Study Of Flavor And Antioxidant Activity In Stichopus Japonisus Gonads Enzymatics And Maillard Reaction Products

As by-products in the processing of stichopus japonisus,gonads were discarded in large quantities,resulting in the waste of nutrients.To improve the instrumentally value of stichopus japonisus gonads,which is a kind of protein-rich resource,it was considered to prepare protease hydrolysate.This paper took the intestines and gonads of stichopus japonisus as the research objects,and the enzymolysis conditions were optimized to prepare protease hydrolysates.The subsequent research objects were determined by comparative analysis of the basic nutrients,free amino acids and sensory evaluation.The enzymatics were divided into three groups by ultrafiltration(F0(non-ultrafiltration group),F1(1～5 k Da)and F2(<1 k Da)),D-xylose and L-cysteine were added to prepare Maillard reaction products(MRPs).The indicators related to the flavor composition(e.g.browing intensity,free amino acids,volatile compounds etc.)were investigated.In addition,the structure of enzymatics and its MRPs were characterized and the change of antioxidant activity was compared.To explore the potential of Maillard reaction in improving the flavor and antioxidant activity of protease hydrolysates,which provide some reference for the development of gonad products of of high-quality flavoring base and functional food by Maillard reaction.With the degree of hydrolysis as the index,the enzymatic conditions of intestine and gonads were optimized.The basic nutrients were determined by national standard methods,and the quality changes of intestine,gonads and enzymatics were compared by amino acids,free amino acids and sensory score.The results show that: The optimal enzymolysis conditions of intestine were liquid-solid ratio 6:1(w/w),enzyme dosage 4100 U/g,temperature 40 ℃,time 3.0 h,hydrolysis degree was 43.51%.The optimal enzymolysis conditions of gonads were liquid-solid ratio 4:1(w/w),enzyme dosage 5000 U/g,temperature 40 ℃,time 3.5 h.Under these conditions,the degree of hydrolysis was 32.6%.The crude protein content of gonad(7.3%)was significantly higher than intestine(3.5%,P<0.05),which was a good raw material for protein hydrolysate.The amino acids in the intestine and gonads were abundant and reasonably composed,which can be used as a good source of high quality protein.The content of glutamic acid was the highest,accounting for 14.16% and 14.84%respectively,which can be used as an ideal seasoning base for seafood.The phenylalanine and leucine were higher content than other free amino acid in intestine enzymatic,which were bitter acids and have poor sensory quality.Glutamic acid was the main umami amino acid in the gonadal enzymatic,which had umami taste and good sensory quality.Therefore,the gonadal hydrolysate was selected as the research object for the follow-up studies.The influence of Maillard reaction on flavor of different peptides was different.The results showed that the browning degree of <5 k Da peptide was significantly increased(P<0.05)and low molecular weight chromophytes had an important contribution to the formation of food color.After the Maillard reaction,umami and sweet free amino acids increased,while bitter free amino acids decreased of 1～5 k Da peptide,which was the best molecular weight range for preparing the taste-related gonadal protein hydrolysate.Macromolecular unsaturated aldehydes such as decanal,nonanal and benzaldehyde have significant contributions to the formation of MRPs flavor,and benzaldehyde was the most different substance before and after Maillard reaction.Secondly,Nitrogen-containing compounds,especially pyrazine compounds,were characteristic flavor substances of <5 k Da MRPs,which effectively improve the overall aroma of the gonadal hydrolysates.After the Maillard reaction,the protein peptide bond broke,structure unfolded and reset,leading to the exposure of aromatic chromophore and hydrophobic groups,UV absorption and fluorescence absorption intensity were increased.Protein hydrolysates and ribose were cross-linked,covalent bonds were formed.The antioxidant activity of gonads protease hydrolysates increased,and the <1 k Da peptide was easy to crosslink with sugar to form volatile compounds with good antioxidant activity.The DPPH radical scavenging activity of <1 k Da peptide MRPs was significantly higher than ascorbic acid with the same concentration,which could be used as a potential natural antioxidant.The Maillard reaction is beneficial to the stability of antioxidant activity of <1 k Da peptide components under high temperature and alkaline environment.The antioxidant activity of <1 k Da peptides MRPs may be mainly related to the polymers(such as heterocyclic compounds and melanoids)generated during the Maillard reaction.