【作者】 郭泽镔；

【导师】 郑宝东；

【作者基本信息】 福建农林大学 ， 农产品加工及贮藏工程， 2014， 博士

【摘要】 淀粉是自然界中第二大天然高分子碳水化合物,产量仅次于纤维素,天然淀粉因不溶于冷水,乳化能力差,易老化,机械稳定性和贮藏稳定性差等不足,极大限制了淀粉的应用。对淀粉进行改性处理使之符合工业化应用的要求已成为当前淀粉研究领域的一大热点。在各种物理改性淀粉方法中,超高压(Ultra High Pressure)技术是非热力物理加工技术,为淀粉改性提供了一种新方法,具有良好的应用前景。本文以莲子淀粉为研究对象,系统研究不同超高压压力、保压时间和淀粉乳浓度处理对莲子淀粉结构和理化特性的影响,探明作用机理,研究经超高压处理后的淀粉对双歧杆菌体外增殖作用以及对罐藏莲子品质的影响,研究结果表明：(1)超高压处理对莲子淀粉颗粒特性的影响莲子淀粉乳在超高压处理下的颗粒形态、偏光十字、粒径大小和分布以及淀粉颗粒的结晶结构发生不同程度的变化。莲子淀粉乳在500MPa压力处理60min以及600MPa压力处理30min条件下的颗粒特性发生明显变化。莲子淀粉乳经600MPa压力后偏光十字消失,颗粒内部有序的晶体结构被破坏,淀粉的X-射线衍射图谱由C-型向B-型转变；淀粉颗粒发生崩溃,表面出现凹陷,糊化的淀粉颗粒粘连在一起,颗粒粒径大小和分布达到最大值。超高压处理对不同淀粉乳浓度的莲子淀粉颗粒特性无显著影响。(2)超高压处理对莲子淀粉分子特性的影响傅立叶红外光谱仪(FTIR)研究发现莲子淀粉乳在超高压处理前后没有出现新的吸收峰或某个特征峰的消失,没有产生新的基团,表明超高压处理淀粉乳是物理改性过程。核磁共振波谱仪(NMR)研究结果表明莲子原淀粉在C1区域出现三重峰,表现出A-型晶体结构特征,经600MPa压力后表现出B-型晶体结构特性。随着超高压处理压力或保压时间的增加,C1和C4区域特征峰的强度逐渐减弱,相对结晶度降低。尺寸排阻色谱与18角度激光光散射仪和示差检测器串联系统(SEC-MALLS-RI)研究结果表明,莲子原淀粉的重均分子量(Mw)和数均分子量(Mn)分别为1.433×107Da和1.118×107Da,多分散系数(MW/Mn)为1.282。超高压处理导致莲子淀粉分子量分布变宽,分子内部结构受到破坏。(3)超高压处理对莲子淀粉糊特性的影响超高压处理提高了莲子淀粉在低温条件下(55℃-75℃)的溶解度和膨胀度；降低了淀粉糊的透光率以及淀粉在高温条件下(85℃～95℃)的溶解度和膨胀度；经500MPa超高压处理10～50min或100～500MPa处理30min有利于改善莲子淀粉糊的凝沉性和冻融稳定性,而随着超高压处理压力和保压时间的增加,淀粉糊的凝沉性和析水率显著升高。与莲子原淀粉形成的凝胶相比,超高压处理改变了莲子淀粉糊的凝胶质构特性,降低了淀粉的胶黏性、硬度、凝聚性、咀嚼性和粘性,而弹性无显著性变化。(4)超高压处理对莲子淀粉糊化和老化特性的影响快速粘度仪(RVA)研究结果表明,超高压处理可以显著提高莲子淀粉糊的峰值粘度、谷粘度和最终粘度,而显著降低淀粉糊的崩解值和回生值,但经600MPa压力处理后的莲子淀粉表现出最小的峰值粘度、谷粘度、最终粘度、崩解值和回生值。在适当超高压压力和保压时间处理下,莲子淀粉糊的峰值时间和成糊温度随着超高压处理压力和时间的增加而增大。差示扫描量热仪(DSC)研究结果表明,莲子淀粉的起始温度、峰值温度、终止温度、糊化温度范围和热焓值均随着超高压处理压力和保压时间的增加而显著下降,莲子淀粉乳经600MPa压力处理后热力学参数均未检出。糊化后的莲子淀粉样品在4℃条件贮藏期间,与莲子原淀粉相比,超高压处理提高了淀粉的Avrami成核指数,降低了重结晶速率常数,表明超高压处理有利于延缓莲子淀粉糊在低温贮藏条件下的老化速率。(5)超高压处理对莲子淀粉流变特性的影响静态流变学特性研究结果表明,经超高压处理前后的莲子淀粉糊均属于非牛顿流体,表现出假塑性流体特征,可用Herschel-Bulkley方程对其流变学特性曲线进行较好的拟合。莲子淀粉糊的表观黏度经超高压处理后发生不同程度的变化,在相同处理条件下,淀粉糊的表观黏度随剪切速率的增大而减小。超高压处理前后的淀粉糊均存在剪切稀化现象,具有明显的触变性。动态流变特性研究结果表明,莲子淀粉糊的储能模量(G’)显著大于损耗模量(G”),二者随超高压处理压力和时间的增加呈先上升后下降的趋势。剪切结构恢复力试验结果表明,经超高压处理后的淀粉糊在经历低速一高速—低速剪切后较难恢复到原始结构。(6)超高压处理莲子淀粉对双歧杆菌体外增殖作用的影响以不同超高压条件处理后的莲子淀粉作为培养双歧杆菌的碳源,研究了其体外促进双歧杆菌的增殖效应以及对双歧杆菌耐酸性、耐胆汁酸盐和模拟胃肠液逆环境耐受性的影响。结果表明,经超高压处理后的莲子淀粉对促进双歧杆菌增殖作用优于对照组(莲子原淀粉组和葡萄糖组)。600MPa压力处理30min的莲子淀粉对双歧杆菌的增殖作用以及对模拟胃肠液逆环境耐受性的效果最显著。(7)超高压处理对罐藏莲子品质特性的影响通过选择能够延缓淀粉老化的超高压处理条件,将其应用于整颗莲子的复杂体系中,结合莲子罐头的加工工艺,研究了超高压前处理对罐藏莲子在贮藏过程中品质特性的变化规律。结果表明,超高压预处理能显著降低莲子罐头在贮藏期间抗性淀粉的含量和莲子的硬度值,延缓莲子返生味的出现时间,具有较好的抗老化效果。验证试验表明,莲子经600MPa压力处理30min后制成的莲子罐头在常温条件下贮藏300d未出现返生味,提示超高压预处理技术具有明显的商业应用价值。更多还原

【Abstract】 Starch is the second most abundant polymer carbohydrates found in nature, next to cellulose. However, unmodified native starches have very limited use in the food industry because of some inadequacies, such as insolubility, easy retrogradation and instability during storage. Therefore, investigation of proper modification processing of starch to fulfill the industrial requirements has been a prevalent urgent realm of the current starch researches. Among various physical modification methods, ultra high pressure (UHP) is a non-thermal and physical processing. It provides a new method for starch modification and has a good application prospect. Lotus seed starch was chosen as raw material in this paper. The starch particle structure and physicochemical properties influenced by