酸浆法改善淀粉的粉丝加工适性机制研究

The pretreatment of starch has a direct impact on the quality of starch noodles. In China, the starch pretreated with sour liquid is a classic approach in starch noodle manufacture, which is the most advantageous in the purification and separation of starches as well as enhancing their processing suitability in starch noodle manufacture. However, the modernization of this traditional process is hindered by a serial of problems including the rule-of-thumb operations, long production cycles, and the product quality which is always influenced by such factors as raw materials, seasonal and geographical conditions. Furthermore, the mechanisms for improving starch properties and the quality of starch noodles are still not clear. In view of this, the aim of this study is to elucidate the mechanism of sour liquid treatment on improving the processing suitability of starches in starch noodle manufacture. The study is attempted to clarify the starch properties and processing characteristics which are essential for the starch noodle making quality by comparing the differences in composition, structural and physicochemical properties of starches isolated by sour liquid processing and centrifugation as well as the differences in quality of starch noodles prepared by the same procedure, and by the correlation analysis of these two differences. The study is also attempted to clarify the effects of sour liquid ingredients on the processing suitability of starches in starch noodle manufacture and the discovery of the key ingredient and the interaction mechanisms between the key ingredient of sour liquid and the starch slurry. The study can reveal the scientific principle of sour liquid processing on improving the processing suitability of starches in starch noodle manufacture and is able to offer an experimental evidence for the modernization of sour liquid processing, and provide new approaches and methods for the regulation of the quality of starches and their products.

淀粉预处理方式直接影响着粉丝的品质。酸浆法是我国粉丝制作工艺中经典的淀粉预处理方式，在淀粉的分离纯化和淀粉的粉丝加工适性提升等方面最具优势，但是存在操作凭经验、生产周期长，产品质量受原料、季节和地理环境因素干扰大等问题，而且酸浆提升淀粉特性及粉丝品质的相关机理至今仍不明确，制约了该传统工艺的现代化进程。本项目主要对酸浆改变淀粉物性的作用机制以及淀粉物性变化与其粉丝加工适性的改善相互关系进行研究。通过对比研究酸浆法与旋流法制取淀粉的组成、结构差异，以及按照统一方法生产的粉丝的品质差异，并将这两种差异进行关联分析，明确淀粉的粉丝加工适性关键指标，通过比较酸浆中各组分对淀粉粉丝加工适性的贡献以确定关键组分，并进一步对酸浆关键组分的作用方式进行探讨，研究将揭示酸浆法提升淀粉的粉丝加工适性的科学原理，以期为建立现代化的酸浆法工艺提供支撑，同时为调控淀粉及其制品的品质提供新的途径和方法。

本项目通过对比研究淀粉在酸浆处理过程中组分结构和理化性质的变化，明确了酸浆关键组分改善淀粉的粉丝加工适性的作用方式，主要结论如下：1）自然酸浆发酵处理使甘薯淀粉制作的粉丝的结晶度明显提高，5.6º（2θ）衍射峰增强，粉丝糊化焓增加；同时使粉丝的复水速率增大，但粉丝的膨润度不受影响；发酵处理使煮熟粉丝冷却过程中回生速度加快，放凉粉丝的不透明度、硬度、胶着性和咀嚼性增加，表明自然酸浆发酵可改善粉丝的烹饪和食用品质。2）甘薯淀粉颗粒的粒度、结晶度、近程有序程度等特征参数未受自然酸浆影响，但发酵导致表观直链淀粉及蛋白质含量下降，灰分增加，淀粉分子的Mw下降，支链淀粉分子的短侧链占比增加，平均链长降低，发酵过程淀粉降解遵循内切型模式。发酵还导致了淀粉糊化温度范围变窄，淀粉糊的回生率增加，这对粉丝的熟化成型有利。3）以粉丝工厂采集的自然酸浆为发酵剂制备人工酸浆，处理甘薯淀粉乳后分离出淀粉。酸浆侵蚀了淀粉颗粒表面，大幅改变了淀粉的糊化特性。酸浆微生物通过代谢产生淀粉酶和酸类物质来对淀粉进行作用，从而导致淀粉结构及物性改变。从中分离鉴定了醋酸杆菌属、葡萄糖醋酸杆菌属和芽孢杆菌属的8种产淀粉酶微生物。研究发现淀粉凝胶特性变化与水解圈存在一定关联性，但中等水解酶活性的独具增加凝胶强度的能力。4）采用改善凝胶特性明显的三株菌分别发酵甘薯淀粉，观测淀粉结构、物性及其粉丝品质的变化。发酵体系pH在最初5d快速下降，10d后稳定维持在pH3.7左右；发酵过程未监测到微生物对淀粉颗粒的粘附现象。发酵降低了直链淀粉含量，淀粉颗粒表面被侵蚀，但未改变淀粉的结晶型，结晶度没有发生变化。发酵使甘薯淀粉的支链淀粉分子发生了较大变化，特别是中长侧链和平均链长增加。这些变化导致了凝胶硬度和内聚性增大，淀粉老化能力提升，粉丝的咀嚼性大幅增加。该研究为酸浆引起淀粉结构及加工性能变化提供了实验证据，也为调控粉丝的品质提供了新方法。