【作者】 马艳萍；

【导师】 刘兴华；

【作者基本信息】 西北农林科技大学 ， 食品科学， 2010， 博士

【摘要】 核桃历来以干制为主。目前,鲜食核桃由于其丰富的营养价值、诸多的医疗保健作用及独特的风味,深受广大消费者喜爱。但因其脂肪、水分含量很高,发芽、发霉现象成为贮藏中的主要问题,也成为限制其贮藏保鲜技术取得快速发展的主要因素。本研究以辽河4号(L4)、西扶1号(X1)和西扶2号(X2)鲜食核桃为试材,研究了它们在冷藏条件下采后生理及品质变化规律；选择其中耐贮性强的L4品种,采用不同剂量的60Coγ射线对其处理,从辐照对鲜食核桃休眠特性、胚芽中内源激素含量、胚芽细胞超微结构及核桃仁品质的影响进行了系统研究。试验取得以下主要结论：(1)通过对L4、X1和X2三品种鲜食核桃在冷藏期间的呼吸强度,脂肪、脂肪酸、蛋白质、氨基酸及VE等营养品质指标,酸价(AV)和过氧化值(PV)两个主要油脂品质指标及贮藏效果(好果率、感官品质)的测定,发现贮藏初期(15d)鲜食核桃呼吸强度迅速下降后维持在很低水平；脂肪含量贮藏90d内变化不大,之后迅速降低；蛋白质含量变化不显著(P>0.05)；不饱和脂肪酸及VE含量总体上呈现下降趋势；AV及PV呈现增大趋势；贮藏中后期(60d后),其好果率及感官品质急剧下降。表明鲜食核桃品种间各指标差异较大,其中L4品种具有较好的耐贮性和高的营养价值,60d为鲜食核桃的适宜贮藏期限。(2)通过对L4鲜食核桃与干核桃主要营养成分含量的比较分析表明,贮藏期间鲜食核桃营养成分损失相对较少,尤其对氨基酸及γ-VE含量的保存有利,鲜食核桃中二者的含量极显著(P<0.01)高于干核桃；脂肪、蛋白质、VE总量及δ-VE含量与干核桃差异不显著(P>0.05)。(3)对L4贮藏期间的发芽率、发芽时间等指标的统计结果表明,L4鲜食核桃不具有明显的生理休眠特性；根据呼吸强度、营养成分、酶活性等多指标对贮藏时间进行聚类分析,结果将鲜食核桃的萌发过程分为三个时期：第Ⅰ期(0～20d)为鲜食核桃胚芽萌动期,为萌发前的准备阶段；第Ⅱ期(20～30d)处于快速发芽期,大量的种子开始发芽；第Ⅲ期(30～40d)为芽体速生期,此期核桃发芽率增加非常缓慢,但芽体生长迅速,芽长快速增加。(4)贮藏时间对鲜食核桃贮藏中各指标影响的回归分析表明,贮藏时间对鲜食核桃呼吸强度影响的数学模型符合二次多项式Y=0.1683X2-7.2101X+156.12；脂肪、可溶性总糖、MDA含量、POD活性均与贮藏时间呈现线性关系,线性方程分别为Y=-0.2838X+52.503、Y=0.045X+1.8822、Y=0.0397X+3.7639和Y=-0.3072X+4.121,相关系数分别为—0.8*、0.98**、0.74*和0.81*；可溶性蛋白质含量与贮藏时间的回归模型为四次多项式,游离氨基酸含量、LOX、SOD及CAT活性与贮藏时间的回归模型均为三次多项式。(5)60Coγ射线辐照处理减缓了鲜食核桃常温贮藏期间脂肪、可溶性总糖、蛋白质及游离氨基酸等营养物质含量的下降,增加了MDA含量,提高了POD活性,抑制了LOX、LPS、SOD、CAT等酶的活性,使其种子活力逐渐下降,最终失去萌芽能力。试验确定≥0.05kGy剂量的60Coγ射线辐照处理,可完全抑制鲜食核桃贮藏中的萌芽现象。(6)内源激素ABA、GA3、IAA及ZR是影响鲜食核桃胚芽萌发的重要因素,其中ABA是萌芽抑制物质,GA3、IAA、ZR是促进物质；胚芽的萌发不仅与各内源激素含量的绝对值有关,还与GA3/ABA、IAA/ABA和ZR/ABA的比值有关；0.1kGy、1.0kGy剂量的60Coγ射线辐照处理提高了鲜食核桃胚芽中的ABA含量,降低了GA3、IAA、ZR含量及三者与ABA的比值,利于其贮藏保鲜。(7)采用透射电子显微镜观察辐照处理对鲜食核桃贮藏期间胚芽细胞超微结构的影响,表明辐照引起了胚芽细胞超微结构的显著变化,对细胞形态及细胞壁破坏尤为突出,细胞变长或呈凹凸状,细胞壁变薄或不连续,发生质壁分离现象；线粒体和内质网数量减少,线粒体内嵴少且模糊；细胞核核仁破损或位置偏离中央；延缓了蛋白质和脂肪的降解速度；随着辐照剂量的增加和贮藏期的延长,其胚芽细胞损伤渐趋加重,以萌发期的损伤最为明显,致使细胞分裂受阻,抑制其萌发。(8)在0.1kGy、0.5kGy、1.0kGy和5.0kGy的辐照剂量处理中,以0.5kGy的60Coγ射线辐照处理明显提高了鲜食核桃冷藏期间的SOD、CAT活性,减少了MDA的积累,抑制了POD、LOX活性,降低了PV值,并对脂肪、脂肪酸、氨基酸及VE等营养成分的保存效果尤为明显,具有明显的贮藏保鲜效果,确定0.5kGy为鲜食核桃最佳辐照剂量。更多还原

