冷冻对糯米淀粉回生的影响
The influence of freezing on the retrogradation of glutinous rice starch
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摘要: 大多糯米食品要在冷冻条件下贮藏,研究冷冻贮藏过程糯米淀粉的回生规律可指导其贮藏工艺的设计。实验结果表明,糯米淀粉浓度由1%增加到25%,冷冻1d糯米淀粉的最低回生率由4.5%增加到15.7%,冷冻7d最低回生率由4.7%增加到32.6%。糯米淀粉乳浓度为1%、5%和25%时冷冻过程的过冷温度会降低淀粉回生率,3d以内的短期冷冻贮藏糯米食品应避开10%15%的淀粉乳浓度。糯米食品不宜在冰箱-18℃下冷冻贮藏,在此条件下贮藏一星期,糯米淀粉的回生率大于40%。糯米淀粉中少量直链淀粉会促进支链淀粉的回生。电镜图片显示,糯米淀粉呈现不规则块状,由6个以上平面组成,面直径为12μm的颗粒较多,每个面的断面比较平。糯米回生淀粉呈粘着层状结构。糯米支链淀粉呈现淀粉冻状,没有规则外形,而糯米支链回生淀粉有明显层状结构,层间距小于1μm。Abstract: Most glutinous rice food was stored under freezing, so it was necessary to study the retrogradation law of glutinous rice starch in frozen conditions for designing storage process.The experimental results showed that the minimum retrogradation rate of glutinous rice starch frozen for 1d increased from 4.5% to 15.7% when its concentration increased from 1% to 25%, from 4.7% to 32.6% when it was frozen for 7d.When the concentrations of glutinous rice starches were 1%, 5% and 25% respectively, the supercooled temperature in frozen storage lowers the retrogradation rate, the concentration of the glutinous rice starch milk should be away from the range of 10% 15% in the short-term refrigerated storage of glutinous rice food within 3d.Glutinous rice food should not be frozen in the refrigerator at-18℃, under these conditions for a week, the retrogradation rate of glutinous rice amylopectin became higher than 40%. A small amount of glutinous rice starch amylose would promote the amylopectin retrogradation.Electron microscopy images showed that glutinous rice starch was irregular block with above 6sides and most surface diameter of the granules was about 1 ~ 2μm, each surface section was flat. The shape of retrograded glutinous rice starch was adhesive layer structure.The shape of glutinous rice amylopectin was like jelly without regular shape. The retrograded glutinous rice amylopectin had obvious layered structure and its layer spacing was less than 1μm.