THE EFFECT OF PROCESSING TEMPERATURES ON THE MICROSTRUCTURE AND FIRMNESS OF LABNEH MADE FROM COWS MILK BY THE TRADITIONAL METHOD OR BY ULTRAFILTRATION

The types of Labneh were made from full-fat cow's milk: (a) traditiona l Labneh was produced by straining cold yoghurt at 7-degrees-C in a cl oth bag, and (b) UF Labnehs were produced by ultrafiltration (UF) of w arm yoghurt at 35-degrees, 40-degrees, 45-degrees, 50-degrees, and 55- degrees-C. The UF Labnehs contained 22.7-23.9% total solids, 7.8-8.3% protein, and 10.6-11.3% fat as compared to 25.3%, 9.1%, and 11.9%, res pectively, in traditional Labneh. Homogenization of the experimental L abneh samples in an ALM homogenizer using the D-170 or D-280 heads mad e the products smoother than unhomogenized Labnehs. Scanning electron microscopy revealed that the largest and least uniform pores were pres ent in traditional unhomogenized Labneh, where the protein clusters we re relatively compact. Homogenization reduced the dimensions of the la rge pores and opened the structure of the protein clusters. Ultrafiltr ation of Labneh at elevated temperatures of 35-degrees to 55-degrees-C resulted in an increase in the dimensions of the casein particles for ming the protein matrix of the Labneh, evidently as the result of exte nded fermentation. Formation of complex casein particle chains, as obs erved by transmission electron microscopy, was associated with increas ed firmness of Labneh samples concentrated at temperatures above 45-de grees-C.