低酯果胶的氨基酸修饰及修饰物凝胶特性研究

Study on gel properties of amino acid modified low methoxyl pectin and its modification

以柑橘低酯果胶为原料,氨基酸为修饰剂,分析了氨基酸种类、果胶质量分数、果胶与氨基酸质量比、pH值及Ca2+质量分数对果胶/氨基酸复合物凝胶强度的影响,考察了果胶/氨基酸复合物的红外光谱、热力学性质、流变学特性及分子间相互作用力。结果表明:向由pH 4.0磷酸缓冲液配制的质量分数为1.5%的低酯果胶溶液中分别添加不同种类氨基酸(赖氨酸、甘氨酸和谷氨酸),当m(果胶)∶m(氨基酸)=5∶1,Ca^2+质量分数为0.5%时凝胶强度最大;修饰效果从强到弱依次为碱性氨基酸、中性氨基酸、酸性氨基酸,其中果胶/赖氨酸复合物的凝胶强度最大,为102g,约为对照组的2倍;果胶/谷氨酸复合物的凝胶强度与对照组的无显著差异。氨基酸的修饰有利于在低Ca^2+质量分数时获得强度高、结构稳定的低酯果胶凝胶。分子间相互作用力研究表明,果胶与氨基酸间主要以酰胺键或静电作用力维持果胶/氨基酸复合物的稳定。

The effects of amino acids types, pectin mass fraction, mass ratio of pectin and amino acid, pH and Ca2+ concentration on the gel strength of pectin/amino acid complex were studied using citrus low methoxyl pectin as raw material and amino acids as modifier. The FT-IR spectrum, thermal mechanical properties, rheological properties and intermolecular interaction force of pectin/amino acid complex were also analyzed. The optimum modification conditions were determined as follows: low methoxyl pectin concentration 1.5%, pH 4.0 phosphate buffer solution, mass ratio of pectin to amino acids(lysine, glycine, and glutamic acid) 5∶1, Ca^2+ concentration 0.5%. The effect of modification decreased in the order of basic amino acids, neutral amino acids and acidic amino acids. The pectin/lysine complex showed the highest intensity(102g), which was 2 times higher than that of the control group. The gel strength of pectin/glutamic acid complex was not significantly different from that of the control group. Modification of amino acids is beneficial for obtaining low methoxyl pectin gel with high strength and stable structure under low Ca^2+ concentration. Intermolecular interaction studies suggested that amide bonds or electrostatic forces between pectin and amino acids were responsible for its enhanced stability.