Study On The Formation Mechanism Of Pea-derived Volatile Off-flavor Compounds And Processing Technology Of Pea Protein Isolate With Low Off-flavor

Pea protein,as an emerging plant protein resource,has attracted consumers' attention.Compared with soy protein,the label of non-GMO,hypoallergenic and high nutritional value of pea protein is more favored by investors,and its market demand is growing rapidly.However,when pea protein replaces traditional animal protein and soy protein in food development,especially when used in vegetable protein beverages and vegetable milk,flavor is the biggest limiting factor.In this paper,the volatile components,odor-active components and their corresponding off-flavor contribution ratios in pea protein isolate(PPI)were systematically characterized;the precursors of pea-derived off-flavor components and endogenous enzymes related to lipoxygenase(LOX)pathway were investigated,and the formation mechanism of key volatile off-flavor compounds was revealed;the effects of processing factors on the formation of key volatile off-flavor components were explained;the adsorption mechanism between the components in pea milk and the key volatile off-flavor compounds was clarified.On this basis,the production process of PPI with low off-flavor was established.The main conclusions are as follows:The volatile compounds,odor-active compounds and their corresponding odor contribution ratios of PPI were systematically characterized,and the formation mechanism of key volatile off-flavor compounds was revealed.The off-flavor of PPI can be classified as nonbeany and beany flavor,of which the non-beany flavor compounds 2-isobutyl-3-methoxy pyrazine and 2-methoxy-3-isopropyl-(5 or 6)-methyl pyrazine accounted for about 46.77% and30.70%,respectively.The representative compounds of beany flavor were(E,E)-2,4-decadienal(7.19%),(E,E)-2,4-nonadienal(7.01%),hexanal(4.34%),2-pentylfuran(1.34%)and 1-octen-3-ol(1.57%).The off-flavor contribution rates of other odor-active compounds waer all less than 1%.Through further analysis,it was found that the key volatile off-flavor compounds in PPI were the results of the interaction of non-LOX and LOX pathways.2-Methoxy-3-isopropyl-(5 or 6)-methyl pyrazine and 2-isobutyl-3-methoxy pyrazine were synthesized by non-LOX pathway.The former was derived from the ripening process of pea,while the latter was synthesized by heating and methoxylation with free amino acids as precursors.The contents and activities of LOX-2 and alcohol dehydrogenase(ADH)in pea were higher,while those of hydroperoxide lyase(HPL)were relatively lower.The endogenous flavor precursor contents and LOX pathway enzyme activities were the dominant factors that determined the contents of key odor-active off-flavor compounds,while the content of lipid content was a secondary factor.The influence of processing factors and membrane separation treatment on the key volatile off-flavor contents in PPI were investigated,and the adsorption mechanism between the components in pea milk and the key volatile off-flavor compounds was clarified.When soaked peas were grinded under alkaline condition with the inhibiton of LOX activity,the contents of off-flavor components related to LOX pathway in pea milk could be reduced by 58%-73%.Heat treatment could destroy the binding of 2-methoxy-3-isopropyl-(5 or 6)-methyl pyrazine with the pea milk components.After heating,about 25% of the pyrazine could be separated into whey.Through the study of membrane separation of the key volatile off-flavor components in different systems,it was found that except for 2-methoxy-3-isopropyl-(5 or 6)-methyl pyrazine,the binding strength between other off-flavors and pea milk components were positively correlated with their log P values.Methoxypyrazine was easily adsorbed tightly on the interface between protein and lipid,resulting in extremely low release in pea milk at room temperature,which could be destroyed by heating.Compared with the conventional process,about 70% of2-methoxy-3-isopropyl-(5 or 6)-methyl pyrazine,86% of 2-isobutyl-3-methoxy pyrazine and most of the beany flavor volatile compounds were removed by membrane separation and acid precipitation.Three rounds of laboratory-scale pilot test were carried out with 20 kg peas per batch.The yields of PPI,starch and fiber were 19.10% ± 0.85%,44.30% ± 1.35% and 16.90% ± 0.80%,respectively.The flavor and solubility of the pilot-scale PPI samples in laboratory were better than commercial product S85 F,which verified the feasibility of process scale-up.According to the results of material balance,a pilot-scale production line of PPI with low off-flavor was designed to process 200 kg of pea seeds per batch and the main production equipments were selected.