Ultrasound treatment alleviates external pericarp browning and improves fruit quality of pomegranate during storage.

BACKGROUND: Ultrasound treatment has a beneficial role in horticultural production from harvest to consumption. The quality traits and microbiological load in pomegranate fruit were explored during 30 days' storage at 20 °C after 10 min and 30 min ultrasound treatments. RESULTS: Ultrasound treatment significantly reduced the microbiological load during storage, providing a relatively clean and suitable storage environment. This was especially true for the 30 min treatment, which also maintained relatively lower weight loss and kept the browning rate below 5% during storage. Meanwhile, the fruit treated with ultrasound had higher ascorbic acid and anthocyanin content, which provided better antibacterial properties and higher nutraceutical properties until the end of storage. The 30 min ultrasound treatment significantly delayed the decrease in catalase (CAT) enzyme activity and the increase in peroxidase (POD) enzyme activity. Combined with weighted gene co-expression network analysis (WGCNA), and correlation analysis, color indicators and antioxidant activity induced by ultrasound treatment were responsible for the relatively higher fruit quality of pomegranate. CONCLUSION: Ultrasound treatment can improve the sensory quality and nutritional characteristics of pomegranate fruits during storage, and reduce the microbiological load. Ultrasound for 30 min was better than 10 min for prolonging the storage life of pomegranate. Our results will provide valuable information for ultrasound application in other horticultural products. © 2023 Society of Chemical Industry.

Overexpression of PgCBF3 and PgCBF7 Transcription Factors from Pomegranate Enhances Freezing Tolerance in Arabidopsis under the Promoter Activity Positively Regulated by PgICE1.

Cold stress limits plant growth, development and yields, and the C-repeat binding factors (CBFs) function in the cold resistance in plants. However, how pomegranate CBF transcription factors respond to cold signal remains unclear. Considering the significantly up-regulated expression of PgCBF3 and PgCBF7 in cold-tolerant Punica granatum 'Yudazi' in comparison with cold-sensitive 'Tunisia' under 4 °C, the present study focused on the two CBF genes. PgCBF3 was localized in the nucleus, while PgCBF7 was localized in the cell membrane, cytoplasm, and nucleus, both owning transcriptional activation activity in yeast. Yeast one-hybrid and dual-luciferase reporter assay further confirmed that PgICE1 could specifically bind to and significantly enhance the activation activity of the promoters of PgCBF3 and PgCBF7. Compared with the wild-type plants, the PgCBF3 and PgCBF7 transgenic Arabidopsis thaliana lines had the higher survival rate after cold treatment; exhibited increased the contents of soluble sugar and proline, while lower electrolyte leakage, malondialdehyde content, and reactive oxygen species production, accompanying with elevated enzyme activity of catalase, peroxidase, and superoxide dismutase; and upregulated the expression of AtCOR15A, AtCOR47, AtRD29A, and AtKIN1. Collectively, PgCBFs were positively regulated by the upstream PgICE1 and mediated the downstream COR genes expression, thereby enhancing freezing tolerance.

Exogenous Arginine Treatment Maintains the Appearance and Nutraceutical Properties of Hard- and Soft-Seed Pomegranates in Cold Storage.

Arginine is a natural preservative; however, its effects on the storage of different cultivars of pomegranates have not been investigated extensively. Therefore, the fruit quality of soft-seed Tunisia and hard-seed Yudazi pomegranates was investigated after treatment with arginine at four concentrations during cold storage for 80 days. Pomegranates treated with 1.0 mM arginine exhibited a relatively lower loss of vitamin C, soluble solid, total phenol, and anthocyanin contents in arils, together with a better fruit appearance. Combined with principal component analysis (PCA), the storage life of fruits treated with 1.0 mM arginine showed a higher correlation with antioxidant enzyme activity (e.g., superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT)) during the first 40 days of cold storage, whereas after 40 days of cold storage, storage life was more dependent on the integrity of the cell membrane affected by malondialdehyde (MDA) content, electrolyte leakage (EL), and hydrogen peroxide (H2O2) accumulation. Arginine treatment contributed significantly to the appearance and inner quality of the hard-seed pomegranate cv. Yudazi fruit during cold storage compared to those of soft-seed Tunisia. Taken together, arginine application combined with cold storage enhanced the nutraceutical properties and marketability of pomegranate fruits.