Study On Changes Of Peanut Protein Conformational And Functional Properties During Germination And Development Of Germinated Peanut Beverage

Peanut (Arachis hypogaea L.) is an important oilseed in the world. Among oilseeds, peanut has excellent potential as a source of protein. The amino acid profile (high essential amino acid content) of defatted peanut shows it could be an ingredient for protein fortification and peanut flours has been added to other food products as a replacement for animal source proteins, can enrich the nutritional values without the astringent flavor of other oilseed flours. Thus, peanut is suggested as an alternative protein source in developing countries where protein deficiencies remain a major health problem. Germination is a practical and widely used processing method for raise the bioavailability of seed nutrients, particularly for its ability to decrease levels of antinutritional factors, at the same time improving the quality and functional properties of seed protein. In this study, three peanut varieties:Bai Ri Hong (BRH), Hua Yu-16 (H-16) and Lu Hua-9 (L-9) were used as the research material. Composition differences and the changes of main physio-biochemistry and protein metabolish of the three peanut varieties during different periods of germination were investigated. Study on the effects of germination on conformational and functional properties of peanut protein. Meanwhile, the germinated peanut protein baverage was developed with the best germination stage. The main results summarized as follows:Analysis of chemical composition in the three peanut varieties. BRH showed higheset content of nitrogen compounds, L-9 shoued highest crude content and there wasno significant difference between H-16 and L-9 in 1000-grain weight (P>0.05). In the process of germination, shoot length, germination rate and respiration rate gradually increased, the content of dry matter decreased; protein contentshowed a decreasing tendency, meanwhile, the soluble protein content followed a decrease-increase-decrease pattern; the content of peptides and free amino acids showed an increasing tendency; the activities of protease and endopeptidase gradually rose throughout the germination period. Correlation analysis of various parameters under investigation demonstrated that major physiological changes had a considerable effect on peanut endogenous protease, then affected protein metabolis.With the bases of composition and germinated characteristics in three peanut varieties, BRH was germinated and isolate protein from it was extracted. The results showed that:The degree of hydrolysis reached 15.01% at the termination stage of the germination period; the SDS-PAGE pattern showed the disappearance or loss of density from the conarachin (50-66 kDa) and acidic arachin (38～49.9 kDa) bonds, together with the appearance of a series of smaller molecular weight subunits; germination process did not affect the content of total nitrogen, but the quantity of protein nitrogen fell by 15.88% with a concomitant increase in the content of non-protein nitrogen (from 2.84 mg/g to 9.20 mg/g) after 96 h of germination; length of peptide chain and molecular weight of peptide chain reduced; the contents of limiting amino acids (Trp+Val) increased as well as the essential amino acid and sulfur-containing amino acid; disulfide content decreases with increasing content of sulfhydryl groups; the denaturation temperature of peanut protein showed the decreasing tendency, a maximum denaturation enthalpy of conarachin was obtained at the initial stage of the germination period while the denaturation enthalpy of arachin had no significant change.The effect of germination on the functional properties of peanut proteinisolate (PPI) was studied. The functional properties of protein from the germinated peanut seeds were evaluated and untreated seeds were used as a control. The results showed that the chemistry composition of peanut protein isolate were changed with the increasing of germination period, the contents of crude fat and total were decreased and the protein and moisture had no significant (P>0.05) change; germination(96 h) significantly(P<0.05) improved the solubility (>70%) of PPI, especially in the pH range of 4-6. After 96 h germination, water holding capacity increased while oil binding capacity decreased and they were1.81 and 0.51 folds of the untreated seeds, respectively. There was a concomitant decrease in the level of emulsifying activity index and emulsifying stability index with the period of germination increased, but no significant changes under the alkaline condition. Foaming capacity was enhanced while foaming stability worse than the control, especially in the alkaline condition. Germinated peanut protein had a least gelation concentration of 80 g/L compared with 100 g/L for the control. The quality and structure analysis showed that the germination of peanut protein gel in such aspects as cohesion, plastic viscosity and resilience improved significantly.Analysis the data of the composition and functional properties showed 72 h germinated peanut protein displayed the best protein nutritional value and processing characteristics, hence,72 h germinated peanut was choosed gas the materials to develop the germinated peanut protein beverage. The best peanut protein extraction technology were: liquid ratio of 1:8, extraction temperature 32.03 ℃, extraction time 32.04 min, NaCl concentration of 0.11 mol/L. Under this condition, the maximum extraction rate is 64.23 ± 3.25%. The percentage addition of non-dairy creamer and fructose-glucose syrup were decided upon, by organoleptic evaluation, at 1.0% and 5.0% relatively. In order to prevent delamination of beverage and precipitation phenomena occur during placement, lecithin and sucrose ester were added and multiplexed with a 7:3 ratio,0.15% addition level. The prescription of stabilizers was:0.10% CMC,0.10% xanthan gum and 0.05% guar gum.