【作者】 陈金；

【导师】 陆胜民；

【作者基本信息】 南京农业大学 ， 食品科学， 2012， 硕士

【摘要】 常山胡柚是我国特有柑橘品种,果实产量高、品质好,深受广大消费者的青睐。然而胡柚的加工比例很低,仅有少量的砂囊、胡柚茶全果饮品和果脯产品供市。目前国内胡柚仍以鲜销为主,近年来种植面积不断扩大,产量节节攀高,充足而价廉的原料需要寻找新的出路。而与澄清型果汁相比,消费者更趋向于混浊果汁,因为后者的风味、口感、色泽等感官品质和营养价值更好。因此,开发混浊型胡柚汁不仅具有原料的优势,也具有区域市场的优势。但混浊型果汁的稳定性比澄清型果汁差,贮存一定时间后易发生沉淀分层现象,影响了果汁及其饮料的消费。本课题以常山胡柚为原料,初步探讨了胡柚汁混浊态丧失的原因,并分析了超高压均质(UHPH)处理对胡柚汁果胶酯酶(PME)活性、混浊稳定性的影响及可能机理,分析了UHPH处理对胡柚汁营养与货架稳定性的影响,为胡柚混浊汁的工业化生产提供理论与技术上的基础,并为UHPH技术在食品工业中的推广应用提供借鉴。研究结果分述如下：(1)研究了胡柚果汁混浊物的主要化学组成；胡柚汁中PME、外源添加PME、酸性蛋白酶、果胶酶及贮藏温度对胡柚汁混浊稳定性的影响。结果表明：胡柚汁混浊物大分子物质主要是果胶和蛋白质；胡柚汁中的PME活性越低,胡柚汁混浊度保持的时间就越长,就越稳定；胡柚汁中的PME活性的存在是导致胡柚汁混浊态丧失的主要因素之一；酸性蛋白酶可以部分降低胡柚汁的混浊度,但各添加量之间差异不显著(P>0.05)；果胶酶可明显降低胡柚汁的混浊度,使胡柚汁混浊稳定性丧失；在贮藏过程中,随着贮藏温度的升高,胡柚汁的混浊度越来越小,常温贮藏不利于胡柚汁混浊稳定性的保持。(2)研究了UHPH处理除了温度因素外对胡柚汁混浊稳定性及理化性状的影响,分析了UHPH处理对胡柚汁混浊稳定性的作用及其可能机理。结果表明：在贮藏过程中,胡柚汁中的PME活性随着均质压力的升高而降低,混浊度随着均质压力的升高而升高；离心沉淀率随着均质压力的升高而降低,120MPa及以上UHPH处理可以很好地防止胡柚汁的分层,但胡柚汁的不稳定悬浮物含量与均质压力没有明显的相关性;UHPH处理后的胡柚汁的粘度比对照组要高,但各处理组之间的差异趋向于不显著；经UHPH处理后,胡柚汁的平均粒径显著减小(P<0.05),粒径分布范围也变小,并且随着均质压力的升高,胡柚汁的平均粒径和粒径分布范围也不断减小；在贮藏过程中,由于胡柚汁中的较大颗粒逐渐沉降下去,使得胡柚汁的平均粒径和粒度分布范围均随着时间的延长而逐渐减小；均质压力越大,分层速度越小,体系越稳定。(3)研究了UHPH处理前后及低温贮藏期间胡柚汁中Vc、pH、可溶性固形物(TSS)、色泽、可滴定酸、还原糖、果胶及可溶性蛋白质含量的变化情况,探讨了UHPH处理对胡柚汁营养与货架稳定性的影响规律和机理。结果表明：UHPH处理可以使胡柚汁中的Vc在贮藏过程中的下降速度变缓,但各处理组之间差异不显著(P>0.05),贮藏过程中胡柚汁的Vc含量随着时间的延长而下降；UHPH处理对胡柚汁的还原糖含量没有明显的影响,贮藏过程中,不同处理的胡柚汁的还原糖含量均呈先下降后上升再下降的趋势；由于UHPH处理能使细胞破碎,使果胶物质释放出来,因而可显著增加胡柚汁的果胶含量(P<0.05),且果胶含量随着均质压力的升高而升高,但120MPa与160MPa UHPH处理组的差异不显著(P>0.05),贮藏过程中胡柚汁的果胶含量随着时间的延长而下降；同样由于细胞的破碎及可溶性蛋白质的溶出,UHPH处理还可以提高胡柚汁中的可溶性蛋白质含量,且可溶性蛋白质含量随着均质压力的升高而升高,但在贮藏过程中随着时间的延长而下降；不同压力UHPH处理对胡柚汁的TSS含量及可滴定酸含量无明显的影响,在贮藏过程中,胡柚汁的TSS含量及可滴定酸含量变化不大,基本保持稳定；UHPH处理能使胡柚汁亮度增加,黄色加强,绿色加强,胡柚汁在贮藏前期亮度下降,黄色减弱,绿色减弱,而在贮藏中后期色泽基本保持稳定。更多还原

