【作者】 王锋；

【导师】 孙骊；

【作者基本信息】 西北农林科技大学 ， 农产品加工与贮藏工程， 2003， 硕士

【摘要】 水稻是中国的主要粮食作物，年产量占世界稻谷总产量的37％左右，居世界首位。大米产量居于高位，而消费增长较慢，造成我国大米库存严重积压并居高不下。根据美国农业部2002年12月份报告，2002年，我国大米期末库存为6735万吨，占世界大米中库存的64.2％，仍然是世界各国大米库存量最大的国家之一。库存量的不断堆积，导致大量劣变及损耗，成为农民和政府财政的负担，挫伤了农民种粮的积极性。积压稻谷中80％是早籼稻。2002年度我国加工业消费的大米仅仅占1.4％左右，远远低于发达国家80％左右的平均水平。研究表明早籼稻是米粉生产的优质原料，传统发酵米粉以其滑爽筋道的口感，深受消费者的喜爱。显然对米粉的生产技术深入研究是解决积压的关键。本文深入研究了自然发酵对大米理化性质的影响及其米粉凝胶形成的机理，为利用早籼米生产高品质米粉奠定了理论基础。主要研究内容与结果如下： 1．自然发酵显著地改变了大米的组成成分。发酵降解了大米总蛋白的33％，总脂肪的61％，总灰分的62％以上；发酵对总淀粉含量影响不大。所以发酵起到了纯化淀粉的作用。 2．自然发酵主要作用于淀粉的无定形区，对结晶区的结构影响不大。淀粉颗粒的显微观察表明发酵没有破坏淀粉颗粒的外形；损伤淀粉的含量增加的程度很小；DSC表明淀粉的晶型未变，但晶区比例增大；FTIR表明没有新的化学键和化学结构产生。 3．自然发酵改变了淀粉的结构和组成，主要是支链淀粉的断链与脱支。发酵使得直链淀粉含量增加3.28％；发酵使大分子区减少，小分子及中间分子增加。大分子区DPn从对照的12597.6GLU降至发酵后的12051.0GLU，而小分子从3061.5GLU增加到3423.1GLU。β-淀粉酶水解率测定发现淀粉分子分支化程度降低，表明支链淀粉发生了断链与脱支。淀粉的RVA曲线最高粘度降低也说明发酵引起了支链淀粉的断链与脱支。 4．自然发酵代谢产物中乳酸的作用效果最明显。发酵过程中产生了大量有机酸，HPLC分析表明90％以上是乳酸；通过不同PH乳酸溶液的浸泡试验验证，表明PH4左右最佳，与自然发酵有类似效果。酶类以蛋白酶、果胶酶和脂酶作用效果为好。小分子糖类与乙醇的存在对米粉拉伸有负面作用。 论文阐述了自然发酵对大米理化性质的影响及其米粉凝胶形成的机理。分析认为，发酵米粉特殊的流变性是自然发酵产酸、酶作用于大米淀粉颗粒对淀粉改性和纯化的结果。乳酸对大米淀粉凝胶性质的改变起着主要作用。乳酸作用于淀粉颗粒的无定形区支链淀粉长链断链，使淀粉的分子量分布趋于均匀，降低了单个支链淀粉的分支化程度，减弱了再结晶性。中间分子和直链淀粉分子比例增加，老化趋势增强。同时低PH值促进直链淀粉迅速聚合老化，形成连续相凝胶网络，将老化慢的支链淀粉和水分包埋起来，构成凝胶的粘性；而直链淀粉老化后再难糊化，构成凝胶的弹性，二者共同构成发酵米粉的粘弹性。更多还原

【Abstract】 Paddy is a main foodstuff crop in China . Its yield accounts for 37% of the global paddy yield per year and take a first in the whole world. The yield of rice is too high to overstock in China, but consumption is very slow. United States Department of Agriculture reported that the yield of China rice came up to 67,350,000 ton in the end of 2002. It accounted for 64.2% of that in the world. China is still one of the country which has the most stock rice. The stocks continuous mount up which not only causes large quantity of deterioration and wastage every year but become the burden of farmer and government. About 80% the overstocked rice is Indica. Consumption of processing rice accounts for 1.4% in our country in 2002 and is far from the average level in the world. Rice cultivars Indica is widely planted with its high yield and good quality for producing rice noodles in south of China. Traditional fermented rice noodles are very popular because of its favorite mouth feel and taste. Processing technology of rice noodles is key for solving overstock. The further theoretical research is needed for its industrialized product. The paper reveals the influence of natural fermentation on the physicochemical characteristics of rice and gel mechanism of rice noodle. The main contents and results are as follows.1. Chemical components of rice flour were significantly modified by whole rice granule fermentation. About 33% of total protein, 61% of total lipid and 62% of total ash content were lost during fermentation period. The rice starch content remained almost constant. So, the natural fermentation improved the purity of rice starch.2. The natural fermentation mainly affected the amorphous region of the starch granule structure. The micrography of starch granule showed that the shape of starch granule remained unchanged. Starch damage didn’t change. Results by the X-ray diffraction indicated that fermentation had little effects on starch crystal structure, but the ratio of crystal area to amorphous area increased. FTIR indicated that starch have not new chemical bond and structure.3. The structure and form of starch were changed by natural fermentation. It is mainly that Amylopectin starch was broken and debranched. The amylose content had 3.28% increase , the area of larger molecular decreased but smaller molecular increased by fermentation. The number of average molecular polymerization was changed from 12597.6GLU to 12051.0 GLU for the area of larger molecular and from 3061.5 GLU to 3423.1 GLU for the area of smaller molecular after fermentation. The -hydrolysis ratio was increased. RVA peak viscosity decreased. They both showed that starch chain was broken and debranched.4. Lactic acid in metabolites of fermentation play an important role in improving the rheologyical properties of rice starch gel. A large quantity of organic acid were produced by natural fermentation. More than 90%of total acid were lactic acid by Ion Chromatography analysis. The rice noodle for PH 4.0 treatment has similar sensory evaluation score compared with the natural fermentation one. Rice granule treated by trypsin, pectinase and lipase also produced good quality rice noodles. Maltose, glucose and ethanol produced during fermentation had negative effects on gel properties.The paper discusses the influence of natural fermentation on the physicochemical characteristics of rice and gel mechanism of rice noodle. Conclusions are that organic acid and enzymes produced by natural fermentation caused starch modification and purification, and further improved the rheological properties of rice noodles. Lactic acid plays a key role, hydrolyzed the external chains of amylopectin among the amorphous region in starch granule, homogenized the starch molecular distribution, decreased the branching degree of single amylopectin molecule, and weaken its re-crystallization trend. Furthermore, fermentation increased the intermedium and amylose content, and enhanced their retrogradation property. Low PH value condition is also beneficial to更多还原