Extraction of citrus pectin using pressurized carbon dioxide and production of its oligosaccharides

In this study, we utilized pressurized carbon dioxide (pCO(2)) 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 pCO(2) was performed at 2.5 MPa and 90 degrees C for 90 min, while the conventional method (CM) for pectin extraction using HCl was performed under atmospheric pressure at 90 degrees C for 90 min. Pectin extraction yields with pCO(2) depended on the type of citrus fruit and were lower than those obtained with the CM. However, pCO(2)-extracted pectin (pCO(2)-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 pCO(2)-pectin using viscozyme L hydrolysis under optimum conditions. These POSs were then designated as CM-POS and pCO(2)-POS, respectively. Both pCO(2)-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, pCO(2)-POS had higher angiotensin-converting enzyme inhibitory activity compared to CM-POS. This study suggests that pCO(2) is a novel method for extracting pectin with unique molecular properties affecting POS functionality in vitro.