Antioxidant And Flavor Characteristics Of Sweet Potato Protein Hydrolysates As Affected By Ultrasound-microwave And Maillard Reaction

Antioxidant peptides have become the focus of international food research due to their unique physiological activities and health benefits.Different treatment assisted enzymatic hydrolysis can improve the activity of antioxidant peptides,and Maillard reaction（MR）has a great influence on their flavor.Sweet potato protein is a potential source of antioxidant peptides due to its good functional properties.A deep study on effects of different treatment assisted enzymatic hydrolysis and MR on antioxidant activity and flavor characteristics of sweet potato protein hydrolysates（SPPH）is of great significance to expand its application in food.In this study,SPPH were prepared by ultrasonic-microwave（UM）assisted enzymatic hydrolysis,and the effect of UM assisted enzymatic hydrolysis on molecular weight distribution,primary fragment and spatial conformation of SPPH were investigated;Furthermore,to improve antioxidant activity and flavor of SPPH,the effects of different types of US,monosaccharides and MR on the structure,antioxidant activity,and flavor of SPPH were studied and compared with Maillard reaction products（MRPs）from other food protein hydrolysates sources,thus to provide theoretical basis for the application of SPPH and its MRPs in food.The specific research results are as follows:（1）To prepare sweet potato peptides with high antioxidant activity,effects of UM assisted enzymatic hydrolysis by Alcalase（ALC）,Flavourzyme（FLA）and their combination（ALC+FLA）on production and characterization of SPPH was investigated.UM assisted enzymatic hydrolysis significantly increased the degree of hydrolysis and antioxidant activity of SPPH as compared to those from untreated samples.Molecular weight（MW）<3 k Da fractions in SPPH from UM assisted ALC and ALC+FLA hydrolysis presented much stronger Fe²⁺-chelating activity,·OH scavenging activity and relatively high ORAC values respectively,from which diverse peptides with potential antioxidant activities were obtained.The peptides’conformational structure and potential antioxidant amino acids disposition in different peptide sequences revealed the structure-activity relationship.Thus,UM treatment presents a great potential utilization on antioxidant peptides production.（2）To improve the antioxidant activity and flavor characteristics of SPPH,effects of 3 different types of US,energy-divergent ultrasound（EDU）,energy-gathered ultrasound（EGU）,energy-gathered ultrasound-microwave（EGUM）on structure,antioxidant activities,aroma,and sensory attributes of SPPH-MRPs were investigated.EGU and EGUM markedly enhanced the MR progress.EGU-MRPs showed the highest antioxidant activities,of which the ORAC value was 92.10μg TE/m L.EGU-MRPs and EGUM-MRPs showed higher content and quality of aroma compounds,higher umami,sweetness,and sourness attributes,and lower bitterness,followed by EDU-MRPs.Thus,US assisted enzymatic hydrolysis coupled with MR might be a promising way to produce natural flavoring with improved antioxidant activities.（3）To obtain MRPs with better antioxidant activity and flavor characteristics,effects of different monosaccharides（arabinose,AR;xylose,XY;galactose,Ga and glucose,GL）on peptide structure,antioxidant activities and flavor characteristics of SPPH-MRPs were investigated.USXY showed the lowest p H value（5.04）,the highest browning intensity,fluorescence intensity and ORAC value（109.15μg TE/m L）,followed by USGA and USAR.USXY exhibited the highest umami intensity score（7.4）,followed by USGA and USAR respectively,and their stronger umami taste was strongly correlated to aldehydes,thiophenes,MW 500–3000 Da peptides.Thus,USXY can be potentially used in food industry due to its good antioxidant activity and flavor.（4）Finally,SPPH-MRPs were compared with MRPs from potato protein hydrolysates（PPH-MRPs）,soybean protein isolate hydrolysates（SPIH-MRPs）,egg white protein hydrolysates（EWPH-MRPs）and whey protein isolate hydrolysates（WPIH-MRPs）,thus to provide basic data for their application in food industry.WPIH-MRPs exhibited the lowest p H value（4.95）,the highest fluorescence intensity and antioxidant activity（ORAC value of 125.24μg TE/m L）,followed by SPPH-MRPs.WPIH-MRPs exhibited the highest umami intensity score,followed by SPPH-MRPs and SPIH-MRPs,respectively.However,compared with WPIH-MRPs（24.73 and 1265μg/kg respectively）,SPPH-MRPs presented less harmful compounds,5-hydroxymethyl furfural and acrylamides,which were 17.11μg/kg and undetected,respectively.Therefore,SPPH has the potential to be used in the production of healthy and safe natural flavoring agents with good antioxidant activity and flavor.