Zinc-binding capacity of yak casein hydrolysate and the zinc-releasing characteristics of casein hydrolysate-zinc complexes

Many factors affect the bioavailability of dietary Zn, which leads to its low availability in some food systems and Zn nutrient deficiency. However, some proteins or peptides can form complexes with Zn and increase its absorption and bioavailability in intestinal conditions. The purpose of this work was to determine the Zn-binding activity of yak casein hydrolysate (YCH) and examine its stability, solubility, and dialyzability in a simulated intestinal environment. The Zn-binding activity of YCH, prepared using alcalase, pepsin, trypsin, Flavozyme (Novo Nordisk Biochem Inc., Franklinton, NC), or papain, was investigated. Evidence for the formation of complexes between Zn and YCH also were detected by UV-visible spectroscopy and Fourier transform infrared spectroscopy. Results were that YCH prepared with alcalase and trypsin possessed the highest Zn-binding capacity compared with YCH prepared with pepsin, Flavozyme, or papain. The 6-h YCH obtained with alcalase showed the highest Zn-binding capacity. Compared with native yak casein, the Zn-binding activity of YCH was significantly lower, but its solubility and dialyzability were markedly higher under intestinal basic pH ranges. This is important because high solubility and dialyzability is associated with better bioavailability. Both UV-visible spectroscopy and Fourier transform infrared spectroscopy spectra indicated that some sites of YCH can bind with Zn ions and form complexes that make Zn more soluble and dialyzable under simulated intestinal conditions. Therefore, YCH-Zn complexes may have potential to improve Zn bioavailability.