Variation of Vitamin D in Cow’s Milk and Interaction with β-Lactoglobulin

Omar Bulgari,Stefania Chessa,Anna Caroli,Carmen Gigliotti,Rita Rizzi

doi:10.3390/molecules180910122

Abstract

Vitamin D is the collective name for a group of closely related lipids, whose main biological function is to maintain serum calcium and phosphorus concentrations within the normal range by enhancing the efficiency of the small intestine to absorb these minerals from the diet. We used a commercially available ELISA method for the determination of vitamin D in bovine milk. Individual milk samples from two different Italian Friesian herds were analysed. The enzyme immunoassay method used was confirmed as a useful tool to measure the vitamin D in the milk as it greatly reduces the time required to perform the conventional HPLC analysis. An interesting variation was found among individual animals that may be associated with management factors and specific genetic effects. A relationship was highlighted between vitamin D and the genetic polymorphism of β-lactoglobulin, the main bovine whey protein which is involved in the transport of small hydrophobic molecules such as retinol and vitamin D. The relatively high content of vitamin D in most milk samples suggests an opportunity to improve the natural content of vitamin D in milk either by acting on the herd management or selecting individuals genetically predisposed to produce milk with a higher vitamin D content.

Highlights

Vitamin D is the collective name for a group of lipids which are closely related
The raw milk sample contained 0.57 IU/mL of vitamin D3, a higher value, as expected, than the activity observed in two samples of unfortified UHT milk, which contained respectively 0.34 IU/mL and 0.44 IU/mL of vitamin D
The enzyme immunoassay method used was confirmed as a useful tool to measure the vitamin D in the milk as it greatly reduces the time required to perform the conventional HPLC analysis

Summary

Introduction

Vitamin D is the collective name for a group of lipids which are closely related. The two major forms are vitamin D3, or cholecalciferol, synthesized by the skin of vertebrates following exposure to ultraviolet radiation (UV) B, and the vitamin D2 or ergocalciferol, produced in various plants, yeasts and fungi, always due to exposure to UV B radiation [1].In the presence of sufficient light, the vitamin D3 is formed in a non-enzymatic way in the skin from7-dehydrocholesterol. Vitamin D is the collective name for a group of lipids which are closely related. The two major forms are vitamin D3, or cholecalciferol, synthesized by the skin of vertebrates following exposure to ultraviolet radiation (UV) B, and the vitamin D2 or ergocalciferol, produced in various plants, yeasts and fungi, always due to exposure to UV B radiation [1]. In the presence of sufficient light, the vitamin D3 is formed in a non-enzymatic way in the skin from. Vitamin D2 has an additional methyl group with respect to the D3 and is formed from ergosterol, following a biochemical process similar to that of vitamin D3 [1]. The active form of vitamin D3, the 1,25-dihydroxycholecalciferol [1,25(OH)2D3] or calcitriol, is formed from vitamin D3 through two independent hydroxylation reactions, in the liver and in the kidneys; vitamin D2 is activated in a similar way. Vitamin D introduced with food is rapidly absorbed in the duodenum and jejunum and, subsequently, distributed, through the lymphatic circulation, almost completely to the adipose tissue, from which is released in small quantities compared to the stored portion [3]

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