Effect of dairy unit operations on immunoglobulins, colour, rheology and microbiological characteristics of goat milk

Raw goat milk was processed by low-temperature long-time (LTLT) and high-temperature short-time pasteurisation, boiling, skimming, microfiltration, and concentration to 25% solids to investigate the effects on composition, rheology, immunoglobulins, lactoferrin and microbial quality. All processing interventions had significant effect on fat, protein and ash content. pH of goat milk was decreased by heating and concentration. Skimming had lesser reduction of immunoglobulin G (IgG), immunoglobulin A (IgA), and lactoferrin (LF), compared with those by microfiltration and heat treatments. Levels of IgG and lactoferrin were the lowest after LTLT pasteurisation, while IgA was the least after boiling. Skimming and microfiltration reduced L∗ values; heating increased b∗ values. Heating increased rennet gelation time and reduced coagulum strength. Microbiologically, heated and microfiltered goat milk were comparable, but the latter had reduced total bacteria and coliform counts. Heat stability maxima were at pH 6.8–7.0 for raw and heated goat milk; peak values were different.