【作者】 夏玉静；

【导师】 王文辉；

【作者基本信息】 中国农业科学院 ， 农产品加工与贮藏工程， 2010， 硕士

【摘要】 梨是我国第三大水果,2008年产量达1367万吨,约为世界总产量的三分之二,居世界第一位。但是我国梨果加工量很少,不到总产量的10%,致使采收期大量梨果涌入市场,销路不畅,甚至造成极大浪费。研究梨果的加工特性,解决产品加工过程中出现的问题,可以有效缓解梨果采后鲜销和贮藏压力,提高果农收入,从而提高梨果产业效益和推动产业发展。本文以鸭梨、砀山酥、黄金、花盖、南果、五九香等23个代表性梨品种为原料,研究了其制汁特性,筛选出适于制汁的3个品种,总结提出了梨果制汁适应性的评价方法；同时研究了秋子梨后熟程度对制汁特性的影响,以及梨果汁酶促褐变的机理、非酶褐变的控制方法,以期为梨果加工品质提高提供技术支撑。1.梨制汁品种的筛选应从理化指标(可溶性固形物、糖、酸)、出汁率、褐变度(酚含量、PPO活性、L值、OD420nm值)3个方面综合考虑。供试品种中秋白、黄金、安梨为最佳的制汁品种。梨果实的果皮中酚类物质含量最高,果心次之,果肉中含量最低,果皮中酚的含量与果汁褐变度有显著的相关性。多数梨品种果皮中的PPO活性很高,果肉中的PPO活性很低,所以定位高档的果汁加工时可考虑去皮以减轻褐变。2.以口味淡薄的鸭梨和砀山酥梨为主要原料进行混合梨汁试验,正交设计确定最优组合：Ⅰ：砀山酥梨汁50ml,安梨汁25ml,锦香梨汁30ml混合；Ⅱ：鸭梨汁50ml,花盖梨汁15ml,尖把儿梨汁20ml混合。3.秋子梨等软肉梨制汁时要先经过后熟。秋子梨的硬度在2.5～4.0kg／0.5cm2时,硬度适当,此时的出汁率较高,单宁含量低,褐变程度也较低,此时适宜制汁。4.黄金梨汁和秋白梨汁贮存过程的非酶促褐变中,氨基酸、还原糖和总酚的含量变化与褐变指数(OD420nm)极显著负相关,与L值极显著正相关。梨汁贮藏过程中非酶褐变发生的类型主要是美拉德反应和酚类物质的氧化。低温贮藏能有效的抑制非酶促褐变反应的发生。5.黄金梨汁和秋白梨汁贮存中褐变指数(OD420nm)随温度和时间的增加而上升。20℃下贮存,黄金梨汁的色值变化符合两阶段复合型,秋白梨汁符合抛物线型。0℃下贮存时,黄金梨汁和秋白梨汁符合1级模型。黄金梨汁贮藏时褐变反应的活化能是Ea=12.13kcal／mol,秋白梨汁的活化能是Ea=10.73kcal／mol,黄金梨汁比秋白梨汁更容易发生褐变。6.南果梨是秋子梨中的优良品种,但制汁时褐变严重,利用抗褐变剂可以有效的抑制其酶促褐变反应的发生。相同浓度下,所选5种抗褐变剂的抗褐变能力：Na2SO3>Vc>L-半胱氨酸>柠檬酸>CaCl2.对PPO活性的抑制能力：L-半胱氨酸>Na2SO3>柠檬酸>Vc>CaCl2。抗褐变剂混合使用效果更佳,建议用量：抗坏血酸0.046%、L-半胱氨酸0.037%、柠檬酸0.0401%的配比。更多还原

【Abstract】 Pear is the third largest output fruits in China,13670 tons was harvested in 2008, which is almost 2/3 of all the world harvested, ranking the first. While, the amount of pear being processed is less than 10% of the total.In the harvest period, there are so many pears in the market that many can’t be sold and rot at last. Studying the pears’ processing characters deeply, solving the problems occurred during processing and storage are effective ways to improve benefits and promote development of the industry. 23 pear varieties such as Yali、TsuLi、Whangkeumbae, Huagai, Nanguo were referred in the experiments, which offered academic guidance for pear industry by studying the pears’ juice-processing characters, screening juicing suitable varieties and summarizing methods to select juicing variety. Effects of ripening degree on juicing performance were also studied, and then mechanism of nonenzymatic browning and the control of enzymatic browning were discussed in order to provide technical support. The experiments investigation indicates:1. Physical and chemical indicators (total sugar, reducing sugar, titratable acid, soluble solid content, juice yield),degree of browning (total phenolics, PPO activity, OD420nm, L) and sensory evaluation (appearance, taste, smell) should be considered before identify a juicing variety, which should be good in taste, high in juice yield, low in browning degree. Jinxiang, Whangkeumbae, Anli were the best varieties of all the 23. Total phnolics are richest in fruit skin, and then in fruit core, poorest in fruit flesh, and total phenolics of pear skin correlated significantly with colour value. Most varieties’ PPO activity in fruit skin is high, while, in flesh is relatively low.2. Juice of Yali and taste less flavor, mix them with palate fullness juice, orthogonal experimental design to get two best recipes:Ⅰ:TsuLi-juice 50ml, Anli-juice 25ml, jinxiang-juice 30ml;Ⅱ:Yali-juice 50ml, Huagai-juice 15ml, jianbaer-juice20ml.3. For Pyrus ussuriensis Maxim, ripen firstly before juice until the firmness is suitable, the juice yield is high, the tannic is less, and the browning is light. When the firmness is 2.5～4.0kg/0.5cm2 can meet the demands above.4. In the nonenzymatic of Whangkeumbae juice and Qiubai juice during storage, the concentration of total amimo acid、sugar and total phenolics decreased, and they are correlated negatively with OD420、positively with L value. Maillaid reaction and phonelics oxidation were the main factor of nonenzymatic browning. Storage in low temperature can inhibit nonenzymatic browning effectively.5. OD420 of Whangkeumbae juice and Qiubai juice increased with both time and temperature. Storaged in 20℃, Whangkeumbae juice fits two stages combined reaction kinetic, and Qiubai juice fits parabola kinetic. While storaged in 0℃, both fit zero order. Browning activation energies of Whangkeumbae juice and Qiubai juice are 12.13kcal/mol and 10.73 respectively, Whangkeumbae juice browns easier than Qiubai juice.6. Antibrowning agents can inhibit enzymatic effectively during pear juice is being processed. With the same concentration, the inhibition ability of studied antibrowning agents was: Na2SO3>Vc>L-Cysteine>Citric acid>CaCl2。The PPO inhibition ability was:L-cysteine> Na2SO3> Citric acid>Vc> CaCl2。Inhibition ability strengthen significantly when mixed, according response surface methodology, the optimum combination was determined as Vc 0.046%、L-Cysteine 0.037%, Citric acid 0.0401%.更多还原