A review:Health promoting lactic acid bacteria in traditional Indonesian fermented foods

Lilis Nuraida

Southeast Asian Food and Agricultural Science and Technology (SEAFAST) Center,and Department of Food Science and Technology,Bogor Agricultural University,Indonesia

Abstract

Keywords:Fermented foods;Probiotics;Diarrhea;Hypocholesterolemic;Antimutagenicity

1.Introduction

Fermentation is known as one of the oldest forms of food preservation in the world.Fermentation can increase the shelflife of meat,fish,fruit and vegetables that are highly perishable due to their high water contents and nutritive values,especially in tropical countries like Indonesia.Preservation of foods occurs through lactic acid,alcoholic,acetic acid and high salt fermentations.Beside preserving foods,fermentation also changes the organoleptic characteristics of foods through developing a wide diversity of flavors,aromas and textures.Moreover,fermentation may improve digestibility and nutritional quality through enrichment of food substrates with vitamins,proteins,essential amino acids and essential fatty acids[1,2].

As in other parts of East Asia,Indonesian fermented foods feature the use of a variety of raw materials,including cereals,soybeans,fruits,vegetables,tubers and fish.In some parts of Indonesia,meat and milk,especially buffalo milk and mare milk,have been used traditionally as raw materials for fermented products.In terms of the fermentation processes,Indonesian fermented foods can be classified into lactic fermentations(fruits,vegetables,cassava,meat,milk),alcoholic fermentations(rice,cassava),mold fermentations(soybeans,peanut press cake)and high salt fermentations(fish,soy sauce,tauco[fermented soybean slurry]).In the fermentation of some products,such as soy sauce,a mold fermentation is followed by a brine fermentation in which LAB and yeasts are involved[3].

Although some fermentations,such as those for tempe(mold fermented soybean)and tape(alcoholic fermented steamed glutinuous rice or cassava),use a starter culture,microorganisms from the environment may contaminate the ferments and grow during the fermentations.Involvement of microorganisms other than molds in tempe fermentation has started since soaking step and continues during mold fermentation[4,5].The presence of other microorganisms such as LAB in tape fermentation contributes to the development of flavor of tape[6].Many Indonesian fermented foods(fruits,vegetables,meat and fish)are produced through natural fermentation by controlling the environment with the addition of salt,or by soaking the raw materials in water,as in the fermentation of raw peeled cassava root.The main role of salt in fruit and vegetable fermentations is to promote the growth of LAB over spoilage bacteria[7,8]and to inhibit pectinolytic and proteolytic enzymes that can cause softening and putrefaction[7].

LAB is a group of Gram-positive,non-spore forming,coccus or rod shaped bacteria.They ferment carbohydrates to almost entirely lactic acid(homofermentation)or to a mixture of lactic acid,carbon dioxide and acetic acid and/or ethanol(heterofermentation).Other compounds,such as diacetyl,acetaldehyde and hydrogen peroxide,are also produced.These compounds contribute to the flavor and texture of fermented foods and may also contribute to the inhibition of undesirable microbes.

The LAB in Asian traditional fermented foods includeLactobacillusplantarum,Lb.pentosus,Lb.brevis,Lb.fermentum,Lb.casei,Leuconostocmesenteroides,Leu.kimchi,Leu.fallax,Weissellaconfusa,W.koreenis,W.cibaria,andPediococcus pentosaceus,many of which are considered to be potential probiotics[7].Most of the LAB present in Indonesian fermented foods areLactobacillusspecies(Table 1).Other genera,such asPediococcus,Lactococcus,Enterococcus,WeisellaandLeuconostoc,are also found in some fermented foods(Table 1).LAB are involved to varying degrees in Asian fermented foods,and may have positive and negative effects on products[9].In cereal alcoholic fermentations,lactic acid bacteria contribute to the characteristic of flavor and taste.Excessive lactic acid generally lowers the quality of alcoholic fermentation products.However,in fruit,vegetable,milk and meat fermentations,LAB play a major role in producing acid necessary to the quality of the products.It is interesting that LAB are generally present in tempe,which is not an acidic fermentation.In tempe fermentation,soybeans are soaked overnight prior to inoculation with starter culture containingRhizopusoligosporusas the primary microorganism.Acid fermentation involving LAB takes place during the soaking[10,11]and some growth of lactic acid bacteria commonly occurs during the stage of mold growth[5,12].

