Microstructure, Proteolysis, and Meltability in Low Moisture Part Skim Mozzarella Cheese as Affected by Proteolytic Starter Cultures and Coagulating Enzymes

This study investigated the use of pre-screened proteolytic starter cultures and different types and levels of coagulating enzyme for making Mozzarella cheese with desired melt characteristics. Low moisture part skim (LMPS) Mozzarella cheeses were made from cow\u27s milk standardized to 1.8% fat. Sixteen Mozzarella cheeses were prepared using four starter cultures combination, and two coagulants (Cryphonectria parasitica and rennet) at two levels (1X or 6X). The experiment was replicated three times. The experimental control was the single starter Streptococcus thermophilus (ST). The treatments were a combination of Streptococcus thermophilus- (strain STB 16) with different proteolytic strains of lactobacilli viz. Lactobacillus delbrueckii spp. Bulgaricus (strain LB12) and Lactobacillus helveticus (strain SHZ or L11). Cheeses were analyzed for fat, protein, moisture, total solids, calcium, salt, and ash on day 1. Changes in melt characteristics and proteolysis during storage (4 °C) were monitored on 1, 7, 15, and 30 days (d). Cheese micro structure was studied during cheese manufacture using scanning electron microscopy (SEM) before and after stretching. The matrix appeared coarse and rough before salting, which became smooth, homogenous, and firm after stretching. During storage, the matrix appeared to have some alignment within the protein matrix with the formation of fat channels and orientation of the starter bacteria forming long chains. The cheeses made with combination of starter cheeses (ST and lactobacilli) showed a higher melt area than the single starter cheeses, while the 6X levels of coagulants exhibited favorable functional attribute, such as meltablity over the 1 X levels. The extent of proteolysis on day 1 and 30 was also estimated by studying the protein breakdown pattern using SDS-PAGE. The extent of proteolysis was higher in mixed starter culture cheeses than the single culture cheeses (ST). Cheeses made using the combination of ST +LH-SHZ with coagulant CP at 6X level of enzyme resulted in highest melt area. The soluble protein fractions measured as water soluble nitrogen (WSN) and trichloroacetic acid soluble nitrogen (TCA) were also highest for this combination. The extent of proteolysis increased with the storage period for all cheeses and resulted into generation of medium, small and very small peptides as supported by the increase in numbers of bands on SDS-PAGE gel due to breakdown of αsl and β-casein fractions on different cheeses. LMPS Mozzarella cheese made using proteolytic starter culture along with CP at 6X level would enable cheese manufacturers to produce tailor made cheeses to meet specific high melt cheese requirements. The present investigation reveals the possible implications of selective proteolysis in cheese to obtain desirable functional characteristics in Mozzarella cheese