Effects of pre- and post-cut storage temperatures on fresh-cut watermelon quality and shelf-life

Fresh-cut watermelon is increasingly popular among consumers but challenges remain in keeping its eating quality. Processing removes the protective skin layer that usually provides a buffer for internal fruit tissues against environmental stresses and maintains elevated CO₂ and lowered O₂ gas levels. Low temperatures are used to slow microbial growth and prolong shelf-life of cut fruit by reducing oxidative, enzymatic and metabolic reactions that lead to accelerated senescence. However, little information is available on the interactive effects of the initial whole fruit temperature with subsequent fresh-cut product storage temperature on the consequences for shelf-life of fresh-cut watermelons. Whole watermelons were stored for 21 h at 4, 21 or 30°C, before being sanitised, cut into cubes, packaged and stored at 4 or 7°C until analysed. Interaction between the factors of storage temperature before and after cutting led to juice drip pH and soluble solid content changes. Lower whole-fruit temperature and lower storage temperature of fresh-cuts significantly reduced O₂ consumption and CO₂ production rates. Headspace ethylene levels were also reduced by lower fresh-cut watermelon storage temperatures. Preliminary trials show fruit aroma levels at day 5 scored higher when whole watermelons were stored at 21°C than either 4 or 30°C. In a second experiment, watermelon cubes were processed together with honeydew, rockmelon, pineapple and apple and then sealed individually or as a fruit-mix and stored at 4°C until analysed. Ethylene levels as high as 95 ppm were measured in the headspace of fruit-mix samples, with increased water soaking appearance of watermelon cubes. Our results demonstrate the need to consider the storage temperature of both whole and fresh-cut watermelons to extend shelf-life by controlling physiological aspects such as respiration. There is also potential for selecting fruits in fresh-cut fruit-mixes that minimise ethylene production to lower the impacts on fresh-cut watermelon shelf-life.