Functional Properties of Microorganisms in Fermented Foods

Fermented foods have unique functional properties imparting some health benefits to consumers due to presence of functional microorganisms, which possess probiotics properties, antimicrobial, antioxidant, peptide production, etc. Health benefits of some global fermented foods are synthesis of nutrients, prevention of cardiovascular disease, prevention of cancer, gastrointestinal disorders, allergic reactions, diabetes, among others. 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.


INTRODUCTION
Existing 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 (Tamang et al., 2016). 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 (Tamang et al., , 2016Farhad et al., 2010;Bourdichon et al., 2012;Thapa and Tamang, 2015). 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 (Axelsson et al., 2012;Holzapfel and Wood, 2014). Species of Bacillus are also present in legume-based fermented foods (Kubo et al., 2011;Tamang, 2015). Species of Bifidobacterium, Brachybacterium, Brevibacterium, and Propionibacterium are isolated from cheese, and species of Arthrobacter and Hafnia from fermented meat products (Bourdichon et al., 2012). 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 (Tamang and Fleet, 2009;Lv et al., 2013). 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 (Chen et al., 2014).
Functional properties of microorganisms in fermented foods include probiotics properties (Hill et al., 2014), antimicrobial properties (Meira et al., 2012), antioxidant (Perna et al., 2013), peptide production (De Mejia and Dia, 2010), fibrinolytic activity (Kotb, 2012), poly-glutamic acid (Chettri and Tamang, 2014), degradation of antinutritive compounds (Babalola, 2014), etc. which may be important criteria for selection of starter culture(s) to be used in the manufacture of functional foods (Badis et al., 2004). 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 (Bernardeau et al., 2006;Bourdichon et al., 2012;Thapa and Tamang, 2015). 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.

Antimicrobial Properties
Many species of LAB isolated from fermented vegetable and milk products have antimicrobial activities due to production of antimicrobial compounds such as bacteriocin and nisin Khan et al., 2010;Gaggia et al., 2011;Jiang et al., 2012;Grosu-Tudor and Zamfir, 2013). Many strains of LAB isolated from kimchi produce antimicrobial compounds such as bacteriocin by L. lactis BH5 (Hur et al., 2000) and L. citreum GJ7 (Chang et al., 2008), and pediocin by P. pentosaceus (Shin et al., 2008). 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 (Patel et al., 2014). Lactococcus lactis isolated from dahi, Indian curd, produces nisin Z that inhibits L. monocytogenes and S. aureus (Mitra et al., 2010). Several LAB species isolated from Romanian traditional fermented fruits and vegetables have antimicrobial activity against L. monocytogenes, E. coli, Salmonella, and Bacillus (Grosu-Tudor and Zamfir, 2013). 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 (Gaggia et al., 2011).

Peptide Production
Bioactive peptides are formed during food fermentation by proteolytic microorganisms (De Mejia and Dia, 2010). In fermented foods peptides have some functional properties such as immunomodulatory (Qian et al., 2011), antithrombic (Singh et al., 2014), and antihypertensive properties (Phelan and Kerins, 2011). Species of Bacillus are involved in enzymatic hydrolysis of 1 | Some functional microorganisms used as commercial starters in food fermentation (amended and compiled from references: Mogensen et al., 2002;Bernardeau et al., 2006;Bourdichon et al., 2012;Thapa and Tamang, 2015).

Production of Enzymes by Microorganisms
Another 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. (Tamang and Nikkuni, 1996;Chettri and Tamang, 2014). 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 αamylase, amyloglucosidase, maltase, invertase, pectinase, ß-galactosidase, cellulase, hemi-cellulase; acid and alkaline proteases; and lipases (Nout and Aidoo, 2002). Taka-amylase A (TAA), an enzyme produced by Aspergillus oryzae in koji has many uses in industry (Suganuma et al., 2007). 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 (Tsuyoshi et al., 2005;Tamang et al., 2007).

Increase in Isoflavones and Saponin and Production of PGA
Isoflavones are daidzein, genistein and glycitein, each of which exists in four chemical forms viz., aglycones, β-glucoside, acetylglucoside, and malonylglucoside in soybeans (Kudou et al., 1991). Isoflavone glucosides are hydrolyzed into their corresponding aglycones during fermentation of some Asian fermented soybean foods such as sufu and douchi of China (Wang et al., 2007b;Yin et al., 2007), miso and natto of Japan (Chiou and Cheng, 2001), chungkokjang and doenjang of Korea , tempe of Indonesia (Lu et al., 2009), and thua nao of Thailand (Dajanta et al., 2009). During tempe fermentation, isoflavone particularly Factor-II and aglycone contents are found to increase (Nakajima et al., 2005). Isoflavones in doenjang increase the activation of an LDL-C receptor, which is beneficial to prevent vascular diseases (Kwak et al., 2012).
Poly-glutamic acid (PGA) is not synthesized by ribosomal proteins (Oppermann-Sanio and Steinbüchel, 2002), but is produced by some strains of Bacillus spp. in fermented soybean foods of Asia (Urushibata et al., 2002;Meerak et al., 2007;Nishito et al., 2010;Chettri and Tamang, 2014). B. subtilis and B. licheniformis are widely used industrial producers of γ-PGA (Stanley and Lazazzera, 2005). 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 (Yoon et al., 2000).

