Whey protein and sphingomyelin but not casein contribute to α-tocopherol bioaccessibility in skim milk

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The Ohio State University

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Bioaccessibility, or the extent to which nutrients can be taken up by enterocytes, is an important predictor of nutrient bioavailability. Despite being fat-soluble, the relatively high bioaccessibility of α-tocopherol (α-T) is unaffected by the fat content of dairy milk. This suggests that physiochemical properties of dairy milk independent of fat are functionally responsible for promoting α-T bioaccessibility. We therefore hypothesized that the emulsifying properties of whey protein (WP) and micellarized casein (CAS) and an amphiphilic phospholipid, sphingomyelin (SM), are responsible for α-T bioaccessibility. To test this, simulated digestions in vitro were performed to define the independent and additive contributions of WP, CAS, and SM relative to non-fat milk on α-T bioaccessibility. Digestions containing 15 mg α-T were performed in non-fat milk (245 mL) or water (245 mL) containing milk-matched levels of WP (1.6 g), SM (16.1 mg), and CAS (6.6 g), alone or in combination (WP+SM+CAS). α-T recovery was evaluated by HPLCECD following the gastric through intestinal phases of digestion. α-T bioaccessibility was expressed as the ratio of α-T recovered in the aqueous fraction relative to that in chyme. α-T bioaccessibility differed in response to treatments as follows (means ± SEM; P<0.05): WP (82.0 ± 1.4%) = SM (81.3 ± 3.9%) > skim milk (57.4 ± 1.8%) > CAS (35.9 ± 2.3%) = WP+SM+CAS (33.6 ± 1.1%). Lower bioaccessibility in WP+SM+CAS treatment compared to skim milk suggests that other components of milk may also contribute to α-T bioaccessibility. Relative to skim milk, isolated SM and WP potentiate α-T bioaccessibility while CAS is inhibitory. These findings suggest that WP and SM partially contribute to α-T bioaccessibility while other factors may also have a potentiating role.



Nutrition, Dairy, Tocopherol, Vitamin E