The Influence of High Heat Treatment at Alkaline pH on the Physicochemical Characteristics and Isomerization of Lactose to Lactulose in Skim Milk

Darwish, M. S.; El-Awady, Asmaa A.; Abd-ElSalam, Rana; Mostafa, M. S.

doi:10.21608/jfds.2023.227934.1125

The Influence of High Heat Treatment at Alkaline pH on the Physicochemical Characteristics and Isomerization of Lactose to Lactulose in Skim Milk

Document Type : Original Article

Authors

Dairy Department, Faculty of Agriculture, Mansoura University, Mansoura 35516, Egypt.

10.21608/jfds.2023.227934.1125

Abstract

The pH of the skim milk was modified, first increased from 6.5 to 7.5, then subjected to high heat treatment at 95°C for 2 min or left unheated for 1 hour. Subsequently, the pH was adjusted back to 6.5, and the samples were analyzed. The concentration of lactulose in skim milk showed a significant increase due to High heat treatment (HHT) (p < 0.05), and this effect was more pronounced when the pH was raised from 6.5 to 7.5 before HHT. Raising the pH of both high heat-treated (HHT) and unheated (UH) skim milk from 6.5 to 7.5 before heating or holding led to an extended heat coagulation time (HCT) at pH 7.2 and resulted a 58.7% increase in the dissociation of κ-casein in HHT milk compared to the total κ-casein content. The adjustment of pH had no significant (p < 0.05) influence on the chemical composition of the high heat-treated skim milk and ethanol stability in the pH range of 6.2-7.2). Besides heating the sample at 95°C for 2 min resulted in a significant decrease in casein micelle size (CMS). These findings offer a foundation for focusing on the negative impact of alkalinization before high heat treatment on casein dissociation, CMS, thermal and alcohol stabilities. Additionally, it is regarded as a promising approach with the potential to enhance the lactulose content in milk.

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