis, the Japanese fermented sour milk containing two peptides VPP and IPP has shown hypotensive effect. L. helvetius in fermented milk reduces elevated blood pressure. Monascus purpureus in fermented red-rice of China locally called angkak, prohibits creation of cholesterol by blocking a key enzyme, HMG-CoA reductase due to presence of mevinolin citrinin.

18Drinking of fermented tea of China prevents heart disease. Some Asian fermented soybean foods have antihypertensive properties as observed in natto and tempe. Isoflavone in doenjang, mold-fermented soybean food of Korea, plays an important role in preventing cardiovascular diseases. Fermented whole-grain intake appears to protect from development of heart disease and diabetes. Moderate consumption of wine is healthier. Polyphenols in red wine probably are synergists of the tocopherol (Vitamin E) and ascorbic acid (Vitamin C), thus they inhibit lipid peroxidation. Regular consumption of the Korean fermented soybean foods by hypertensive and Type 2 diabetic patients results in favorable changes in cardiovascular risk factors and reduction of hypocholesterolemic effect. ACEs inhibitory peptides derived from food proteins are used for treating hypertension. Fermented foods, which are rich in fibrinolytic enzymes, are useful for thrombolytic therapy to prevent rapidly emerging heart diseases.

19Some LAB-fermented foods have antimutagenic and anticarcinogeinc activities. Kefir is used for the treatment of cancer. Sauerkraut, fermented vegetable of Germany, contains s-methylmethionine, which reduces tumourigenesis risk in the stomach. Consumption of fermented milk products containing live cells of L. acidophilus decreases ß-glucuronidase, azoreductase, and nitroreductase (catalyze conversion of procarcinogens to carcinogens), probably removes procarcinogens, and activate the immune system of consumers. Similarly, Indian dahi has anti-carcinogenic property. Cancer preventive potential of W. cibaria, and L. plantarum has been reported in kimchi. Consumption of yogurt can reduce bladder, colon and cervical cancer has been observed.

20Lactic acid bacteria present in fermented foods may decrease number of incidence, duration and severity of some gastrointestinal disorders. Administration of some strains of Lactobacillus improves the inflammatory bowel disease, paucities and ulcerative colitis. L. rhamnosus GG is effective in the treatment of acute diarrhea and administration of L. helveticus-fermented milk in healthy older adults produced improvements in cognition function. Consumption of fermented milk products containing live bacteria has immunomodulation capacity, and cures diarrhea. Korean kimchi is suitable for control of inflammatory bowel diseases.

21Lactobacillus kefiranofaciens M1 isolated from kefir grains has an anti-allergic effect. Digestion of caseins during maturation of fermented milk products has shown to facilitate loss of allergenic reactivity thus increases tolerance. Chongkokjang has anti-allergic effect such as dermis thickness, decreased ear thickness, auricular lymph node and infiltrating mast cells. Lactobacillus species isolated from kimchi are found to modulate Th1/Th2 balance by producing a large amount of IL-12 and IFN-γ with ability to alleviate atopic dermatitis and food allergy. Fermented fish oil, which is rich with Omega-3 polyunsaturated fatty acids, can reduce sensitization of allergy.

22Intake of high fiber foods may decrease the insulin requirements in diabetic persons, and may increase the sensitivity to insulin for non-diabetic persons. Probiotic dahi-supplemented diet significantly delays the glucose intolerance, hyperglycemia, hyperinsulinemia, oxidative stress and dyslipidemia indicating a lower risk of diabetes. Daily consumption of chungkokjang may increase the insulin resistivity thus controls diabetics.

23Vitamin K2 present in natto stimulates the formation of bone, which may help to prevent osteoporosis in older women in Japan. Mineral such magnesium, calcium, phosphorus, potassium, and also protein present in yogurt may function together to promote formation of healthy bones.

24Some people suffer from lactose malabsorption, a condition in which lactose, the principal carbohydrate of milk, is not completely digested into glucose and galactose due to lack of ß-D-galactosidase. L. delbrueckii subsp. bulgaricus and S. thermophilus used in production of yogurt contain substantial quantities of ß-D-galactosidase which improve the symptoms of lactose malabsorption in lactose intolerant people. Consumption of fresh yogurt (with live yogurt cultures) has been demonstrated better lactose digestion and absorption than with the consumption of a pasteurized product. Kefir can minimize the symptoms of lactose intolerance by providing extra source of β-galactosidase.

25One of the important health risks in fermented foods is presence of biogenic amines. Biogenic amines are low molecular weight organic compounds by microbial decarboxylation of their precursor amino acids or by transamination of aldehydes and ketones by amino acid transaminases, which are are present in some fermented foods such as sauerkraut, fish products, cheese, wine, beer, dry sausages, etc.. Enterobacteriaceae and enterococci are major biogenic amine producers in foods. Foods with high levels of biogenic amines could be considered as unhealthy. High levels (>100 mg/kg) of histamine and tyramine can cause adverse effects to human health. Fermentation of cabbage with certain lactic starters such as L. casei subsp. casei, L. plantarum and L. curvatus could reduce the biogenic amine content of sauerkraut. The ingestion of food containing small amounts of histamine has little effect in healthy individuals, but it can result in histamine intolerance in persons characterized by impairment of diamine oxidase activity, either due to genetic predisposition, gastrointestinal diseases, or medication with monoamine oxidase inhibitors. A maximum limit of 100 mg/kg of histamine in food indicates a safe level for consumption.

26Some fermented foods and beverages have health benefits due to presence of functional microorganisms. Although, some fermented foods and beverages are marketed globally as health foods, functional foods, therapeutic foods, nutraceutical foods, bio-foods, however, due to urbanization, changes in life-style, and the shifting from traditional food habits to commercial fast foods, the production and consumption of traditional fermented foods is in decline mostly in Asia and Africa. Reliance on fewer providers of fermented foods is also leading to a decline in the biodiversity of microorganisms. We recommend that validation of health claims by clinical trials and animal models of some common fermented foods of the world may be studied in details, and also introduction of new fermented food products containing well-validated functional microorganism(s) may emerge in global food market.

27JPT (70% – data collection, analysis, writing), D-HS (10% – data collection), S-JJ (10% – data collection) and S-WC (10% – data collection).

28The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.