Effects of calcium chloride treatment on softening in red raspberry fruit during low-temperature storage

Fruit softening is an inevitable event during ripening of red raspberry fruit even when stored at low temperature. In this research, the effects of CaCl₂ treatment on softening of red raspberry during storage at 4°C were studied. The results indicated that CaCl₂ treatment effectively delayed the decrease of firmness and reduced the respiration rate of red raspberry fruit during storage. The CaCl₂-treated fruit maintained higher protopectin content and lower soluble pectin content compared with controls. The cellulose and starch contents in the fruit treated with CaCl₂ kept higher than in the control during storage. Moreover, CaCl₂ treatment decreased activities of polygalacturonase (PG), pectin methylesterase (PME), and cellulase (Cx) mainly at the early stage of softening. Application of CaCl₂ lead to the decreased activities of amylase (AM) and β-galactosidase (β-gal) compared with controls during the entire storage periods. These results indicated that CaCl₂ treatment might delay postharvest softening of red raspberry fruit stored at low-temperature by retarding cell wall degradation and starch hydrolysis. PRACTICAL APPLICATIONS: Red raspberry fruit is very popular with consumers because of its high-nutritional value and anticancer effects. However, it has a very short postharvest life and softens easily even when stored at low temperature, which limits its distribution to distant market. Our data indicated that CaCl₂ treatment delayed postharvest softening of red raspberry fruit stored at low temperature. The results could provide preliminary yet essential information to research community to further study the molecular mechanisms of softening in red raspberry fruit, and also provide reference data for maintaining quality of postharvest red raspberry fruit.