Heat-induced whey protein gels: protein-protein interactions and functional properties.

Heat-induced gelation (80 degrees C for 30 min or 85 degrees C for 60 min) of whey protein concentrate (WPC) solutions was studied using small deformation dynamic rheology, small and large deformation compression, and polyacrylamide gel electrophoresis (PAGE). The WPC solutions (15% w/w, pH 6.9) were prepared by dispersing WPC powder in water (control), 1% (w/w) sodium dodecyl sulfate (SDS) solution, and N-ethylmaleimide (NEM) solution at a protein/NEM molar ratio of 1:1 or in 10 mM dithiothreitol (DTT) solution.

Altered specificity of lactococcal proteinase p(i) (lactocepin I) in humectant systems reflecting the water activity and salt content of cheddar cheese.

By using various humectant systems, the specificity of hydrolysis of alpha(s1)-, beta-, and kappa-caseins by the cell envelope-associated proteinase (lactocepin; EC 3.4.21.

Serine metabolism in Lactobacillus plantarum.

This study investigated the metabolism of (L-) serine by Lactobacillus plantarum B3089 isolated from cheese. Serine was deaminated by growing cells to ammonia with the corresponding formation of acetate and formate. Serine was also deaminated by non-growing cells to ammonia but with the formation of acetate only (no production of formate).

Practical implications of lactate and pyruvate metabolism by lactic acid bacteria in food and beverage fermentations.

This article reviews the metabolism of pyruvate and lactate by lactic acid bacteria (LAB) involved in food and beverage fermentations with an emphasis on practical implications. First, the formation of pyruvate and lactate from a range of substrates, including carbohydrates, organic acids and amino acids, is briefly described. The catabolism of pyruvate and lactate by LAB is then reviewed.

Milk and dairy products in the 21st century. Prepared for the 50th anniversary of the journal of agricultural and food chemistry.

Dairying into the 21st century will largely continue with the trends seen in the past few decades, although there is always the possibility of an unlikely but disruptive event. The politics of globalization will potentially be important in freeing up global trade in dairy products. Production on the farm will become increasingly efficient, resulting in continuing price benefits to the consumer.

The resistance to heat of thermo-resistant streptococci attached to stainless steel in the presence of milk.

Skim milk residues had a significant impact on the sensitivity to heat of a dairy isolate of the thermo-resistant, Streptococcus thermophilus. Cells of S. thermophilus (H) suspended in water or in milk had D values at 60 degrees C of 2.

Structural features of bovine caseinomacropeptide A and B by 1H nuclear magnetic resonance spectroscopy.

Samples of bovine caseinomacropeptide (CMP) were isolated from kappa-casein A and kappa-casein B and fractionated to give aglycosylated CMP A and CMP B and monoglycosylated CMP A. The secondary structures of these three peptides were compared under neutral and acidic (pH 4.2) conditions, using two-dimensional (2D) 1H nuclear magnetic resonance (NMR) spectroscopy.

Functional grouping of thermophilic Bacillus strains using amplification profiles of the 16S-23S internal spacer region.

Molecular and biochemical assays were used to determine the identification of thermophilic bacilli isolated from New Zealand milk powder. One hundred and forty one isolates of thermophilic bacilli were classified into six species using biochemical profiles. Geobacillus stearothermophilus represented 56% of the isolates.

Aqueous two-phase extraction and purification of animal proteins.

Aqueous two-phase systems provide a rapid, easily scalable method for separation of soluble proteins from insoluble materials and other undesired proteins. The method can be operated in continuous mode. It is particularly useful for animal proteins, as it overcomes difficulties of other methods in removing bulk insoluble material, while at the same time providing purification with respect to total soluble protein.

Heat-induced destabilization of oil-in-water emulsions formed from hydrolyzed whey protein.

The emulsifying ability, heat stability, and coalescence stability of oil-in-water emulsions prepared with whey protein of varied degrees of hydrolysis (DH), and at varied protein contents, was studied. Whey protein hydrolysates (WPH) with a DH of 4% and 10% had poorer emulsifying ability than non-hydrolyzed whey protein concentrate (WPC), but were more heat stable. Increasing DH between 10 and 27% improved emulsifying ability and further improved the heat stability of the emulsion droplets.

Determination of fat in dairy products using pressurized solvent extraction.

Gravimetric fat data were obtained for a wide range of dairy products with fat contents ranging from 0.5 to 83% using pressurized solvent extraction at elevated temperatures and pressure (80-120 degrees C; 10.3 MPa).

Aroma compounds of fresh milk from New Zealand cows fed different diets.

