The effect of buttermilk or buttermilk powder addition on functionality, textural, sensory and volatile characteristics of Cheddar-style cheese.

The influence of buttermilk or buttermilk powder addition to cheese milk or cheese curds respectively on cheese functional properties, free fatty acid profiles and subsequent volatile and sensory characteristics was investigated. Buttermilk addition to cheese milk resulted in a softer cheese compared to other cheeses, with a significantly reduced flowability, while buttermilk powder addition had no influence on cheese firmness but cheese flowability was also reduced compared to the control cheese. Larger pools of free fat, higher levels of free fatty acids, volatile compounds and significant differences in sensory profiles associated with off-flavour were also observed with the addition of buttermilk to cheese milk. Application of light microscopy, using toluidine blue stain, facilitated the visualisation of fat globule structure and distribution within the protein matrix. Addition of 10% buttermilk powder resulted in significant increases in volatile compounds originating from proteolysis pathways associated with roasted, green aromas. Descriptive sensory evaluation indicated few differences between the 10% buttermilk powder and the control cheese, while buttermilk cheeses scored negatively for sweaty, barnyard aromas, oxidized and off flavors, correlating with associated volatile aromas. Addition of 10% buttermilk powder to cheese curds results in cheese comparable to the control Cheddar with some variations in volatile compounds resulting in a cheese with similar structural and sensory characteristics albeit with subtle differences in overall cheese flavor. This could be manipulated to produce cheeses of desirable quality, with potential health benefits due to increased phospholipid levels in cheese.

Redefining the effect of salt on thermophilic starter cell viability, culturability and metabolic activity in cheese.

This study investigated the differential effect of salt concentration in the outside and inside layers of brine salted cheeses on viability, culturability and enzyme activity of starter bacteria. The high-salt environment of the outside layer caused a sharp decrease in L. helveticus viability as measured by traditional plate counts. Remarkably, this was associated with lower release of intracellular enzymes (LDH), reduced levels of proteolysis and larger membrane integrity as measured by flow cytometry (FC) following classical Live/Dead staining. FC analysis of light scattering properties highlighted a significant reduction in size and granularity of the microbiota located in the cheese surface, suggestive of cell shrinkage and condensation of internal macromolecules probably due to hyperosmotic stress. The microbiota of the cheese surface were found to experience greater oxidative stress, as measured by FC analysis of the total levels of reactive oxygen species, compared to that of the interior layer. These results lead us to postulate that the physiology and health status of the microbiota were significantly different in the outer and inner layers of the cheese. The hyperosmotic environment of the outer layer resulted in reduced cell lysis, as measurable by assays based upon membrane integrity, but rather triggered cell death via mechanisms involving cell shrinkage and ROS-mediated damage of vital intracellular components. This study challenges the current thinking on how salt controls microbial activity in ripening cheese, especially in cheeses which are brine salted as local variations in biochemical ripening indices can differ significantly from the outside to the inside of a ripening cheese.

Influence of buttermilk powder or buttermilk addition on phospholipid content, chemical and bio-chemical composition and bacterial viability in Cheddar style-cheese.

The effect of buttermilk powder addition post-curd formation or buttermilk addition to cheese milk on total and individual phospholipid content, chemical composition, enzyme activity, microbial populations and microstructure within Cheddar-style cheese was investigated. Buttermilk or buttermilk powder addition resulted in significant increases in total phospholipid content and their distribution throughout the cheese matrix. Addition of 10% buttermilk powder resulted in higher phospholipid content, moisture, pH and salt in moisture levels, and lower fat, fat in dry matter, L. helveticus and non-starter bacteria levels in cheeses. Buttermilk powder inclusion resulted in lower pH4.6/Soluble Nitrogen (SN) levels and significantly lower free amino acid levels in 10% buttermilk powder cheeses. Buttermilk addition provided a more porous cheese microstructure with greater fat globule coalescence and increased free fat pools, while also increasing moisture and decreasing protein, fat and pH levels. Addition of buttermilk in liquid or powdered form offers potential for new cheeses with associated health benefits.

The role of 1,25-dihydroxyvitamin D in the mechanism of acquired vitamin D deficiency.

OBJECTIVE: We wished to assess the effect of changes in the plasma concentration of 1,25-dihydroxyvitamin D on the plasma elimination half-time for 25-hydroxyvitamin D in man. DESIGN: The turnover of 25-hydroxyvitamin D in plasma was investigated after intravenous doses of the radioactively labelled metabolite had been given to a group of patients (n = 17) with disorders of bone and mineral metabolism before and after oral treatment with calcium or 1,25-dihydroxyvitamin D. PATIENTS: Seven patients with post-menopausal osteoporosis, five with hypoparathyroidism, three with hypophosphataemic osteomalacia, one with renal osteodystrophy and one patient with coeliac disease were studied. MEASUREMENTS: Intravenous injections of 3H-labelled 25-hydroxyvitamin D were given and plasma elimination half-time assessed over periods of 4-14 days during which frequent measurements of plasma calcium, phosphate, parathyroid hormone, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were made. Changes in the plasma elimination half-time for 3H-25-hydroxyvitamin D before and after treatment with calcium and 1,25-dihydroxyvitamin D were evaluated by non-parametric statistical analysis. RESULTS: The elimination half-time for 3H-25-hydroxyvitamin D in plasma was significantly shortened by raising the circulating concentration of 1,25-dihydroxyvitamin D. Conversely, in a patient with intestinal malabsorption of calcium, the metabolic clearance of 3H-25-hydroxyvitamin D was prolonged when the concentration of 1,25-dihydroxyvitamin D in plasma was decreased by suppressing secondary hyperparathyroidism with large calcium supplements. In the longer-term studies (n = 10) there was a highly significant inverse relation (r = -0.88, P < 0.001) between the change in the plasma concentration of 1,25-dihydroxyvitamin D and the induced change in the elimination half-time of 3H-25-hydroxyvitamin D. There was also a significant correlation (r = 0.66, p < 0.0025) between the observed fall in the plasma concentration of unlabelled 25-hydroxyvitamin D and the predicted fall calculated from the measured value for the half-time of the 3H-labelled metabolite. In acute studies in patients with post-menopausal osteoporosis (n = 7), enhanced metabolic inactivation of 3H-25-hydroxyvitamin D was detectable within 24 hours of oral administration of 1,25-dihydroxyvitamin D. CONCLUSIONS: The effect of 1,25-dihydroxyvitamin D on the catabolism of 25-hydroxyvitamin D can contribute to the development of vitamin D deficiency in many clinical disorders. When the natural supply of vitamin D is limited by sunlight deprivation, a sustained increase in the plasma concentration of 1,25-dihydroxyvitamin D due to primary or secondary hyperparathyroidism will lead to accelerated depletion of vitamin D stores.