Influence of ohmic heating/osmotic dehydration treatments on polyphenoloxidase inactivation, physical properties and microbial stability of apples (cv. Granny Smith)

Abstract

Abstract The combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI), on the polyphenoloxidase (PPO) inactivation, physical properties and microbial stability of apples stored at 5 °C or 10 °C was analyzed. The treatments were performed using a 65% (w/w) sucrose solution and with ohmic heating at 13 V/cm at 30 °C, 40 °C or 50 °C for 90 min. Examination of the dehydrated samples showed that the water loss and the solid gain were greater with the OD/OH and VI/OH treatments at 50 °C. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. There was a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values for these parameters were stable when PPO was inactivated. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C. The shelf-life of the apples treated with VI/OH at 50 °C and stored at 5 °C was extended to more than 4 weeks. Therefore, the VI/OH treatment at 50 °C was determined to be the best process for dehydrating apples. Industrial relevance The aim of this research was 1 to study the combined effect of ohmic heating (OH) and osmotic dehydration (OD) with vacuum impregnation (VI) on the polyphenoloxidase inactivation and microbial stability of osmotically dehydrated apples stored at either 5 °C or 10 °C. Two technologies, OH and OD were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm and conventional heating for 90 min. The results showed a correlation between the PPO activity, the color change and the browning index of the treated and stored samples; the values were stable when PPO was inactivated. PPO was completely inactivated by the OD/OH and VI/OH treatments at 50 °C. The shelf-life of the apples treated was extended to more than 4 weeks. Under the investigated conditions, VI/OH treatment at 50 °C and stored at 5 °C may be considered the better minimal processing that preserves the fresh-like properties.