different pressure, pressure holding time and starch concentration were investigated. In addition, the proliferation effects of lotus seeds starch on Bifidobacterium as well as the quality of canning lotus seed treated by UHP were studied. The results were concluded as follows:The degrees of change in the granule morphology, polarization cross, particle size distribution and crystal structure of lotus seed starch after ultra high pressure treatment were different. The particle characteristics of lotus seed starch exhibited significant change when treated at500MPa for60min or600MPa at30min. The UHP-treated lotus seed starch granules at600MPa showed a complete loss of birefringence and the ordered crystallite structural disrupted. X-ray diffraction analyses revealed that UHP treatment converted native starch (C-type) to a B-type pattern. The UHP treatments altered the shape of starch granules and the starch granules presented irreversible loss of the particle structure and showed viscous gel-like appearance. The diameters and particle size distribution of lotus seed starch granules were maximum after UHP treatment at600MPa. However, UHP treatment had no significant effect on the particle characteristics of lotus seed starch with different starch concentration.The Fourier transform infrared spectra (FTIR) analysis of lotus seed starch showed that UHP is a physical modification processing because no new groups formed and changed. The13C CP/MAS NMR results showed that native lotus seed starch showed multiplicity in the resonance peak of the Cl site, which exhibited A-type crystal structure. However, starch subjected to600MPa displayed a typical B-type crystal structure and the relative crystallinity and intensity in the crystalline state gradually decreased with increasing pressure or pressure holding time. Analysis of SEC-MALLS-RI suggested that the Mw, Mn and Mw/Mn were1.433×107Da,1.118×107Da and1.282respectively. UHP treatment resulted in broadening the molecular weight distribution of lotus seed starch, indicating damage of the internal structure of starch molecule.Light transmittance of lotus seed starch decreased after UHP treatment. The treatment of starch suspension with UHP resulted in a significant decrease of swelling power and solubility at85℃and95℃, but opposite trends were found at55℃,65℃and75℃. Compared with the native starch, the freeze-thaw stability and retrogradation of lotus seed starch were improved under the suitable UHP treatment conditions (100～500MPa for30min or500MPa for10～50min). However, the retrogradation and syneresis rate of lotus seed starch improved significantly with the increasing pressure or pressure holding time. UHP treatment changed the textural properties of lotus seed starch. The gumminess, hardness, cohesiveness, chewiness and stickiness of lotus seed starch decreased significantly after UHP treatment. There was no significant change of the springiness.The RVA viscograms revealed that UHP-treated lotus seed starch revealed an increase in paste viscosity, peak time, and pasting temperatures and a reduction in breakdown and setback viscosity compared to native