Does high hydrostatic pressure affect fruit esters?

The effect of high hydrostatic pressure on ester formation and hydrolysis was studied. Six esters and the corresponding carboxylic acids and alcohols were subjected to high-pressure treatments of 400 and 800MPa under three different pH conditions (namely, buffer solutions of pH 4, 6 and 8). The selected compounds were dissolved into buffer solutions, subjected to the pressure treatment and then extracted using dichloromethane. The analysis and quantification were carried out by gas chromatography with flame ionization as detector. High pressure appeared to have no effect on ester formation or hydrolysis under the investigated conditions. In all cases, a small decrease at the levels of carboxylic acids and esters was observed without any evidence of further reaction. This decrease, referred to as decomposition, depended on pressure and pH conditions. Ester decomposition was minimised when a high-pressure treatment of 400MPa in basic conditions (pH 8) was applied. Carboxylic acid decomposition was minimal in basic conditions and it was independent of the pressure applied.