Table 1Occurrence of lactic acid bacteria in some Indonesian fermented foods.

LAB in fermented foods are of interest not only for their role in fermentation but also for their role in promoting positive health impacts.The concept of beneficial health effects of LAB has existed since Metchnicoff in 1908 proposed that acid producing microorganisms in fermented dairy products could lead to a prolongation of the life span of consumers[36].Although historically the fermented products associated with beneficial LAB were milk-based,much research has been directed to exploring LAB from other fermented foods as potential probiotics.A probiotic is defined as a live microorganism that will confer beneficial effects on the host when ingested in sufficient amount[37].The probiotic bacteria used in commercial products are mainly members of the generaLactobacillusandBifidobacterium[36].Probiotic bacteria are usually those bacteria that have adapted to the gastrointestinal environment.However,recent research has shown promising probiotic activity of LAB isolated from fermented foods[9].The progress in research on the beneficial health effects of microorganisms,especially LAB,isolated from Indonesian fermented foods is discussed below.

2.Potential of lactic acid bacteria isolated from Indonesian fermented foods as probiotics

Probiotic and other functional properties are strain dependent and all probiotic strains are unique and different;therefore,their properties and characteristics need to be well defined[38].Several criteria have to be met in selecting probiotic strains,including acid and bile tolerance,survival through the gastrointestinal track,ability to adhere to intestinal surfaces,antimicrobial activity against potentially pathogenic bacteria,and good technological properties[39].Functional properties of probiotics include hypocholesterolemic activity by lowering plasma cholesterol[40],preventing and treating diarrhea[37],and altering the immune system[41,42].The mechanisms by which probiotics exert their beneficial effects on the host include the reduction of luminal pH,competition with pathogens for adhesion sites and nutritional sources,secretion of antimicrobial substances,toxin inactivation,and immune stimulation[43].

Based oninvitrostudies,LAB isolated from Indonesian fermented foods have promising characteristics as probiotic candidates(Table 2).Invitroassessment shows that many LAB isolates tolerate bile salt and low pH environment and possess antagonistic activity against foodborne pathogens.These characteristics are similar to those of intestinal microorganisms,such asLactobacillusacidophillusandLb.caseithat are commonly used as probiotics[9].The research results suggest that the LAB in Indonesian fermented food have adapted to environments that resemble the gastrointestinal track and,hence,have potential as probiotic microorganisms.Adaptation of LAB isolated from fermented foods on specific environment such as high salt concentration,acidic condition,has also been reported such asL.mesenteroidesin Kimchii,cane juice,Leu.oenosin grape juice andTetragenococcushalophillusin soy sauce[9].It has been suggested that adaptation involves the human food cycle,from soil to raw materials,to fermented product,to human intestine,to feces and then to soil again[9].

Table 2Characteristic and functional properties of lactic acid bacteria isolated from Indonesian fermented foods based on in vitr o studies.

Adhesion properties similar to those of probiotic strains have also been shown by some isolates from fermented foods,such asLactobacillusreuteriIS-27560,LactococuslactisIS-16183 andLb.rhamnosusIS-7257 from dadih that adhere to mucus layers and Caco-2 cells[32].Lc.lactisIS-16183 andLb.rhamnosusIS-7257 significantly inhibited adhesion ofEscherichiacoliO157:H7.Accordingly,these two strains may be potential candidates for use as probiotic strains.The adhesion properties of dadih isolates were relatively comparable to the commercial probiotic strains,Lb.caseiShirota andLb.rhamnosusGG.Another study on dadih isolates(Lb.plantarumIS-10506 and IS-20506;EnterococcusfaeciumIS-27526,IS-23427 and IS-16183)showed thatLb.plantarumIS-10506 was the most adhesive and can significantly reduce pathogen adhesion to mucus[29].Lb.plantarum,isolated from fermented fruit(mandai),also showed good adhesive properties on enterocyte-like HCT-116 cells,withLb.plantarumMB427 showing the strongest inhibition of adhesion ofListeriamonocytogenesATCC 13932,enteropathogenicE.coli(EPEC)K1.1 andSalmonellaentericaserovar Typhimurium ATCC 14028[17].These findings suggest that antimicrobial effects of fermented food isolates also involve adhesion properties.Production of substances other than organic acids as shown by certain isolates from bakasang,dadih and growol[25,28,44]may enhance their activity in inhibiting the growth of pathogens.

