【作者】 刘坚；

【导师】 江波；

【作者基本信息】 江南大学 ， 食品科学与工程， 2007， 硕士

【摘要】 超高压处理技术是一种新型的食品加工技术,与传统热处理技术相比有着许多优越性。蛋白质是食品的主要成分之一,是食品科学中的重要研究对象。鹰嘴豆是世界第二大消费豆类,产量居世界豆类总量的14%。鹰嘴豆蛋白氨基酸组成均衡,营养丰富。本文以鹰嘴豆分离蛋白(Chickpea protein isolate,简称CPI)为研究对象,研究超高压对CPI功能性质、结构和酶解性质的影响,旨在探讨超高压作用对CPI功能性质的影响规律和作用机理。CPI溶液的表面疏水性和紫外吸收光谱测定结果说明超高压处理导致了CPI内部疏水基团暴露到分子表面。CPI溶液的游离巯基含量随处理压力升高不断下降,说明压力处理导致了新的二硫键的形成。并通过使用高效液相、凝胶电泳,激光动态光散射等仪器的分析发现,超高压使Tris-HCl缓冲体系中的CPI分子在300 MPa以上压力处理后,分子发生了聚集现象,形成分子量和流体动力学半径很大的可溶性聚集体,同时伴随着在400 MPa以上压力处理后CPI解聚成了蛋白质亚基等小分子。超高压对CPI功能性质的影响很好地反映了超高压对CPI结构造成的改变。本文研究了超高压对CPI溶解性、乳化性和起泡性的影响,并考查不同缓冲体系中(磷酸盐和Tris-HCl缓冲体系)超高压及一些条件因子(包括压力、保压时间、体系pH和离子强度)对其功能性质的影响。处于两种不同缓冲体系中的CPI经超高压处理后表现出溶解性的变化差异。在非抗压型磷酸盐缓冲体系pH范围内(pH6.0-8.0),升高压力(尤其是400 MPa以上)或延长保压时间(大于5 min),都会使溶解性显著下降,而增大离子强度(大于0.4 mol/L)能提高超高压条件下蛋白质的稳定性,从而保持良好的溶解性。而在抗压型Tris-HCl缓冲体系中,压力、保压时间、pH和离子强度对CPI溶解性的影响不显著。处于两种不同缓冲体系中的CPI经超高压处理后乳化性能均得到显著改善。在非抗压型磷酸盐缓冲体系中,升高压力或延长保压时间,都能使乳化活性显著提高,并在400 MPa处理和保压时间10 min时达到最大值,而乳化稳定性在400 MPa以上压力处理或者延长保压时间时呈下降趋势。在缓冲体系pH范围内(pH6.0-8.0)和0-1.0 mol/L离子强度下,超高压处理均能使CPI乳化活性得到不同程度的提高。在抗压型Tris-HCl缓冲体系中,不同条件下乳化活性的提高和磷酸盐缓冲体系一致,但在升高压力时CPI乳化稳定性保持升高趋势。处于两种不同缓冲体系中的CPI经超高压处理后起泡性能均得到显著提高。在非抗压型磷酸盐缓冲体系中,升高压力或延长保压时间,都能使起泡能力显著提高,并在500 MPa处理和保压时间10 min时达到最大值,而泡沫稳定性在400MPa以上压力处理或者延长保压时间时呈下降趋势。在缓冲体系pH范围内(pH6.0-8.0)和0-1.0 mol/L离子强度下,超高压处理均能使CPI起泡能力得到不同程度的提高。在抗压型Tris-HCl缓冲体系中,不同条件下起泡能力的提高和磷酸盐缓冲体系一致,但在升高压力或者延长保压时间时CPI泡沫稳定性保持升高趋势。在对CPI进行酶解之前,采用超高压处理(尤其处理压力在300 MPa以上时)和热处理(50-70℃)均能有效提高CPI水解速率,因为这两种处理方式均能使CPI结构部分展开,使得酶与底物的亲和力增强,从而使水解速率提高。利用动力学模型考查了两种预处理方式对CPI酶解敏感性的影响。结果表明,Alcalase水解对于热处理比胰凝乳蛋白酶水解更加敏感,即加热更有利于Alcalase对CPI进行酶解,而对胰凝乳蛋白酶解影响相对略小。而超高压预处理对于胰凝乳蛋白酶水解的影响比Alcalase水解更大,即超高压处理更有利于使用胰凝乳蛋白酶对CPI进行水解。当使用Alcalase和胰凝乳蛋白酶在超高压处理(100-300 MPa)过程中进行酶解时,同样的水解时间下,水解度急剧上升,大大超过了采用超高压预处理或热处理时的水解度,说明在超高压处理过程中酶解能显著提高酶解反应的速率,使在超高压处理过程中进行酶解成为一种新颖高效的酶解方式。更多还原