Degradation of Anti-nutritive Compounds
Some microorganisms present in fermented foods may degrade anti-nutritive substances and thereby convert the substrates into consumable products (Nout, 1994;Tamang, 2015). 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 (Babalola, 2014). 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 (Lambri et al., 2013;Babalola, 2014;Bamidele et al., 2015). In tempe, Rhizopus oligosporus eliminates the flatulence causing indigestible oligosaccharides such as stachyose and verbascose into the absorbable monosaccharides and disaccharides (Hesseltine, 1983;Sanchez, 2008). Degradation of anti-nutritive compounds by B. subtilis has been reported in kinema (Sarkar et al., 1997). Phytic acid is reduced during fermentation of idli (Reddy and Salunkhe, 1980) and rabadi, a fermented cereal food of India (Gupta et al., 1992).

HEALTH BENEFITS OF FERMENTED FOODS
Ethnic foods have in-built systems both as foods and medicine to meet up hungry and also curative (Shin and Jeong, 2015;Thapa and Tamang, 2015). 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 (Willcox et al., 2004). Korean kimchi has been claimed to possess health-promoting benefits (Cheigh, 1999;Lee et al., 2011;Park et al., 2014;Han et al., 2015). 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; Tsubura, 2012;Nagai, 2015). Kinema has also some health promoting benefits (Omizu et al., 2011;Tamang, 2015). Indian popular fermented milk dahi has anti-carcinogenic property (Arvind et al., 2010). Lactic acid produced in kimchi may prevent fat accumulation and to improve obesity-induced heart diseases (Park et al., 2008). Anti-obesity effects have been reported in kimchi Park et al., 2012) and in doenjang (Kwak et al., 2012) based on clinical trials Jung et al., 2014). Red wine has anti-aging property due to presence of melatonin that regulates the body clock (Corder et al., 2006;Walker, 2014).
Ethnic 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.

Synthesis of Nutrient
Enrichment of substrates with vitamins, essential amino acids, and bioactive compounds occur during food fermentation Frontiers in Microbiology | www.frontiersin.org (Holzapfel et al., 1995;Steinkraus, 1996;Thapa and Tamang, 2015). 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 (Astuti, 2015), whereas vitamin B 12 is synthesized by nonpathogenic strains of Klebsiella pneumoniae and Citrobacter freundii (Liem et al., 1977;Okada, 1989;Keuth and Bisping, 1994). Contents of thiamine, riboflavin and methionine in idli, a rice-legume based fermented food of India and Sri Lanka enhance during fermentation (Ghosh and Chattopadhyay, 2011). 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 (Ramirez et al., 2004). Riboflavin and niacin contents are increased in many Bacillus-fermented Asian fermented foods (Sarkar et al., 1998;Kim and Hahm, 2002;Nagai, 2015). Riboflavin and folic acid were found to be synthesized in kimchi by L. mesenteroides and L. sakei (Jung et al., 2013). Yeasts Saccharomyces cerevisiae, Candida tropicalis, Aureobasidium sp., and Pichia manschuria isolated from idli and jalebi, fermented cereal foods of India and Pakistan produce vitamin B 12 (Syal and Vohra, 2013). Free amino acids are increased in fermented soybean foods (Nikkuni et al., 1995;Sarkar and Tamang, 1995;Tamang and Nikkuni, 1998;Kiers et al., 2000;Dajanta et al., 2011).

Prevention of Hypertension and Heart Disease
Antihypertensive properties of many fermented milk products have been validated using animal models and clinical trials (Seppo et al., 2002;Sipola et al., 2002). Consumption of fermented milks or probiotic bacteria (Agerholm-Larsen et al., 2000) and fermented soybean foods (Liu and Pan, 2010) lowers the risk of heart diseases. Fermented whole grain foods can lower the serum LDL-cholesterol values, hypertriacylglycerolaemia, Resveratol Anti-diabetic Ramadori et al., 2009 Frontiers in Microbiology | www.frontiersin.org hypertension, coronary heart disease, insulin resistance, and hyperhomocysteinaemia (Anderson, 2003). Consumption of some fermented foods reduces the cholesterol level in tempe (Hermosilla et al., 1993), fermented soybean foods (Lee, 2004), and kefir (Otes and Cagindi, 2003). Calpis, the Japanese fermented sour milk containing two peptides VPP and IPP has shown hypotensive effect (Nakamura et al., 1996). L. helvetius in fermented milk reduces elevated blood pressure (Aihara et al., 2005;Shah, 2015). 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 (Pattanagul et al., 2008). Drinking of fermented tea of China prevents heart disease (Mo et al., 2008). Some Asian fermented soybean foods have antihypertensive properties as observed in natto (Nagai, 2015) and tempe (Astuti, 2015). Isoflavone in doenjang, moldfermented soybean food of Korea, plays an important role in preventing cardiovascular diseases (Kwak et al., 2012;. Fermented whole-grain intake appears to protect from development of heart disease and diabetes (Anderson, 2003). Moderate consumption of wine is healthier (Walker, 2014). Polyphenols in red wine probably are synergists of the tocopherol (Vitamin E) and ascorbic acid (Vitamin C), thus they inhibit lipid peroxidation (Feher et al., 2007). 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 (Lim et al., 2014). ACEs inhibitory peptides derived from food proteins are used for treating hypertension (Jakubczyk et al., 2013). Fermented foods, which are rich in fibrinolytic enzymes, are useful for thrombolytic therapy to prevent rapidly emerging heart diseases (Mine et al., 2005;Singh et al., 2014).

