The physical properties of fresh highbush blueberry epicarp were determined in order to increase the effectiveness of chitosan-based coatings. The measured roughness of the blueberry epicarp was 42 ± 10 μm. The surface free energy, γSV of blueberry epicarp with and without epicuticular wax was calculated using the "acid-base" theory. Blueberry epicarps with or without wax have mainly an apolar (Lifshitz-van der Waals) character with a small polarity (Lewis acid-base). In both cases, blueberry surface is a low-energy surface. With wax γSV = 29.1 ± 0.1 mJ m-2 while after the wax removal, γSV was increased significantly to 38.3 ± 2.8 mJ m-2. Various chitosan-based coatings were applied to the blueberry epicarp. The surface tension, the cohesive energy and the spreading coefficient were calculated for each solution. In particular, the effects of concentration of a plasticizer (glycerol) and a surfactant (Tween 20) on the wetting of blueberry epicarp were studied. A mathematical relationship between concentrations and spreading coefficient S was proposed. Finally, the optimal concentrations of chitosan-based solutions were determined according to S.
- Surface free energy