Vitamin B12 and its binding proteins in milk from cow and buffalo in relation to bioavailability of B12

Abstract

Milk is an important source of highly bioavailable vitamin B 12 (cobalamin) in human nutrition. In most animal products, vitamin B 12 is strongly bound to various specific protein carriers. The 2 vitamin B 12specific proteins, predominantly transcobalamin (TC) and haptocorrin (HC), were earlier found in milk from Holstein Friesian cows and in human or sow milk, respectively. As the type of vitamin B 12 binders may influence bioavailability of the vitamin, we examined vitamin B 12 carriers in pooled milk specimens derived from European and Indian cow and buffalo herds. The total endogenous vitamin B 12 concentration was comparable in all milk pools (≈3 nM), but the vitamin carriers varied considerably: TC + caseins in Danish cows, TC + HC in Indian cows and buffaloes, and mainly HC in Italian buffaloes. Danish cow milk contained half as much TC as vitamin B 12 , and the surplus vitamin was all attached via a single coordination bond to abundantly available histidine residues of casein. The specific binding proteins in Indian cow milk (TC + HC) approximately matched the molar content of vitamin B 12 . Milk from the 2 buffalo breeds contained more specific binders than vitamin B 12 , and the surplus proteins included the unsaturated TC ≈ 3 nM (Indian stock), or both TC ≈ 4 nM and HC ≈ 23 nM (Italian stock). The abundant HC of the latter sample bound nearly all endogenous vitamin B 12 . We tested (in vitro) the transfer of vitamin B 12 from milk proteins to human carriers, involved in the intestinal uptake. The bovine TC-vitamin B 12 complex rapidly dissociated at pH 2 (time of half reaction, τ 1/2 < 1 min, 37°C) and was susceptible to digestion with trypsin + chymotrypsin (pH 7.5). Transfer of vitamin B 12 from the precipitated bovine casein (pH 2) to human carriers proceeded with τ 1/2 ≈ 7 min (37°C) and τ 1/2 ≈ 35 min (20°C). Liberation of vitamin B 12 from buffalo HC was hampered because of its pH stability and slow proteolysis. Nutritional availability of vitamin B 12 is expected to be high in cow milk (with TC-vitamin B 12 and casein-vitamin B 12 complexes) but potentially constrained in buffalo milk ). This especially concerns the Italian buffalo milk, where a high excess of HC was found. We speculate whether the isolated stock of Italian buffalo maintained the ancestral secretion of carriers (HC ≫ vitamin B 12 , TC ≈ 0), whereas intensive crossbreeding of cows and buffaloes from other regions caused a change to TC ≤ vitamin B 12 , with low or absent HC. The substitution of HC by less sturdy carriers is apparently more beneficial to human consumers as far as vitamin B 12 bioavailability is concerned.

Regulation of Reactive Oxygen Species-Mediated Damage in the Pathogenesis of Schizophrenia

“…Many foods are also known to be good sources of vitamin B6 including starchy vegetables, such as potatoes, non-citrus fruit, fish, fortified cereals, poultry, and organ meats such as beef liver. Natural sources of vitamin B12 include fish, milk and dairy, poultry, meat, and eggs [ 175 , 198 , 199 ]. Although plant-based diets are not adequate sources of vitamin B12, vegetarians can obtain this nutrient through fortified cereals.…”

Bioavailability of Micronutrients From Nutrient-Dense Whole Foods: Zooming in on Dairy, Vegetables, and Fruits

“…Milk contains ~0.40–0.45 μg of vitamin B12 per 100 mL, whereas cheese can contain up to 2 μg per 100 g ( Table 2 ). The major derivatives of vitamin B12 in bovine milk are hydroxycobalamin, adenosylcobalamin, and methylcobalamin, and it is mostly bound to the proteins haptocorrin, transcobalamin and casein depending on the cow breed ( 62 , 63 ). Vitamin B12 bound to transcobalamin appeared to be better released in vitro , whereas this was cumbersome when bound to haptocorrin (mainly present in buffalo milk) and this may have implications for in vivo bioavailability ( 63 ).…”

“…The major derivatives of vitamin B12 in bovine milk are hydroxycobalamin, adenosylcobalamin, and methylcobalamin, and it is mostly bound to the proteins haptocorrin, transcobalamin and casein depending on the cow breed ( 62 , 63 ). Vitamin B12 bound to transcobalamin appeared to be better released in vitro , whereas this was cumbersome when bound to haptocorrin (mainly present in buffalo milk) and this may have implications for in vivo bioavailability ( 63 ). A study in healthy adults > 60 y old, however, revealed that ~65% of vitamin B12 from milk was absorbed ( 64 ), whereas, in comparison, absorption of vitamin B12 from animal foods is generally 50% or lower and even <5% for synthetic supplements ( 62 , 65 ).…”

Effects of Prolonged Whey Protein Supplementation and Resistance Training on Biomarkers of Vitamin B12 Status: A 1-Year Randomized Intervention in Healthy Older Adults (the CALM Study)

“…Epidemiological dietary surveys indicate that the B12 status in humans is positively correlated to the intake of dairy products [6][7][8]. In cow s milk, B12 is evenly distributed between the whey and the casein micelle fraction, bound to transcobalamin in the whey, and via coordination to histidine residues of the caseins, respectively [9,10]. Compared to other foods, whey (and whey protein isolate) is a readily available source of B12 with high bioavailability, which may be attributed to the easily digestible properties of whey proteins [10][11][12].…”

“…In cow s milk, B12 is evenly distributed between the whey and the casein micelle fraction, bound to transcobalamin in the whey, and via coordination to histidine residues of the caseins, respectively [9,10]. Compared to other foods, whey (and whey protein isolate) is a readily available source of B12 with high bioavailability, which may be attributed to the easily digestible properties of whey proteins [10][11][12]. In 2017, Dhillon et al showed that eight weeks daily intake of whey protein isolate improved biomarkers of B12 status in Australian older adults with subclinical B12 deficiency [13].…”