Comparison of the aggregation behavior of soy and bovine whey protein hydrolysates.

Soy-derived proteins (soy protein isolate, glycinin, and beta-conglycinin) and bovine whey-derived proteins (whey protein isolate, alpha-lactalbumin, beta-lactoglobulin) were hydrolyzed using subtilisin Carlsberg, chymotrypsin, trypsin, bromelain, and papain. The (in)solubility of the hydrolysates obtained was studied as a function of pH. At neutral pH, all soy-derived protein hydrolysates, particularly those from glycinin, obtained by hydrolysis with subtilisin Carlsberg, chymotrypsin, bromelain, and papain showed a stronger aggregation compared to the non-hydrolyzed ones.

Enzymatic hydrolysis as a means of expanding the cold gelation conditions of soy proteins.

Acid-induced cold gelation of soy protein hydrolysates was studied. Hydrolysates with degrees of hydrolysis (DH) of up to 10% were prepared by using subtilisin Carlsberg. The enzyme was inhibited to uncouple the hydrolysis from the subsequent gelation; the latter was induced by the addition of glucono-delta-lactone.

Acid-induced cold gelation of globular proteins: effects of protein aggregate characteristics and disulfide bonding on rheological properties.

The process of cold gelation of ovalbumin and the properties of the resulting cold-set gels were compared to those of whey protein isolate. Under the chosen heating conditions, most protein was organized in aggregates. For both protein preparations, the aggregates consisted of covalently linked monomers.

Cold-set globular protein gels: interactions, structure and rheology as a function of protein concentration.

We identified the contribution of covalent and noncovalent interactions to the scaling behavior of the structural and rheological properties in a cold gelling protein system. The system we studied consisted of two types of whey protein aggregates, equal in size but different in the amount of accessible thiol groups at the surface of the aggregates. Analysis of the structural characteristics of acid-induced gels of both thiol-blocked and unmodified whey protein aggregates yielded a fractal dimension (2.

Flavor release and perception of flavored whey protein gels: perception is determined by texture rather than by release.

Five whey protein gels, with different gel hardnesses and waterholding capacities, were flavored with ethylbutyrate or diacetyl and evaluated by a 10-person panel to study the relation between the gel structure and the sensory perception, as well as the nosespace flavor concentration during eating. The sensory perception of the flavor compounds was measured by the time-intensity method, while simultaneously the nosespace flavor concentration was monitored by the MS-Nose. The nosespace flavor concentration was found to be independent of the gel hardness or waterholding capacity.

Physical and chemical interactions in cold gelation of food proteins.

pH-Induced cold gelation of whey proteins is a two-step process. After protein aggregates have been prepared by heat treatment, gelation is established at ambient temperature by gradually lowering the pH. To demonstrate the importance of electrostatic interactions between aggregates during this latter process, beta-lactoglobulin aggregates with a decreased iso-electric point were prepared via succinylation of primary amino groups.

A novel pH-dependent dimerization motif in beta-lactoglobulin from pig (Sus scrofa).

beta-Lactoglobulin (BLG) is a lipocalin and is the major protein in the whey of the milk of cows and other ruminants, but not in all mammalian species. The biological function of BLG is not clear, but a potential role in carrying fatty acids through the digestive tract has been proposed. The capability of BLG to aggregate and form gels is often used to thicken foodstuffs.

Dimerization, stability and electrostatic properties of porcine beta-lactoglobulin.

The study of homologous proteins belonging to the same family can provide a rationale for important molecular properties such as oligomer formation, folding mechanism and mode of binding. We report here a physico-chemical characterization of porcine beta-lactoglobulin, purified from pooled milk: size-exclusion chromatography, CD and NMR measurements were used to study the aggregation and stability of this protein. In spite of the high sequence identity and homology of porcine beta-lactoglobulin with the widely studied bovine species, the two proteins exhibit very different behaviours.

Formation of disulfide bonds in acid-induced gels of preheated whey protein isolate.

Cold gelation of whey proteins is a two-step process. First, protein aggregates are prepared by a heat treatment of a solution of native proteins in the absence of salt. Second, after cooling of the solution, gelation is induced by lowering the pH at ambient temperature.

Molecular and functional analyses of the metC gene of Lactococcus lactis, encoding cystathionine beta-lyase.

The enzymatic degradation of amino acids in cheese is believed to generate aroma compounds and therefore to be essential for flavor development. Cystathionine beta-lyase (CBL) can convert cystathionine to homocysteine but is also able to catalyze an alpha, gamma elimination. With methionine as a substrate, it produces volatile sulfur compounds which are important for flavor formation in Gouda cheese.

Role of calcium in activity and stability of the Lactococcus lactis cell envelope proteinase.

