Quality of heat-treated strawberry fruit during refrigerated storage

Abstract

Strawberries cv. Selva were heat-treated in an air oven (45 °C, 3 h) and then stored at 0 °C for 0, 7 or 14 days. Afterward, fruits were placed at 20 °C and monitored after 24, 48 or 96 h and the effect of heat treatment on the following parameters was recorded: weight loss, external color, anthocyanin content, firmness, titratable acidity, total and reducing sugars, fruit decay and count of colony forming units (CFUs) for bacteria and molds. Heat-treated fruits showed higher hue angle than controls, indicating the delay of red color development. The treatment diminished fruit lightness (L*), although the effect reverted during holding at 20 or at 0 °C. The application of the treatment caused an initial weight loss close to 2% but afterwards, heat-treated fruits showed lower weight loss rate at 20 °C. Heat-treated fruits had lower acidity than controls, but there was no difference in the content of total sugars between control and treated fruits. Heated fruits were slightly firmer at the end of the treatment, and they softened less than controls after 24 h at 20 °C. Heat-treated fruits remained firmer than controls after 7 days of cold storage, and the relative difference in softening persisted after 48 h at 20 °C. However, no difference in treated and control fruit firmness was observed after 14 days of storage at 0 °C and following 48 h at 20 °C. In the absence of storage, heat-treated fruits showed lower decay at 20 °C than controls. After 7 days at 0 °C followed by 72 h at 20 °C, the percentage of decayed fruits was lower in heat-treated than in control fruits. The treatment decreased the initial bacterial population, but did not modify the amount of mold initially present. After 7 days of cold storage, the CFU number for bacteria were lower in treated than in control fruits. This difference was still significant after 48 h at 20 °C. In the case of molds, heat-treated fruits that were stored for 7 or 14 days at 0 °C and then transferred to 20 °C for 48 h showed lower CFU value than controls.