Study On Regulation And Mechanism Of Acrylamide In Wheat Bread By Mixed Fermentation

In recent years,China’s baked goods industry has undergone rapid changes,with per capita consumption of baked goods,market scale and enterprise registration increasing year by year.However,the safety of baked goods,especially the presence of Acrylamide AM,is one of the most difficult issues facing the current bakery industry.Therefore,it is of great guiding significance to study the formation mechanism of acrylamide in baked goods during the heating process and explore effective regulation methods for the safety of acrylamide in baked goods.As one of the frontiers of bakery and food science research in recent years,sourdough fermentation technology has been widely welcomed.In this paper,inhibition of acrylamide in bread and asparagine/glucose simulation system by fermented sour dough fermented by lactic acid bacteria,yeast and their mixed strains was studied respectively,and inhibition of acrylamide in wheat bread by fermented sourdough with added strains and its inhibition mechanism was systematically studied.The results of this study will provide the bakery industry with a better way to reduce AM generation in order to obtain safe,natural and acceptable bakery products,and expand the utilization value of sour dough.At the same time,it has important significance to guarantee the safety of baked goods,and establishment of AM related food safety standard.The main research results are as follows:(1)Four strains of lactic acid bacteria were selected:Pediococcus pentosaceus(PP),Lactobacillus plantarum(LP),Lactobacillus fermentum,LF),Weissella confusa(WC)and 4 strains of yeast:Saccharomyces cerevisiae-I(SH),Saccharomyces cerevisiae-Ⅱ(ST),Yeast-Ⅰ(GH),Yeast-Ⅱ,As a single strain,wheat flour was used as the substrate to prepare sourdough.The bacterial growth,colony number,organic acid metabolism,reducing sugar and protein metabolites and other physicochemical indexes were measured by HPLC,powder analyzer,ultraviolet spectrophotometer and other research methods.The experimental results showed that the lactic acid bacteria and yeast in MRS And YPD medium reached logarithmic growth stage at 4-16 h,and the strains grew well in wheat flour substrate and rapidly increased after entering logarithmic growth stage at 4 h.The growth rate of PP was the highest,and the number of colonies reached 8.87(Log CFU/g sourdough)after 12 h fermentation,a large amount of reducing sugar was produced(47.11 mmol/kg sourdough),and the protein degradation was 9.56%.ST was the fastest growing yeast.At 16 h of fermentation,the number of colonies was 8.44(Log CFU/g sourdough),the reducing sugar content was 44.67 mmol/kg sourdough),and the protein degradation was 8.82%.Compared with natural fermentation(pH value decreased by 2.10%,lactic acid 1.77(mg/g sourdough),acetic acid 1.23(mg/g sourdough)),pH value of PP-s group decreased the fastest(33.3%,lactic acid 14.69(mg/g sourdough),acetic acid 1.57(mg/g sourdough)).The ST-s group was the second(pH value decreased by 13.3%,lactic acid 7.29(mg/g sourdough),acetic acid 2.70(mg/g sourdough)),which were better than natural fermentation and other single bacteria fermented sourdough.Combined with the maximum acid production amount and rate,the stability of soluble protein degradation and the advantages of lactic acid bacteria and yeast,the ratio of the mixed strains of pentococcus and saccharomyces sanguinis was selected.(2)The Pediococcus pentosaceus(PP)and Saccharomyces cerevisiae-Ⅱ(ST)were further selected and added into the small sour dough according to different proportions.The results showed that when PP:ST=1:1,the two strains could achieve synergistic growth.The pH values of mixed fermentation(FH-s)samples were all lower than those of ST-s and PP-s alone,indicating that FH-s promoted the production of more organic acids.The contents of maltose,glucose,fructose and sucrose in FH-s increased first and then decreased,and the contents were the lowest.The content of free amino acids decreased slightly and then increased gradually,and the total amino acid of mixed fermentation samples was higher than that of ST-s and PP-s alone fermentation.In addition,the contents of serine,tyrosine and threonine in FH-s were higher than those in PP-s and ST-s.The inhibition rate of AM in wheat bread was 49.66%by FH-s,42.23%by PP-s and 38.22%by ST-s,which were significantly higher than those in natural fermentation group(NU-s)(P<0.05).Correlation analysis showed that the inhibition rate of acrylamide in wheat sourdough was significantly positively correlated with the decrease of pH value and protein content in fermented sourdough(P<0.05).Finally,the effects of strain fermentation of sourdough on bread quality were investigated by means of texture analyzer,colorimeter and differential calorimetry scanner.The results showed that compared with the control group,the bread brightness of all strains fermented sourdough groups was improved,and FH-b group was significantly better than natural fermented sour dough bread in the aspects of bread hardness,moisture content and aging(P<0.05).(3)Under the optimal ratio(PP:ST=1:1),a chemical reaction simulation system of asparagine/glucose(Asn/Glc)was established to systematically study the inhibition of AM in asparagine/glucose(Asn/Glc)by fermented sourdough under different strains and different fermentation time.The results showed as follows:In the Asn/Glc system,the inhibition rate of acrylamide was the highest in the fermented sour dough for 12 h.PP-s,ST-s and FH-s could significantly inhibit the formation of acrylamide in the simulation system(P<0.05),but the inhibition effect on acrylamide was weakened in the elimination kinetic stage of acrylamide.The kinetic model analysis results show that the Logistic exponential kinetic model is the most suitable to describe the kinetic process of acrylamide in this study.There are two mechanisms involved in the reduction of acrylamide formation in single and mixed fermentation of sourdough.First,the overall reduction of the relevant precursor substance prevents the Maillard positive reaction:firstly,the reduction of reducing sugar content;secondly,the increase of amino acid components competitively inhibits the formation of 3-APA into acrylamide.Finally,the formation of HMF is reduced,again reducing the precursor material associated with AM formation.Second,it prevents protonation reaction during the formation of acrylamide and accelerates the elimination of acrylamide.Preventing protonation reaction is the accumulation of organic acids,which causes the decrease of pH value and the increase of H+,and prevents the protonation process of the reaction between amino group and carbonyl group.The elimination process is due to the improvement of the positive voltage of Maillard simulation system.Maintaining a high positive voltage can promote the oxidation of acrylamide and promote the reaction of acrylamide with free radicals to eliminate.