不同成熟条件下冬枣果皮褐变差异研究

Difference in Browning of Winter Jujube Pericarp Under Different Ripening Conditions

冬枣(Zizyphus Jujuba Mill.)是我国特有的鲜食枣类品种,以其优良的感官品质与极高的营养价值,深受消费者的喜爱.但其采后极易发生褐变,不耐贮藏,流通期短,制约冬枣产业的发展.为探究不同成熟条件下冬枣果皮褐变差异,研究选取白熟期(W)、自然半红熟(NR)与采后半红熟(CR)冬枣为材料,通过番红-固绿染色和扫描电子显微镜观察不同时期冬枣果皮解剖结构和微观结构,并结合总酚、总醌、丙二醛含量、相关酶活性等生理指标对测定结果进行分析.结果表明,自然半红熟与采后半红熟冬枣果皮均有褐变发生,且采后半红熟冬枣果皮褐变现象更为严重.酶活性与总酚含量对冬枣果皮褐变程度有一定相关性,但相关性不强,微观结构与解剖结构的变化是冬枣果皮褐变的主要原因.自然半红熟冬枣果皮褐变机理为:冬枣成熟过程中,衰老导致的膜脂过氧化、细胞结构破坏和酶活性的提高,使得酚类物质与氧化酶接触发生氧化反应,引发褐变.采后半红熟冬枣果皮褐变机理为:离体胁迫及低温导致膜质过氧化加剧、细胞变形、木质化严重引发无氧呼吸,打破细胞间隔,使得酶与底物直接接触引发褐变.此外,角质层破损脱落,加速果皮水分流失也会导致果皮结构塌陷,进一步加速褐变,引起果皮亮度下降,颜色发暗.

Winter jujube(Zizyphus Jujuba Mill.)is a unique fresh jujube variety in China.It is deeply loved by consumers for its excellent sensory quality and high nutritional value.However,its development is limited due to its extreme susceptibility to browning after harvest,susceptibility to deterioration during storage,and short circulation period.To explore the differences in the browning of winter jujube,white ripening(W)jujube,natural semi-red ripening(NR)jujube,and postharvest semi-red ripening(CR)jujube were studied.Safranin-O fast green staining and scanning electron microscopy were used to observe the anatomical structure and microstructure of the winter jujube pericarp.The results of physiological indexes such as total phenol content,total quinone content,malondialdehyde content,and enzyme activity were combined to analyze the differences in browning.The results showed that both the NR and the CR jujube pericarps were browning,but the CR jujube pericarp showed a greater degree.The enzyme activity and total phenol content had a certain effect on the jujube browning,but the correlation was not strong.The changes in the microstructure and anatomy were the main causes of the browning.The browning mechanism of the NR jujube pericarp is as follows:during the red jujube ripening process,membrane lipid peroxidation,cell structure destruction and enzyme activity improvement caused by aging lead to the oxidation reaction of phenolic substances in contact with oxidase,which leads to browning.The browning mechanism of the CR jujube pericarp is as follows:in-situ stress and low temperature lead to increased membrane peroxidation,cell deformation,and severe lignification,which triggers anaerobic respiration,breaks the cell interval,and causes enzymes and substrates to directly contact,resulting in browning.In addition,the cuticle is damaged and peeled off,and water loss will cause the pericarp structure to collapse,further accelerate browning,and cause a reduction in the pericarp brightness.