Effect of ß-lactoglobulin A and B whey protein variants on cheese yield potential of a model milk system.

Cheese yield mainly depends on the amount and proportion of milk constituents; however, genetic variants of the proteins present in milk may also have an important effect. The objective of this research was to study the effect of the variants A and B of ß-lactoglobulin (LG) on cheese yield using a model system consisting of skim milk powder fortified with different levels of a mixture containing α-lactalbumin and ß-LG genetic variants (A, B, or A-B) in a 1:2 ratio. Fortified milk samples were subjected to pasteurization at 65 °C for 30 min. Miniature cheeses were made by acidifying (pH=5.9) fortified milk and incubating with rennet for 1h at 32 °C. The clot formed was cut, centrifuged at 2,600 × g for 30 min at 20 °C and drained for determining cheese yield. Cheese-yielding capacity was expressed as actual yield (grams of cheese curd per 100g of milk) and dry weight yield (grams of dried cheese curd per 100g of milk). Free-zone capillary electrophoresis was used for determining ß-LG A or B recovery in the curd during rennet-induced coagulation. The presence of ß-LG variant B resulted in a significantly higher actual and dried weight cheese yield than when A or A-B were present at levels ≤ 0.675% of whey protein (WP) addition. Results of free-zone capillary electrophoresis allowed us to infer that ß-LG B associates with the casein micelles during renneting, as shown by an increase in the recovery of this variant in the curd when ß-LG B was added up to a maximum at 0.45% (equivalent to 0.675% WP). In general, actual or dried weight cheese yield increased as WP addition was increased from 0.225 to 0.675%. However, when WP addition ranged from 0.675 to 0.90%, a drastic drop in cheese yield was observed. This behavior may be because an increase in the aggregation of casein micelles with a concomitant inclusion of whey protein in the gel occurs at low levels of WP addition, whereas once the association of WP with the casein micelles reach a saturation point at addition levels higher than 0.675%, rearrangements of the gel network result in larger whey expulsion and syneresis. This knowledge is expected to be useful to maximize cheese yield and optimize processing conditions during cheese and cheese analogs manufacturing.

Composition, yield, and functionality of reduced-fat Oaxaca cheese: effects of using skim milk or a dry milk protein concentrate.

The effect of adding either skim milk or a commercial dry milk protein concentrate (MPC) to whole milk on the composition, yield, and functional properties of Mexican Oaxaca cheese were investigated. Five batches of Oaxaca cheeses were produced. One batch (the control) was produced from whole milk containing 3.5% fat and 9% nonfat solids (SNF). Two batches were produced from milk standardized with skim milk to 2.7 and 1.8% fat, maintaining the SNF content at 9%. In the other 2 batches, an MPC (40% protein content) was used to standardize the milk to a SNF content of 10 and 11%, maintaining the milk fat content at 3.5%. The use of either skim milk or MPC caused a significant decrease in the fat percentage in cheese. The use of skim milk or MPC showed a nonsignificant tendency to lower total solids and fat recoveries in cheese. Actual, dry matter, and moisture-adjusted cheese yields significantly decreased with skim milk addition, but increased with MPC addition. However, normalized yields adjusted to milk fat and protein reference levels did not show significant differences between treatments. Considering skim milk-added and control cheeses, actual yield increased with cheese milk fat content at a rate of 1.34 kg/kg of fat (R=0.88). In addition, cheese milk fat and SNF:fat ratio proved to be strong individual predictors of cheese moisture-adjusted yield (r(2) ≈ 0.90). Taking into account the results obtained from control and MPC-added cheeses, a 2.0-kg cheese yield increase rate per kg of milk MPC protein was observed (R=0.89), with TS and SNF being the strongest predictors for moisture adjusted yield (r(2) ≈ 0.77). Reduced-fat Oaxaca cheese functionality differed from that of controls. In unmelted reduced-fat cheeses, hardness and springiness increased. In melted reduced-fat cheeses, meltability and free oil increased, but stretchability decreased. These changes were related to differences in cheese composition, mainly fat in dry matter and calcium in SNF.

Effect of beta-lactoglobulin A and B whey protein variants on the rennet-induced gelation of skim milk gels in a model reconstituted skim milk system.

The effect of fortifying reconstituted skim milk with increasing levels of the beta-lactoglobulin (beta-LG) genetic variants A, B, and an A-B mixture on rennet-induced gelation was studied by small deformation-sensitive rheology. Free-zone capillary electrophoresis and high-sensitivity oscillatory rheology were used to elucidate the role of potential heterotypic associative interactions between whey proteins and casein in a mixed colloidal system, subjected to moderate heating (65 degrees C for 30 min) prior to renneting, on the gelling properties of the system. Increasing levels of added whey protein, in the concentration range of 0.225 to 1.35% of added protein, led to a concomitant progressive increase in the equilibrium shear storage modulus, G' (recorded after approximately 10,800 s), in the order beta-LG B > beta-LG A and beta-LG A-B, as the general expected consequence of the setup of denser casein gel networks. The preferential effect of beta-LG B over beta-LG A on the mechanical strength of the gels may be due to the formation of cross-links and aggregates involving whey proteins and rennet hydrolysis products or an increase in the size of the casein micelle caused by the grafting of beta-LG B to its surface, or both. The results of free-zone capillary electrophoresis were consistent with the notion that beta-LG B (and not beta-LG A) binds to the casein micelle under an optimal stoichiometry of 1:0.045 (mg/mg), even in the absence of heat treatment. The liquid-like character of the gel networks formed, tan delta, was a parameter sensitive to the level of addition of beta-LG A in particular. At low concentrations (up to 0.45%) of beta-LG A, tan delta increased by almost twice as much, which was interpreted as a result of the increase in the loss modulus, G'', of the sol fraction because of the presence of unbound beta-LG A. At greater incremental concentrations of beta-LG (>0.45%), the formation of smaller whey protein aggregates confined to the sol fraction may have led to a progressive decrease in tan delta. The critical gel time, t(gel), was also affected by the concentration of added whey protein and described 3 zones of behavior, irrespective of the type of whey protein variant. The critical gel time was slightly shorter for beta-LG B than for beta-LG A at 0.45% of added whey protein, but this difference became larger at 0.67%. Even when only beta-LG B was found to associate with casein prior to renneting, both beta-LG A and beta-LG B, either alone or mixed, had a profound influence on the mechanical strength and coagulation kinetics of the rennet-induced casein gels. This knowledge is expected to be useful to exert better control and optimize processing conditions during the manufacturing of cheese and cheese analogs.