Organic acid treatments on citrus insoluble dietary fibers and the corresponding effects on starch in vitro digestion.

Three environmentally friendly organic acids, acetic acid, citric acid and oxalic acid, were used to treat citrus insoluble dietary fiber (CIDF) in present study, aiming to explore the changes in structural properties as well as their inhibitory effects on starch digestion. The results showed that organic acid treatment significantly reduced the particle size of all three CIDFs, with rougher and folded surfaces, improved crystallinity and thermal stability. During in vitro digestion, it was found that organic acid treatment could increase the particle size and viscosity of digestion, and also effectively enhance the inhibitory ability of α-glucosidase activity, resulting in a further blockage of starch digestion. The starch digestion in oxalic acid-treated group (with 3 wt% addition) was significantly reduced by 18.72 % compared to blank group and 9.05 % compared to untreated. These findings provide evidence of the potential of organic acid-treated insoluble dietary fiber as a functional food.

Effects of different particle-sized insoluble dietary fibre from citrus peel on adsorption and activity inhibition of pancreatic lipase.

Insoluble dietary fibre from citrus peels (CIDF) was found to have adsorption and inhibitory effect on the activity of pancreatic lipase (PL). CIDF-400 exhibited the greatest adsorption and activity inhibition effect on PL. The fluorescence quenching spectra indicated that CIDF could quench PL through a dynamic quenching process induced by the electrostatic interactions with only one binding site between them. The synchronous fluorescence and three-dimensional fluorescence spectra showed that CIDF might combine with PL to induce the increase in hydrophobicity and the reduction in polarity of tyrosine (Tyr) and tryptophan (Try) residues, which further led to the conformational alternations of PL. Moreover, circular dichroism (CD) showed that CIDF altered the secondary structure of PL, decreased α-helical structure content, and increased ß-sheet structure content, potentially resulting in PL structure opening and its active site exposure. This study provides new perspectives for the application of CIDFs produced from agricultural waste in regulating lipid metabolism.