Resumen de Mode of action of the drying emulsion used in dried vine fruit production.: I. The effect of inorganic ions and fatty acid esters
Birgit A. Uhlig, Rob R. Walker, R. Storey
Drying of Sultana grapes (Vitis vinifera L.) in Australia is enhanced by the berries being dipped in or sprayed with an alkaline oil‐in‐water drying emulsion consisting of K2CO3 and a mixture of ethyl esters of fatty acids. The relative importance of the nature of the cation and anion of the alkali salts of the drying emulsion and the relative effectiveness of the different fatty acid esters on the drying rate was investigated. When salt solutions used as dip were applied with commercial drying oil, water loss increased with decreasing hydrated ionic radius of the alkali cation and followed the lyotropic series Cs+ > Rb+ > K+ > Na+= Li+, with Ca2+= Li+. Carbonate was the most effective anion, while S2O52‐‐, HP2O5‐‐, OH‐, I‐and Cl‐ gave responses which were similar to or less than the water control, depending on the presence or absence of drying oil. The interaction between cation and commercial drying oil seemed to be additive or synergistic. Without commercial drying oil, the CO32– salts of Cs+, Rb+, K+ and Na+ all produced higher drying rates than those of Li+ and Ca2+, with the Cs+ and Rb+ salts having the greatest effect. When emulsified with 2% ethyl oleate instead of commercial drying oil, all salts with CO32– as anion produced faster drying, and their ranking was the same with both emulsifiers. However, when the Cl“salts were used with 2% ethyl oleate, all cations produced similar and fast drying. The saturated fatty acid esters, caprylic acid ethyl ester and stearic acid ethyl ester, had little effect on drying rates whereas the unsaturated fatty acid esters, ethyl oleate, butyl oleate and ethyl linoleate, increased water loss two‐fold compared with H2O treatment. The results are discussed with particular emphasis on the role of the molecular structure of the cuticle in regulating water loss from grape berries.
