Effect of industrial processing and storage procedures on oxysterols in milk and milk products

Abstract

Oxysterols are products of enzymatic and/or chemical cholesterol oxidation. Their measurement during and after a milk production chain could represent a useful tool to monitor and increase the commercial and nutritional value of milk.

Oxysterols in stored powders as potential health hazards

“…Also Risso et al 34 analysed the 7β-HC changes in milk powder during storage. They found that the content of 7β-HC reached 0.265 µg g −1 cholesterol and 0.569.83 µg g −1 in skim milk powder and whole milk powder, respectively, after 12 months, and these amounts are potentially toxic in several in vitro and in vivo experimental studies.…”

Oxysterols: From redox bench to industry

“…Several studies have focused on the quantification of oxysterols in a broad range of dairy ingredients and products including, but not limited to, dairy and cheese spreads, butter, butter oil, cheese (both aged and fresh, whole and grated), milk (both raw and processed, liquid, powdered, condensed, and evaporated), buttermilk, infant formula, and yogurt [ [114] , [115] , [116] , [117] , [118] , [119] ]. In these kinds of products, total non-enzymatic (or partially enzymatic) oxysterols were found to be in the broad range of 0–366 μg/g, depending on several factors such as the type of analyzed matrix, the age of the tested product, the processing conditions employed.…”

“…While most of the studies present in literature have quantified 7βOHC and 7KC, fewer studies analyzed the broader array of these compounds together, such as 7αOHC, α-epoxy, β-epoxy, 25OHC, 27OHC and triol ( Table 3 ). Regarding enzymatic oxysterols, to our knowledge so far only a single study recorded and quantified the presence of 27OHC in dairy and dairy products [ 117 ].…”

“…In milk and dairy products this may be due to cholesterol in milk being located mainly in the milk fat globule membrane (MFGM) that, during dairy processing, is prone to substantial damage, which increases its susceptibility to oxidation [ 136 ]. Although very early studies showed how no or only limited amounts of oxysterols are formed during milk processing, more recent publications have highlighted how, instead, industrial processes and storage procedures may significantly impact the oxysterol profile of milk and dairy products [ 116 , 117 ]. This is likely due to the technological methodologies and more sensible methods for COPs determination that have been developed in more recent times, although there is still a need for a harmonized analytical method to quantify cholesterol oxides using the same standards, reagents, protocols, and calibration materials to reduce interlaboratory variations and sources of errors [ 113 , 118 ].…”

“…Pasteurization at high temperatures (85 °C) affects the generation of oxysterols differently, depending on the presence of fat in the product. More specifically, while their cholesterol ratios increased significantly after skimming and processing of skimmed milk and milk products, this was not observed after processing whole milk and milk cream [ 117 ]. In general, other factors that drive COPs formation include radiation, presence of unsaturated fatty acids, metal ions (like Fe, Cu, Co, Mg, Ni), natural dyes (for example, chlorophyll) and presence of free radicals/peroxides [ 109 , 118 ].…”