【作者】 陈学红；

【导师】 郑永华；

【作者基本信息】 南京农业大学 ， 食品科学， 2012， 博士

【摘要】 绿芦笋(Asparagas Officinalis L.)嫩茎味美鲜嫩,富含维生素、矿物质、氨基酸以及其它营养物质,是一种低热量、营养价值高的蔬菜,深受广大消费者的喜爱。但绿芦笋采收期相对集中,采后呼吸旺盛,常温下2-3d后即木质化变老而失去商品性。除了利用控制贮藏条件来延长芦笋的货架寿命外,还需开发芦笋加工产品以延长供应期。芦笋汁是一种相对较新的加工产品,其加工过程一般要进行热烫、榨汁、酶解和杀菌等加工单元操作。研究表明这些加工操作对果蔬汁的品质和风味均会产生不同程度的影响,但有关加工工艺条件对芦笋汁品质和抗氧化活性的影响缺乏系统研究。本论文以绿芦笋为试验材料,在研究不同品种、不同采收期绿芦笋的品质、抗氧化活性及其制汁适应性的基础上,重点研究了不同取汁方法、酶澄清、真空浓缩、热力杀菌和超高压杀菌等加工工艺对芦笋汁品质、抗氧化活性和风味的影响,同时还研究了贮藏温度、光照条件和包装材料对芦笋汁贮藏期色泽和汁液稳定性的影响,以期为绿芦笋汁产品的开发提供科学依据。研究结果分述如下：1.不同品种、不同采收期绿芦笋的品质、抗氧化活性及制汁适应性存在很大差异。通过主成分分析筛选出6项具有代表性的品质指标a*、维生素C、木质素、微量元素、氨基酸(或总黄酮)和总酚,利用模糊数学隶属函数法对绿芦笋的品质进行综合评价,不同品种绿芦笋的品质优劣排列顺序依次是“格兰德”、“阿特拉斯”、“UC301”、“UC157"和"UC800"。不同采收期“格兰德”绿芦笋的品质排列顺序依次是5月、4月、7月和6月,春季采收的绿芦笋的品质优于夏季。“格兰德”和"UC157"的抗氧化活性最强,其次依次分别是“阿特拉斯”、“UC301”和"UC800”。5月份采收的“格兰德”绿芦笋抗氧化活性最强,其次是4、7和6月份采收的绿芦笋。“格兰德”绿芦笋的出汁率和可溶性固形物含量位列5种绿芦笋之首,且芦笋汁在贮藏期间色泽稳定性好,沉淀量少,较适宜制作芦笋汁。5月份采收的“格兰德”绿芦笋所制汁在贮藏期间色泽稳定性高,沉淀量少,较适宜制作芦笋汁。2.91℃.3min热烫处理能够将绿芦笋中的POD钝化,且能很好地保持绿芦笋的色泽。取汁工艺显著影响绿芦笋汁的品质和抗氧化活性。热烫、破碎取汁能够保持芦笋汁的色泽,提高维生素C的稳定性。热烫、破碎、榨汁及纤维素酶处理后取汁有利于提高芦笋汁的可溶性固形物、总糖及总黄酮含量,维持芦笋汁的品质,增强芦笋汁的抗氧化活性。但这两种取汁工艺均降低了芦笋汁中的可溶性蛋白和总酚含量。3.利用响应曲面法(RSM)建立了不同条件下纤维素酶和果胶酶处理芦笋汁的二次多项式的数学模型,经检验该模型极显著,拟合度高。通过响应曲面分析,确定纤维素酶的最佳作用条件是温度42.96℃,pH5.03,酶用量0.07%,果胶酶的最佳作用条件是温度40.56℃, pH4.43,酶用量1.45%。经复合酶处理的芦笋汁出汁率和可溶性固形物含量显著提高,同时1,1-二苯基苦基苯肼(DPPH)自由基清除能力无显著改变。4.浓缩工艺对芦笋汁的品质和抗氧化活性有明显影响。随着浓缩汁固形物含量的增加,芦笋汁的绿色加深,可溶性蛋白、总糖和总酚含量增加,而芦笋汁的色泽亮度、维生素C、总黄酮含量和抗氧化活性逐渐降低。采用SPME方法富集芦笋汁中的挥发性风味化合物,经GC-MS检测,鉴定结果表明芦笋汁中主要的挥发性风味成分是醛类。其次是醇类、酮类、含氮化合物和酚类,还含有少量的酯类和有机酸。浓缩处理对芦笋汁挥发性风味成分有明显影响。浓缩芦笋汁固形物含量达10%时,芦笋汁中主要挥发性风味物质醛、醇和酮均有损失；随着浓缩程度的增大,风味成分含量增加,当固形物含量达30%时,风味成分含量最高,其醇、醛、酮及其它化合物的含量均达到最高,风味最佳；进一步浓缩至固形物含量达45%时,芦笋汁的风味成分含量降低,风味变差。5.121℃、3min的热杀菌(TP)处理能有效杀灭芦笋汁中的微生物至未检测出水平,延长芦笋汁的贮藏寿命。TP处理有效抑制了芦笋汁可溶性蛋白和总糖含量的降低,抑制了芦笋汁总酚、总黄酮含量和DPPH自由基清除能力的下降。这些研究结果充分表明了热力杀菌技术在延长芦笋汁贮藏寿命、保存芦笋汁品质方面的有效性。然而热力杀菌技术也在一定程度上对芦笋汁的品质产生了负面影响,如维生素C的破坏和绿色的损失等。超高压杀菌(HPP)处理较TP处理能更有效地保持芦笋汁的绿色,保存较高的维生素C、芦丁含量及较强的抗氧化活性,保留了更多的醇和酮类物质含量,并且显著增加了醛类物质的含量。400-600MPa的HPP处理能够确保芦笋汁的安全性,有效保持其品质和抗氧化活性,并有利于保留芦笋汁中的风味成分。经GC-MS检测鉴定,结果表明醛类物质是芦笋汁中的主要风味成分,代表性物质是己醛,其次是2-庚烯醛、戊醛、2-丁烯醛(或2-甲基-2-丙烯醛)、2-戊烯醛、2-辛烯醛、2-己烯醛、壬醛和辛醛。醇类物质的含量仅次于醛类,代表性物质是1-辛烯-3-醇,其次是壬醇。酮类物质的代表性物质是1-辛烯-3-酮,其次是3-辛酮、6-甲基-5-庚烯-2-酮、香叶基丙酮和β-紫罗兰酮。在其它化合物中,甲氧基苯基肟含量最高,其次是2,4-二叔戊基苯酚和2-戊呋喃。酯类物质主要是异丁基邻苯二甲酸酯。有机酸主要是已酸。6.贮藏温度、光照和产品包装材料对芦笋汁色泽稳定性产生很大影响。采用低温(5℃)、玻璃瓶包装和避光贮藏可有效延缓芦笋汁叶绿素、维生素C、总酚和还原糖含量的降低,抑制类胡萝卜素含量的上升和聚合体色泽的产生,从而较好地维持了芦笋汁色泽的稳定性。芦笋汁沉淀物的主要成分是糖,其次还包括蛋白质、果胶和总酚。果糖是芦笋汁沉淀物中主要的糖,葡萄糖也参与了沉淀的形成。芦笋汁沉淀物中的酚类物质主要是酚酸类和黄酮类物质,芦笋汁贮藏前后酚酸类物质明显减少,这些酚酸如绿原酸、咖啡酸和阿魏酸等有可能与芦笋汁沉淀的形成有关。芦笋汁贮藏前后组氨酸和赖氨酸明显降低,而沉淀中这两种氨基酸的比例相对较高,因而它们有可能是易与多酚发生相互作用的氨基酸。芦笋汁沉淀中脯氨酸含量虽相对较高,但由于芦笋汁贮藏前后脯氨酸含量并没有明显降低,因而芦笋汁沉淀的形成有可能与脯氨酸没有直接关系。更多还原

