| Zein residue was the by-product of corn starch during the wet processing,the potential application prospects of which had gained widely attention from scientists around the world in the food processing,chemical industry,medicine and materials.The grafting modification and application of zein were researched in this paper.And it was analyzed and confirmed that zein was grafted with the starch under the different conditions of heating treatment.The preparation and physicochemical property of compounds were elucidated.Besides,the application of zein in which Zein/Wcs film and Zein/DP film was compared.The results revealed as follow:To compare the consumption of free amino acid in the protein/starch system under four methods including dry-heating,microwave heating,high pressure heating and wet-heating.The result showed that the consumption of free amino acid was the most in wet-heating,but there were too much post treatments.Microwave heating has only takes lower energy consumption yet the higher reaction efficiency.Based on results the conditions of microwave heating were evaluated by single factor test.The result showed that the value of DG increased by nearly 20 times after microwave-heating as microwave power increased from 160 w to 800 w,indicating a positive correlation between the microwave power and the value of DG.But The value of DG increased first and then decreased when the concentration of zein from 5% to 30%.The effect of on the physic-chemical properties of composite was analyzed.And the solubility,gelatinization temperature,apparent viscosity,rheological properties and thermal stability of composite has improved significantly after dry heating treatment.Compared with the protein/starch composite without the heating process,the solubility of zein increased by 34.5%.Analysis of pasting property of composite indicated that gelatinization temperature had obviously decreased trend as the reaction degree increasing,and the apparent viscosity decreased by 32.4%,showing a fluid state.And the starch's setback viscosity still decreased,indicating the improved gel stabilities.Analysis of rheological property of composite showed that the composite well fitted to the characteristic of the yield-pseudo plastic fluid according to the data analyzing of Herschel-Balkley.Analysis of thermodynamics property of composite showed that gelatinization onset temperature and gelatinization peak temperature dropped by 1.59 and 1.08,respectively.While the gelatinization enthalpy increased by 1.02.These results suggest that the interactions between starch and zein were reinforced,and it did cause internal structure of composite has changed during dry heat treatment.The SEM images showed that microwave dry heating treatment could promote zein molecule‘s depolymerization and immigration attributed to the dry-heating treatment.the contact area's increasing and thereby improve the reaction efficiency.Analysis of amino acids in system indicated that more amino-acid residue exposed as a result of accelerating the interactions between starch and zein,especially Leu,Gly and Tyr,which could prove free amino were mainly derived from these amino-acid.Analysis of FT-IR showed that the structure of zein wcs not changed because characteristic absorption peaks of protein and starch had no obvious displacement but zein molecule was grafted with the starch molecule by covalent bond.That was why the functional properties of the compound changed.In addition,the results of fluorescence also proved that zein thermo-modification is a safety method because the grafting was in the middle stage of Maillard reaction and there no melanoidin was found during the reaction.In conclusion,to compare the unheated,the hydrophobicity of two types starch film increased by 44.2% and 46.6%,the tensile strengths increased by approximately 60% and 20% with dry heating,respectively.The result confirmed that dry heating treatment could promote the compatibility between starches and zein by promoting physical or chemical interactions to form a tight network structure.zein thermo-modification could be used as a promising modification method for improving the functionality of composite films. |
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