【Abstract】 Dried walnut was always dominated in walnut sales. At present, fresh walnut is well received by a number of consumers because of its rich nutritional value, health care role and a unique flavor. However, the high content of fat and moisture in fresh walnut cause germination and mold, which has also become the main issues during storage and key factors limiting the development of its storage and preservation technology.In this paper, the respiration intensity and quality changes of’Liaohe4’,’Xiful’and ’Xifu2’fresh walnut were discuss which were stored d at the temperature about (O±1)℃. Having selected out the strong variety L4, using different doses of 60Coy-ray irradiated them, and then studied the effect of irradiation on the quality and post-harvest physiology, such as Germination physiology, endogenous hormone levels and the ultrastructure of germ cells. All the results are showed below:(1) To explore respiration intensity and quality changes of’Liaohe4’,’Xifu1’and’Xifu2’ fresh walnut, the main indicators, such as the respiration intensity, the fat, fatty acid, protein, amino acid content, acid value, peroxide value, the fine rate, were tested regularly during storage. The results indicated that, during the initial storage (15d), the respiration rate of fresh walnut decreased dranatically, then kept low and stabilized. The fat content changed slightly before 90d, then decresed sharply. Protein content changed slightly(P> 0.05).The unsaturated fatty acid and VE content showed a downward trend. The amino acid content was the highest when storing for 30d, then followed by the overall downward trend. Acid value and peroxide value showed an upward trend, fine fruit rate and sensory quality dropped drastically after 60 days’storage. The results showed that the different species had different indicators and L4 were the best in quality and nutrition during storage,60d was the suitable storage period for fresh walnut.(2) Through the comparison of main nutritional components in fresh walnut and dry walnut respectively,it showed that fresh walnut lost relatively less nutrient during storage, especially for amino acids and y-VE content. The content of the two composition in fresh walnut was significantly (P<0.01) higher than in dry walnut. The fat, protein, VE,δ-VaE content didn’t show significant differences (P>0.05) between them.(3) According to the indicators of germination rate, germination time during storage, L4 fresh walnut didn’t show an obvious physiological dormancy characteristic. According to the cluster analysis result between the indicators of the respiration intensity, nutrition, enzyme activity, et al and storage time, process of the germination of fresh walnuts is divided into 3 stages. The stageⅠwas germ sprout period of fresh walnut, which was the pre-preparation phase of germination. The stageⅡwas in rapid germination period and a large number of seeds began to germinate. The stageⅢwas the period in which shoot grow rapidly, this period of walnut germination rate increased very slowly, But the buds grow rapidly in the length of buds.(4) According to the regression analysis between various indicators and storage time, The relationship between the respiration intensity(Y) and storage time(X) could be described with a quadratic polynomial formula:Y=0.1683X2-7.2101X+156.12. The relation model between fat, total soluble Sugar, MDA content, POD activity and storage time showed a linear relationship and linear equations were Y=-0.2838X+52.503, Y=0.045X+1.8822, Y =0.0397X+3.7639, and Y=-0.3072X+4.121 separately, their correlation coefficients were-0.8*,0.98**,0.74* and 0.81* respectively. The regression models between the free amino acid content, LOX, SOD, CAT activity and storage time were in line with cubic polynomial.(5) The result showed that irradiation slowed down the decreasing of the content of fat, total sugar, protein and free amino acids, increased MDA content and the POD activity, inhibited the activity of LOX, LPS, SOD and CAT and the respiratory metabolism. Ultimately the irradiation make the seed vigor decreased and lose germination capacity. The study indicated preliminarily that 0.05kGy can completely inhibit the germination of embryo of fresh walnut.(6) Endogenous hormones ABA, GA3, IAA and ZR were very important factors in the process of the germ germination of fresh walnut. ABA was an inhibitory substance and GA3, IAA, ZR were promotion material. The germ germination of fresh walnut was related to the absolute content of endogenous hormone and the ratio of GA3/ABA, IAA/ABA and ZR/ABA. 0.1 kGy, 1.0kGy dose 60Co-γirradiation increased the ABA content,reduced GA3, IAA, ZR content and the ratio of GA3/ABA, IAA/ABA and ZR/ABA in germ of fresh walnut, which was advantageous for storage and preservation of fresh walnut.(7) Electron microscope was used to observe the influence of 60Coγ-irradiation on ultrastructure of the embryonic bud of’Liaohe4’fresh walnut stored at room temperature and low temperature. The results showed that irradiation with 60Co-γled to ultrastructure changes and greatly damaged the morphological change of cells and the structure of cell walls.Meanwhile the irradiated cells were elongated and cell walls became thin or discontinuous, separation between cytoplasm and cell wall appeared, decrease of endoplasmic reticulum, mitochondrion and cristae illegibility were seen,and nucleolus were damaged or deviated from the central location; the degradation of protein and fat was delayed. It might be concluded that the damage degree became more serious with the increasing of irradiation dosage and the prolong of storage time.The observed damages were of higher magnitude in sprouting period than the others’ storage time which blocked cell division, thereby inhibiting the process of embryo germination during storage.(8) In all treatments of radiation dose of 0.1kGy,0.5kGy, 1.0kGy and 5.0kGy,0.5kGy of 60Coγ-ray irradiation treatment, having compared with the control, significantly increased SOD, CAT activity, reduced the accumulation of MDA, inhibited the activity of POD and LOX, reduced the PV of fresh walnut during refrigerated storage. The preservation of fat, fatty acids, amino acids and VE are particularly obvious and the fresh-keeping was the best. So the study indicated 0.5kGy was optimum irradiation dose of fresh walnut.更多还原