Among potential health beneficial effects,invitroassessment of fermented foods isolates for their hypocholesterolemic effect has been done by some researchers[16,31,45].Cholesterol binding by LAB in the small intestine may reduce the amount of dietary cholesterol absorbed[31].Several mechanisms for lowering cholesterol absorption have been hypothesized[46],including enzymatic deconjugation of bile acids by bile-salt hydrolase(BSH),assimilation of cholesterol,co-precipitation of cholesterol with deconjugated bile,binding of cholesterol to the cell walls of probiotic bacteria,incorporation of cholesterol into the cell membranes of probiotics,conversion of cholesterol to coprostanol,and production of short-chain fatty acids by probiotics in the presence of prebiotic substrates.BSH hydrolyzes conjugated glycodeoxycholic acid and taurodeoxycholic acid,leading to the deconjugation of glyco-and tauro-bile acids.Once deconjugated,bile acids are less soluble and absorbed by the intestines,leading to their elimination in the feces.Cholesterol is used to synthesize new bile acids in a homeostatic response,resulting in lowering of serum cholesterol.The ability of cholesterol-binding appeared to be growth and strain specific.

Other potential health benefits shown by LAB isolates from fermented foods are the ability of aL.plantarumisolate from dadih to remove microcystin-LR,a cyclic heptapeptide hepatoxin produced by cyanobacteria[47]and the ability to produce-glucosidase[48,49].Cyanobacteria produce a number of potent hepato-and neurotoxins,collectively called cyanotoxins,which have potent acute hepatotoxicity and tumor promoting activity[47].Lb.plantarumIS-10506 and IS-20506 have shown ability to efficiently remove the toxins.Meanwhile,-glucosidase activity is widespread among LAB and presumably plays a role in interactions with the human host[50].-Glucosidase releases a wide range of plant secondary metabolites from their-D-glucosylated precursors.The conversion of glucoside isoflavones into their bioactive aglycones by LAB has been observed in soymilk fermentation[48].

LAB isolated from fermented foods has potential as producers of bioactive compounds.Gamma-aminobutyric acid(GABA)has various physiological functions and could be produced by LAB[54].SomeLactobacillusspecies have been reported to produce equol[7-hydroxy-3-(40-hydroxyphenyl)chroman],a nonsteroidal estrogen of the isoflavone class in fermented soymilk[55].

Most established probiotics are LAB and Bifidobacteria although recently certain yeasts(e.g.Saccharomycesboulardii[56–58])and spore-forming bacteria(e.g.Bacilluscoagulans[59–61])have been considered as probiotics.WhileS.boulardiihas been shown to be effective in preventing the recurrence ofClostridiumdifficile-induced pseudomembranous colitis as well as the antagonistic action ofE.coli,the long-term advantages of using spores as probiotics is that they are heat-stable and can survive transit across the stomach barrier,properties that cannot be assured with other probiotic bacteria that are given in the vegetative form[61].Yeasts are commonly present in many fermented foods[6,11,12,62]and starter culture[63].Spore-forming bacteria could also be part of the microbial consortium in traditional Indonesian fermented foods,such as tempe[5]and tape[6,64]as well as their starter cultures[62].

