Potential role of exogenous melatonin involved in postharvest quality maintenance of Vitis labrusca × vinifera 'Kyoho'.

BACKGROUND: Melatonin is an endogenous free radical scavenger with antioxidant activity that preserves the commercial value of postharvest fruits and delays fruit senescence. To explore the effect of exogenous melatonin on antioxidants and aroma volatile compounds of grapes (Vitis labrusca × vinifera 'Kyoho'), the grapes were treated with distilled water (control), 50 µmol L-1 of melatonin (M50), and 100 µmol L-1 of melatonin (M100) for 30 min and were then stored at 4 °C for 25 days. RESULTS: Exogenous melatonin decreased the rachis browning index, the decay development, the weight loss rate, the berry abscission rate, and the respiration rate, promoted the accumulation of total phenolics and total flavonoids, and delayed the reduction of anthocyanins and total soluble solids. In volatile compounds, the accumulation of esters, aldehydes, and alcohols in grapes was promoted, and the terpenes content was reduced by exogenous melatonin. CONCLUSION: Exogenous melatonin had potentially positive effects on the postharvest life and quality maintenance of grapes. These findings provide theoretical support for the application of melatonin in grape storage and preservation. © 2023 Society of Chemical Industry.

The Grade of Dried Jujube (Ziziphus jujuba Mill. cv. Junzao) Affects Its Quality Attributes, Antioxidant Activity, and Volatile Aroma Components.

Jujube (Ziziphus jujuba Mill. cv. Junzao) has attracted a large number of consumers because it is rich in nutrients, such as carbohydrates, organic acids, and amino acids. Dried jujube is more conducive to storage and transportation, and has a more intense flavor. Consumers are affected by subjective factors, and the most important factor is the appearance of the fruit, including size and color. In this study, fully matured jujubes were dried and divided into five grades according to their transverse diameter and jujube number per kilogram. In addition, the quality attributes, antioxidant activities, mineral elements, and volatile aroma components of dried jujube were further analyzed. As the dried jujube grade increased, the total flavonoid content increased, which was positively correlated with the antioxidant activity. The results showed that small dried jujube had a higher total acidity and lower sugar-acid ratio than large and medium dried jujube, thus, large and medium dried jujube had a better flavor than small dried jujube. However, the antioxidant activity and mineral elements of medium and small dried jujube were superior to large dried jujube. From the edible value analysis of dried jujube, medium and small dried jujube were better than large dried jujube. Potassium is the highest among the measured mineral elements, with contents ranging from 10,223.80 mg/kg to 16,620.82 mg/kg, followed by Ca and Mg. Twenty-nine volatile aroma components of dried jujube were identified by GC-MS analysis. The main volatile aroma components were acids including n-decanoic acid, benzoic acid, and dodecanoic acid. The fruit size affected the quality attributes, antioxidant activity, mineral elements, and volatile aroma components of dried jujube. This study provided a piece of reference information for further high-quality production of dried jujube fruit.

Partial compression increases acidity, but decreases phenolics in jujube fruit: Evidence from targeted metabolomics.

Jujube fruit (Ziziphus jujuba Mill.) is extremely susceptible to mechanical injury by extrusion and collision during storage, transportation and processing. In this study, we examined the morphology and endogenous metabolism of jujubes at three developmental stages after applying partial compression (PC) to mimic mechanical injury. Generally, PC did not affect the total soluble solids content, but increased the acidity and decreased the amount of phenolics in the jujube fruit. Targeted metabolomics analysis further confirmed that acid and phenolics content were differentially altered in response to PC. To our knowledge, this is the first study to characterize metabolic variations in ready-to-eat fruit that occur in response to physical damage. The results will provide insight into the understanding the consequences of mechanical injury on fruit nutrition and health benefits.