Acid coagulation properties of milk powder

Abstract

The relationship between heat treatment classification and the acid coagulation properties of reconstituted skim milk powders was investigated. Fifteen samples of commercial skim milk powder, acidified with glucono-δ-lactone (GDL), were analysed using a Bohlin C-VOR rheometer. Powders varied in stated heat treatment classification (based on WPNI) and country of manufacture. It was shown that low heat powders (WPNI ≥ 6.0) and powders without heat classification coagulated more slowly than medium heat or high heat treated powders. Gel strength (storage modulus, G’) of the acidified milks was also influenced by heat treatment classification. Low heat and unclassified powders produced weaker gels (40-50 Pa) than medium and high heat milk powders (>228 Pa), however low heat powders from Sweden did not follow the same trend. Using reversed-phase high performance liquid chromatography (RP-HPLC), concentrations of major proteins were determined. It was shown that powders with lower levels of native whey protein had better coagulation characteristics (faster coagulation times and higher gel strengths) than milk powders with higher native whey protein concentration. This correlated to increasing heat treatment classification and WPNI. These findings suggest that the heat induced modifications of milk proteins enhance coagulation properties, and that low heat milk powders are less suitable for acid milk gel applications.