Vacuum Pulsation Drying Kinetics and Quality Characteristics of Cracked Jun Jujubes at Different Maturity Stages

Fruit cracking significantly reduces the commercial value of Ziziphus jujuba cv. 'Junzao'. To minimize these losses, this study investigated the cracking characteristics and microbial dynamics of fruits at different sampling periods and evaluated the effects of fruit maturity on drying kinetics, microstructure, color, and physicochemical properties during pulsed vacuum drying (PVD). Both the cracking rate and grade were markedly influenced by maturity, showing an initial increase followed by a decline, with consistent trends. Microbial load at cracked sites increased over time, reaching the acceptable limit on day 3 and exceeding it after day 4, suggesting that cracked fruits should be harvested within 3 days to ensure microbial safety. PVD drying time significantly decreased with increasing maturity. Higher maturity led to elevated total sugar, reducing sugar, and total acidity levels but decreased vitamin C, total phenolics, flavonoids, and antioxidant activity. SEM analysis revealed that PVD induced cellular rupture and porous structures, with pore size enlarging as maturity increased, thereby improving drying rate and rehydration ability. PVD also enhanced the release of phenolic and flavonoid compounds, improving antioxidant potential. Correlation analysis showed strong relationships among sugar-acid balance, color, bioactive compounds, and microstructure. Overall, PVD proved to be an efficient processing method for Junzao, and fruit maturity played a critical role in determining cracking behavior, drying performance, and final quality attributes. PRACTICAL APPLICATIONS: Determining the optimal harvest time for cracked Jun jujubes and evaluating the characteristics of vacuum-pulsed processing at different harvest stages for practical applications to minimize agricultural product damage. The Jun-jujube industry suffers from an annual fruit cracking rate of approximately 35% or higher, primarily during the growth stage, which often leads to complete spoilage by harvest. This study aimed to determine the post-cracking window before microbial growth renders the fruit inedible. Within this critical period, we investigated the quality of jujubes at different maturity stages and further processed them using vacuum pulsation technology to evaluate the quality of the final products. The goal was to explore the feasibility of harvesting and processing incompletely matured jujubes on a large scale.