Influence of protein standardization and UHT heating on the furosine value and freezing point of milk

Abstract

Milk containing ∼ 1.7% fat, but protein in the range ∼ 2.6-3.4% was prepared by mix∼ing calculated quantities of whole milk, skim milk and an ultrafiltration (UF) permeate obtained ∼from skim milk or quarg acid whey. The freezing point (PP) of each milk was measured before and ∼after ultra-high temperature (UHT) heating. The concentration of lactuloselysine, determined indirectly ∼as furosine value (FV), was measured after 1, 4 or 12 weeks storage of the UHT milk at 4 or 25°C. ∼After UHT heat treatment, the FV was ∼ 2-4-fold higher in indirect UHT milk (∼ 18-47 mg/L), ∼compared to direct UHT milk (∼9-12 mg/L). Upon storage at 4°C, the FV did not change appreciably, ∼but after 12 weeks at 25°C, it increased by - 1.5-4-fold; some direct UHT milk products stored at ∼25°C had a greater FV than indirect UHT milk stored at 4C. Standardization with skim milk per∼meate or acid whey permeate caused the FV of UHT milk to decline, but the effect was small com∼pared to the influence of storage conditions. The use of increasing amounts of skim milk permeate for ∼protein standardization caused the FP to increase progressively, while the opposite occurred upon stan∼dardization with acid whey permeate. Direct or indirect UHT heating had no effect on the FP of any ∼milk, indicating that irreversible changes in milk salt equilibria did not occur and that thermal inter∼actions of lactose, including its participation in the Maillard reaction, did not affect the FP.