The mature lactococcal cell envelope proteinase (CEP) consists of an N-terminal subtilisin-like proteinase domain and a large C-terminal extension of unknown function whose far end anchors the molecule in the cell envelope. Different types of CEP can be distinguished on the basis of specificity and amino acid sequence. Removal of weakly bound Ca2+ from the native cell-bound CEP of Lactococcus lactis SK11 (type III specificity) is coupled with a significant reversible decrease in specific activity and a dramatic reversible reduction in thermal stability, as a result of which no activity at 25 degrees C (pH 6.

Selective hydrolysis of milk proteins to facilitate the elimination of the ABBOS epitope of bovine serum albumin and other immunoreactive epitopes.

Milk proteins are hydrolyzed to prevent immunological reactions, but immunoreactive epitopes, including the ABBOS epitope of bovine serum albumin (BSA), can still be detected in commercially available milk protein hydrolysates. We used lactococcal cell-envelope proteinase (CEP) for the hydrolysis of the individual milk proteins and of mixtures thereof, or for the hydrolysis of sodium caseinate (contaminated with whey proteins). CEP exclusively degraded casein, leaving the four major whey proteins intact.

Incomplete elimination of the ABBOS epitope of bovine serum albumin under simulated gastrointestinal conditions of infants.

Objective: Because the bovine serum albumin residues 126-144 (ABBOS) have been reported to be responsible for the autoimmune reaction directed against pancreatic islet cells, it was our aim to study the potential survival of the ABBOS epitope during digestion in the gastrointestinal tract.

Research Design And Methods: Either nontreated (commercially available) or heat-treated bovine serum albumin (BSA) was hydrolyzed in vitro with pepsin at a pH of 2.0, 3.

The occurrence of two intracellular oligoendopeptidases in Lactococcus lactis and their significance for peptide conversion in cheese.

Two intracellular oligopeptide-preferring endopeptidases have been detected in Lactococcus lactis. A neutral thermolysin-like oligoendopeptidase (NOP) has been purified to homogeneity and an alkaline oligoendopeptidase has been partially purified. The specificity of the oligoendopeptidases towards important intermediary cheese peptides, produced by chymosin action on the caseins, clearly differs from that of the cell-envelope proteinase (CEP).

Purification and Characterization of Cystathionine (beta)-Lyase from Lactococcus lactis subsp. cremoris B78 and Its Possible Role in Flavor Development in Cheese.

An enzyme that degrades sulfur-containing amino acids was purified from Lactococcus lactis subsp. cremoris B78; this strain was isolated from a mixed-strain, mesophilic starter culture used for the production of Gouda cheese. The enzyme has features of a cystathionine (beta)-lyase (EC 4.

Evidence for a large dispensable segment in the subtilisin-like catalytic domain of the Lactococcus lactis cell-envelope proteinase.

The Lactococcus lactis SK11 cell-envelope proteinase contains various inserts, located in external loops of the catalytic domain compared with related subtilisins. In this study, protein engineering was employed to determine the function of the largest loop insertion (residues 238-388) relative to the subtilisin structure. By site-directed mutagenesis we have deleted the fragment of the proteinase gene encoding these 151 residues and analyzed the mutant delta 238-388 proteinase for activity, (auto)processing and cleavage specificity.

Engineering of the substrate-binding region of the subtilisin-like, cell-envelope proteinase of Lactococcus lactis.

The substrate-binding region of the cell-envelope proteinase of Lactococcus lactis strain SK11 was modelled, based on sequence homology of the catalytic domain with the serine proteinases subtilisin and thermitase. Substitutions, deletions and insertions were introduced, by site-directed and cassette mutagenesis of the prtP gene encoding this enzyme, based on sequence comparison both with subtilisin and with the homologous L.lactis strain Wg2 proteinase, which has different proteolytic properties.

Diversity of cell envelope proteinase specificity among strains of Lactococcus lactis and its relationship to charge characteristics of the substrate-binding region.

The biochemical and genetical diversity of the subtilisin-like cell envelope proteinase (CEP) among Lactococcus lactis strains was investigated. The specificities of the proteinases of 16 strains toward the important cheese peptide alpha s1-casein fragment 1 to 23 and toward two differently charged chromophoric peptides have been determined. On the basis of the results, these strains could be classified into seven groups.

Specificity of two genetically related cell-envelope proteinases of Lactococcus lactis subsp. cremoris towards alpha s1-casein-(1-23)-fragment.

The specificity of two genetically related cell-envelope serine proteinases (PI-type and PIII-type) of Lactococcus lactis subsp. cremoris towards the alpha s1-casein-(1-23)-fragment, an important intermediate product of primary chymosin-directed proteolysis in cheese, has been established. Both enzymes showed, at pH 6.