Submitted to: Journal of American Society of Horticulture Science
Publication Type: Abstract Only
Publication Acceptance Date: 12/19/1996
Publication Date: N/A
Interpretive Summary: A major thrust of postharvest research is to reduce the use of fungicides in controlling decay and losses of fruit during storage. Previous research has shown that postharvest calcium treatment of apples maintains fruit firmness and reduces decay due to fungal pathogens. However, it is difficult to get enough calcium into the fruit without injuring the fruit surface. We tested a wide range of surfactants and found that pretreating apple fruits with a specific class of surfactants before postharvest calcium treatments resulted in at least a doubling of calcium uptake into the fruit under conditions which were less likely to injure the fruit surface and which are more likely to be commercially applied. This information also will enable apple growers to reduce their postharvest use of synthetic fungicides and to develop alternate strategies to maintain the quality of stored fruit.
Technical Abstract: The effects of 36 organosilicone and conventional carbon-based surfactants on postharvest infiltration of radiolabeled and unlabeled calcium solutions into 'Golden Delicious' apples (Malus domestica Borkh) were examined to devise a more efficient pressure infiltration technique to increase fruit calcium concentration. Both radiolabeled calcium infiltration and the proportional increase in fruit calcium estimated by fruit weight gain from calcium solutions of known concentration were significantly enhanced by a range of surfactants having differing chemical structures. Tween 60 and 80, Triton X-45, X-100, X-114, X-305 and X-405, and Silwet L-77 and L-7604 stimulated Ca infiltration. The two organisilicone surfactants, Silwet L-77 and Silwet L-7604, known for their greater capacity to lower the surface tension of solutions than conventional carbon-based surfactants, were the best surfactants tested at augmenting calcium infiltration. Applications of surfactants to fruit were as effective or more effective when used as a pretreatment rather than mixing the surfactant with the calcium solutions. The pressure necessary to increase calcium to levels considered sufficient to maintain fruit firmness and resist decay during storage could be lowered in fruit treated with organosilicone surfactants. Sequential postharvest surfactant and calcium treatments may offer a practical means of increasing the calcium concentration of apple fruit.