【Abstract】 Green asparagus (Asparagas Officinalis L.) is very popular with consumers for its appealing flavor, high vitamins, minerals and other nutritive compounds. It is a vegetable with low calorific energy and high nutritive value. The harvest period of green asparagus is relatively concentrated. After harvest, the vegetable rapidly lignifies, senesces and loses its commodity due to its high respiration rate. It has2-3days shelf life under ambient temperature. It is urgent to deeply develope asparagus product to extend supply time except for prolonging its shelf life by controlling storage condition. Asparagus juice is a relatively new product. Blanching, squeezing, enzymatic treatment, and pasteurization are usual unit operations during asparagus juice processing. These processing treatments affect the quality and flavor of fruit and vegetable juices. However, there is no systemic study on the effect of processing technologies on quality and antioxidant activity of asparagus juice. The present study was designed to investigate the quality, antioxidant activity and juice processing characteristics from different green asparagus species in different harvest period. The studies were primarily carried out about effects of processing technologies, such as juice extraction methods, enzymatic clarification treatment, vacuum concentration, thermal and ultra-high pressure pasteurization, on the quality, antioxidant activity and flavor of green asparagus(Asparagas Officinalis L. cv. Grande) juice. In addition, the effects of storage temperature, light condition and package materials on color and juice stability of green asparagus juice during storage time were also explored. The aim is to provide scientific basis for the development of green asparagus juice product. The results were as follows:1. Significant differences were found in quality, antioxidant activity and juice processing characteristics of green asparagus from different species and different harvest periods. The quality indexes a*, vitamin C, lignin, microelements, amino acids or total flavornoids and total phenolics contents of green asparagus were evaluated by principal component analysis (PCA) and membership function in fuzzy mathematics. The quality of ’Grande’green asparagus was the best. Then, it was’Altas’,’UC301’,’UC157’and ’UC800’. The quality of’Grande’green asparagus harvested on May was the best. Secondly, it was respectively green asparagus harvested on April, July, and June. Generally, the quality of green asparagus harvested in spring was better than that one in autumn. Great antioxidant activity was found in green asparagus’Grande’and’UC157’. Then, it is’Altas’,’UC301’and’UC800’.’Grande’ green asparagus harvested on May showed greater antioxidant activity than those one on April, July, and June.’Grande’green asparagus was appropriate for juice processing due to its high juice yield, soluble solids, and better color stability and minor sediment in its juice during storage time.’Grande’green asparagus harvested on May was appropriate for juice processing due to better color stability and minor sediment in its juice during storage time.2. Blanching at91℃for3min could inactive peroxidase (POD) activity and preserve the color of green asparagus. Juice extraction