Storage Stability of Milkfat Globule Membrane

Abstract

To investigate changes in structure and function of milk fat globule membrane (MFGM) components due to oxidation of membrane lipids, freeze‐dried MFGM were stored under controlled temperature and relative humidity (RH) conditions. It was found that while membranes underwent extensive lipid oxidation when stored under air, fluorescent compounds were formed. These compounds exhibited fluorescence with excitation maxima at 350 nm and emission maxima at 440 nm; which were similar to those of the fluorescent substances derived from the reaction of oxidized fatty acids and primary amines. Formation of high molecular weight proteins was detected by SDS‐PAGE in samples stored under air, but not in samples stored under nitrogen and was also affected by time and relative humidity. Activity of xanthine‐oxidase, an important prooxidative agent, was greatly influenced by temperature and complete inactivation was observed when MFGM's were stored at 37°C, 50% RH for 1 day.

Bioactives in bovine milk: chemistry, technology, and applications

“… 117 MFGM undergoes lipid oxidation along with structural and functional changes during storage. 118 The phospholipids of the MFGM, which contains 40%–60% unsaturated fatty acids, are susceptible to oxidation and could develop oxidized flavor defects. 119 …”

Effect of Extraction Procedures on Fluorescent Chromophores in Milk

“…Freeze-dried membranes kept at -40°C were used as controls. Two different extraction procedures for fluorescent chromophores in oxidized freeze-dried MFGM were used to follow lipid oxidation development during storage under conditions in which high fluorescence intensity was expected (Bouzas et al, 1984): (a) Stored samples were directly extracted with 5 mL CI,CH:CH30H (2:l v/v), vortexed for 5 min, filtered twice by SS#589 filter paper; (b) Stored samples were reconstituted to the initial moisture content and 1 mL of membrane suspension was extracted with 5 mL Cl-,CH-CH30H (2: 1 v/v), 5 mL HzO, vortexed for 5 min, centrifuged at IO4 rpm for 8 min. the upper aqueous phase was taken by aspiration and the remaining organic extract was filtered by SS#589 filter paper .…”

Role of Milk Fat Globule Membrane in Autoxidation of Milk Fat

“…FAT IN MILK is in the form of globules surrounded by a membrane which contains a mixture of unsaturated phospholipids, proteins, glycoproteins and other minor components (Keenan et al, 1983). The unsaturated phospholipids of the membrane were reported to play a role in initiating oxidation of milk fat (Krukovsky, 1952;Mulder and Walstra, 1974;Bouzas et al, 1985). Reconstituted milk was found more stable than regular milk due to removal of membrane material (Krukovsky, 1952).…”

“…King found that the isolated MFGM material oxidized very fast in model systems depending on concentrations of ascorbic acid and copper (King, 1962 and1963). Xanthine oxidase, abundant in the MFGM, may also be partially responsible for susceptibility of the membrane to lipid oxidation (Aurand et al, 1977;Bouzas et al, 1985).…”