不同成熟度橄榄果实冷藏期间细胞壁代谢对采后冷害的响应特性

研究冷藏期间橄榄果实细胞壁代谢的变化,探讨不同成熟度橄榄果实冷害发生与细胞壁组分含量、细胞壁降解酶活性的关系。以白露、寒露、立冬、大雪节气时采摘的‘檀香’橄榄果实为材料,在温度(2±1)℃、相对湿度85%~90%冷库内贮藏,定期测定橄榄果实冷害指数、果肉细胞壁组分含量和细胞壁降解酶活力的变化。结果表明,不同成熟度橄榄果实冷藏期间冷害发生与其细胞壁组分降解密切相关,冷害指数与离子结合型果胶(ionic-soluble pectin,ISP)、共价结合型果胶(covalent-soluble pectin,CSP)、半纤维素和纤维素含量呈负相关;且果胶甲酯酶(pectin methylesterase,PME)、多聚半乳糖醛酸酶(polygalacturonase,PG)、β-半乳糖苷酶(β-galactosidase,β-Gal)和纤维素酶(cellulase,CEL)等细胞壁降解酶的活力变化不平衡或活力提高是导致冷藏橄榄果实细胞壁结构解体、细胞壁代谢异常、冷害发生的主要原因。同时,与成熟度Ⅰ、Ⅲ和Ⅶ的橄榄果实相比,成熟度Ⅴ保持较低的果实冷害指数及冷藏中后期果肉PME、PG、β-Gal和CEL活力,延缓冷藏中后期果肉水溶性果胶、ISP、CSP、半纤维素和纤维素含量降低。因此认为,成熟度Ⅴ的橄榄果实可较好维持细胞壁结构的完整性,有效减轻冷害发生。

Characteristics of Cell Wall Metabolism of Harvested Chinese Olive Fruits with Different Maturities in Response to Chilling Injury During Cold Storage

Changes in the cell wall metabolism of Chinese olive fruits during cold storage were examined to explore the relationships between chilling injury and cell wall components and cell wall-degrading enzyme activities in four maturities of Chinese olive fruits. ‘Tanxiang’ Chinese olive (Canarium album (Lour.) Raeusch cv. Tanxiang) fruits harvested at the solar terms of White Dews, Cold Dews, Winter Begins and Heavy Snow were stored at (2 ± 1) ℃ and 85%–90% relative humidity. During storage, chilling injury index, cell wall component contents and cell wall-degrading enzyme activities in the fruit pulp were periodically determined. The results showed that the chilling injury symptoms were closely related to the degradation of cell wall components, and that the chilling injury index of fruits with different maturities was negatively correlated with the contents of ionic-soluble pectin (ISP), covalent-soluble pectin (CSP), semicellulose and cellulose. Cell wall structure disintegration, cell wall metabolism abnormality and chilling injury occurrence were in large part due to the imbalance of pectin methylesterase (PME) and polygalacturonase (PG) activities, as well as the increase of β-galactosidase (β-Gal) and cellulase (CEL) activities. Meanwhile, compared with maturities Ⅰ, Ⅲ, and Ⅶ, maturity Ⅴ could maintain lower chilling injury index during the entire storage and lower activities of PME, PG, β-Gal and CEL in pulp during the middle and late storage stages while retarding the decline in water-soluble pectin, ISP, CSP, semicellulose and cellulose. From these results, it can be concluded that maturity Ⅴ could maintain the integrity of cell wall structure and alleviate chilling injury symptoms in Chinese olive fruits during cold storage.