starch. However, starch treated at600MPa exhibited the lowest PV, PT, BD and SB values. The peak time and pasting temperatures increased under suitable pressure or pressure holding time. The DSC results showed a obvious reduction in gelatinization temperatures and gelatinization enthalpy with increasing UHP treatment pressure or pressure holding time. There were no thermal parameters detected in starch pressurized at600MPa, indicating a total loss of the native crystalline structure and molecular order. During storage, UHP-treated starch gels had higher Avrami exponent values and lower recrystallization rates compared with native starch, which suggested a lower retrogradation tendency.The static rheological properties investigation demonstrated that the native and UHP-treated lotus seed starch pastes were non-Newtonian flow with pseudoplastic flow behaviour. Based on the results determined from static flow curves, the Herschel-Bulkley model can be used to fit well on the flow behavior of starch pastes. Under the same processing conditions, the apparent viscosity of lotus-seed starch pastes decreased with the increasing treatment time. The lotus seed starch pastes displayed shear-thinning pseudoplastic behavior after UHP treatment, with significant thixotropy. The determination of dynamic rheological properties indicated that their storage modulus (G’) and loss modulus(G") increased first and then decreased with the increasing treatment pressure or pressure holding time. The in-shear structural recovery test revealed that it is difficult for the UHP-treated starch pastes to recover their original structure under low-high-low shear conditions.Lotus seed starches treated by UHP were used as carbon source to cultivate Bifidobacterium. The proliferation effect of UHP-treated lotus seed starch on the Bifidobacterium in vitro and its influence on the acid, bile salts and simulated gastrointestinal fluid tolerance of Bifidobacterium were studied. The results showed that UHP-treated starch could significantly promote the proliferation of Bifidobacterium than the control group (native lotus seed starch and glucose). Compared with other substrates, lotus seed starch treated at600MPa for30min could significantly enhance the acid, bile salts and simulated gastrointestinal fluid tolerance of Bifidobacterium.The effective UHP treatment conditions for delaying lotus seed starch retrogradation was selected to apply in the complex system of whole lotus seed, combining with the processing technology of canning lotus seed. The effect of UHP treatment on the quality of canning lotus seed during storage was investigated. The results showed that the content of RS, hardness of canning lotus seed decreased significantly during storage. In addition, the back to raw taste appeared later than control group, indicating good anti-retrogradation effect. The experiment that canning lotus seed storage under room temperature for300days showed that the back to raw taste didn’t appear when lotus seed treated at600MPa for30min. The technology of UHP pre-treatment has great commercial application value in the processing of canning lotus seed.更多还原