【作者】 李静；

【导师】 郑永华；

【作者基本信息】 南京农业大学 ， 食品科学与工程， 2017， 硕士

【摘要】 莴苣肉质翠绿,青脆爽口,同时富含莴苣素、无机盐、维生素及微量元素锌、铁等营养物质,深受广大消费者喜爱。莴苣叶容易损伤腐烂,茎内表皮易木质化,不耐贮藏,莴苣在食前要去皮,非常适用于鲜切加工。但是莴苣经切割处理后易于感染微生物,生理生化反应加剧,从而加速衰老。已有研究表明,果蔬在受到机械损伤后,常会引起多酚类物质的合成与累积地增多,后者不仅可以抵御外界伤害,还可以提高鲜切果蔬的抗氧化性。此外研究证明,适当剂量的短波紫外线(Ultraviolet-C,UV-C)处理在鲜切果蔬贮藏保鲜方面效果良好,可以有效抑制微生物的生长,保持品质,同时可促进多酚类物质的合成,提高鲜切果蔬的抗氧化活性。但切割方式和UV-C处理对莴苣品质和抗氧化活性的影响尚未见报道。本论文在比较不同切割方式(片状、1/4片状、丝状)对鲜切莴苣品质及抗氧化活性影响的基础上,研究了不同剂量的UV-C处理对鲜切莴苣品质、抗氧化活性及保鲜效果的影响,并从苯丙烷类和活性氧代谢两个方面对UV-C的作用机理进行探讨,为鲜切莴苣的加工保鲜和科学食用提供依据。研究结果如下:1.探究了不同切割方式对鲜切莴苣在5 ℃,48 h贮藏期内品质及抗氧化活性的影响。新鲜莴苣被切成片状、1/4片状、丝状,这三种切割方式的损伤强度分别为5.7 cm2/g、7.8 cm2/g、13.6 cm2/g。研究发现鲜切处理均会造成莴苣叶绿素、抗坏血酸等品质指标的下降,但是各切割方式之间差异并不显著,并且不同切割方式在贮藏期间均能显著激活莴苣中PAL的活性,提高酚类物质的合成与积累以及DPPH自由基清除能力,此外还增强了 SOD、CAT等抗氧化相关酶的活性,从而提高了鲜切莴苣的抗氧化能力,并且丝状莴首的总酚含量和抗氧化活性在24h时达到最高。这些结果表明,不同切割方式对莴苣品质无显著影响,但鲜切加工可显著诱导酚类物质的合成,从而提高鲜切莴苣的抗氧化活性。2.研究了不同照射强度(0、0.1、0.5、1.0和3.0kJ/m2)的UV-C处理对鲜切莴苣丝品质及抗氧化活性的影响。实验发现不同强度的UV-C处理均可抑制鲜切莴苣丝中菌落总数的增长以及褐变的产生,延缓叶绿素和VC含量的下降,有效提高了鲜切莴苣中酚类化合物的含量以及DPPH自由基清除能力,并且照射剂量为1.0 kJ/m2时效果最好。研究结果表明,UV-C处理可以有效保持鲜切莴苣的品质并且提高其抗氧化活性。3.研究了照射强度为1.0 kJ/m2的UV-C处理对鲜切莴苣丝苯丙烷类及活性氧代谢的影响。实验发现UV-C处理鲜切莴苣丝能够有效诱导苯丙烷类代谢途径中关键酶PAL、C4H和4-CL活性的增加,促进酚类化合物的积累,抑制抗坏血酸的下降,提高DPPH自由基清除率。同时,1.0 kJ/m2的UV-C处理还可以通过协调活性氧代谢相关酶(SOD、CAT、POD、APX等)的活性来调节O2·-的生成速率以及H202的含量,缓解ROS对莴苣丝的毒害作用。更多还原

