Dynamic surface tension and adsorption properties of β-casein and β-lactoglobulin

The adsorption kinetic behaviour of β-lactoglobulin and β-casein solutions studied by dynamic surface tension measurements was interpreted by diffusion-controlled models. Approximate solutions of the model led to diffusion coefficients for short and long adsorption times. The coefficients associated with the short time region were found to be unexpectedly high. From the long time approximation, the coefficients reflect a slower process in the adsorption layer which is possibly superimposed by rearrangement processes.     

Preparation and characterization of monoclonal antibodies directed against bovine β-casein

Using hydridoma technology, three monoclonal antibodies (mAbs) specific for β-casein were isolated. ELISA and immunoblot analysis with β-casein and some of its purified and partially purified proteolytic fragments, identified the epitope of the mAbs in the second half of the molecule between residues 105 and 193. Our data differ from those of Kobayashi et al. (Biochim. Biophys. Acta, 1077, (1991) 11–18) who recently identified the epitope of an anti-bovine β-casein monoclonal antibody at residues 193–202 of the β-casein molecule.     

Variety and germination time effect on total β‐glucan,water‐insoluble β‐glucan,water‐soluble β‐glucan components and β‐glucanase levels in improved sorghum varieties SK5912, KSV8 and ICSV400 before and after malting and their relationships to wort viscosity

The effects of variety and germination time on β‐glucan components – total β‐glucan (TBG), water insoluble β‐glucan (WIBG) and water soluble β‐glucan (WSBG) and β‐glucanase (BG) levels – before and after malting in improved sorghum varieties SK5912, KSV8 and ICSV400 and their relationships to wort specific viscosity (SV) were studied. This study was part of efforts to aid local malting and brewing industries in the application of sorghum varieties that are abundantly available to reduce costs. At the fifth day of germination, variety ICSV400 had the lowest TBG, WIBG and WSBG levels in its raw and malt samples. Variety SK5912 had the highest TBG, WIBG and WSBG levels in its raw samples, while variety KSV8 had the highest levels of TBG, WIBG and WSBG in its malt samples. Similarly, variety ICSV400 malts developed the highest BG levels, while the KSV8 malts gave the lowest level. The effect of variety, germination time and variety × germination time interaction was significant (p < 0.05) on the TBG, WIBG and BG levels and was not significant on the WSBG levels. Weak and significant correlation of TBG levels with SV (0.25, p < 0.05 for SK5912; 0.24, p < 0.05 for KSV8; and 0.31, p < 0.05 for ICSV400) was observed in all the samples, suggesting that the low β‐glucan levels may not be primarily and solely responsible for any viscosity impediments associated with sorghum worts during run‐off. With improvement in the effective utilization of sorghum, ICSV400 appeared the most suitable variety for malting and brewing in Nigeria.Copyright © 2016 The Institute of Brewing & Distilling     

Release of β-casomorphins 5 and 7 during simulated gastro-intestinal digestion of bovine β-casein variants and milk-based infant formulas

The release of β-casomorphin-5 (BCM5) and β-casomorphin-7 (BCM7) was investigated during simulated gastro-intestinal digestion (SGID) of bovine β-casein variants (n = 3), commercial milk-based infant formulas (n = 6) and experimental infant formulas (n = 3). SGID included pepsin digestion at pH 2.0, 3.0 and 4.0 and further hydrolysis with Corolase PP™. β-Casein (β-CN) variants were extracted from raw milks coming from cows of Holstein-Friesian and Jersey breeds. Genomic DNA was isolated from milk and the β-CN genotype was determined by a PCR-based method. Phenotype at protein level was determined by capillary zone electrophoresis in order to ascertain the level of gene expression. Recognition and quantification of BCMs involved HPLC coupled to tandem MS. Regardless of the pH, BCM7 generated from variants A1 and B of β-CN (5–176 mmol/mol casein) the highest amount being released during SGID of form B. As expected, the peptide was not released from variant A2 at any steps of SGID. BCM5 was not formed in hydrolysates irrespective of either the genetic variant or the pH value during SGID. Variants A1, A2 and B of β-CN were present in all the commercial infant formulae (IFs) submitted to SGID. Accordingly, 16–297 nmol BCM7 were released from 800 ml IF, i.e. the daily recommended intake for infant. Industrial indirect-UHT treatments (156 °C × 6–9 s) did not modify release of BCM7 and, during SGID, comparable peptide amounts formed in raw formulation and final heat-treated IFs.     

Comparative study of enzymatic hydrolysis of α/β- and γ-gliadins

Enzymatic hydrolysis of proteins and fractionation of hydrolysates is a route of diversifying their functional properties. Chymotryptic hydrolysis of different sulphur-rich gliadins (α/β- and γ-types), major wheat storage proteins, was studied. The peptides formed in the course of digestion were characterised by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate (SDS-PAGE) and reversed-phase high performance liquid chromatography (RP-HPLC). With reference to previous work, a general scheme of degradation was assessed for γ-gliadins. Limited hydrolysis released two types of polypeptides, comprising respectively the repetitive and the non-repetitive moieties of the protein. In spite of strong sequence homologies between the two groups of sulphur-rich gliadins, it was not possible to prepare similar peptide fractions from α/β-gliadins. They were more resistant to hydrolysis and the region where the two domains merge appeared inaccessible to chymotrypsin. Restricted accessibility of cleavage sites was attributed to the less expanded conformation of α/β-type than γ-type gliadins. A first step of scaling-up was performed. This offers opportunities to prepare functional peptides from wheat storage proteins.     

