In this study, we utilized pressurized carbon dioxide (pCO2) for pectin extraction from citrus residues because of its potential to produce acid without chemicals, that is non-toxic, green technology for humans and the environment. The pCO2 was performed at 2.5 MPa and 90 °C for 90 min, while the conventional method (CM) for pectin extraction using HCl was performed under atmospheric pressure at 90 °C for 90 min. Pectin extraction yields with pCO2 depended on the type of citrus fruit and were lower than those obtained with the CM. However, pCO2-extracted pectin (pCO2-pectin) provided a higher degree of esterification (DE), neutral sugar side-chain substitution on the pectate backbone, and greater molecular size than those of pectin extracted using the conventional method (CM-pectin). Pectin oligosaccharide (POS) was prepared from CM-pectin and pCO2-pectin using viscozyme L hydrolysis under optimum conditions. These POSs were then designated as CM-POS and pCO2-POS, respectively. Both pCO2-POS and CM-POS stimulated the growth of Lactobacillus and Bifidobacterium species, and induced them to produce short-chain fatty acids, and slightly suppressed immunoglobulin E production in U266 cells. Furthermore, pCO2-POS had higher angiotensin-converting enzyme inhibitory activity compared to CM-POS. This study suggests that pCO2 is a novel method for extracting pectin with unique molecular properties affecting POS functionality in vitro.
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