【作者】 张喻；

【导师】 谭兴和；

【作者基本信息】 湖南农业大学 ， 园艺产品采后科学与技术， 2010， 博士

【摘要】 马铃薯淀粉是我国第二大商品淀粉,其产量和用量仅次于玉米淀粉。尽管马铃薯淀粉具有淀粉颗粒大、糊化温度低、糊透明、口味温和等优良特性,但与其他天然淀粉一样,也存在冷水溶解性差,淀粉糊黏度高且稳定性差,酶解和化学反应活性低等性质上的不足,限制了马铃薯淀粉在某些领域的应用。为此,采用物理、化学或生物方法对马铃薯淀粉进行改性处理,扩大其应用范围已成为一项重要的研究课题。γ-射线辐照作为淀粉改性的一种物理方法,具有经济、环保、高效、方便可行的优点,但有关淀粉的辐照效应还需系统地研究。本试验采用不同辐照剂量处理马铃薯淀粉,深入系统地研究了辐照剂量对马铃薯淀粉颗粒性质、分子结构、理化性质、流变特性和酒精发酵的影响,旨在为将来辐照技术在淀粉工业中的应用以及辐照淀粉的最终使用提供参考和理论依据。本研究对于拓展辐照技术应用领域,扩大马铃薯淀粉的应用范围具有重要的现实意义。具体研究内容和结果如下：(1)采用扫描电子显微镜、偏光显微镜和X-射线衍射仪,对不同辐照剂量处理后马铃薯淀粉的颗粒特性进行了研究。结果表明：当辐照剂量为50～400kGy时,随着辐照剂量的增加,马铃薯淀粉颗粒形貌没有明显变化：辐照处理后马铃薯淀粉在室温下浸泡1h,颗粒表面从一端开始出现凹坑、洞穴,破损程度随辐照剂量的增加而增加；偏光十字数量随辐照剂量的增加而逐渐减少甚至消失；淀粉的特征衍射峰强度逐渐变弱,结晶度显著下降,当辐照剂量达400kGy时,马铃薯淀粉结晶度由40.33%降至33.65%。说明马铃薯淀粉经辐照处理后,外部结构虽保持完整,但内部分子结构已从一端开始遭到破坏；辐照处理在一定程度上破坏了淀粉分子链有序排列的结晶结构。(2)采用红外光谱仪、核磁共振仪、凝胶渗透色谱仪和化学分析方法,对经50-400kGy剂量辐照处理后马铃薯淀粉的分子结构特性进行了研究。结果表明,随着辐照剂量的增加,马铃薯淀粉的分子量和直链淀粉含量则显著降低；淀粉的羰基含量和羧基含量逐渐增加；淀粉的分子结构发生了改变,淀粉分子链发生断裂,但经辐照后马铃薯淀粉的结构单体没有变化。说明辐照处理是降解淀粉的一种有效方法；淀粉降解是辐照处理过程中主要反应,同时伴随氧化、水解反应的发生。(3)对经50-400kGy剂量辐照处理后马铃薯淀粉的理化性质进行了研究。结果表明,随着辐照剂量的增加,马铃薯淀粉的颜色随之加深；淀粉溶解度和酸度显著增加,膨胀度则显著减小；淀粉中总糖含量逐渐减小而还原糖含量逐渐增加；糊化温度和淀粉糊粘度逐渐降低；辐照剂量不超过200kGy时,辐照可显著降低马铃薯淀粉的糊化焓值,辐照剂量达400kGy时,糊化焓值反而升高。说明马铃薯淀粉经辐照处理后理化性质发生了很大的变化。(4)采用流变仪研究了经50-400kGy剂量辐照处理后马铃薯淀粉糊的流变学特性。静态流变特性测定结果表明,不同辐照剂量处理后马铃薯糊淀粉均呈假塑性流体特征,符合幂定律；辐照剂量越高,淀粉糊的表观粘度越低,越接近牛顿流体,并能显著地降低淀粉糊剪切稀化。动态流变特性测定结果表明,辐照剂量影响马铃薯淀粉的G′和流变特征参数,随辐照剂量的增加,G′逐渐降低；流变特征参数中的弹性模量峰值G′m和20℃弹性模量G′20显著下降,弹性模量峰值所对应的峰值系统温度T′m则逐渐降低。由此可见,辐照处理能有效地改变马铃薯淀粉的糊性质。(5)采用经50-1000kGy剂量辐照处理后的马铃薯淀粉为原料,进行了酒精发酵试验。结果表明,辐照可有效地杀灭淀粉原料中的杂菌；辐照处理后淀粉对酶的敏感性增加,可不经糊化直接酶解糖化；辐照剂量不超400kGy时,辐照后淀粉的糖化醪对酵母生长有利；辐照处理可明显提高马铃薯淀粉酒精产量,但以辐照剂量不超过400kGy为宜。由此可见,辐照淀粉无蒸煮酒精发酵工艺是完全可行的。更多还原

