纳米抗菌包装对胚芽米储藏过程中陈化的抑制作用

【目的】胚芽米的营养价值相当丰富,具有广阔的市场前景,但其极易变质且不易储藏的现状是影响其推广的一大问题。探索胚芽米陈化过程中的成分变化及劣变情况,开发一种符合市场需求的、能够延缓胚芽米陈化的新型纳米抗菌包装材料。【方法】以五优稻4号胚芽米为试材,以普通聚乙烯包装材料为对照,分别制备两种不同的纳米抗菌包装材料,在常温环境下(25℃、65%湿度)储藏胚芽米28 d。每7 d取样一次,分别检测包装材料内部气体组成及胚芽米储存过程中菌落总数、脂肪酶活力、脂肪酸总量、淀粉糊化特性等指标;在初期和末期检测脂肪酸组成,胚芽米胚乳切面微观结构,以及纳米包装薄膜本身的抗菌性。比较抗菌性纳米包装材料对延缓胚芽米陈化的作用。【结果】包装袋内部气体组成检测数据表明,纳米包装材料改变了包装袋内部气体组成,降低了O2/CO2的比值,低氧环境也抑制了胚芽米的呼吸作用。抑菌性试验数据显示,两种纳米抗菌包装材料的抑菌性能较好,对大肠埃希氏菌与大米霉菌的抗菌率分别达99%与95%以上。普通包装下的胚芽米常温贮藏第28天菌落数即达41×10~4 cfu/g,而同期两种纳米包装下的胚芽米霉菌数仅分别为17×10~4 cfu/g与18×10~4 cfu/g(P0.05);抗菌包装中的胚芽米脂肪酶活性值较低,减少了游离脂肪酸的产生;胚芽米的脂肪酸组成适宜人体,较为合理,其初始不饱和比例为71.22%,贮藏28 d后普通包装下的胚芽米脂肪酸不饱和度为65.95%,而两种抗菌包装分别下降至69.10%与67.41%,变化幅度较小;抗菌包装中的胚芽米淀粉糊化特征值变化小,即口感劣变较慢;从胚乳切面微观结构上看,纳米抗菌包装材料在一定程度上具有延缓胚芽米陈化的作用,其内部淀粉质体裂解程度较低。【结论】常温环境下胚芽米陈化较快,霉菌繁殖、脂肪分解及结构等变化反应了胚芽米的陈化过程。纳米抗菌包装材料抑制了霉菌生长并能调节包装材料内部气体组成,达到降低胚芽米劣变速度与延缓陈化的作用。

The Inhibition Effect of Nano-Antibacterial Packages on the Aging of Milled Rice with Embryo During Storage

【Objective】Milled rice with embryo is easy to deteriorate and difficult to store, which is always a big problem to hinder the promotion. The study was intended to explore the aging mechanism and metamorphism of milled rice with embryo during preservation. The results would provide some references for developing a new packaging material which caters for both market demand and rice preservation.【Method】Milled rice with embryo of WuYou 4 was used as experimental material. Two different kinds of nano-antimicrobial polyethylene (PE) packaging materials were made for the experiment. It was stored at 25℃ and 65% relative humidity for 28 days. And it used ordinary polyethylene (PE) packaging as a comparison. Both of them were sampled once per 7 days. The effect of the nano-packaging material on the quality of stored milled rice with embryo was studied by tracking the changes in the gas proportion in the packages, total colony number, lipase activity, total amount of fatty acids, gelatinization characteristics, fatty acids composition, the cross-section microscopic structure of milled rice with embryo and studying antibacterial property of common plastic packaging film. 【Result】 The results indicate that antimicrobial package material played a part in regulating the gas in the package by decreasing the value of O₂/CO₂, which decreases rice depletion. The data of the bacteriostatic experiment proved that compared with the common packaging materials, the antibacterial effects of two nano-antimicrobial packaging materials are better, whose antibacterial percent to Escherichia coli and rice mold are higher than 99% and 95%. The number of colony preserved in PE packages at room temperature for 28 days is 410 000 cfu/g, while the numbers of those preserved in two kinds of nano-packages in the same condition are just around 170 000 cfu/g and 180 000 cfu/g and the results indicate significant differences (P＜0.05). The decrease of the number of molds in antimicrobial packages reduced the lipase activity and prevented the fatty acids from accumulation. Milled rice with embryo is suitable for human body for its rational acid contents. The initial fatty acid composition consists of 71.22% unsaturated fatty acids. After 28 days of preservation, the fatty acid composition of rice stored in PE packages consists of 65.95% unsaturated fatty acids, while those stored in two kinds of nano-packages in the same condition are closer to the initial data and just around 69.10% and 67.41%. The nano-packages also show special quality in keeping gelatinization characteristics, which affect the taste. As is shown in the microstructure of endosperm section, to some extent, the nano-packaging material makes a difference in delaying the aging of milled rice with embryo.【Conclusion】Milled rice with embryo is easy to aging at room temperature. The growth of the mold, the breakdown of fat and the change of structure show the aging process. The nano-packaging material retards the aging and keeps gelatinization characteristics of rice by stopping the mold from breeding and changing the gas composition.