Effects of different levels of gum arabic, low methylated pectin and xylan on in vitro digestibility of beta-lactoglobulin.

Plant hydrocolloids used in the food industry to improve texture and stability of food, such as dairy products, can reduce protein digestibility and, consequently, modify the bioavailability of amino acids. We studied the in vitro hydrolysis at 37 degrees C of beta-lactoglobulin (beta-lg) in mixed dispersions containing either gum arabic or low-methylated pectin or xylan at levels of 0, 1, 10, 20, 30, and 50% weight. Proteolysis used either pepsin alone by progressive reduction of pH during proteolysis or pepsin followed by trypsin and chymotrypsin in two different dialysis bags with a molecular weight (MW) cutoff of 1000 or 8000 Da. Results showed that beta-lg was almost resistant to pepsin digestion and that the three plant hydrocolloids inhibited significantly beta-lg digestibility as determined using dialysis bag with a 1000-Da MW cutoff. Among the three polysaccharides used, xylan showed a digestibility decrease greater than that obtained with gum arabic and low-methylated pectin. On the other hand, no significant effect of polysaccharides on the in vitro beta-lg digestibility was detected using the dialysis bag with an 8000 Da MW cutoff. This mainly suggests that peptides with MW in the range 1000 to 8000 Da may interact with polysaccharides more than peptides and proteins with a greater molecular weight to decrease the protein digestibility, and that the nature of the polysaccharides plays a role in the interaction.