【Abstract】 As a unique citrus variety, Changshan-huyou has high fruit yield, good quality, and has been well received by the majority of consumers in China. However, the processing of huyou fruit has a very low percentage, with a small amount of whole fruit drinks and preserved fruit products for the market. Currently, huyou fruit has still been mainly fresh saled, but in recent years, as the area under cultivation expanded and the production raised in a large extent, it is needed to find a new way for the outlet of the adequate and cheap raw materials. Simultaneously, compared with the clarified juice, consumers tend to choose cloudy juice because of its better sensory quality (such as flavor, texture and color, et al.) and nutritional value. Therefore, the development of cloudy huyou juice not only has the advantage of utilizing raw materials, but also has a regional market advantage. However, the stability of the cloudy juice is worse than that of the clarified juice. After a certain period of storage, it is easy to precipitate and separate into layers, which influences the juice consumption. In order to provide the theoretical and technical foundation for industrialized production of huyou cloud juice, and provide a reference for ultra-high pressure homogenization(UHPH) technology on popularization and application in the food industry, we studied in this work the reasons for the cloud loss in huyou juice, analyzed the impact and possible mechanism of UHPH on pectinesterase(PME) activity in huyou juice and the cloud stability of the juice, and investigated the influence of UHPH on the nutrition and shelf stability of huyou juice. The results were as follows:(1) The composition of huyou juice cloud was investigated. The effects of PME activity in juice, addition of PME、acid protease and pectinase, storage temperature on the cloud stability of huyou juice were studied. The results showed that huyou juice cloud mainly consisted of pectin and protein. The lower PME activity in huyou juice, the longer the turbidity of the juice remained, and the more stable the juice was. The presence of PME activity in huyou juice was one of the main factors of cloud loss. Acid protease could partially reduce the turbidity of the huyou juice, but the variation was not significant (P>0.05). Pectinase could significantly reduce the turbidity of huyou juice, resulting in cloud loss. The turbidity of huyou juice was getting lower with the increasing storage temperature. Ambient temperature storage was unbeneficial for the cloud stability of huyou juice.(2) Influence of UHPH in addition to the temperature factor on the cloud stability and physical and chemical properties of huyou juice was investigated. The effects of UHPH on the cloud stability of huyou juice and possible mechanism were discussed. The results showed that PME activity in huyou juice decreased with increasing homogenization pressure, and the turbidity increased as homogenization pressure increased. Centrifugal sedimentation rate was reduced with increasing homogenization pressure.120and more than120MPa UHPH could commendably prevent huyou juice from layering, but there was no obvious correlation between the suspended substance content and homogenization pressure. The viscosity of huyou juice treated by UHPH was higher than that of the control, but the differences between each treatment group tended to be no significance. After UHPH treatment, the average particle diameter of huyou juice was significantly reduced (P<0.05) and the particle size distribution range became narrow, and both of them continued to reduce with the homogenization pressure increased and the time prolonged. Due to the larger particles in the huyou juice sedimentation down gradually, both of the average particle diameter and the particle size distribution range were reduced with the time prolonged during storage. The greater the homogeneous pressure was, the smaller the layering speed was, and the more stable the system was.(3) Changes of Vc, pH, total soluble solid(TSS), color, titratable acidity, reducing sugar, pectin and soluble protein content before and after UHPH treatment and during low temperature storage were investigated. The impact mechanism of UHPH on huyou juice’s nutrition and shelflife stability were discussed. The results showed that UHPH treatment could result in a slow loss of Vc in huyou juice during storage, but the differences between the treatment groups was not significant (P>0.05), and Vc content decreased with prolonging storage time. UHPH had no significant effect on reducing sugar content, with a trend of decrease first and then increase following a decrease again during storage. UHPH could significantly increase pectin content in huyou juice(P<0.05) because of it making cell disruption and releasing pectin substances, and pectin content increased with increasing homogenization pressure, however, the difference between120and160MPa UHPH treatment groups was not significant (P>0.05), and pectin content in the juice decreased with prolonging storage time. Because of making cell disruption and releasing the soluble protein, UHPH could also improve the soluble protein content in huyou juice with a trend of increasing with increasing homogenization pressure and decreasing with prolonged storage time. Different pressure in UHPH treatments had no significant effect on TSS and titratable acid content of huyou juice, and TSS and titratable acid content changed slightly and remained stable during storage. After UHPH, the brightness of the juice increased, and yellowness and greenness strengthened. All of the brightness, yellowness and greenness declined in the early days of storage, but the color remained stable during the half and late period of storage.更多还原