Anatomical observation on the differences in the fruit texture between Huizao and Dongzao jujube and related enzyme activities

【Objective】In this study, the microstructure of fruit pulp cells of two jujube (Zizyphus jujuba Mill.) varieties with obvious differences in fruit texture was observed, the water content, hardness and activity of cell-wall-related metabolic enzymes were measured, and correlation analysis was carried out to explore the key factors affecting the formation of the two types of textures.【Methods】The moisture content, hardness, pulp cell morphology, cell wall components and metabolic enzyme activities of dried jujube Z. jujuba‘Huizao’and fresh jujube Z. jujuba‘Dongzao’were used as test materials after 31 days (S1), 63 days (S2), 78 days (S3), 98 days (S4) and 108 days (S5) after flowering.【Results】(1) As the fruit developed, the water content of both Huizao and Dongzao showed a trend of first increasing and then decreasing, hardness showed a trend of decreasing, and Huizao’s hardness was persistently higher than that of Dongzao. (2) The pulp cell changes of two varieties were presented first rapid increase and then slow increase trend, but Dongzao’s pulp parenchyma cell area was significantly larger than that of Huizao’s. (3) Fruit pulp cell ultrastructural observation showed that at the S5 period, thepectin layer of fruit pulp cell wall of the two varieties was obviously degraded, but the degradation of pectin layer and inclusions in Dongzao was slower compared to Huizao. (4) The total pectin and cellulose content of the two varieties as a whole showed a trend of gradual decrease, and Dongzao was always lower than the Huizao. (5) Fruit hardness was significantly and positively correlated with total pectin and cellulose content, and highly significantly and negatively correlated with β-Gal, α-Af and PL enzyme activities, and the correlation between PG enzyme and Dongzao’s fruit hardness and water content was highly significant, but the correlation with Huizao was not significant.【Conclusion】The difference in texture quality between Huizao and Dongzao was related not only to the differences in total pectin and cellulose content of cell wall fractions and the microstructure of pulp cells, but also to the cell wall metabolism-related enzymes β-Gal, α-Af and PL enzymes. Moreover, the PG enzyme played a key role in the Dongzao texture changes.