Protein hydrolysis using immobilized proteases may present problems, which are mainly caused by the diffusion of macromolecular substrate. Pre-hydrolysed substrate could be a viable alternative in this process. The aim of this work was to test the casein and β-lactoglobulin hydrolysis using immobilized papain on glyoxyl-agarose, following substrate pre-treatment with immobilized trypsin. Although immobilized papain showed difficulties to degrade the milk proteins, after 10 min of trypsin pre-hydrolysis, the immobilized papain was able to achieve the maximum degree of hydrolysis in shorter time. For pre-hydrolysate casein, the immobilized papain reached 98.9% at 60 min total reaction (including the 10 min pre-digestion). As for β-lactoglobulin, immobilized papain was capable of achieving maximum levels after just 60 min of reaction, where the free enzyme only achieved 60% of its maximum. Pre-hydrolysis with trypsin appears to have worked well as a pre-treatment method to increase the proteolytic action of immobilized papain.
The thermal denaturation of β-lactoglobulin in the presence of urea and alkylurea solutions were measured. In the presence
of a high concentration of urea this protein shows not only heat but also cold denaturation. For studying the effect of temperature
two methods were used, differential scanning calorimetry (DSC) and UV-spectroscopy. DSC provides direct model-independent
determination of the transition enthalpy in comparison with UV-spectroscopy, which gives only apparent or van't Hoff enthalpy
of transition. The UV-melting curves were analyzed on the basis of a two-state approximation. The apparent standard enthalpies
of thermal denaturation, ΔHapp.o
, were compared with calorimetric ones.
Authors:Agata Górska, Ewa Ostrowska-Ligęza, Karolina Szulc, and Magdalena Wirkowska
β-Lactoglobulin (β-LG) is a major whey protein possessing nutritional value as well as functional characteristics [ 1 , 2 ]. Due to its amino-acid sequence and 3-dimensional structure, β-LG has been reported
The thermal properties of Β-lactoglobulin (Β-LG) were studied by differential scanning calorimetry (DSC) under different medium conditions.pH, neutral salts, protein perturbants, and polyols all affected the DSC characteristics of Β-LG. Acylation with fatty acids also changed the thermal properties, particularly peak width at half-height. The results suggest that the structural stability of Β-LG is controlled by non-covalent forces, particularly electrostatic and hydrophobic interactions. Disulfide bonds did not contribute to the thermal response of Β-LG. Fatty N-acyl-amino acids caused marked increases in thermal stability and decreases in denaturation enthalpy, and additional peaks were observed in the presence of some palmitoyl derivatives.
The thermal behavior ofΒ-lactoglobulin (Β-lg) disperesed in distilled water (pH=3.2) is studied dy differential scanning calorimetry (DSC) in the temperature range 20‡C–120‡C and within a concentration region of 3.5% to 24%.
Authors:S. Jovanović, M. Barać, O. Maćej, and J. Denin Djurdjević
Changes that occur in milk proteins during heat treatment were studied. Milk was heat treated at 87 °C for 10 min. Samples of untreated milk, demineralised whey powder and heat treated milk were analysed by discontinuous PAGE and by densitometric analysis of destained gels. PAGE experiments showed that heat treatment induces changes on milk proteins. During heating at 87 °C for 10 min all amount of β -lactoglobulin present in milk interacted with casein, while small amount of α -lactalbumin did not interact with casein. It could be hypothesised that heating of milk at 87 °C for 10 min influences complete denaturation of β-lactoglobulin and formation of complex with casein, while α -lactalbumin denatures and interacts with β-lactoglobulin when β-lactoglobulin has already linked with casein micelles.