technology significantly affected the quality and antioxidant activity in asparagus juice. Juice extraction for blanching and breaking could preserve the color of green asparagus juice and improve the stability of vitamin C. Juice extraction for blanching, breaking and cellulase treatment increased the soluble solids, total sugar, total flavornoids contents and improved antioxidant activity in green asparagus juice. The soluble protein and total phenolics contents in green asparagus juice were decreased by these two juice extraction technologies.3. Cellulase and pectinase treatment conditions for green asparagus juice were optimized by using response surface methodology (RSM). The results showed the response and variables were fitted well to each other by multiple regressions and the proposed second-order polynomial model was adequate. According to response analysis, the optimal enzymatic treatment condition for cellulase was concentration of0.07%, incubation temperature of42.96℃, and pH of5.03, and that for pectinase was concentration of1.45%, incubation temperature of40.56℃and pH of4.43. The clarity, juice yield and soluble solid contents in asparagus juice were significantly increased by enzymatic treatment at the optimal conditions.1,1-diphenyl-2-picryhydrazyl (DPPH) radical scavenging capacity was maintained at the level close to that of raw asparagus juice.4. Condensation technology significantly affected the quality and antioxidant activity in green asparagus juice. The greenness, soluble protein, total sugar, and total phenolics contents in green asparagus juice were increased as soluble solids contents were increased. And while the lightness, vitamin C, total flavornoids contents, and antioxidant activity were decreased. Volatile flavoring compounds enriched with SPME were identified by GC-MS. The results indicated that aldehydes were main volatile flavoring compounds in green asparagus juice. Secondly, alcohols, ketones, compounds containing nitrogen, and phenols were found in green asparagus juice. Few esters and organic acids were also contained in green asparagus juice. Condensation treatment significantly affected volatile flavoring compounds in green asparagus juice. The main volatile flavoring compounds, such as aldehydes, alcohols, and ketones, showed significant loss when soluble solids content was10%. Further concentrating treatment increased flavoring compounds. When soluble solids content was30%, green asparagus juice show the best flavor due to its high flavor compounds contents, such as alcohols, aldehydes, ketones, and other compounds. Green asparagus juice showed poor flavor due to its low flavor compounds contents as soluble solids contents was45%.5. Thermal pasteurization (TP) at121℃for3min could effectively kill microbials to the undetectable level and prolong the storage time of green asparagus juice. TP treatment effectively inhibited the decreases of soluble protein and