3.Health beneficial effect of lactic acid bacteria isolated from fermented foods

3.1.Animal studies

Only a few promising LAB isolated from Indonesian fermented foods have been assessed in animal studies for their potential health benefits(Table 3).Evaluation ofL.plantarumsa28k,Lb.acidophilusFNCC116 andLb.caseiFNCC262 in lowering cholesterol in rats,revealed that rats that received milk fermented by the three LAB had significantly lower serum cholesterol levels than rats feeds non-fermented milk[45].Lb.acidophilusKBc andLb.brevisKBa,from fermented mare milk,were able to adhere and colonize gut mucosal epithelium of rats[35].Administration of these isolates significantly reduced cholesterol levels in blood serum of hypercholesterolemic rabbits.The cholesterol-lowering activity of milk fermented byLactococcuslactissubsp.lactisIS-10285 andLc.lactissubsp.lactisIS-29862 has been evaluated in hypercholesterolemic rats[65].The isolates had high taurocholate-deconjugating activity.Only milk fermented byLc.lactissubsp.lactisIS-10285 significantly reduced the total serum cholesterol,LDL cholesterol and total bile acids.Neither milk nor fermented milk influenced HDL cholesterol levels.The authors suggested that the hypocholesterolemic effect ofLc.lactissubsp.lactisIS-10285 was due to its ability to suppress the reabsorption of bile acids into the enterohepatic circulation and enhance the excretion of bile acids in feces of hypercholesterolemic rats.These results indicate that strains of LAB isolated from Indonesian fermented foods could be considered as probiotic strains that have beneficial effects in reducing serum cholesterol levels.

Table 3Health benefits of lactic acid bacteria isolated from Indonesian fermented foods as assessed in animal studies.

Candidate probiotic strains isolated from Indonesian fermented foods have also been evaluated in the treatment or prevention of diarrhea caused by EnteropathogenicE.coli(EPEC)infection.Lb.plantarumMB427 from mandai at 109cfu/mL reduced the incidence and severity of diarrhea and shortened the duration of diarrhea in EPEC-induced diarrhea in Sprague-Dawley rats[17]and increased secretion of serum IgA and IgB.Supplementation of dadih isolate,P.pentosaceus,at a dose of 2×108cfu/g reduced stool frequency,lowered tumor necrosis factor-levels and improved the balance of gut microflora in EPEC-induced diarrheal mice(Musmuscullus)[66].Similar results were observed with aW.paramesenteroidesstrain also isolated from dadih[67].The researchers suggested that probiotic supplementation may protect against mucosal epithelial cell damage byE.coliexposure and protect cell against further damage by TNF-and interferon(IFN)-.Probiotics are able to downregulate T helper(Th)-1 responses and inhibit the production of proinflammatory cytokines,such as TNF-by dendritic cells.The decreased the concentration of TNF-in the feces,decreased the serum levels of TNF-,and stool frequency.These studies indicate that potential probiotic bacteria isolated from fermented foods could improve the immune system and reduce diarrhea incidents.Diarrhea is the third leading cause of death,following tuberculosis and pneumonia,in Indonesia[66].The most common causes of diarrhea in children,both in developed and developing countries areE.coli,Rotavirus,Salmonellaspp.,Shigellaspp.,Campylobacterjejuni,EntamoebahistolyticaandGiardialamblia[68].The promising features of LAB isolated from fermented foods in reducing/preventing the incident of diarrhea needs to be confirmed in human studies.

Modification of gut bacterial activities has also correlated with antimutagenicity.Potential probiotic bacterium,E.faeciumIS-27526 isolated from dadih,showedinvivoanti-mutagenic properties toward Trp-P1 of rats[30].Milk cultured withE.faeciumIS-27526 significantly lowered fecal mutagenicity and the recovery of Trp-P1 in urine was significantly lower than in control rats fed skim milk.The anti-mutagenic properties was considered due to binding ability of the bacterial cell wall of dadih lactic cultures toward chemicals mutagen.

3.2.Human studies

Human studies on LAB isolated from Indonesian fermented foods are very limited.Two potential probiotics originating from dadih have gone through a clinical study in humans[69,70].Surono et al.[69]evaluated the effect ofE.faeciumIS-27526 in milk on humoral immune response and on bodyweight of young children aged between 15 and 54 months.A 90 days randomized,double-blind,placebo-controlled study was conducted with two groups of young children,placebo and probiotic group.Ultra high temperature treated,low fat milk was used as the carrier of 2.3×108cfu/day of the probiotic.The results showed thatE.faeciumIS-27526 had a significant positive effect on humoral immune response and salivary IgA in underweight young children,and on their weight gain.However,the total serum IgA did not significantly increase in the probiotic group compared with the placebo group.