Volatile compounds were extracted from fresh milk produced by New Zealand cows using the newly developed solvent-assisted flavor evaporation (SAFE) technique. The two samples that were used came from cows that had been fed on different diets and represented the considerably different flavors of Northern hemisphere and New Zealand milk. Using gas chromatography-olfactometry (GC-O), 71 aroma compounds were found from the milk extracts, 66 of which were identified.

Effect of turbulent-flow pasteurization on survival of Mycobacterium avium subsp. paratuberculosis added to raw milk.

A pilot-scale pasteurizer operating under validated turbulent flow (Reynolds number, 11,050) was used to study the heat sensitivity of Mycobacterium avium subsp. paratuberculosis added to raw milk. The ATCC 19698 type strain, ATCC 43015 (Linda, human isolate), and three bovine isolates were heated in raw whole milk for 15 s at 63, 66, 69, and 72 degrees C in duplicate trials.

In vitro adherence properties of Lactobacillus rhamnosus DR20 and Bifidobacterium lactis DR10 strains and their antagonistic activity against an enterotoxigenic Escherichia coli.

Adhesion and colonisation properties of three probiotic strains namely, Lactobacillus rhamnosus DR20, L. acidophilus HN017, and Bifidobacterium lactis DR10, were determined in vitro using the differentiated human intestinal cell-lines including HT-29, Caco-2, and HT29-MTX, and compared with properties of L. acidophilus LA-1 and L.

Streptococcus thermophilus in cheddar cheese--production and fate of galactose.

The behaviour of Streptococcus thermophilus in combination with Lactococcus lactis subsp. cremoris or subsp. lactis mesophilic starters in experimental Cheddar cheese is reported.

Peptides affecting coagulation.

Based on amino acid sequence similarities that exist between the fibrinogen gamma-chain and kappa-casein, and also functional similarities between milk and blood coagulation, considerable effort has been made to investigate the effects of milk proteins and peptides on platelet function and thrombosis. In particular, a number of peptides derived from the glycomacropeptide segment of kappa-casein, have been shown to inhibit platelet aggregation and thrombosis. KRDS, a peptide from lactoferrin has also been shown to inhibit platelet aggregation but to a lesser extent than its fibrinogen analogue RGDS.

Oligosaccharides and glycoconjugates in bovine milk and colostrum.

Oligosaccharides and glycoconjugates are some of the most important bioactive components in milk. A great deal of information is available on the biological function of the components from human milk. Their primary role seems to be in providing protection against pathogens by acting as competitive inhibitors for the binding sites on the epithelial surfaces of the intestine.

Rapid detection of Bacillus stearothermophilus using impedance-splitting.

An impedance splitting method was used to detect Bacillus stearothermophilus in suspension and attached to stainless steel surfaces. The effects of bacterial metabolism on the impedance of the culture medium and the ionic layers of the measuring electrodes were recorded using the BacTrac 4000 microorganism growth analyser. Impedance changes were measured at 55 degrees C.

The growth of Bacillus stearothermophilus on stainless steel.

Aims: To determine the potential for Bacillus stearothermophilus cells to form biofilms of significance in dairy manufacture.

Methods And Results: The ability of isolates of B. stearothermophilus from dairy manufacturing plants to attach to stainless steel surfaces was demonstrated by exposing stainless steel samples to suspensions of spores or vegetative cells and determining the numbers attaching using impedance microbiology.

Destabilization of Oil-in-Water Emulsions Formed Using Highly Hydrolyzed Whey Proteins.

Oil-in-water emulsions (4 wt % soy oil) were prepared with 0.5-5 wt % whey protein hydrolysate (WPH) (27% degree of hydrolysis), in a two-stage homogenizer using various first-stage pressures of 10.3, 20.

Effect of milk concentration on the irreversible thermal denaturation and disulfide aggregation of beta-lactoglobulin.

The kinetics of beta-lactoglobulin (beta-LG) denaturation in reconstituted skim milk samples of various concentrations (9.6-38.4% total solids) over a wide temperature range (75-100 degrees C) was studied.

The influence of recipe modification and nutritional information on restaurant food acceptance and macronutrient intakes.

Objective: To examine the influences of nutritional information and consumer characteristics on meal quality expectations, food selection and subsequent macronutrient intakes of consumers offered a reduced-fat option in a restaurant.

Design: A target, full-fat (FF) main restaurant meal option was developed in a version substantially reduced in fat and energy (RF). Restaurant patrons were randomly placed into one of four treatment groups varying in provision of menu information about the target dish, and the actual version of that dish served (if ordered).