Biophysical Characterization of Autochthonous and New Apple Cultivar Surfaces

Apples have long been known for their beneficial effects on human health due to the presence of various bioactive compounds. It is therefore very important to understand the biophysical properties of apple cuticle that dictate apples' storability and quality. The purpose of this work was to determine the roughness, hydrophobicity, surface potential, and color of various autochthonous and new apple cultivars. The surface roughness was measured by optical profilometer, hydrophobicity by tensiometer, zeta potential by electro kinetic analyser, and surface color by chroma meter. Measurements reveal that the new cultivar Elstar has the roughest surface while the autochthonous cultivar Crown Prince Rudolph has the lowest roughness. Under normal physiological conditions, all apple surfaces were negatively charged, with Wax apple having the lowest and Crown Prince Rudolph the highest values; most cultivars had an isoelectric point at around pH = 3. The surfaces of the new cultivars were slightly more hydrophobic than those of the autochthonous. We conclude that autochthonous and new apple cultivars differ in biophysical surface properties, which might impact transpiration, bacterial/fungi adhesion and, consequently, apple storage and shelf life potential.