Another human study[70]evaluated the effect of probioticL.plantarumIS-10506(originally isolated from dadih)and zinc supplementation on humoral immune response and zinc status of Indonesian infants aged 12–24 months in a 90-day randomized,double-blind,placebo-controlled trial.A combination of microencapsulatedLb.plantarumIS-10506 at a dose of 1010cfu/day and 8 mg of elemental zinc showed a potential ability to improve the zinc status of the infants.Supplementation with the probiotic and zinc resulted in a significantly increased humoral immune response,as well as improved zinc status.The effects of probiotics on the humoral immune response was suggested to be the result of colonization and adhesion to epithelial cells,and production of SIgA production induced by the cell wall component of probiotics,such as lipoteichoic acids and peptidoglycan[69].Both strong immune responses and gut integrity play important roles in the repair of intestinal brush border damage as a result of the balance of microbiota.Zinc and probiotics workviadifferent mechanisms,but they are possible to have a synergistic effect.While zinc is necessary for the activity of some immunity mediators,probiotic supplementation could improve the integrity of the intestine,which in turn will optimize the absorption of zinc.The researchers considered that the health beneficial effects of zinc and probiotics could be amplified when they are taken together,more specifically,resulting in improved mineral absorption or a higher cellular immune response.

4.Future perspectives

Many traditional Indonesian fermented foods are potential sources of microorganisms,especially LAB,with promising beneficial health effects.Among the functional properties explored,LAB originating from Indonesian fermented foods showed promising effects on hypocholesterolemia,stimulation of the immune system,and in the prevention of diarrhea.These beneficial health effects could contribute to promoting the health status of Indonesians.However,the functional properties of many promising LAB originating from Indonesian fermented foods have not been fully investigated.Studies are mainly of a preliminary nature and need to be confirmed in animal and human studies.Although most Indonesian fermented foods are historically safe,exploiting a single microorganism should also be supported with studies to confirm its safety,especially for strains belonging to genera that have been reported to pose safety issues.In addition,the ability of LAB of to produce bioactive compounds is an area that needs to be explored extensively in order to maximize the beneficial health impact.

Consumers are aware that fermented foods contain microorganisms and,hence,they become suitable matrixes as probiotic carriers.Among Indonesian fermented products,tempe,as a cheap meat substitute,is an important part of the daily diet.However,tempe is commonly consumed after cooking,which would kill any live probiotic LAB.Other fermented foods,such as dadih,tape,sayur asin and beverages,that are consumed without cooking are more suitable as probiotic carriers.When fermented foods are used as carriers of probiotic bacteria,factors that may influence the ability of the probiotic to survive in the product,during fermentation and marketing,and their activity when entering the human gastrointestinal track,must be considered.LAB with beneficial health effects in fermented foods could serve both as probiotics and as the fermentative organism.Ideally,probiotic cultures to be incorporated into fermented products should have multifunctional characteristics.They should be able to grow and ferment the product,or at least not have any negative impact on the organoleptic properties of the food,while maintaining their probiotic properties.

Exploration of potentially beneficial microorganisms in Indonesian fermented foods needs to be extended to microorganisms other than LAB that are also present in fermented foods.Yeasts and some species ofBacillusfor examples are the potential microorganisms for probiotic.

Traditional Indonesian fermented foods,utilizing a variety of raw materials,have been handed down for many generations.Although challenges remain,the microorganisms present and involved during fermentation as well as their metabolic products may contribute health benefits to consumers.Therefore,more evidence on the health impacts of beneficial microorganisms and understanding of the relationships between fermented foods,beneficial microorganisms and human health are essential if use of beneficial microorganisms to promote health is to be fully exploited.

Acknowledgement

The author would like to thank Dr.J.D.Owens of University of Reading,UK for his assistance in reading and correcting the manuscript.