Prevention from Cancer
Some LAB-fermented foods have antimutagenic and anticarcinogeinc activities . Kefir is used for the treatment of cancer (Otes and Cagindi, 2003;Yanping et al., 2009). Sauerkraut, fermented vegetable of Germany, contains s-methylmethionine, which reduces tumourigenesis risk in the stomach (Kris-Etherton et al., 2002). 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 (Goldin and Gorbach, 1984;Macouzet et al., 2009). Similarly, Indian dahi has anti-carcinogenic property (Mohania et al., 2013). 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 (Chandan and Kilara, 2013).

Protection against Gastrointestinal Disorders
Lactic acid bacteria present in fermented foods may decrease number of incidence, duration and severity of some gastrointestinal disorders (Verna and Lucak, 2010). Administration of some strains of Lactobacillus improves the inflammatory bowel disease, paucities and ulcerative colitis (Orel and Trop, 2014). L. rhamnosus GG is effective in the treatment of acute diarrhea (Szajewska et al., 2007) and administration of L. helveticus-fermented milk in healthy older adults produced improvements in cognition function (Chung et al., 2014). Consumption of fermented milk products containing live bacteria has immunomodulation capacity (Granier et al., 2013), and cures diarrhea (Balamurugan et al., 2014). Korean kimchi is suitable for control of inflammatory bowel diseases .

Anti-allergic Reactions
Lactobacillus kefiranofaciens M1 isolated from kefir grains has an anti-allergic effect (Hong et al., 2010). Digestion of caseins during maturation of fermented milk products has shown to facilitate loss of allergenic reactivity thus increases tolerance (Alessandri et al., 2012). 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 (Won et al., 2011). Fermented fish oil, which is rich with Omega-3 polyunsaturated fatty acids, can reduce sensitization of allergy (Han et al., 2012).

Protection from Diabetes and Osteoporosis
Intake of high fiber foods may decrease the insulin requirements in diabetic persons (Meyer et al., 2000), and may increase the sensitivity to insulin for non-diabetic persons (Fukagawa et al., 1990;Anderson, 2003). Probiotic dahi-supplemented diet significantly delays the glucose intolerance, hyperglycemia, hyperinsulinemia, oxidative stress and dyslipidemia indicating a lower risk of diabetes (Yadav et al., 2007). Daily consumption of chungkokjang may increase the insulin resistivity thus controls diabetics Tolhurst et al., 2012).
Vitamin K2 present in natto stimulates the formation of bone, which may help to prevent osteoporosis in older women in Japan (Yanagisawa and Sumi, 2005). Mineral such magnesium, calcium, phosphorus, potassium, and also protein present in yogurt may function together to promote formation of healthy bones (Chandan and Kilara, 2013).

Alleviation of Lactose Malabsorption
Some 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 (Shah, 2015). 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 (Pedone et al., 2000). Kefir can minimize the symptoms of lactose intolerance by providing extra source of β-galactosidase (Hertzler and Clancy, 2003).

HEALTH RISK OF FERMENTED FOODS
One 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 (Zhai et al., 2012), which are are present in some fermented foods such as sauerkraut, fish products, cheese, wine, beer, dry sausages, etc. (Halász et al., 1994;Suzzi and Gardini, 2003;Spano et al., 2010;Visciano et al., 2014). Enterobacteriaceae and enterococci are major biogenic amine producers in foods (Nout, 1994). Foods with high levels of biogenic amines could be considered as unhealthy (Latorre-Moratalla et al., 2010). High levels (>100 mg/kg) of histamine and tyramine can cause adverse effects to human health (Rauscher-Gabernig et al., 2009). 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 (Rabie et al., 2011). 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 (Maintz and Novak, 2007). A maximum limit of 100 mg/kg of histamine in food indicates a safe level for consumption (Halász et al., 1994).

CONCLUSION
Some 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.