Effect Of Subunit-Lacking On Thermal Properties Of Arachin

Peanut protein is one of the major plant protein resources in China. The lacking of processing-special varieties seriously hampered the healthy development of peanut processing industry. We took the arahcin extracted from the mutant peanut lines as research material and investigated the basic physico-chemical properties of arachin with/without this subunit. On the basis of the results of physico-chemical properties, the thermal property was selected as research focus and the thermal properties and structure variation of arachin in different peanut lines during different heat treatment were observed. To identify the 35.5kDa subunit, the proteomics methods and bioinformatics approaches were used. The mechanism of diffrences in thermal properties of the lacking or the normal arachin was analysised. Results were listed below:For the effect of subunit lacking on the physico-chemical properties, results were as follow. Arachin with 35.5 kDa subunit was much easier denatured by heat treatment and conformed more aggregation supported by the measurment of DSC and viscosity. For the solubility, arachin fraction of the lacking ones showed a better solubility than the normal ones in weak acidic environment(pH 5-7), while in the strong acidic environment(pH <3), the lacking arachin was much easier to soluble than the normal one and the results was just obbsite when the pH value comes to basic region(pH>8). As to the molecular conformation properties, arachin with 35.5 kDa subunit exhibit a higher surface hydrophobicity(123.36) than that of the lacking ones(58.83) and so as to the data revealed by sulfhydryl contents(p<0.05). The jointing of this subunit in arachin could lead to a less rigid structure and a higher ratio of hydrophobic segments.For the effect of subunit lacking on the thermal properties, results were as follow. For the solubility, the 60℃ and 90℃(10min,20min)treatment, the solubility of the lacking and the normal arachin both decreased, while the 120(10min,20min)treatment, the solubility had an significant increase. For thermal stability, at the Tonse tand Td value, the normal archin was significantly lower than the lacking arahcin, while at ΔH and ΔT value the normal one was higher than the lacking one, indicating the lacking arachin need more energy to go a complete degeneration stage. For the variation of viscosity, the increase the temperature could result in an increase in viscosity of arahin and the viscosity of the normal ones was always higher than that of the lacking one. The variation of non-newtonian index(n) was not accordance with temperature. For the viscoelastic, the storage module and the loss module of the lacking arachin was always higer than the normal one, indicating a higher gelling ability in the lacking arachin.For the effect of heat treatment on the structure variation, results were as follow. For the existing state in PBS(10mM, pH 7.9), the lacking arachin was existed most in dimer, while in the normal arachin, the ratio of monomer and dimer were substantially equal. For the conformation, at 90℃, internal sulfhydryl group of lacking arahin was more fully exposed than that of the normal arachin, leading to a looser structure in molecular structure, which was More conducive to further aggregation or cross-linking occurance. For the aggregation behavior, at 60℃ heat treatment, the lacking and the normal arachin could form soluble aggregation, while at 90℃, archin could form the reversible and irreversible aggregation, and the irreversible aggregation was mostly deduced by the formation of disulfide bond. For the 120℃, irreversible aggregation was generated and a series of small molecular weight substances was produced. To further identify this subunit, we devoted 2-D and Q-TOF-MS technologies to sequence this polypeptide, which resulted in an isoform of Ara h3, post-translated in the in protein storage vacuoles.This study compared the thermal characteristics of proteins with different subunit composition, which will lay the theoretical foundation of thermal mechanism at the molecular level. This article definited the effect of 35.5kDa subunit lacking on the molecular aggregation behavior during heat treatment, which will provide a guide of directional control by changing the heating conditions for food processing industry.