Abstract
Bovine lactoferrin (bLF), a multifunctional protein, is easily digested by pepsin in stomachs of adult people, but bLF is likely to exert a variety of immuno-stimulatory effects in the small intestine if delivered in intact form. In this study, with an emphasis of bioactivities of intact bLF in the small intestine, we explored food proteins that protect bLF from gastric digestion and facilitate intact bLF to be delivered to the small intestine. Among four kinds of food proteins investigated, such as casein (CN), whey protein isolate, ovalbumin, and soy protein, only CN inhibited in vitro digestion of bLF with pepsin. The inhibitory effect became stronger as the ratio of CN/ bLF increased. Each major subunit, i.e., αs-, β-, and κ-CN, also inhibited digestion of bLF, but the effect was more prominent in the case of β-, and κ-CN. CN hydrolysates showed weaker inhibitory effects than CN, and the effects decreased as degree of hydrolysis increased. The effect of CN on inhibiting peptic digestion of bLF was also confirmed in in vitro digestion assays using raw milk and an experimental liquid formula containing bLF and CN. Further, delivery of intact bLF to the small intestine was observed in mice fed the liquid formula. Thus, ingestion of bLF with CN protects bLF from gastric digestion, possibly thereby exerting immuno-stimulatory activities in the small intestine.
