ABSTRACT
BACKGROUND: The thermal unfolding and rheological properties of patatin gels were compared with those of commonly used proteins (ß-lactoglobulin, ovalbumin, glycinin). RESULTS: A significant difference between these proteins was observed in both the denaturation temperature (59 °C for patatin; about 20 °C lower than the other proteins) and the onset temperature of gel formation (50-60 °C, compared to 70-85 °C for the other proteins). At low ionic strength the minimal concentration was only 6% (w/v) for patatin, compared to 8-11% for the other proteins. This effect was attributed to the relatively high exposed hydrophobicity of patatin as determined by hydrophobic interaction chromatography. For gels compared at 'iso-strength', the frequency dependence was found to be close to identical, while small differences were observed in the strain at fracture. CONCLUSIONS: Patatin was found to form gels with comparable small-deformational rheological properties as typical food proteins. In addition, at concentrations where the elastic modulus was similar for all proteins, the frequency and strain dependence were also comparable. From this it is concluded that patatin is a promising protein to be used in food applications as a gelling agent.
Subject(s)
Carboxylic Ester Hydrolases/chemistry , Globulins/chemistry , Lactoglobulins/chemistry , Ovalbumin/chemistry , Plant Proteins/chemistry , Protein Denaturation , Rheology , Soybean Proteins/chemistry , Elasticity , Food Technology , Gels , Hydrophobic and Hydrophilic Interactions , Solanum tuberosum/chemistry , TemperatureABSTRACT
Beta-casein, which is present in the form of micelles at atmospheric pressure, has been hydrolyzed during pressure treatment to improve the accessibility of the protein. Two proteolytic enzymes with different specificities were used. Trypsin was aimed at mainly hydrolyzing hydrophilic segments of beta-casein and chymotrypsin at hydrolyzing hydrophobic segments of beta-casein. Measurements on aggregation during hydrolysis at atmospheric pressure showed that probably not micelle disruption, but disruption of much larger aggregates, occurs in the process. Peptide profiles were measured via reversed-phase chromatography. Measurements on enzyme activity after pressure treatments showed that trypsin was inactivated by pressure, which could explain all differences in peptide profiles compared to atmospheric experiments. Pressure did not influence the reaction mechanism, probably because the hydrophilic part of beta-casein is sufficiently accessible. However, chymotryptic proteolysis under pressure yielded new peptides that could not be explained by a change in enzyme activity. Here, pressure altered the mechanism of hydrolysis, by changing either enzyme specificity or substrate accessibility, which led to different peptides that can have different properties.
Subject(s)
Caseins/chemistry , Chymotrypsin/chemistry , Trypsin/chemistry , Animals , Atmospheric Pressure , Cattle , Hydrolysis , Peptide MappingABSTRACT
In a previous study, peptides aggregating at pH 7.0 derived from a whey protein hydrolysate made with Bacillus licheniformis protease were fractionated and identified. The objective of the present work was to investigate the solubility of the fractionated aggregating peptides, as a function of concentration, and their aggregating capacities toward added intact proteins. The amount of aggregated material and the composition of the aggregates obtained were measured by nitrogen concentration and size exclusion chromatography, respectively. The results showed that of the four fractions obtained from the aggregating peptides, two were insoluble, while the other two consisted of 1:1 mixture of low and high solubility peptides. Therefore, insoluble peptides coaggregated, assumedly via hydrophobic interactions, other relatively more soluble peptides. It was also shown that aggregating peptides could aggregate intact protein nonspecifically since the same peptides were involved in the aggregation of whey proteins, beta-casein, and bovine serum albumin. Both insoluble and partly insoluble peptides were required for the aggregation of intact protein. These results are of interest for the applications of protein hydrolysates, as mixtures of intact protein and peptides are often present in these applications.
Subject(s)
Bacillus/enzymology , Bacterial Proteins/metabolism , Milk Proteins/chemistry , Peptide Hydrolases/metabolism , Peptides/chemistry , Animals , Cattle , Hydrolysis , Milk Proteins/isolation & purification , Peptides/isolation & purification , Solubility , Whey ProteinsABSTRACT
The objective of this work was to identify the dominant aggregating peptides from a whey protein hydrolysate (degree of hydrolysis of 6.8%) obtained with Bacillus licheniformis protease. The aggregating peptides were fractionated with preparative reversed-phase chromatography and identified with liquid chromatography-mass spectrometry. The results showed that the dominant aggregating peptide, at pH 7.0, was beta-lg AB [f1-45]. In addition, the peptides beta-lg AB [f90-108]-S-S-alpha-la [f50-113], alpha-la [f12-49]-S-S-alpha-la [f50-113], beta-lg AB [f90-108]-S-S-beta-lg AB [f90-108], beta-lg A [f90-157], and beta-lg AB [f135-157/158] were also identified as main aggregating peptides. The results further showed that aggregation, via hydrophobic interactions, prevented further digestion (at pH 8.0), thereby explaining the large size of the aggregating peptides. It is hypothesized that B. licheniformis protease breaks down hydrophilic segments in the substrate and, therefore, preserves hydrophobic segments that aggregate once exposed to the solvent.
Subject(s)
Bacillus/enzymology , Milk Proteins/metabolism , Peptide Fragments/analysis , Peptide Hydrolases/metabolism , Amino Acid Sequence , Chemical Fractionation , Hydrolysis , Hydrophobic and Hydrophilic Interactions , Lactalbumin/chemistry , Lactoglobulins/chemistry , Milk Proteins/chemistry , Molecular Sequence Data , Peptide Fragments/chemistry , Whey ProteinsABSTRACT
This paper provides a brief overview of the effects of protein hydrolysis on aggregation and gel forming properties of protein systems. Among the food globular proteins, whey proteins and soy proteins are the most extensively studied for their ability to form different textures upon proteolysis. Recent studies were focused on identifying aggregating peptides and on mechanisms of aggregation and gelation.
Subject(s)
Gels/chemistry , Models, Chemical , Multiprotein Complexes/chemistry , Peptide Hydrolases/chemistry , Proteins/chemistry , Enzyme Activation , HydrolysisABSTRACT
The effects of several conditions on the amounts and compositions of aggregates formed in mixtures of whey protein hydrolysate, made with Bacillus licheniformis protease, and whey protein isolate were investigated using response surface methodology. Next, the peptides present in the aggregates were separated from the intact protein and identified with liquid chromatography-mass spectrometry. Increasing both temperature and ionic strength increased the amounts of both intact protein and peptides in the aggregates. There was an optimal amount of added intact WPI that could aggregate with peptides, yielding a maximal amount of aggregated material in which the peptide/protein molar ratio was around 6. Under all conditions applied, the same peptides were observed in the protein-peptide aggregates formed. The dominant peptides were beta-lg AB [f1-45], beta-lg AB [f90-108], and alpha-la [f50-113]. It was hypothesized that peptides could form a kind of glue network that can include beta-lactoglobulin via hydrophobic interactions at the hydrophobic binding sites at the surface of the protein.
