Altering the physico-chemical and processing characteristics of high heat-treated skim milk by increasing the pH prior to heating and restoring after heating. (15th April 2018)

• Record Type: Journal Article
• Authors: Lin, Yingchen; Kelly, Alan L.; O'Mahony, James A.; Guinee, Timothy P.
• Is Part Of: Food chemistry. Volume 245(2018)
• Page Start: 1079
• Page End: 1086
• Publication Date: 2018-04-15
• Subjects: Skim milk -- Biochemical changes -- High heat treatment -- PH at heating -- Rennet gelation -- Heat stability -- Ethanol stability; Food -- Analysis -- Periodicals; Food -- Composition -- Periodicals; 664
• DOI: 10.1016/j.foodchem.2017.11.063
• Languages: English
• ISSNs: 0308-8146

Abstract

Highlights: Skim milk was adjusted from pH 6.6 to 7.5, and heated to 95 °C or unheated. The pH of the skim samples was restored to pH 6.6 and assayed. The pH at heating affected casein dissociation, serum Ca and casein micelle size. Heat treatment affected rennet gelation, ethanol stability and heat stability. The pH at heating affected heat stability. Abstract: Skim milk was pH-adjusted from 6.6 to 7.5, high heat treated (HHT, 95 °C × 2 min) or held unheated for 1 h, re-adjusted to pH 6.6, and analysed. HHT at pH 6.6 resulted in denaturation of ∼ 67% of total whey protein, partial association of denatured whey protein with the casein micelle, an increase in casein micelle size, and reductions in concentrations of serum casein, Ca and P. These changes were paralleled by a marked deterioration in rennet coagulability, higher ethanol stability in the pH range of 6.2–6.6 ( P < .05), and a reduction in the pH of maximum heat coagulation time (HCT) ( P < .05). Increasing the pH before heat treatment led to increases in casein dissociation and the concentrations of κ-casein and denatured whey protein in the serum, and a reduction in casein micelle size ( P < .05). Simultaneously, HCT at pH 6.6–6.7 and 7.2 increased significantly.