葡萄果肉组织的能量水平和细胞壁代谢对其自溶软化的影响

Effects of Energy Level and Cell Wall Metabolism on Aril Breakdown in Grape Fruits

为研究葡萄采后贮藏过程中自溶软化与能量水平及细胞壁代谢的关系,比较贮藏初期和末期果皮超微结构的变化。采后葡萄经钙联合涂膜和热处理后,低温((4.0±0.5)℃)贮藏,定期测定果肉自溶指数、硬度、腐烂率、膜透性、能量物质(三磷酸腺苷(adenosine triphosphate,ATP)、二磷酸腺苷(adenosine diphosphate,ADP)、单磷酸腺苷(adenosine monophosphate,AMP))含量及能荷(energy charge,EC)、细胞壁降解酶活力和细胞壁成分的变化,扫描电子显微镜观察贮藏初期和末期不同处理果实内果皮的超微结构,以未处理组为对照。结果显示:随贮藏时间的延长,果实自溶指数、腐烂率和膜透性升高,硬度和能量物质下降,多聚半乳糖醛酸酶(polygalacturonase,PG)、果胶甲酯酶(pectinesterase,PE)和纤维素酶(cellulase,Cx)活力上升,β-半乳糖苷酶(β-galactosidase,β-Gal)活力在贮藏30 d内下降,之后急剧升高。细胞壁组分原果胶、纤维素和半纤维素含量下降,水溶性果胶含量前期上升,后期下降;葡萄内果皮的超微结构破坏,出现了大的孔洞。葡萄果实自溶指数与能量水平、细胞壁降解酶活力和细胞壁组分紧密相关,果实自溶指数与ATP、ADP含量极显著负相关(P<0.01),和AMP显著负相关(P<0.05),与EC无明显相关性(P>0.05);与PG、PE、Cx活力极显著正相关(P<0.01),与β-Gal活力无明显相关性(P>0.05);与原果胶、水溶性果胶、纤维素和半纤维素含量极显著负相关(P<0.01)。钙联合涂膜和热处理能够维持组织的高能量状态和致密的超微结构,抑制PG、PE和Cx活力的升高,延缓细胞壁降解,延缓自溶软化,其中涂膜显著优于热处理(P<0.05)。

In order to understand the relationship of aril breakdown with energy levels and cell wall metabolism in harvested grapes, the ultrastructural changes in the inner pericarp were examined during the early and late stages of storage. ‘Red globe’ grapes were subjected to CaCl2 immersion combined with chitosan coating or heat treatment and then stored at （4.0 ± 0.5） ℃, and the untreated samples were used as a control. Changes in aril breakdown index, hardness, decay percentage, cell membrane permeability, energy contents （adenosine triphosphate （ATP）, adenosine diphosphate （ADP） and adenosine monophosphate （AMP））, energy charge （EC）, cell wall-degrading enzyme activities and cell wall components were monitored at regular intervals during storage. The results indicated that aril breakdown index, decay incidence and cell membrane permeability increased, hardness and energy contents declined, and the activities of the cell wall-degrading enzymes polygalacturonase （PG）, pectinesterase （PE） and cellulase （Cx） ascended with storage time; however, β-galactosidase （β-Gal） activity dropped during the flrst 30 days, followed by a sharp increase. The contents of cell wall components such as protopectin, cellulose and semi-cellulose continuously decreased during storage, while water-soluble pectin dropped after an initial increase. Furthermore, the ultrastructure of the inner pericarp was damaged as indicated by the appearance of large holes. Aril breakdown index showed a highly signiflcant inverse correlation with ATP and ADP contents and the contents of cell wall components （P 〈 0.01）, a highly signiflcant positive correlation with PG, PE and Cx activities （P 〈 0.01）, and a signiflcant inverse correlation with AMP level （P 〈 0.05）, but it had no signiflcant correlation with EC or β-Gal activity （P 〉 0.05）. In conclusion, combined treatment with calcium chloride and chitosan or heat could delay aril breakdown in grapes by maintaining the integrity of the cell membrane and high energy status, inhibiting the transformation of protopectin to water-soluble pectin, inhibiting the activities of cell wall-degrading enzymes （PG, PE and Cx）, and suppressing the degradation of cell wall components （proto-pectin, cellulose and semi-cellulose）, and chitosan coating was signiflcantly more effective than heat treatment （P 〈 0.05）.