Influence of forced air cooling regimes on postharvest quality of strawberries during the marketing period

The aim of this study was to develop an improved strawberry postharvest handling regime to minimize postharvest losses during marketing. The experiment was conducted with the strawberry cultivars 'Clery', 'Darselect', 'Elsanta' and 'Everest' grown in the Lake Constance region of southwestern Germany. Half of the batch for each cultivar was harvested between 7 and 8 am and the other half between 12 and 2 pm Fruit were either rapidly cooled with forced air or slowly cooled in a conventional cool room to 2 or 8°C, respectively. Depending on harvest time and daily temperatures, the cooling treatments took 30 min for rapid cooling or 4-8 h for slow cooling. All treatments were then subjected to a simulated cool chain marketing process for 2 d at 8°C followed by 2 d at 18°C. The packaging material was also evaluated in this study. The standard cardboard (wood pulp) 500-g punnet was compared to plastic (PET), or flowpack (PET + perforated foil) punnets. At 2-d intervals, fruit were assessed for the percentage of marketable and non-marketable and for the quality parameters fruit firmness, colour, weight loss, total soluble solids, titratable acidity, fruit gloss and freshness of the sepals. Results showed that the method and speed of pre-cooling had no effect on all assessed quality criteria. The greatest fruit quality losses were observed during the simulated shelf-life period at 18°C. Fruit quality was similarly well maintained in the PET or cardboard punnet packaging material. The extreme cooling to 2°C (rapid or in a cold room) tended to have lower quality, especially with warmly harvested strawberries from 12 to 2 pm, as these subsequently had slightly less gloss and lower freshness of the sepals. For the early harvest time at 7-8 am, there were no differences between 2 or 8°C cooling. In conclusion, at the optimum harvest date extremely rapid cooling to 2°C showed no advantage over a rapid moderate cooling to 8°C or a room cooling.