The effect of ultrasound on casein micelle integrity.

Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20 kHz to investigate the effect of ultrasonication. For fresh skim milk, the average size of the remaining fat globules was reduced by approximately 10 nm after 60 min of sonication; however, the size of the casein micelles was determined to be unchanged. A small increase in soluble whey protein and a corresponding decrease in viscosity also occurred within the first few minutes of sonication, which could be attributed to the breakup of casein-whey protein aggregates. No measurable changes in free casein content could be detected in ultracentrifuged skim milk samples sonicated for up to 60 min. A small, temporary decrease in pH resulted from sonication; however, no measurable change in soluble calcium concentration was observed. Therefore, casein micelles in fresh skim milk were stable during the exposure to ultrasonication. Similar results were obtained for reconstituted micellar casein, whereas larger viscosity changes were observed as whey protein content was increased. Controlled application of ultrasound can be usefully applied to reverse process-induced protein aggregation without affecting the native state of casein micelles.

Hot topic: sonication increases the heat stability of whey proteins.

The thickening or gelling of protein-based dairy streams and ingredients upon exposure to heat has been an ongoing problem in dairy processing for many decades. This phenomenon can restrict the range of dairy product options and reduce manufacturing efficiencies by limiting the type and extent of heat treatment that can be used. In this report, we outline a novel approach to overcoming this problem. The use of preheating treatments to induce whey protein aggregate formation in whey products is well known in the field. However, we show that the application of ultrasound for a very short duration after such a heating step breaks down these aggregates and prevents their reformation on subsequent heating, thereby reducing the viscosity increase that is usually associated with this process. This novel technique has the potential to provide significant economic benefit to the dairy manufacturing industry.

Solubility of Calcium Phosphate in Concentrated Dairy Effluent Brines.

The solubility of calcium phosphate in concentrated dairy brine streams is important in understanding mineral scaling on equipment, such as membrane modules, evaporators, and heat exchangers, and in brine pond operation. In this study, the solubility of calcium phosphate has been assessed in the presence of up to 300 g/L sodium chloride as well as lactose, organic acids, and anions at 10, 30, and 50 °C. As a neutral molecule, lactose has a marginal but still detectable effect upon calcium solubility. However, additions of sodium chloride up to 100 g/L result in a much greater increase in calcium solubility. Beyond this point, the concentrations of ions in the solution decrease significantly. These changes in calcium solubility can readily be explained through changes in the activity coefficients. There is little difference in calcium phosphate speciation between 10 and 30 °C. However, at 50 °C, the ratio of calcium to phosphate in the solution is lower than at the other temperatures and varies less with ionic strength. While the addition of sodium lactate has less effect upon calcium solubility than sodium citrate, it still has a greater effect than sodium chloride at an equivalent ionic strength. Conversely, when these organic anions are present in the solution in the acid form, the effect of pH dominates and results in much higher solubility and a calcium/phosphate ratio close to one, indicative of dicalcium phosphate dihydrate as the dominant solid phase.

Crystallisation of minerals from concentrated saline dairy effluent.

An understanding of crystallisation within saline effluents is important for the design of both brine crystallisers and brine disposal ponds. In this work, crystallisation of a saline effluent concentrate from the Australian dairy industry has been examined at 22 wt% and 30 wt% total solids and at temperatures between 10 and 70 °C. The precipitation occurs more rapidly at higher temperatures. This trend is dictated by precipitation of calcium phosphate salts, albeit the major constituents of the mixture are NaCl and lactose. The crystallisation induction time can be shortened by introducing cavitation induced by ultrasound. In particular, the use of two short acoustic pulses between 3.7 J/g and 16 J/g at 20 kHz spaced ten minutes apart has maximum impact upon both induction time and crystal size. It is believed that the first ultrasound pulse either generates new nuclei or enhances the mass transfer of solute toward the surface of sub-micron growing crystals. Conversely, the second pulse disrupts the growing crystals and forms secondary nuclei. The ultrasound cannot shift the solution equilibrium and so is not able to improve the low crystal yield. To increase this total yield, further evaporation is necessary. The work provides direction to personnel in the dairy industry of the feasibility of brine crystallisation with respect to energy demand and solid recovery.

Low-fat mozzarella as influenced by microbial exopolysaccharides, preacidification, and whey protein concentrate.

Low-fat Mozzarella cheeses containing 6% fat were made by preacidification of milk, preacidification combined with exopolysaccharide- (EPS-) producing starter, used independently or as a coculture with non-EPS starter, and preacidification combined with whey protein concentrate (WPC) and EPS. The impact of these treatments on moisture retention, changes in texture profile analysis, cheese melt, stretch, and on pizza bake performance were investigated over 45 d of storage at 4 degrees C. Preacidified cheeses without EPS (control) had the lowest moisture content (53.75%). These cheeses were hardest and exhibited greatest springiness and chewiness. The meltability and stretchability of these cheeses increased most during the first 28 d of storage. The moisture content in cheeses increased to 55.08, 54.79, and 55.82% with EPS starter (containing 41.18 mg/g of EPS), coculturing (containing 28.61 mg/g of EPS), and WPC (containing 44.23 mg/g of EPS), respectively. Exopolysaccharide reduced hardness, springiness, and chewiness of low-fat cheeses made with preacidified milk in general and such cheeses exhibited an increase in cohesiveness and meltability. Although stretch distance was similar in all cheeses, those containing EPS were softer than the control. Cocultured cheeses exhibited the greatest meltability. Cheeses containing WPC were softest in general; however, hardness remained unchanged over 45 d. Cheeses made with WPC had the least increase in meltability over time. Incorporation of WPC did not reduce surface scorching or increase shred fusion of cheese shreds during pizza baking; however, there was an improvement in these properties between d 7 and 45. Coating of the cheese shreds with oil was necessary for adequate browning, melt, and flow characteristics in all cheese types.

Effects of pH, temperature, supplementation with whey protein concentrate, and adjunct cultures on the production of exopolysaccharides by Streptococcus thermophilus 1275.

Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS culture on the exopolysaccharide (EPS) production by Streptococcus thermophilus 1275 were studied. The organism was grown in 10% reconstituted skim milk (RSM) in a Biostat B fermenter for 24 h at various pH (4.5, 5.5 and 6.5) and temperatures (30, 37, 40, and 42 degrees C), and supplementation with WPC 392, and non-EPS producing S. thermophilus 1303 and the amount of EPS produced were determined. Bacterial counts were enumerated and the concentrations of lactic acid, lactose, glucose, and galactose were also determined. A maximum of 406 mg/L of EPS was produced in RSM at 37 degrees C after 24 h of fermentation at pH 4.08 when the pH was not controlled. A pH of 5.5 and temperature of 40 degrees C were found to be optimal for EPS production by S. thermophilus 1275, yielding 458 mg/L. The EPS production increased when RSM was supplemented with WPC 392. At optimum pH and at 37 degrees C with WPC supplementation, the level of EPS increased to 1029 mg/L. Co-culturing S. thermophilus 1275 with non-EPS S. thermophilus 1303 increased EPS production at 37 degrees C and pH 5.5 to 832 mg/L. High temperature (42 degrees C) reduced the amount of EPS production, and EPS production ceased at pH 4.5 when maintained constantly at this pH. The level of lactose utilization and lactic acid production depended on growth conditions of the organism. No glucose was detected, while galactose was found to accumulate in the medium.