Effect of charge density of polysaccharides on self-assembled intragastric gelation of whey protein/polysaccharide under simulated gastric conditions

This study focuses on the behavior of mixed protein and polysaccharides with different charge densities under simulated gastric conditions. Three types of polysaccharides, namely, guar gum, xanthan gum and carrageenan (neutral, medium negatively, and highly negatively charged, respectively) were selected for heating together with whey protein isolate (WPI) at a biopolymer ratio ranging from 0.01 to 0.1. Upon mixing with simulated gastric fluid (SGF), all WPI-guar gum samples remained soluble, whereas WPI-xanthan gum and WPI-carrageenan at biopolymer ratio higher than 0.01 led to self-assembled intragastric gelation immediately after mixing with SGF. The mechanism behind the intragastric gelation is believed to be the cross-linking between oppositely charged protein and polysaccharides when pH was reduced to below the pI of the protein. Higher biopolymer ratio led to a higher degree of intermolecular interaction, which tends to form stronger gel. More negatively charged carrageenan also formed a stronger gel than xanthan gum. SDS-PAGE results show that the digestibility of protein was not affected by the presence of guar gum as well as xanthan gum and carrageenan at biopolymer ratio lower than 0.02. However, intragastric gel formed by WPI-xanthan gum and WPI-carrageenan at biopolymer ratio higher than 0.02 significantly slows down the digestion rate of protein, which could potentially be used to delay gastric emptying and promote satiety.