Mustapha Najib
University of Lille, France
Title: The mechanisms of the heat-induced interactions of milk components during the process of Qishta: A Lebanese cream
Biography
Biography: Mustapha Najib
Abstract
Milk and milk products are nutritious foods which contain numerous essential nutrients. They are considered as a source of calcium, phosphate, riboflavin, vitamin B12, proteins and fat. There are several principal categories of milk products such as liquid/beverage milk, cheese, milk powders, concentrated milks, fermented milk products, butter, some of which are produced from byproducts of other milk-products, ice-cream, infant formula, creams, protein-rich products, and lactose. In addition, several product sub-categories exist and many are defined by the process they have been subjected to. Products may be altered by acid, enzymes or microorganisms, or a combination of these. The most important part of milk processing has turned to be the heat treatments, demonstrating the common practice to restrain the microbial development in milk. Qishta is one of the traditional dairy products that exist in Lebanon. It is a heat-treated dairy product made by subjecting a small sector of a large shallow stainless-steel pan that is filled with whole milk, to high temperature. Qishta is related to the cheese family, especially to cream cheese varieties due to the presence of milk proteins as well as their particular coagulation process during Qishta development. Protein’s aggregation is considered as a key point during the process of Qishta. During the Qishta preparation, heat treatment of milk induces an increase in acidity, due to the degradation of lactose. This last is involved with the proteins in the Maillard reaction. The dimer of β-Lg dissociates between 30 and 55°C, but these changes are reversible and the monomers can rebound by cooling if the temperature does not exceed 60°C. When temperatures are above 60-70°C, the tertiary and also partly secondary structure of the monomer starts to unfold, leading to exposure of the free thiol group (Cys121) and hydrophobic parts of the residues chain, resulting in a reactive monomer. The main aggregates formed as a consequence of heat treatment of milk, are complexes formed by aggregation of denatured whey proteins and complexes between β-Lg and κ-casein on the surface of the casein micelles via disulphide bonds and hydrophobic interactions.