In this study, the effects of light and dark conditions on the expression of candidate clock genes (SoLHY, SoPRR5, and SoTOC1), photoreceptor genes (SoPHYA, SoPHYB, and SoZTL), ascorbic acid (AsA) synthesis genes (SoVTC2 and SoGLDH), an AsA degradation gene (SoAPX), an AsA regeneration gene (SoMDHAR), and AsA content of spinach during the pre- and postharvest periods were investigated. The AsA content decreased under constant dark storage, whereas the AsA content was efficiently maintained under a light/dark cycle. Gene expression with rhythmic signals confirmed by the JTK_CYCLE method (P <= 0.05) was used for the analysis of partial correlation coefficients. Strong correlations between SoLHY and SoVTC2 were observed under all investigated conditions. AsA synthesis regulation via the clock gene LHY was stable and likely not altered by harvesting stress and/or external light stimuli. After harvesting, SoPRR5 was negatively correlated with SoVTC2. This finding suggested that a reduction in the SoPRR5 expression level might be an alternative way to induce/maintain AsA content during storage. Additionally, the expression of the photoreceptor genes SoPHYA and SoZTL was moderately correlated with that of SoVTC2 during cultivation. Surprisingly, these correlations were not observed during storage even in the presence of light. Instead, SoPHYA expression was correlated with that of another AsA synthesis gene, SoGLDH, under light/dark storage. Moreover, under constant dark storage, SoZTL expression showed a strong correlation with SoVTC2. The considerable variation in the relationship between the expression levels of AsA-related genes and photoreceptor genes during cultivation and storage indicates the contribution of light regulators to maintaining AsA rhythm in spinach. In summary, this study is the first to suggest possible crosslinking of external signals (light/dark), photoreceptor genes, clock genes, and AsA metabolism genes, which are related to changes in the quality of spinach during the pre- and postharvest periods.

The circadian system plays an essential role in plant cells, and numerous physiological events are generally modulated by circadian clock genes. To further improve postharvest handling of fresh produce, it is vital to understanding the behavior of clock gene expression and its underlying interactions with changes in quality. In this study, the effect of temperature and controlled atmosphere storage on the expression of clock genes (GmLCL1, GmPRR7, GmGI, GmTOC1, and GmLUX), postharvest quality characteristics and their related genes in soybean sprouts were investigated. By fitting the obtained gene expression level using the qPCR method with the cosine curve equation, it was successfully found that the circadian rhythm existed under constant dark storage conditions of soybean sprouts. A significant rhythm in clock gene expression was observed in control soybean sprouts. In contrast, low temperature storage diminished the cyclic expression of GmLCL1, GmPRR7, and GmTOC1, which also affected GmGI and GmLUX expression. Additionally, high CO2 concentrations during storage disturbed the circadian clock by affecting the phase and amplitude of each gene; for low O2 concentrations, it was only affected by amplitude. Interestingly, low temperature, low O2, and high CO2 maintained postharvest quality, including reduced respiration, weight loss and browning incidence. The expression behaviors of postharvest quality attribute-related genes (GmFUM1, GmCS, Gm2-OGDH, GmPPO1, GmPAL) were also influenced by the storage treatments. Overall, the findings first suggest a possible link between clock disruption and postharvest quality maintenance of soybean sprouts.

Sprouts are of great interest to consumers owing to their easy growth, beneficial traits, and health-promoting compounds. However, maintaining freshness after harvest and improving the shelf life of sprouts is challenging because of their rapid deterioration rate. This is the result of several factors, including high respiration rate, rapid dehydration, discoloration, texture changes, and high susceptibility to several foodborne pathogens. Therefore, various decontamination and storage techniques have been used to maintain quality and eliminate pathogens during postharvest handling of sprouts. This review summarizes sprout quality attributes and their dynamic changes during storage. Additionally, approved postharvest technologies to maintain sprout quality, minimize microbial growth, and prolong shelf life are discussed. Finally, the need for further research to develop or modify postharvest technologies, which can ensure both the safety and quality of this popular vegetable, is considered.