Permeability of Different Wax Coatings and Their Effect on Citrus Fruit Quality

Abstract

Gas and water vapor permeability (WVTR) of seven coatings, used commercially for citrus, was determined by coating these on highly permeable films. Oranges and mandarins were coated with the same seven coatings, and weight loss, appearance, internal gas composition, presence of ethanol and acetaldehyde, and flavor of these fruits were determined. There was a relationship between low concentrations of oxygen, which lead to off-flavors, and the presence of ethanol and acetaldehyde in the fruit. There was also a relationship between WVTR and weight loss of the fruit with most coatings, but no correlation between CO2 and O2 permeability of the coatings and concentration of these gases in the fruit. The above findings were validated in a semi-industrial trial. Keywords: Wax coatings; permeability; citrus fruits

Approaches to optimising surface coatings for fruits

“…In summary, whereas changes to ^H,O achieved by coating would depend largely on the permeance to water of the coating layer overlying the cuticle, depression in p' o2 would depend more on the proportion of pores blocked by the coating. Other evidence consistent with this proposition has recently been published for citrus (Mannheim & Soffer 1996). Given the range of ratios of permeances to H2O and O 2 in coating materials used for fruits (between New…”

“…1992;Wong etal. 1992;Avena-Bustillos & Krochta 1993;Avena-Bustillos et al 1994;Koelsch 1994;Mc Hugh & Krochta 1994;Gontard et al 1996;Mannheim & Soffer 1996). Such information will be important in the identification and development of materials suitable for application to fruits as surface coatings.…”

“…Blockage of pores can result in very low values for skin permeance to O 2 which can depress p' Ol excessively and result in anaerobiosis, fermentation, development of off-flavours (Kester & Fennema Banks et al-Surface coatings for fruits 1986;Cohen etal. 1990;Hagenmeier& Shaw 1992;Mannheim & Soffer 1996) and uneven ripening (Smith et al 1987;Meheriuk & Lau 1988;McGuire & Hallman 1995). These effects are exacerbated by elevated rates of respiration resulting from keeping produce at high temperatures, an effect which can be inferred from Equation 1 given that respiration is numerically equivalent to rate of oxygen transfer (r Oi , mol/kg s) for a fruit at, or close to, steady state.…”

“…Recently, there has been a substantial increase in research activity on surface coatings (Hagenmaier & Shaw 1992;Baldwin 1995;Hagenmaier & Baker 1995;Nussinovitch & Lurie 1995;Gontard et al 1996;Mannheim & Soffer 1996), made from food grade ingredients, which must have appropriate physical and chemical characteristics to achieve desired effects.…”

The control of postharvest blue and green molds of citrus in relation with essential oil–wax formulations, adherence and viscosity

“…In our study, C. zeylanicum EO (0.5%) efficacy was improved (in the preventive treatment) when supplemented with shellac than with the other waxes (carnauba, paraffin and polyethylene). This may be due to the lower permeability for gases of shellac compared to the other waxes (Mannheim and Soffer, 1996;Alleyne and Hagenmaier, 2000;Bai et al, 2003), thus keeping more EO on fruit surface. Moreover, for the same EO-wax formulation, disease control was reduced when treatment was done 24 h versus 4 h before citrus fruit infection.…”