Identification And Selection Of Microorganisms From Fermented Potato And The Impact On Gluten-free Steamed Bread Quality

So far,the sensory and flavor characteristics of gluten-free potato steamed bread need to be improved,and there is a lack of special starter for potato steamed bread production.In this study,firstly,the effects of different pretreatment methods,such as steaming,boiling and high hydrostatic pressure,on the microbial composition,nutritional and functional composition of fermented potato were compared and the best pretreatment method was selected;secondly,the dominant lactic acid bacteria(LAB)and yeast in the fermented potato were screened out by strain isolation,culturing and molecular biological identification;then,by comparing the effects of different proportion of dominant strains on the physicochemical,nutritional and flavor properties of gluten-free potato steamed bread,the optimal proportion of different strains in the mixed starter was preliminarily optimized;on this basis,by comparing the effects of different fermentation temperature and time on the sensory,nutritional,flavor and other quality characteristics of gluten-free potato steamed bread,the optimal fermentation temperature and time of the mixed starter were preliminarily determined.The results were as follows:Weissella and Saccharomyces cerevisiae were found to be the most dominant LAB and yeast in fermented potato respectively.Fermentation increased protein and dietary fiber contents(9.68 ± 0.68% and 9.48 ± 0.37%)of boiled fermented potato and steamed fermented potato but the highest protein content(8.18 ± 0.22%)was recorded in boiled fermented potato.Steamed fermented potato had better quality compared to other treated samples as it contains high amount of iron and the high abundance of Weissella(35.84%)and Gluconobacter(20.80%)in this sample resulted in lowering of pH(4.39 ± 0.09)and inhibition of undesirable bacteria and fungi.A total of 3 LAB species(Weissella sp.strain IMAU50209,Pediococcus pentosaceus strain W2SR04,Pediococcus sp.NBRC 107186 strain)and 2 yeast species(Pichia sp.strain AQGWD7 and Saccharomyces cerevisiae strain YJM1592)were isolated and identified from fermented potato.Weissella and Saccharomyces generated more Ethanol and 3-methyl-1-butanol as compared to other isolates.However,Weissella produced high amount of acids and esters in addition to alcohols.In addition,Weissella showed good proteolytic ability,and recorded the highest exopolysaccharide content(824.44±4.19 mg/L),while Saccharomyces recorded high gas retention value(1740.00 ± 86.27mL).According to the physicochemical and nutritional value,the optimal combination ratio of commercial yeast and Weissella was 5:1(weight to weight).In addition,mixed starter generated other important aroma and flavor compounds(lactic acid,acetic acid and butylated hydroxytoluene)alongside alcohols in gluten-free potato steamed bread.Furthermore,organic acid produced in samples with Weissella influenced the hydrolysis index and expected glycemic index.Fermentation at 40 °C for 180 min was considered the optimum with respect to the sensory quality(odour,texture and overall acceptability),flavor and aroma compounds(acetic acid and butylated hydroxytoluene).The highest exopolysaccharide yield(8.51 ± 0.78 mg/g)was recorded in sample fermented for 180 min at 40 °C.More so,exopolysaccharide yield showed correlation with specific volume,hardness and chewiness.This study revealed that steaming prior to fermentation could facilitate nutrients availability for LAB growth as well as inhibit growth of undesirable microorganisms.More so,steamed fermented potato retained more nutrients.Weissella and Saccharomyces exhibit better technological attributes and generated more alcohols as compared to other isolates from fermented potato.The optimum combination ratio of mixed starter was 5: 1 commercial yeast and Weissella according to improved nutritional value and generation of other important aroma and flavor compounds alongside alcohols.It can be concluded that fermentation at 40 °C for 180 min was the best for optimum performance of the fermenting microorganisms as well as generation of metabolites and obtaining good quality GFP steamed bread.