【作者】 郭善广；

【导师】 仇农学；

【作者基本信息】 陕西师范大学 ， 食品科学， 2004， 硕士

【摘要】 苹果浓缩汁褐变、后混浊一直是困扰着我国乃至世界果汁加工业的重大技术难题，目前尚无成熟可靠的控制方法。褐变、后混浊严重影响果汁的品质，增加了我国果汁出口的难度。因此，如何安全、无污染地减缓、降低和控制苹果浓缩汁褐变、后混浊而又最大限度地保存果汁中的营养成分，是提高果汁质量、增加附加值的关键。 本文研究了苹果浓缩汁贮存对褐变、后混浊的影响，确定了引起褐变、后混浊的主要诱因；检测了苹果浓缩汁生产加工过程对褐变、后混浊及其诱因的影响；分析了榨季不同时期苹果浓缩汁色值和浊度的变化；探讨了LSA—800B吸附树脂对果汁中色素及色素前体(诱因)吸附的动力学特征；尝试了使用金属微滤膜控制、减轻褐变、后混浊的方法。希望通过研究能为生产高品质苹果浓缩汁提供理论及数据支持。试验研究结果表明： 1．苹果浓缩汁加工单元操作中前巴氏杀菌杀处理能够钝化PPO的活性，在前巴氏杀菌后的加工单元操作及贮存过程中引起果汁褐变的主要原因是美拉德反应。 2．苹果浓缩汁贮存过程中温度对后混浊影响很大，在较高温度下更易于形成后混浊，而在较低温度下后混浊形成缓慢。贮存过程中浊度变化经历三个典型的阶段：迟滞期、增长期和稳定期。以浊度(NTU)计算三个不同贮存温度5℃、20℃和37℃条件下果汁形成后混浊的速率基本符合一级反应动力学。 3．不同贮存温度条件下果汁褐变变化速率符合一级动力学。温度对褐变的影响随着温度的提高褐变速率明显加快，5℃、20℃和37℃贮存条件下果汁褐变度分别增加了12.45％、46.86％和415.28％。以色值和吸光值计算三个不同贮存温度条件下果汁褐变速率基本符合一级反应动力学。 4．苹果浓缩汁中的蛋白质(Pro)、总酚(PP)及单宁(Tan)含量随贮存时间延长而下降，且在37℃贮存时下降速率明显大于5℃和20℃时的下降速率。 5．5—羟甲基糠醛(HMF)含量与果汁的褐变速率成指数关系，方程相关系数达到0.90以上。说明果汁在贮存时的褐变主要由美拉德反应引起且初期HMF微量的增加，就能产生很大程度的褐变，控温可以减缓果汁的褐变。苹果浓缩汁中的氨基态氮(AAN)含量随贮存时间增加而下降、随贮存温度升高下降速率加快。果汁中氨基态氮含量变化与果汁褐变速率呈线性相关，同样说明褐变是由美拉德反应引起。 6.在加工过程前期低温条件及高温短时杀菌情况下，美拉德反应速率缓慢，对果汁褐变的影响不显著。在后巴氏杀菌较长时间高温处理时，美拉德反应速率很快。加工过程中除了超滤对氨基态氮(AAN)几乎没有影响外，其它单元操作都可降低果汁中AAN的含量，特别是吸附、浓缩和后巴氏杀菌对其均有明显的影响。果汁中总酚(PP)和单宁(几n)的含量在酶解后的各加工单元操作中呈明显下降趋势。加工过程中的酶解能显著降低可溶性蛋白质(Pro)含量，超滤和吸附对其影响也比较显著，而浓缩和后巴氏杀菌工艺对其影响较弱。 7.正常苹果浓缩汁和后混浊苹果汁的初始浊度有显著差异。产生后混浊果汁的初始浊度要高于正常果汁的初始浊度，在生产中控制果汁的初始浊度非常必要，可以降低果汁在贮存过程中发生后混浊的几率。 8.LSA一800树脂吸附果汁中色素为吸热过程，主要是物理吸附。不同树脂浓度25℃吸附初始平衡时间平均为9.73h，而且随着温度提高初始平衡时间有所减少。在2一4叭果汁的树脂浓度范围内，吸附效果比较明显，超过此范围则单位质量树脂吸附效果有所下降。在试验温度范围内较高温度的吸附平衡常数(Kad)值较大。 9.金属膜过滤前后果汁的色值变化差异不大，三次试验中平均色值仅降低了0.43%;经纸板过滤的果汁色值则差异很大，三次试验中平均色值降低幅度达10.11%。.金属微滤膜与纸板过滤对浊度的影响都很显著，处理后果汁的浊度分别下降T 73.5既和47.50%。 1 0.选择成熟度合适的苹果能控制，减缓褐变、后混浊的发生。苹果贮存时间与色值的关系不明显，但随贮存时间延长浊度有下降趋势。更多还原