【Abstract】 Lettuce,which contains rich lettuce element,inorganic salt,vitamin and some trace elements such as zinc,iron,etc.,at the same time,because of its green,crisp and tasty sarcocarp,are favored by the vast number of consumers.Lettuce leaves easy to damage even rot,inner epidermis easy to lignify,so they are not resistant to store.Lettuce need to be peeled before eating,which is very suitable for fresh-cut processing.But lettuce after cutting treatment susceptible to microbes,and physiological and biochemical reactions intensify,thereby accelerating aging.Previous studies have shown that fruits and vegetables after the mechanical damage,the synthesis and accumulation of polyphenols will increase,the latter not only can resist external damage,but also can improve the oxidation resistance of fresh-cut fruits and vegetables.In addition,studies have shown that the appropriate dose of Ultraviolet-C(UV-C)is advantageous to the fresh-cut fruits and vegetables storage and fresh-keeping,and can effectively inhibit the growth of microor-ganisms during storage of fresh-cut fruits and vegetables,keep the better quality of fruits and vegetables.At the same time,UV-C is conducive to the synthesis of phenolics within certain radiation intensity,and improve the antioxidant activity of fresh-cut fruits and vegetables.But the effects of cutting style and UV-C treatment on quality and antioxidant activity of lettuce have not been reported.In this paper,the effect of the different doses of UV-C treatment on the quality,antioxidant activity and the fresh-keeping of fresh-cut lettuce were studied on the basis of comparing the effects of different cutting styles(slices,1/4 slices,and shreds)on the quality and antioxidant activity of fresh-cut lettuce.The mechanism of UV-C was discussed from the two aspects of phenylpropane and reactive oxygen metabolism,which provided the basis for the processing,fresh-keeping and scientific edible of fresh-cut lettuce.The results are as follows:1.The effects of different cutting styles on the quality and antioxidant activity of fresh-cut lettuce at 5 ℃and 48 h were studied.Fresh lettuce was cut into slices,1/4 slices,and shreds,and the wonmding intensities of the three cutting styles were 5.7 cm/g,7.8 cm2/g and 13.6 cm2/g,respectively.The study showed that the fresh-cut processing could decrease lettuce’s some quality indexes of lettuce such as the chlorophyll and ascorbic acid and so on,but the difference was not significant between the different cutting styles.The different cutting styles significantly increased the activity of PAL,and synthesis and accumulation of phenolics,as well as DPPH radical scavenging capacity of lettuce during storage.In addition,the cutting treatment also enhanced the activities of antioxidant enzymes such as SOD and CAT,and improved the antioxidant capacity of fresh lettuce.The total phenolic content and antioxidant activity of shreds lettuce were the highest at 24 h.These results demonstrated that cutting styles didn’t have much effect on the quality,but significantly induced the synthesis of phenolic compounds,thereby improving the antioxidant activity of fresh-cut lettuce.2.The effects of different irradiation intensities(0,0.1,0.5,1.0 and 3.0 kJ/m2)of UV-C on the quality and antioxidant activity of fresh-cut shreds lettuce were studied.It was found that UV-C treatment could inhibit the growth of the total number of colonies of fresh-cut lettuce and browning,delay the decrease of chlorophyll and VC content,and improve effectively the content of phenolic compounds and DPPH radical scavenging capacity,and when the irradiation dose was 1.0 kJ/m,the effect is the best.The research results showed that UV-C treatment could effectively maintain the quality of fresh-cut lettuce and improve its antioxidant activity.3.The effects of UV-C treatment at 1.0 kJ/m2 on the phenylpropane metabolism and the reactive oxygen metabolism of fresh-cut lettuce were studied.It was found that UV-C treatment could effectively promote the activities of PAL,C4H and 4-CL in the phenylpropane metabolic pathway,increase the accumulation of phenolic compounds,inhibit the decrease of ascorbic acid and increase the DPPH free radical scavenging rate of fresh-cut lettuce.At the same time,UV-C treatment at 1.0 kJ/m2 could also regulate O2·-generation rate and the content of H2O2 by adjusting the activities of reactive oxygen metabolism related enzymes(SOD,CAT,POD,APX,etc.),alleviate the toxic effect of ROS on fresh-cut lettuce.更多还原