Freezing of Aqueous Solutions of Glycosylated Bovine Beta-Casein

摘要

Genetic engineering of milk proteins allows control of their physicochemical properties in foods and dairy products during processing, storage, and consumption. Robust methods for the estimation of the quality and function of the proteins during downstream processing are sought. The foucus of this study is a systematic microscopic investigation of the freezing of submicroliter pendent droplets of buffer solution of glycosylated bovine beta-casein. The freezing and crystallization is observed with a sacnning confocal microscope fitted with a stage cooled with vapor boiled off a liquid nitrogen dewar Four liquid samples (with glycosylated bovine beta-casein concenrations of 35, 125, 500, and 1000 #mu# g/ml)are compared against the control (10 mg/ml of wild type non-glycosylated bovine beta-casein). The freezing of similar size samples consisting of de-ionized water, ice-nucleating mixture (Pseudomonas syringae), and pure buffer solution is also examined for comparison. Higher concentrations of the engineered-beta casein result in increasing antifreeze action, corresponding to depression of the freezing point, and thermal stabilization of the supercooled liquid. This conclusion is supported by a non-parametric statistical analysis based on the Jonckheere test. A freezing point assay can thus be made to assess the quality of glyco-bovine beta-casein.