Limited Proteolysis Of Soy Proteins And Analysis And Identification Of The Bitterness Substances

Soy proteins with low viscosity, low gel and high dispersity have wide application insolid protein drinks. Limited enzymatic hydrolysis is an important means to obtain theproteins with above properties. The main purpose of this study was investigating the influenceof enzyme types and dosage on the functionality and bitterness of modified soy proteins,separating and identifying the bitterness substances.Soy protein isolates were hydrolyzed by seven kinds of commonly used commercialenzymes (Alcalase, Neutrase, Protamex, Papain, Bromelain, PC10F Protease and SD NY10Protease) to prepare modified soy protein products with low DH. One kind of enzyme whichcan prepare the hydrolyzate with low bitterness and the functional properties required wasscreened by comparing.Two DH hydrolyzates were prepared by controlling E: S=0.08%and E: S=0.15%. Bycomparing viscosity, bitterness, gelation, emulsification and dispersion, we could find thatseven kinds of enzymes could reduce viscosity and gelation, improve emulsification anddispersion with different extent. The hydrolyzate of PC10F Protease had the lowest bitternessand viscosity and without gelation. In general, the hydrolyzate of Papain had all the propertieswe needed.The bitterness substances of low DH hydrolyzates were extracted, isolated and identified.70%ethanol extracts (EE70) were much bitterer by sensory evaluation.That means bitternesssubstances could be enriched by70%ethanol. The rate of hydrophobic amino acids waspositive correlated with bitterness value by amino acid analysis. The study showed that theweighted average retention time of the peak area was positive correlated with bitterness valueby analyzing RP-HPLC graphs of EE70. The200Da～5000Da molecular weight of EE70ofthe same enzyme was positive correlated with bitterness value by SEC-HPLC analysis.With the increase of DH, the content of aglycone isoflavones in modified proteins wasincreased. However, the ratio of aglycone isoflavones was not positive correlated with bitter-ness values of enzymatic proteins. That means aglycone isoflavones was not contributionfactor of bitterness. Hydrophobic bitter peptides were decisive factors.The powder actived carbon was used to absorb EE70and eluted by25%,50%and75%ethanol solutions respectively. Three eluted fractions were gained-EET25, EET50andEET75.Study showed that the bitterness of EET75was strongest and the weighted averageretention time of the peak area of EET75was biggest. The molecular weight of EET75wasmainly distributed in200Da～1000Da.EET75was separated by Superdex peptide gel column. Peak fractions were collected andsensory evaluated to find the bitterest component. This component was isolated and identifiedby LC-MS. The results showed that the bitterness substances of different hydrolysates weremicromolecule hydrophobic peptides. Alcalase hydrolysate: LLPH, YVVL, VYFV; Neutraseand Protamex hydrolysates: LVRN, LYH, YVVL, FY; Papain hydrolysate: VVM, FAFT, PLM;Bromelain hydrolysate: KVRK, LATL, NVP, LKYK; PC10F Protease hydrolysate: LVRN, HLSY, FY; SD NY10Protease hydrolysate: LVRN, LYH, LFGF, FY.