Study On Enzymatic Hydrolysis Of Defatted Peanut Meal And Sensory Tatse Of Its Hydrolysate

Defatted peanut meal is the main byproduct during peanut oil production, which is rich inproteins. The use in food industry is limited by its poor protein solubility, dark color andunpleasant flavor resulted from hot pressing and solvent extracted. The aim of the presentstudy was to recycle defatted peanut proteins by enzymatic hydrolysis technologic forimproving its value-added and extending utilization. The defatted peanut meal washydrolysated efficiently by protease prepared from Aspergillus oryzae to obtain condimentsrich in taste peptides. Several isolation and separation technologies were done on peanutprotein taste peptides, and the taste peptides were identified the amino acid sequence. Thedifferent taste characteristics between the target taste peptides and the peptides by solid-phasesynthesis were analyzed to ravel the taste mechanism. We discussed in-depth the Maillardreaction activity, Thermal combining ways and releasing rule of flavor of Maillard reactionproducts derived from peptides and reducing sugar. This information will be useful to selectthe technological strategies to enhance taste characteristics of peanut protein peptides.The defatted peanut meal which was designated as the nitrogen source of culture mediumwas used to induce Aspergillus oryzae to secrete proteases which could specificallyhydrolysate defatted peanut meal proteins. The study on nutrient source of Aspergillus oryzaerevealed that flour, defatted peanut meal and CaCl2had great influence. The optimalparameters were obtained by single factor experiment and response surface methodology. Thebest fornula was flour2.24g, defatted peanut meal8.46g and CaCl20.028g, and the neutralprotease activity got15478.00U/g (at40℃). Crude proteases were purified by ammoniumsulphate precipitate, ultrafiltration and Sephadex G-75gel filtration chromatography. Theneutral protease activity of purified protease was79551.60U/g (at40℃). Purified proteaseexhibit a single band on SDS-Polyacrolymide gel and the molecular weights are determinedto be about50KDa. Maximal neutral protease activity was found at pH7.0. Optimaltemperature was40℃, and high stability was obtained from40to55℃. Metal ions had nosignificance activation role for protease activity.Four proteases (crude protease extract (CPE), Alcalase, Protamex and Papain) were used tohydrolyze defatted peanut meal. The results of protein recovery, degree of hydrolysis andmolecular weight distribution of peptide in defatted peanut meal hydrolysates were compared.Suggesting that CPE could efficiently hydrolysate defatted peanut meal proteins, the proteinrecovery and degree of hydrolysis were80.6%and43.4%, respectively. Furthermore, thehydrolysate by CPE was comprised of many (15.9%) small peptides of below1KDa. whereas 3–6KDa fraction was observed to be the main fraction of the hydrolysates from the otherthree commercial proteases. Factor analysis was employed to reduce the dimensional data ofthe contents of amino acids of hydrolysates by different proteases. The results indicated thatthe datas could be divided into three factors, the first factor was described as nutritional value,and the second was sensory taste. Nutrition evaluation results indicated that the content ofessential amino acid and the nutritional value of defatted peanut meal proteins could beimproved by CPE. Whereas the improvement effects by commercial proteases were notsignificant. The results of sensory analysis revealed the hydrolysate by CPE had the highestintensity scores for umami, salty and full-bodied, while the lowest bitterness. The differenttaste characteristics could be dependent on the free amino acids and peptides.Two taste peptides were isolated and purified by ultrafiltration, gel filtrationchromatography and reverse high-performance liquid chromatography (RP-HPLC). Theactive peptides were identified to be Ser-Ser-Arg-Asn-Glu-Gln-Ser-Arg (umami peptide) andGlu-Gly-Ser-Glu-Ala-Pro-Asp-Gly-Ser-Ser-Arg (umami-enhancing peptide) byMALDI-TOF-MS, respectively. The two purified peptide were both the first to be foundwhich showed good umami or umami-enhancing taste. The two identified peptides weresynthesized by solid-phase synthesis, name TP-A (Taste Peptide-A) and TP-B (TastePeptide-B), respectively. The purity of both peptides was above95%. In addition, themolecular weight and sequence structure of the two peptides equated with the fact. The tastecharacteristics of synthetical peptides was evaluated by taste dilution analysis, the resultsshowed the umami taste threshold of TP-A was160mg/L, and the umami-enhancingthreshold of TP-B was5mg/L.Comparison of eluted characteristics on pure proteins/peptides standards and hydrolysatesbetween Superdex Peptide HR10/30and TSK gel G2000SWXL, the results showed theformer chromatogram was appropriate to analyze the molecular weight distribution ofhydrolysates with small peptides or detect the changes of molecular weight distribution ofhydrolysates during separation and purification.The particle and molecular weight distribution of thermal reaction products were analysed.The results showed the lager peptides mainly occurred thermal degradation by heat treatment,while peptide degradation and cross-linking were simultaneously occurred during theMaillard reaction. The Maillard reaction activity of peptides was negatively related to theirmolecular weight, which was the smaller molecular weight, the higher reaction activity, eventhe higher antioxidant activity. There were only some aldehydes and acetic acids in peanuthydrolysate and its peptide fractions. A series of aldehydes and furans would formed by heat treatment, and nitrogenous compounds formed during Maillard reaction. In addition, thereaction between the lecithin lipid oxidation and degradation products and Maillard reactionintermediate products would producted more nitrogenous compounds, which could be affluentin the flavour of products, and the other hand enhance their antioxidant activity.