Evaporation Of Milk Essay

INTRODUCTION

Milk is a very complex system. The continuous phase is an aqueous solution of a specific sugar, lactose, globular proteins, inorganic salts and hundreds of minor constituents, for example vitamins, at trace levels. Dispersed in the aqueous phase as an oil-in-water emulsion are lipids in the form of small globules and a second, unique group of proteins, the caseins, which exist as large colloidal particles known as casein micelles, with an average diameter of approximately 150 nm and containing approximately 5000 protein molecules.

Owing to the physical state, milk is an unstable system. The fat globules, which are less dense than the aqueous phase, rise to the surface where they form a cream layer. The fat-rich cream can be skimmed off and used for the manufacture of butter, butter oil, ghee or other fat-rich products. Alternatively, the fat-depleted lower layer or as know as skimmed milk may be run off, for example through a valve at the bottom of a

The minimum requirements of this step are to pasteurise the milk to ensure food safety and to bring its temperature to the boiling point in the first effect of the evaporator, for thermal efficiency. However, the functionality of the final product can be determined and modified by this processing step; preheating conditions range from conventional pasteurisation to 90°C for 10 minutes or 120°C for 2 minutes. The most significant result of such heating is denaturation of β-lg, to a degree depending on the severity of heating. During subsequent evaporation and, if applied, spray-drying, relatively little denaturation of the whey proteins occurs, as the temperature of the milk generally does not exceed 70°C (Singh and Creamer, 1991). However, further association of whey proteins with the casein micelles can occur during evaporation, probably because the decrease in pH reduces protein change, facilitating association