【Abstract】 Browning and haze in apple juice concentrate (AJC) have been long-standing problems in processing and there is no reliable solution to them. So, how to safely better cope with these problems and to protect the nutrition of juice is important to produce high quality AJC.Effect of storage on browning and haze of AJC is investigated and some inducements are determined in the paper; effect of processing on browning and haze is researched; the change of color and turbidity during producing season is carefully observed; kinetics on the adsorption of dark colored compounds from apple juice using LSA-800B adsorbent resin is studied; also micro-filtration is attempted to retard browning and haze development by using metal membrane. Theories and data are supplied to resolve the problems in AJC processing. The results of the work are listed as follows:1.First pasteurization of the raw juice may inactivate or denature polyphenoloxidase (PPO), so in the following processing and storage, accumulation of brown color is mainly due to Maillard reaction.2. During storage time, haze is liable to form at high temperature but low temperature. Haze development during storage reveals three distinct phases which may be labeled as follows: a lag phase, a growth phase, and a stable phase. The rate of haze formation at all three temperatures 5℃, 20℃, and 37℃, as measured by the increase ’in turbidity, can be described by first-order reaction kinetics.3. The rate of browning at all three temperatures fit first-order kinetic model. The Maillard reaction occurs preferably at high temperature, for the rate of this reaction at high temperature is faster than that at low temperature. The browing increases of juice samples which are stored at 5℃, 20℃, and 37℃ are 12.45%, 46.86%, and 415.28%, respectively. According to colour value (T440) and browning index (A420) changing, the rates of browning at all three temperatures can be described by first-order reaction kinetics.4.The contents of soluble protein (Pro), amino acid nitrogen (AAN), polyphenol (PP), and Tannin (Tan) in AJC decrease by increasing storage time and the decreasing rate at 37℃ is evidently greater than that at 5℃ and 20℃.5. The relation between 5-hydroxymethylfurfural(HMF)and browning of juice can be described as exponential and the regression coefficient is larger than 0.90. So, the reason why AJC becomes browning during storage is Maillard reaction; browning changes greatly by little change of HMF, At the beginning of storage, lower temperature can prevent browning of juice. AAN contents of the AJC samples decrease as a function of storage and temperature. The linear relation between AAN and browning is also indicated that the cause of browning is Maillard reaction.6. At initial processing stage, low temperature and instant high temperature sterilization, Maillard reacts slowly, which has no obvious effect on the browing. The rate of Maillard reaction is increase at second pasteurization for the sake of high temperature and long-playing. Ultrafiltration (UF) has hardly effect on AAN, however, other unit operations can reduce the content of ANN especially in concentration, adsorption and second pasteurization. The tendency of PP and Tan changing is declining after enzymolysis during processing. Solubled protain can be reduced markedly by enzymolysis as well as by UF and adsorption, but concentration and second pasteurization.7. The initial turbidity of hazed AJC is remarkably higher than that of normal AJC, thereby, controlling the initial turbidity of juice is important.8. The adsorption of color compounds on LSA-800B adsorbent resin was an endothermic process, and controlled by physical mechanisms only. The initial equilibrium time of adsorption is average 9.73h at 25 ℃ for all concentrations of adsorbent resin, and may tend to decrease as the adsorption temperature increases. Within the adsorbent resin concentration of 2-4g/L juice, the effect of adsorption is distinct; exceeding the scope, the efficiency per unit adsorbent decrease更多还原