Comparative study on the characteristics and oxidation stability of commercial milk powder during storage

摘要

The quality of milk powder can decrease during storage.In this study, the characteristics of 12 kinds ofcommercial milk powder from China were investigated.Changes in various indicators were tracked to comprehensivelyestimate the oxidation stability of differentcommercial milk powders. The components of the commercialmilk powder were different. The percentages ofmilk fat, protein, and carbohydrates ranged from 9.8to 28.5 g/100 g, 15.0 to 24.0 g/100 g, and 32.0 to 67.5g/100 g, respectively. The water activities ranged from0.2394 to 0.5286. The diameters of the milk fat globulesin different commercial milk powder ranged from 13.99to 41.09 nm. At the same time, the peroxide value ofthe control sample was low (≤0.14 mEq/kg). After3 mo of storage, the peroxide values of some of thecommercial milk powder increased significantly. Thechanges in the thiobarbituric acid values during storagedid not follow a common trend. The contents of free fatin the different control samples were 0.21 to 1.67 g/100g, and these values did not increase during storage.After 3 mo of storage, the hydroxymethyl furfural valuesand b color values of the different commercial milkpowder reached their highest levels. The concentrationsof typical oxidized flavor compounds in different commercialmilk powder increased greatly with prolongedstorage time. The level of hexanal was the highest, andthe contents in all the samples ranged from 28.56 to4,071.28 μg/kg after 6 mo of storage and from 5.91 to6,281.37 μg/kg after 12 mo of storage. Free radicalswere found in some of the stored milk powder, andthese were shown as single peaks or multiple peaks. Theratios of the peak areas and masses reached 12.42 × 10~6to 14.26 × 10~8. However, the presence of free radicalsin the commercial milk powder was not consistent. Thewater activities and diameters of the fat globules in thecommercial milk powder were highly correlated withtheir oxidation stabilities during storage.