【Abstract】 Ultra high pressure (UHP) is an innovative technology for food processing, which has many advantages compared to traditional heat treatment. Protein is a major ingredient in food, so it has become an important research object in food science. Chickpea is the second most important pulse crop and accounts for 14% of the production of pulses in the world. Chickpea provides high-quality protein with balanced amino acid composition and nutrition. Effect of UHP on functional properties, structure and hydrolysis of chickpea protein isolate (CPI) has been investigated in order to find out the rules and mechanisms of the change induced by UHP.Analysis by surface hydrophobicity and ultraviolet difference spectra showed that more hydrophobic groups exposed to surface of CPI. Free sulfhydryl group (SHF) determination showed the decrease of SHF leading to create more new disulfides (S-S). Study of conformation by gel filtration, dynamic light scattering and electrophoresis proved the emergence of aggregation of CPI after treatment higher than 300 MPa, while some were dissociated into subunits with small molecular weight and kinetic radius after high pressure processing above 400 MPa.Influence of UHP on functional properties of CPI could be explained by the structural changes induced by UHP. Effect of UHP on solubility, emulsifying ande foaming capacity of CPI were studied, as well as effect of functional properties of CPI in different buffers (phosphate and Tris-HCl buffer) and with certain conditional factors such as pressure intensity, treatment time, pH and ionic strength.Effect of UHP on solubility of CPI in different buffers (phosphate and Tris-HCl buffer) has been investigated at pressures ranging from 100 to 600 MPa. Results showed that solubility of CPI decreased significantly at phosphate buffer pH with pressure intensity above 400 MPa and treatment time longer than 5 min, while ionic strength higher than 0.4 mol/L could effectively prevent the decrease of solubility due to pressurization. In Tris-HCl buffer, effect of UHP on solubility of CPI was not significant under the conditions above.UHP treated CPI displayed much better emulsifying capacity in different buffers. In non-resistent buffer (phosphate buffer), emulsifying activity was significantly enhanced with elevated pressure and prolonged treatment time. Maximum emulsifying activity was achieved at 400 MPa treated for 10 min, while emulsifying stability decreased with pressure higher than 400 MPa and treatment time longer than 10 min. Emulsifying activity improved to different extent at phosphate buffer pH (6.0-8.0) and different ionic strength (0-1.0 mol/L). In resistant buffer (Tris-HCl buffer), the increase of emulsifying activity was consistent with the change in phosphate buffer, while emulsifying stability increased at higher pressure. Foaming property of CPI significantly improved in different buffers. In non-resistent buffer (phosphate buffer), foaming capacity was significantly increased with elevated pressure and prolonged treatment time. Maximum foaming capacity was achieved at 500 MPa treated for 10 min, while foaming stability decreased with pressure higher than 400 MPa and treatment time longer than 10 min. Foaming capacity was enhanced to different extent at phosphate buffer pH (6.0-8.0) and different ionic strength (0-1.0 mol/L). In resistant buffer (Tris-HCl buffer), the increase of foaming capacity was consistent with CPI in phosphate buffer, while foaming stability kept increasing with higher pressure and longer treatment time.CPI hydrolysis by Alcalase orα-chymotrypsin was effectively accelerated after high pressure (above 300 MPa) and heat pretreatment (50-70℃). This increased hydrolysis was due to unfolding of CPI and facilitation of binding of the substrate to the enzyme induced by pressure and heat pretreatment.Kinetic model was used to describe the effect of these two pretreatments on CPI hydrolysis. Results showed that hydrolysis by Alcalase was more sensitive to heat pretreatment as compared to hydrolysis byα-chymotrypsin. However, hydrolysis by Alcalase was less sensitive to pressure pretreatment as compared to hydrolysis byα-chymotrypsin.The rate of hydrolysis by Alcalase orα-chymotrypsin during high pressure treatment (100-300 MPa) was increased dramatically much higher than the rate of hydrolysis after pressure and heat pretreatment. Therefore, hydrolysis under high pressure became an innovative way of enzymatic hydrolysis with high efficiency.更多还原