【Abstract】 Potato starch is the second most popular commercially available starch product in terms of sales volume and output below corn starch in China. Potato starch is well known for its relatively larger granule particle, low gelatinization temperature with transparence and good mouth feel. However, like other kinds of natural starch, property limitations of potato starch such as poor solubility in cold water, high viscosity, poor stability, poor chemical and enzymatic activities greatly restrict its application in food industry and other related areas. Hence, proper modification of potato starch by physical, chemical and biological methods has been becoming the main focus in recent years. Studies on the modification of potato starch by y-ray radiation as a kind of physical modification proved to be cost efficient, environment friendly and convenient for operating. Nevertheless, the effects of y-ray radiation on starch need to be further studied systematically.By irradiating potato starch with different doses, the experiment systematically investigated the effects of irradiation dose on the granule properties, molecular structure, physicochemical properties, rheological properties and alcoholic fermentation process so that some valuable data could be collected and analyzed and laid a firm theoretical foundation for irradiation technology application in starch modification industry. The study explored the possibility of irradiation in the modification of potato starch and found out following results:(1) The granule properties of potato starch was investigated after irradiated with doses of 50～400kGy by observing its structure under scanning electron microscopy; polarized light microscope and X-ray diffractiometry. The study showed that there was no significant altering of granule shape with increased dose of y-ray irradiation. But some pits or even cavities appeared on the end of the granule particles after irradiated and soaked for 1 h at room temperature and the degree of fragility increased with the increase of irradiation dose.The number of polarization cross decreased gradually and even nearly disappeared.The intensity of characteristic peaks got weak gradually and the crystallinity of starch decreased significantly from 40.33% of blank control to 33.65% of irradiated starch with dose of 400 kGy. All these revealed that the internal molecule structure of granule starch was damaged although outside appearance remained unchanged. Certain amount ofγ-ray radiation of potato starch might destroy the ordered arrangement of starch molecular chain.(2) By adopting Fourier transform infrared spectroscopy, nuclear magnetic resonance, gel permeation chromatography and chemical analysis, the molecular structure properties of potato starch were systematically studied after irradiated with doses of 50～400kGy. The study indicated that with increased dose of treatment, molecular weight of starch and amylose content reduced significantly and the carbonyl and carboxyl content of starch increased steadily. Starch molecule structure changed and long starch molecule chain got fractured, but there was no significant altering of monomer structure after irradiation. All these showed thatγ-ray radiation was an efficient method for degradation of starch molecules. In this process apart of the degradation of macromolecules to create smaller chains as the preferential reaction,oxidation and hydrolysis occur simultaneously.(3) The physiochemical properties of potato starch were also studied after irradiated with doses of 50～400kGy. The study indicated that with the increased irradiation dose, the color of potato starch got brown; the solubility and acidity increased dramatically and swelling power decreased significantly; total sugar content decreased gradually whereas reducing sugar content increased; the gelatinization temperature and viscosity got lower and lower. When the irradiation dose did not exceed 200kGy, irradiation could significantly reduce the gelatinization enthalpy of potato starch but thereafter reversed. These facts showed that the physiochemical properties of potato starch changed dramatically after irradiation.(4) By adopting rheometer, the rheological properties of potato starch was also studied after irradiated with doses of 50～400kGy. The static rheological properties investigation revealed that the paste of potato starch after treated with different dose of irradiation showed a phenomenon of so-called pseudo-plastic fluid characteristics and this was consistent with power law. The higher the irradiation dose, the lower the apparent viscosity and it performed similar like Newtonian fluid. Different dose of irradiation could significantly reduce the share-thinning nature of the paste. The determination of dynamic rheological properties indicated that the irradiation dose had an impact on G’and rheological characteristic parameters. With the increase of irradiation dose, G’decreased gradually and the maximum elastic modulus G’m and G’20 at 20℃decreased sharply but the T’m in correspondence to G’m reduced gradually. All these facts indicated that irradiation treatment could efficiently influence the rheological properties of potato starch paste.(5) Finally, by using potato starch irradiated with doses of 50～1000kGy as substrate, alcoholic fermentation experiment was carried out to study the effect of different dose of irradiation to alcohol fermentation. The study showed that irradiation could efficiently eliminate contaminated microbes in the starch and increased the susceptibility to enzymatic hydrolysis of starch, hence, irradiated starch could be enzymatic saccharificated directly without gelatinization first. Saccharification broth of irradiated potato starch was beneficial for the growth of yeast if the irradiation dose was below 400 kGy and irradiation treatment could significantly increased the alcohol yield during fermentation if the treated dose did not exceed 400 kGy. It can be concluded that a noncooking alcohol fermentation is entirely possible by treating potato starch with gamma radiation prior to saccharification and fermentation更多还原