Yunyang Wang
College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi, China
Traditional hot water blanching has a slow heat transfer rate, whereas radio frequency (RF) heating has the advantages of a much faster heating rate and a higher penetration depth. The present research studied the effects of radio frequency (RF) heating on the heating uniformity, the relative activity of polyphenol oxidase (PPO), weight loss, texture, color, and microstructure of potatoes. Potato cuboids were treated in a pilot-scale, RF heating system (27.12 MHz, 6 kW) under different operating conditions.
The results showed that the dielectric constant increased first and then decreased with temperature, whereas the loss factor increased as the temperature increased. The optimum RF heating uniformity was obtained at an electrode gap of 120 mm, a sample height of 60 mm and when immersed in NaCl solution of 0.5 s m–1. The central heating pattern was presented in a sample. Cold spots were located at the edge of the top surface of the sample. The results of the present study reveal that the relative activity of potato PPO decreased with increasing temperature. The highest PPO inactivation was achieved under the electrode gap of 120 mm. Enzyme extract showed the lowest PPO relative activity, followed by the cuboids and puree, about 0.19%, 3.24%, and 3.54% when heating temperature reached 85 °C, respectively. Circular dichroism (CD) analysis indicated that RF heating changed the secondary structure of PPO, as α-helix content decreased. Both electrode gaps and temperatures had significant effect (P＜0.05) on weight loss, color, and texture of the potato cuboids. Microstructure analysis showed cell collapse and starch gelatinization of samples during RF heating.
The present study provides valuable information with respect to understand the effect of RF heating on improving heating uniformity and preventing browning of vegetables and also demonstrates the potential of this technology for future industrial applications.
