| Wheat bread is an important staple food consumed world-wide.The main starch in wheat bread is considered easily digestible,which causes a high glycemic response,measured as glycemic index(GI)upon consumption.White kidney beans(Phaseolus vulgaris L.),which account for 50%of the world's edible legumes,have attracted attention due to their high dietary fiber,resistant starch content,and low glycemic index when consumed.However,raw kidney beans contain lipoxygenase that causes the"beany"taste and a large number of anti-nutritional factors(ANF)which affects protein digestibility.In this study,Lactobacillus plantarum(L1)or Pediococcus pentosaceus(J28)and Kluyveromyces marxianus(KM)were used as starters to explore the influence of mixed fermentation and heat moisture treatment(HMT)on physicochemical properties of white kidney bean sourdough and bread starch digestibility.Furthermore,the effects of heat moisture treatment and multi-bacterial fermentation on baking quality,nutritional and flavor properties of bread were elaborated.The main findings and conclusions were as follows:1.The results showed that the SY-LK group had the lowest p H and the highest lactic acid content after mixed strain fermentation.After HMT and/or multi-bacterial fermentation,were ANF content was decreased differently.Acidification may have improved the extraction of phenolic compounds,this resulted in total phenol content increase by 1.61 to 1.97 times after mixed strain fermentation:the highest increase was observed in the HY-LK group.The degradation of peptides was less after multi-bacterial fermentation than after HMT treatment,however,the small molecular weight peptide content was highest after combined HMT and mixed strain fermentation treatment.No significant change was observed in the SDF content after HMT,whereas,multi-bacterial fermentation significantly increased the SDF and reduced the IDF(p<0.05).2.RVA,XRD and FTIR,and SEM methods were used to analyze viscosity,crystalline and microscopic morphological properties of lyophilized sourdough powder.The dough and bread microstructures were also observed using SEM and CLSEM methods,respectively.In addition,starch digestibility of sourdough bread after HMT and/or multi-bacterial were also determined.The results showed that the gelatinization temperature increased after HMT and multi-bacterial fermentation.The viscosity,retrogradation value,and disintegration value decreased in all samples,however,a higher reduction rate was observed in HMT treated group.Both HMT and multi-bacterial fermentation treatment changed the crystal type of kidney bean flour from type C to type A.For FTIR results,the ratio of 1047/1022cm-1 in the groups increased,which indicated that the order of starch increased.The SEM microstructure showed that after HMT,the relatively loose starch granules became dense granules and the starch granules were embedded in the protein after multi-bacterial fermentation.Also,the microstructure of bread dough revealed that HMT treatment reduced the dissolution of starch particles,while,multi-bacterial fermentation promoted gluten protein cross-linking in the dough.Interestingly,when the treatments were combined,starch and gluten protein in dough were more tightly bound.The different treatments were beneficial to inhibit?-amylase activity,thereby reducing starch digestibility.Therefore,in the HY-LKB group,?-amylase activity inhibition rate was highest at 64.11%,and the bread starch digestibility and GI values were subsequently the lowest,as the GI value dropped from 56.09 to 39.54.3.The specific volume,texture,nutritional characteristics including the amino acid content,in vitro protein digestibility,and nutritional evaluation of bread after different treatments were measured.The results showed that after multi-bacterial fermentation,and HMT-multi bacterial fermentation treatment,the specific volume of bread increased,hardness decreased,structure of bread core capsule was more uniform,protein digestibility improved(p<0.05),and the bread had a higher nutritional value of protein.However,the specific volume of bread decreased and the hardness increased after HMT.4.The flavor compound of bread after HMT and mixed fermentation were determined by electronic nose,electronic tongue and SPME-GC-MS.The results of electronic nose and electronic tongue showed that there were significant differences in the flavor and taste of bread in different groups.Raw kidney bean bread had the strongest bitterness and astringency.After HMT and/or multi-bacterial fermentation,the bitterness and astringency were reduced.The difference was that sweetness was enhanced after HMT treatment,while,the sourness and saltiness were enhanced after multi-bacterial fermentation.GC-MS results showed that the content of volatile flavor compound in the HMT and/or multi-bacterial fermentation bread group was higher than the control.Furthermore,type and content of flavor compounds of n-hexanol and hexanal,commonly related to the“beany taste”were significantly reduced in HMT-mixed strain fermentation group.In addition,the odor activity value of aldehydes and ester flavor substances(3-methylbutyraldehyde,2,4-decadienal,ethyl acetate,ethyl octanoate,and?-nonanolactone)increased in their relative odor activity value. |
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