Radio frequency (RF) has the advantages of high efficiency and penetrability, but the ef-fects of RF on meat thawing have not been thoroughly examined compared with air thawing. The effects of RF thawing and air thawing on efficiency, physicochemical properties, microstructure, and the total viable counts (TVC) of mutton were investigated using a 6 kW, 27.12 MHz RF system. Thawing from - 18-4 degrees C, RF thawing (0.5 h) took less time than air thawing (8.1 h). RF-thawed samples maintained better color and texture than air-thawed samples. The thawing loss, the total volatile basic nitrogen (TVB-N) content, and the TVC in RF-thawed samples were less than in air-thawed samples. Furthermore, RF thawing reduced myofibrillar protein content compared with air thawing. Micrographs also showed that the microstructure was slightly damaged with RF thawing, whereas the organizational structure was damaged much more severely with air thawing. Based on this study, RF heating has great potential application value in the thawing of meat.(c) 2023 Published by Elsevier Ltd on behalf of Institution of Chemical Engineers.

Yogurt is one of the most popular dairy products fermented by Lactobacillus bulgaricus and Streptococcus thermophilus. The present study introduced dielectric properties as a new technique for yogurt fermentation monitoring. Dielectric properties of cow milk and yogurt at different time of fermentation were measured from 10 to 3000 MHz at 42 °C using open-ended coaxial-line probe technology by an impedance analyzer. Meanwhile, pH and titratable acidity of yogurt at different fermentation time were measured. Results showed that the dielectric loss factor of yogurt was positively correlated with fermentation time and had an irregular change at the endpoint of fermentation (7 h, pH ≈ 4.6). The polynomial determination coefficients of dielectric loss factor with pH and titratable acidity decreased with increasing frequency and were found highest at 10 MHz (0.927 and 0.963, respectively). The linear coefficients of determination between measured values and calculated values were 0.990 for titratable acidity and 0.965 for pH at 10 MHz, respectively. Accordingly, dielectric loss factor can be a promising indicator for online monitoring of industrial yogurt fermentation process.

This paper is focused on the effects of radio frequency (RF) heating on the relative activity of polyphenol oxidase (PPO), weight loss, texture, color, and microstructure of potatoes. The results showed that pure mushroom PPO was almost completely inactivated at 80 °C by RF heating. The relative activity of potato PPO reduced to less than 10% with increasing temperature (25-85 °C). Enzyme extract showed the lowest PPO relative activity at 85 °C after RF treatment, followed by the potato cuboids and mashed potato, about 0.19 ± 0.017%, 3.24 ± 0.19%, and 3.54 ± 0.04%, respectively. Circular dichroism analysis indicated that RF heating changed the secondary structure of PPO, as α-helix content decreased. Both electrode gap and temperature had significant effect (P < .05) on weight loss, color, and texture of the potato cuboids. Microstructure analysis showed the changes of potato cell and starch during RF heating.