Effects of Different pH Treatments on the Postharvest Quality of Two Kinds of Loose-Skin Citrus Fruit

Loose-skin citrus fruits have severe water loss and rapid quality deterioration after harvest. In this study, different pH solutions (acidic, pH6; neutral, pH7; alkaline, pH8 and 9) were used to treat loose-skin citrus fruits (Satsuma and Ponkan), and fruit quality was measured to analyze the effect of pH on fruit quality during postharvest. Our results indicated that alkaline (pH9) treatment induced faster water loss of loose-skin citrus fruits during postharvest. For Satsuma mandarin, the pH9 treatment maintained a high titratable acidity (TA) content, and total soluble solids (TSS) concentration was slightly influenced by different treatments. Meanwhile, the pH9 treatment also induced a constant rise in the respiration rate, while the other treatments caused fluctuating changes. After different pH treatments, the fruit firmness was less influenced. For Ponkan mandarin, various pH treatments increased the TSS/TA ratio at 28 days of storage. The acidic (pH6) treatment significantly reduced fruit respiration over the 7 days of storage while slightly increasing fruit firmness compared to the alkaline treatment. These results indicated that the alkaline treatment had less impact on the content of sugars and acids but speeded up postharvest water loss in citrus fruits. The acidic treatment maintains fruit firmness and reduces respiration rate during short-term storage.