Xanthan Gum Coating with Citric Acid and Ascorbic Acid to Preserve Strawberry Quality and Control Oxidative Stress

Strawberry fruit is highly perishable and susceptible to oxidative stress and rapid quality deterioration during postharvest storage. This study evaluated the effectiveness of an edible coating based on xanthan gum (XG), enriched with citric acid (CA) and/or ascorbic acid (AA), in preserving the quality of ‘Rossetta’ strawberries stored at 4 ± 1 °C for 9 days. Coated fruits showed higher values of firmness, titratable acidity, and color parameters compared to the control, along with a more gradual increase in total soluble solids, indicating reduced dehydration and delayed ripening. In addition, treated samples retained higher levels of bioactive compounds, including total phenolics, flavonoids, and anthocyanins, as well as antioxidant activity, confirming improved nutraceutical quality during storage. By the end of storage, the combined XG+CA+AA coating modulated the antioxidant enzymatic system, enhancing the activity of superoxide dismutase (44.6%), catalase (31.6%) and ascorbate peroxidase (44.6%) in counteracting oxidative stress, accompanied by a 32.8, 45.9 and 29.8% reduction in polyphenol oxidase and lipoxygenase activities, as well as malondialdehyde content, compared to the control, respectively. Overall, the combined XG+CA+AA coating was the most effective, highlighting a synergistic action of the acids and confirming its potential to extend shelf life and preserve strawberry quality.