Scientists at Universitat Politècnica de València with CTP-IVIA of Valencia have applied starch–gellan (80:20) coatings incorporating thyme (Thymus zygis) essential oil (EO) to apples and persimmons to evaluate: (1) the postharvest behaviour of coated fruit in terms of weight loss, respiration rates, and mechanical properties, and (2) the antifungal efficacy of these coatings applied as a curative treatment against Botrytis cinerea in apple Golden Delicious and Alternaria alternata in persimmon Rojo Brillante during postharvest.
Thyme essential oil (EO) was incorporated (0.25 and 0.5 g per g of polymer) directly or encapsulated in lecithin to enhance antifungal action. Coatings did not reduce weight loss or firmness changes in apples, but they prevented water loss in persimmons. In contrast, no significant effect of the coatings was detected on the respiration rates and the respiration quotient of persimmons, whereas the respiration rates and quotient was increased in apples. On the other hand, the coatings without lecithin reduced the incidence and severity of black spot caused by Alternaria alternata in persimmons, regardless of the content of essential oil. Likewise, these reduced the severity of gray mold caused by Botrytis cinerea in apples. No positive effect of lecithin in coatings was observed on the postharvest quality and decay in either apples or persimmons, nor did EO show antifungal action despite its validated effectiveness in in vitro tests.
"The study showed the potential of starch–gellan coatings without lecithin or thyme EO to be used in persimmons in order to control weight loss and reduce the incidence of infections caused by A. alternata".
Source: Mayra Sapper, Lluís Palou, María B. Pérez-Gago, Amparo Chiralt, 'Antifungal Starch–Gellan Edible Coatings with Thyme Essential Oil for the Postharvest Preservation of Apple and Persimmon', 2019, Coatings, 9, 333.