Coatings of yellow apples (Malus domestica) of the Golden Delicious variety: Carnauba wax and candelilla wax versus chitin-chitosan biopolymers

Abstract

Edible coatings increase the shelf life of fruits as part of post-harvest treatments. Polymers such as chitin and its deacetylated derivative, chitosan (Q-Qn), obtained from cephalothorax and exoskeletons of crustacean (shrimp, Litopenaeus vannamei) present benefits when applied to horticultural products and might be enhanced adding orange essential oil, OEO. In this research, two natural waxes, carnauba (Copernicia prunifera) and candelilla (Euphorbia antisyphilitica Zuuc), were compared with Q-Qn with and without OEO and a control of commercial chitosan from the Sigma® brand using a blank group without any coating. The climacteric fruit used was the apple (Malus domestica) of the 'Golden Delicious' variety. The fruit groups obtained were stored for 18 days at three different temperature conditions: Optimal (4°C), typical (25°C), and adverse (35°C). The evaluation parameters were pH value, percentage of acidity, percentage of humidity, degradation of ascorbic acid, concentration of soluble solids, and sensory parameters (color, firmness, and growth of fungi and/or black spots visually). The outstanding results indicated that at refrigeration temperature, the coatings were not decisive in prolonging shelf life, although they behaved as a post-harvest complement under these conditions. At ambient and adverse temperatures, both the waxes and the experimental chitin-chitosan biopolymer allowed delaying some ripening effects such as color change, softening, starch degradation, and moisture loss. These results were reflected when calculating the theoretical time estimated with the Arrhenius kinetic model on the loss of acidity. With the same model, the estimated useful life was positively affected under optimal and adverse conditions by applying the experimental Q-Qn coating. Despite not increasing the shelf life compared to the waxes, it allowed the shelf life to be extended by at least eight days compared to the blank. The sensory evaluation, with one hundred untrained judges who evaluated color, aroma, texture, and flavor of jams made with apples covered with the evaluated coatings and the control, indicated that the coatings altered the sensory properties, obtaining significant differences in the coloration and texture of the apple jams. The analysis of variance determined that there were no significant differences in consumer preferences for jams.