Preparation Of Maillard Reaction Intermediates Of Salt-reducing Soybean Peptide And Their Processing Flavor Formation

Saltiness,as the main flavor of the five basic flavors,determines consumers’ perception and acceptance of products directly.In the food industry,salt is mainly used as salting agent,excessive intake of salt will cause a series of health problems.Thus,it is imperative to develop salt reduction products.In this study,soybean protein isolate was used as raw material and controlled enzymatic hydrolysis technology was employed to prepare soybean peptides with saltiness and umami enhancing effect.The soybean peptides Maillard reaction intermediates(MRIs)were further prepared using the soybean peptides as substrate.The formation of the MRIs was promoted by the combined dehydration method of vacuum concentration,spray drying and vacuum drying.To analyze and characterize the soybean peptides MRIs during the vacuum drying process,UV spectrum analysis,water activity and moisture state analysis,and quantitative analysis of browning precursors were employed.Also in this study,the reaction products of Maillard reaction intermediates at different stages were prepared and their flavor formation ability in different cooking systems was investigated to broaden their food processing adaptability.The following contents were the main research contents.The soybean protein isolate was enzymatically hydrolyzed by the combined action of protamex Ⅰ and aminopeptidase and the preparation parameters of soybean peptides with saltiness and umami enhancing effect were optimized: the substrate concentration was 8%,the added amount of protamex Ⅰ was 3500 U/g substrate,hydrolyzed for 4 h at 60℃ and p H of8.0,the added amount of aminopeptidase was 460 U/g substrate,hydrolyzed for 2.5 h at 50℃and p H of 7.0.Under this condition,92.17% of the soybean enzymatic hydrolysates were composed of substances with molecular weight less than 1000.Moreover,free amino acids constituted just 7.11% of total amino acids,suggesting that small molecular peptides were the predominant component of the enzymatic hydrolysis.The electronic tongue analysis indicated that the saltiness and umami value of 0.4%(w/w)salt solution containing 0.3%(w/w)soybean peptides reached 7.48 and 9.76,respectively,which were significantly higher than5.29 and 4.47 of 0.5%(w/w)salt solution in the control group,indicating that the soybean peptides had a significant saltiness and umami enhancement effect.Using cysteine as a tracer,the formation times of the soybean peptides MRIs with different sugar sources were determined by two-stage temperature-variable Maillard reaction.Under the temperature of 80℃,the formation time were as follows: 40 min for ribose,60 min for arabinose,fructose,glucose,and galactose.After that the corresponding soybean peptides MRIs were prepared in the aqueous solutions.The electronic tongue analysis combined with sensory evaluation were employed to analyze the taste characteristics of soybean peptide MRIs with different sugar sources.The result showed that the glucose-soybean peptide MRIs had the best saltiness and umami enhancing effect,thus it was selected as the follow-up research object.The soybean peptide-glucose MRIs were prepared efficiently by primarily low temperature thermal reaction,followed by the combined dehydration method of vacuum concentration,spray drying and vacuum drying.After that the characterization of the soybean peptide-glucose MRIs during the vacuum drying process was investigated.The analysis of UV spectrum,water activity and moisture state all indicated that the MRIs continued to accumulate during the vacuum drying process.It was also found that the browning precursors accumulated continuously during the vacuum drying process,and the amino acid analysis showed that the formation and degradation of MRIs existed simultaneously during the vacuum drying process,which proved that the Maillard reaction had not yet reached the advanced stage.The electronic tongue analysis showed that the saltiness enhancing effect of the MRIs gradually weakened during the vacuum drying process,and the higher the vacuum drying temperature,the faster the decrease.At 100℃,the saltiness value of the MRIs salt solution decreased from 6.37 to 5.89,still all samples could achieve the effect of reducing salt by 20%,and could significantly improve the umami characteristics.The study preliminarily determined that the decrease of the saltiness enhancing effect of the MRIs was caused by the Maillard reaction of small peptides.Using the salt-reducing soybean peptide as raw material,the reaction products of soybean peptides MRIs at different stages were prepared,and their flavor formation ability during thermal processing was investigated.The results showed that the total volatile flavor compounds of the MRIs reacted for 120 min were the highest,so the MRIs with different reaction time of 120 min and before were selected for follow-up study.The reaction products of soybean peptides MRIs at different stages were applied to the simulated hot pot,stir-frying and baking systems respectively,and the products with the best flavor formation ability in different systems were screened.The reaction product of soybean peptides MRIs of reaction time of 90 min was more suitable for hot pot system,while the MRIs reaction product of reaction time of 120 min was more suitable for cooking and baking system.The result of actual thermal processing system showed that in the hot pot,fried vegetables and baked biscuits,the reaction products of soybean peptides MRIs could not only increase the content of volatile substances but also form new volatile flavor substances,which could enrich the overall flavor of food.