Enhancing hydrothermal extraction of plant cell wall polysaccharides using radio frequency energy: A case study on extracting pectin from pomelo peels

Abstract

Radio frequency (RF) heating and hydrothermal treatment, as environmentally friendly and efficient technologies, have been widely applied in food processing. This study aims to investigate the effect of RF-assisted hydrothermal extraction (RFAHE) of plant cell wall polysaccharides, using pomelo peel pectin (PPP) as a case study. Based on the optimized RFAHE operating conditions, the yield, physicochemical, and structural properties of PPP obtained from RFAHE, acidic RFAHE (ARFAHE), microwave-assisted HE (MWAHE), and hydrothermal extraction (HE) alone were compared. The optimized RFAHE conditions are as follows: heated at 122 °C and liquid/solid ratio of 40 mL/g for 17 min. The pectin yields were 20.8 ± 0.7, 20.6 ± 0.8, 23.8 ± 0.6, and 18.7 ± 0.6 % for RFAHE, MWAHE, ARFAHE, and HE alone, respectively. Among the four samples, the RFAHE sample had the highest degree of esterification and antioxidant capacity, as well as the lowest molecular weight, while the ARFAHE sample exhibited the opposite characteristics. The GalA content of the RFAHE sample was higher than that of the MWAHE sample but slightly lower than the standard for commercial food-grade pectin. FTIR, XRD, and ¹H NMR analysis indicated that there were no significant differences in the main chemical structures among the four samples. The results from this study confirm that the extraction efficacy of RFAHE is superior to that of MWAHE, and offer fundamental insights into the application of RFAHE for recovering cell wall polysaccharides from plant food wastes and byproducts.