Effects of pH and ionic strength of NaCl on the stability of diacetyl and (−)-α-pinene in oil-in-water emulsions formed with food-grade emulsifiers

The aim of the present study was to assess the influence of pH (3, 7 and 9) as well as ionic strength of NaCl (0 mmol/l, 100 mmol/l, 200 mmol/l and 400 mmol/l) on the retention and release characteristics of diacetyl and (−)-α-pinene in oil-in-water (o/w) emulsions prepared with dried egg yolk (DEY) or starch sodium octenylsuccinate (SOE). Increase of pH from 3 to 9 progressively enhanced retention of diacetyl in emulsions prepared with both DEY and SOE. Whereas, in samples flavoured with (−)-α-pinene, the highest and lowest retention time-courses were detected at pH 9 and pH 7 as well as pH 7 and pH 3 regarding emulsions prepared with DEY as well as SOE, respectively. With increasing salt concentration, the retention of diacetyl was decreased, irrespectively of the applied emulsifier type, whereas generally opposite effects were observed in the case of (−)-α-pinene. The parameters of release characteristics i.e., release rate constants (k) and release mechanism factors (n), were calculated using Avrami’s equation. ANOVA revealed significant effects (p < 0.001) of pH and NaCl concentration on k parameters, whereas relationship between applied environmental conditions and n factors was dependent on hydrophobicity of the odourant. Sensory evaluation revealed higher correlation values between odour intensity and aroma compound concentration in emulsions aromatized with (−)-α-pinene than with diacetyl.