ABSTRACT
The effect of pH in the range 6.0-8.0 on the denaturation and aggregation of beta-lactoglobulin (beta-lg) was investigated. Results were interpreted in terms of the reaction scheme for the denaturation and aggregation of beta-lg proposed by Roefs and De Kruif (Eur. J. Biochem. 1994, 226, 883-889). The rate of conversion of native beta-lg increased strongly at higher pH values, whereas the molecular mass of the aggregates decreased strongly. In the pH range 6.4-8.0 aggregates were formed mainly by intermolecular disulfide bonds, but even at pH 6.0, thiol/disulfide exchange reactions were involved, although to a lesser extent. The time course of the exposure of the thiol group in native beta-lg upon heating and the subsequent disappearance of this group through the formation of disulfide-linked aggregates was investigated by reaction with 5,5'-dithiobis(2-nitrobenzoic acid) and varied strongly with pH. These observations could be used, in combination with the reaction steps of the reaction scheme, to describe qualitatively the strongly pH-dependent isothermal calorimetry curves, measured at 65 degrees C.
Subject(s)
Lactoglobulins/chemistry , Animals , Calorimetry , Cattle , Hot Temperature , Hydrogen-Ion Concentration , Protein Denaturation , ThermodynamicsABSTRACT
We give a quantitative treatment of the destabilization of three types of milk protein dispersions. For this we consider the proteins as adhesive-hard-sphere bio-colloids. If the attractive interactions become strong enough the system passes the percolation threshold and gels. Macroscopic properties of these gels are studied by measuring viscoelasticity and permeability coefficients. These coefficients are related to structural (fractal) properties of the gels which were measured using scattering and confocal scanning laser microscopy (CLSM) techniques. The behaviour of the protein gels can be understood on a qualitative level.
Subject(s)
Gels/chemistry , Milk Proteins/chemistry , Milk/chemistry , Animals , Chemical Phenomena , Chemistry, PhysicalABSTRACT
BACKGROUND: The purpose of this study was to determine if the Healthier People Health Risk Appraisal and the RiskPlan Report, two different methods for measuring health risks of an employee population, produce the same estimates of health risk prevalence. METHODS: The prevalence of each of seven risk factors, directly measured by the Healthier People Health Risk Appraisal and predicted by the RiskPlan Report using demographic and normative data, were compared for a group of 239 employees participating in a voluntary health screening. Further, the 239 participants and 426 nonparticipants were compared with respect to demographic factors gleaned from personnel records, and risk factor prevalence derived from the RiskPlan Report. RESULTS: Significant differences were found in the prevalence of six of the seven risk factors measured by the Healthier People Health Risk Appraisal and predicted by the RiskPlan Report. Also, risk factor prevalence predicted by the RiskPlan Report was not significantly different in the participants and nonparticipants although three critical sociodemographic variables were significantly different. DISCUSSION: The results suggest that the prevalence of health risks based on normative data and the demographic profile of a population are not similar to those directly measured, and some doubt is raised about predicting health risks based on these data.
