Biochemical and functional changes in pomegranate fruit (Punica granatum) during cold storage

Pomegranate (Punica granatum) is a fruit that can be affected by chilling injury. This disorder affects the organoleptic quality of the fruit. A commercial attribute of this fruit is its high content of antioxidants, of which 92% are anthocyanins and tannins. The present investigation tries to determine how certain quality parameters and the antioxidant capacity of pomegranate fruits are affected after being stored for a long period at low temperatures. The novelty is to study the possible influence of ethylene on changes in their functional capacity as defence mechanism to cold, and also to evaluate the effect of different postharvest treatments to prevent chilling injury in this fruit. Different treatments were applied to pomegranates fruits stored in a cold chamber at 2°C, taking samples of all treatments after 20, 60, 100 and 120 days of storage. The following treatments were applied: exogenous ethylene (0.5, 1 and 1.5 μL L^-1); one competitive inhibitor of ethylene action: 1-methylcyclopropene (1-MCP; 1 μL L^-1); passive modified packaging in X-Tend bags; a combined treatment (1MCP-X-Tend bags); macro-perforated bags (control treatment) and one group maintained as control at room temperature. At each sampling day, different quality parameters like firmness, colour, acidity and electrolyte leakage, among others, were measured. In addition, the concentration of anthocyanins and tannins were measured. The results indicated that treatment at low temperatures caused an increase in the concentration of anthocyanins in both peel and aryls. In the case of peel, an increase of up to 12 times the initial concentration of anthocyanins in the fruits treated with ethylene was observed. For the tannins, a non-significant variation was observed. Although more studies are needed, early results give evidence that in the case of pomegranates, it is possible to increase the concentration of certain antioxidants like anthocyanins after subjecting the fruit to a cold storage or a treatment with ethylene.