total sugar contents. The decreases in total phenolics, total flavomoids contents and DPPH radical scavenging capacity were inhibited by TP treatment. The results showed that TP treatment was an effective technology for extending the storage time and keeping the quality of green asparagus juice. However, TP treatment had negative effects on the quality indexes of green asparagus juice, especially vitamin C and greenness. High pressure pasteurization (HPP) treatments preserve better greenness, vitamin C, rutin and antioxidant activity than TP treatment. Alcohols and ketones contents were kept at a higher level and aldehydes contents were significantly increased by HPP treatments. HPP treatments for400-600MPa could ensure the safety of green asparagus juice and effectively keep the quality and antioxidant activity. The results identified by GC-MS showed that aldehydes were main volatile flavoring compounds in green asparagus juice. The representatives were hexanal,2-heptenal, pentanal,2-butenal or2-methyl-2-propenal,2-pentenal,2-octenal,2-hexenal, nonal, and octanal. The representatives of alcohols were1-octen-3-ol and nonanol. The representatives of ketones were1-octen-3-one,3-octanone,6-methyl-5-hepten-2-one, geranyl acetone, β-ionone. In other compounds, methoxy-phenyl-oxime was high, then2,4-di-tert-amyl phenol and2-pentyl-furan. Ester was mainly isobutyl phthalate. Organic acid was hexanoic acid.6. Storage temperature, light and package materials obviously affected the color stability of green asparagus juice during storage time. The decreases of chlorophyll, vitamin C, total phenolics and reducing sugar contents packaged in glass bottle were inhibited at refrigeration and light-resistant condition. At the same condition, the increase of carotenoids contents and the production of polymeric color were prevented and the color stability of green asparagus juice was effectively kept. The principle component in sediment of asparagus juice was sugar. Secondly, protein, pectin, and total phenolics were contained in sediment. Fructose was the main sugar in sediment of green asparagus juice. Glucose was also related to the production of sediment. Phenolics compounds in sediment were phenolics acids and flavornoids. The decreases of phenolics acids contents were observed in green asparagus juice after storage. Thus, it is inferred that these phenolics acids, such as chlorogenic acid, caffeic acid, and ferulic acid, were probably related to the formation of sediment. The histidine and lysine were decreased in green asparagus juice after storage. These two arnino acids had high proportion in sediment. It is inferred that they probably interacted with polyphenolics compounds. The proline in sediment of green asparagus juice was high. However, the proline content was not decreased after storage. Thus, it is probably that the formation of sediment in green asparagus juice was not directly connected with proline.更多还原