Functional Characteristics of Milk Protein Concentrates and Their Modification.

A major deterrent to the usage of milk protein concentrate (MPC), a high-protein milk product with increasing demand as a food and sports drink ingredient, has been its poor functional characteristics when compared with other milk protein products such as whey protein concentrate and sodium caseinates. This review discusses the recent research on functional properties of MPC, focusing on factors that may contribute to the poor functional characteristics before, during, and after production. Current research, methods employed, and new understanding on the causes of poor solubility of MPC at mild temperatures (about 20°C) has been presented, including loss of solubility during storage as these areas have received unprecedented attention over the past decade, and also affects other useful functional properties of MPC, such as emulsifying properties, gelation, and foaming. Processing methods, which include heat treatment, high-pressure application, microwave heating, ultrasound application, and enzyme and salts modification, have been used or have potential to modify or improve the functional properties of MPCs. Future research on the effects of these processing methods on the functional properties, including effects of enzyme hydrolysis on bitterness and bioactivity, has also been discussed.

Effect of ultrasound pretreatment on rennet-induced coagulation properties of goat's milk.

The effects of ultrasound (US) pretreatment on goat milk before rennet-induced coagulation were studied in order to improve the milk coagulation properties. Skimmed goat milk was subjected to US at 800 W for different times (0-20 min) and various parameters were evaluated. The particle sizes in US pretreated goat milk under the transmission electron microscopy were smaller than in untreated samples. For US pretreated samples, the degree of whey protein denaturation, contents of soluble calcium and phosphorus increased by 9.57%, 16.90% and 13.68%, respectively. The gel firmness, coagulum strength, final storage modulus, cohesiveness, water holding capacity and cross-linking of gels demonstrated marked increase. The turbiscan stability index (TSI) also confirmed the improvement of goat milk coagulation properties with increasing duration of US pretreatment, whereas the gelation time was prolonged.

Effect of power ultrasound pretreatment on peptidic profiles and angiotensin converting enzyme inhibition of milk protein concentrate hydrolysates.

BACKGROUND: The use of power ultrasound as a pretreatment to enhance the hydrolysis of milk protein concentrate (MPC) and subsequent angiotensin converting enzyme (ACE) inhibitory activity has been studied. Liquid chromatography was used to analyse peptide profiles of Neutrase-derived MPC hydrolysates after pretreatment at 0, 1, 3, 5 and 8 min at an ultrasound power level of 800 W. RESULTS: The peptide profiles indicated an increase in number of peptides when ultrasound pretreatment was applied. There was also an increase in the degree of hydrolysis of MPC hydrolysates. The profiles indicated that new small peptides in ultrasound pretreated samples (1-5 min) which were not present in the control samples and 8 min pretreated samples, could be responsible for increased ACE inhibitory activity. These small peptides were digested in the 8 min pretreated samples. CONCLUSION: Ultrasound pretreatment of MPC increases the ACE inhibitory activity of the hydrolysates because of the production of new small peptides. This can be used as a means to derive potent ACE inhibitory peptides at industrial scale in complex protein sources.

Purification and characterization of chromium-binding substances from high-chromium yeast.

As a highly efficient and easily absorbable source of chromium, the identities of the chromium-binding substances in yeast remain unclear. In this study, a mild extraction procedure involving extraction with ammonia, three-gel filtration, and high-performance liquid chromatography was adopted to obtain two chromium-binding substances from high-chromium yeast. A low-molecular-weight chromium-binding substance was identified, with mass-to-charge ratios (m/z) of 769 and 712, which included glutamic acid, glycine, and cysteine in an approximate ratio of 1:1:1, as well as nicotinic acid and chromium(III). Furthermore, it significantly potentiated (by 51%) the action of insulin to stimulate the conversion of (14)C-glucose into lipid in adipocytes. A novel high-molecular-weight chromium-binding substance was also isolated: electrospray ionization tandem mass spectrometry tentatively identified it as HUB1 target protein-1, glyceraldehyde-3-phosphate dehydrogenase, or ribosomal protein L2A(L5A)(rp8)(YL6). This is the first report of a high-molecular-weight chromium-binding substance in yeast and merits further studies.