Effect Of Maillard Reaction On Structure And Enzymatic Hydrolysis Of Peanut Protein Isolate

Peanut production in our country is the first in the world,there are about 6 million tons peanut meal which is peanut oil by-product per year,only as feed or fertilizer.High value utilization of low value peanut meal resources can effectively solve the problem of protein resource lack in our country.Peanut protein beverage has balanced nutrition,aromatic flavor,loved by the masses.But researches on the effect of thermal treatment process on the structures and digestion characteristics of beverages contain proteins are still relatively lack.At the same time,the processing of peanut meal for more high value using has not formed the scale at present and needs further research and development.Peanut protein is the research object of this article,discusses the degree of Maillard reaction and the structural characteristics changes of PPI after the simulation of thermal sterilization condition.The results showed that: with the aggravating thermal treatment,browning,intermediate products and degree of graft(DG)increased,indicating that the extent of Maillard reaction(MR)deepened.When the temperature increase to 121 ℃,the extent of Maillard reaction(MR)deepened significantly and intermediate products transform to end-product.Thermal treated for 30 min at 121 ℃,browning extent reaches the maximum.SDS-PAGE,Circular dichroism(CD),Differential scanning calorimetry(DSC)and Field emission scanning electron microscope(FESEM)are employed to characterize secondary structure,tertiary structure,thermal properties and macrostructure changes of PPI.Because of thermal treatment,crosslinking between PPI and glucose come into being,thermal stability is improved,the enthalpy value gradually reduce;Secondary structure of PPI-glucose mixture gradually converts to a more ordered and continuous arrangement;tryptophan residues was encased partly,phenylalanine residues further exposed.In order to research the effect of thermal sterilization on the subsequent simulated gastrointestinal digestion,PPI and glucose were thermal-treated in thermal sterilization conditions,then subjected to a simulated gastrointestinal digestion in vitro.Absorbance in 294/420 nm of thermal-treated samples,degree of hydrolysis(DH),protein digestibility(PD),molecular weight distribution,free amino acid composition of simulated gastrointestinal digestion products were measured.The results showed that: compared to the control group,PPI heat-treated without glucose have also been a certain degree of browning,PPI heat-treated with glucose caused stronger MR.with the aggravating thermal treatment,reaction degree deepened.Heat treatment and MR leaded to an increase of larger molecular weight peptides content.From a general view,MR goes against the digestive and utilizable performance of PPI.Amino acids,whose content is more than 2% and have high Maillard reaction activity are Leu、Tyr、Lys、Ile and(Cys)2,Lys has the highest reaction activity among them.At last,enzyme properties of peanut protein isolate was studied,and the development of umami basic material was conducted.The study found that: the optimal conditions of PPI enzymolysis are as follows: flavor protease and novozymes 11039 hydrolase distribution by 1:2(w/w),the substrate concentration is 10%(w/w,according to the protein),total enzyme concentration is 4%(w/w,based on protein),pH 7.0,enzymolysis temperature is 55 ℃,enzymolysis time is 15 h.And found that mild maillard reaction between enzymatic hydrolysates and xylose can significantly improve the umami strength.The optimal conditions of Maillard reaction are as follows: xylose 0.5%(w/w),pH 6.5,the reaction temperature is 100 ℃,the reaction time is 80 min.