Evaluation of high pressure (HP) treatment for rapid and uniform pH reduction in carrots

Acidification (pH < 4.6) of marginally low acid foods allows them to be treated like high acid foods and, hence, has the potential to improve quality and reduce energy costs by lowering the severity of processing conditions. The objective of this study was to evaluate high pressure (HP) treatment for rapid and uniform pH reduction of low acid foods using carrot. Three organic acids (citric, malic and glucono-delta-lactone) were used in the study. Conventional acidification tests were carried out at atmospheric pressure at different temperatures (36–48 °C) and different treatment times (0–36 min). HP treatments were given at room temperature (maximum process temperature <32 °C) with different pressures (200–300 MPa) and treatment times (0–14 min). Time dependent acid infusion and the resulting pH reduction were used to evaluate the acidification kinetics. Results showed that the pH reduction rates were described by a first order kinetic model. No significant differences (p > 0.05) in acidification rates were observed between the acidifying agents either in conventional or HP acidification process. Pressure (HP acidification) and temperature (conventional acidification) significantly (p < 0.05) reduced decimal reduction time (D) for pH drop. The associated D values were 2.4–4.4 times higher in conventional (slower) as compared with HP acidification. For conventional acidification, the z values (temperature sensitivity) were 34–44.8 °C and for HP acidification, the z values (pressure sensitivity) were 206–222 MPa. HP acidification provided more rapid and uniform pH reduction as compared to conventional method.