Comparative study on the effect of radio frequency and high-pressure pasteurization on the texture, water distribution, and rheological properties of Nostoc sphaeroides

Nostoc sphaeroides has been used as herbal medicine and dietary supplement in Asian countries from prehistoric times. When N. sphaeroides is pasteurized using conventional high-pressure (HP) steam (121 degrees C, 30 min), its natural texture and nutritional ingredients are negatively affected. This study investigated the effect of radio frequency (RF) heating on the degree of microbial kill, texture, water distribution, and theological properties of N. sphaeroides and compared the effect of HP steam (121 degrees C, 30 min) pasteurization on these parameters. RF (6 kW, 27 MHz) pasteurization was carried out for 10, 20, and 30 min at 67 degrees C. The results showed that the RF heating carried out for 20 min achieved a 3 log reduction of bacteria which met the safety standard. The effects of RF pasteurization on the texture, water distribution, and rheological properties of N sphaeroides were significantly lower than that in HP steam pasteurization. Therefore, the application of RF heating in N sphaeroides would help broaden its application in food, health, and pharmaceutical formulations.