Interactions of polysaccharides with β-lactoglobulin spread monolayers at the air–water interface

In the present work we have studied the static (film structure and elasticity) and dynamic characteristics (surface dilatational properties) of β-lactoglobulin (βLG) monolayers spread at the air–water interface in the presence of polysaccharides in the aqueous phase, at 20 °C and at pH 7. The measurements were performed on a fully automated Wilhelmy-type film balance. As polysaccharides with interfacial activity we have used propylene glycol alginates (PGA). To evaluate the effect of the degree of PGA esterification and viscosity, different commercial samples were studied-kelcoloid O (KO), kelcoloid LVF (KLVF) and manucol ester (MAN). Xanthan gum (XG) and λ-carrageenan (λC) were studied as non-surface active polysaccharides. The results reveal a significant effect of surface active and non-surface active polysaccharides on static—when the polysaccharide was added in the subphase the π-A isotherms shifted to higher surface pressure values as the time increased-and dynamic—the presence of polysaccharide in the aqueous phase decreased the surface dilatational modulus of a pure β-lactoglobulin monolayer-characteristics of β-lactoglobulin monolayers. To explain the observed effects three phenomena were taken into account: (i) the ability of the polysaccharide to adsorb at the interface by it-self and to increase the surface pressure, (ii) the interfacial complexation of the polysaccharide with the adsorbed protein and (iii) the existence of a limited thermodynamic compatibility between the protein and polysaccharide, depending on the protein-polysaccharide system.     

Emulsification of chemical and enzymatic hydrolysates of β‐lactoglobulin: characterization of the peptides adsorbed at the interface

Bovine β‐Lactoglobulin (BLG) was cleaved by BNPS‐skatole (2‐(2′‐nitrophenylsulfenyl)‐3‐methyl‐3′‐bromoindolenine( trypsin, or pepsin in 40% ethanol before emulsification with hexadecane in order to characterize the peptides active at the interfaces. The total digests and the different phases obtained after emulsification were analyzed by RP‐HPLC to separate the peptides according to their gradual order on a hydrophilicity‐to‐hydrophobicity scale. In each case, hydrophobic peptides were recovered in the creamed phase and characterized by mass spectrometry and sequencing. After tryptic hydrolysis, short peptides were identified at the interfacial layer as fragments S₂₁–L₃₂, V₄₁–L₅₇, V₄₁–K₆₀, and W₆₁–K₇₀linked to L₁₄₉–I₁₆₂ by a C₆₆–C₁₆₀bond. It indicates that the hydrophilic/hydrophobic distribution of the amino acids in the sequence of the fragments is more relevant to adsorption than the length of the peptide. BNPS‐skatole and peptic hydrolysis produced larger hydrophobic peptides which were also recovered in the creamed phase of the emulsion and characterized.     

Deterioration of β-carotene in certain hydrogenated fats. II.—Products of β-carotene deterioration and nature of the green pigment

The non-saponifiable fraction from a sample of β-carotene-hardened palm kernel oil which had developed a green discoloration has been examined. A number of β-carotene oxidation products were found and these included a number of β-carotene epoxide derivatives. A compound thought to be β-apo-3-carotenal was also found, but the apo-2- and apo-4-carotenals were not present in more than trace amounts. A major component was similar to, but not identical with, mutatochrome (β-carotene 5,8-epoxide). It is suggested that the green discoloration of the carotenised fat was due to oxidation of β-carotene to epoxide derivatives by traces of peroxyacids and the conversion of these epoxides into green-blue ionised forms by the action of an acidic material present in the fat.     

Extraction and Isolation of β‐Glucan from Grain Sources—A Review

A collective report on the extraction and isolation of β‐glucan from grain sources, namely, oat, barley, and wheat is presented. An analysis on the effect of medium, pH, and temperature on the purity and yield of the β‐glucan derived under acidic/alkaline/aqueous/enzymatic conditions is also made. Water extraction and alkali extraction processes are preferred as the yield and recovery of extracted β‐glucan were good. Cost‐effective development of the process for deriving high molecular weight β‐glucan is the current requirement for its wide applications in food and pharmaceutical industries.     

Synthesis of β‐Galactooligosaccharides from Lactose Using Microbial β‐Galactosidases

Abstract: Galactooligosaccharides (GOSs) are nondigestible oligosaccharides and are comprised of 2 to 20 molecules of galactose and 1 molecule of glucose. They are recognized as important prebiotics for their stimulation of the proliferation of intestinal lactic acid bacteria and bifidobacteria. Therefore, they beneficially affect the host by selectively stimulating the growth and/or activity of a limited number of gastrointestinal microbes (probiotics) that confer health benefits. Prebiotics and probiotics have only recently been recognized as contributors to human health. A GOS can be produced by a series of enzymatic reactions catalyzed by β‐galactosidase, where the glycosyl group of one or more D‐galactosyl units is transferred onto the D‐galactose moiety of lactose, in a process known as transgalactosylation. Microbes can be used as a source for the β‐galactosidase enzyme or as agents to produce GOS molecules. Commercial β‐galactosidase enzymes also do have a great potential for their use in GOS synthesis. These transgalactosyl reactions, which could find useful application in the dairy as well as the larger food industry, have not been fully exploited. A better understanding of the enzyme reaction as well as improved analytical techniques for GOS measurements are important in achieving this worthwhile objective.     

Isolation,structural features and rheological properties of water‐extractable β‐glucans from different Greek barley cultivars

β‐Glucans were isolated from six Greek barley cultivars (Persefoni, Kos, Thessaloniki, Athinaida, Dimitra and Triptolemos) by water extraction at 47 °C, enzymatic removal of starch and protein and subsequent precipitation of the water‐soluble β‐glucans with 37% (w/v) ammonium sulfate saturation. The purity of barley β‐glucans was high (>93% dry basis) with some small contamination by protein (<3.84%). The molecular size of the β‐glucan isolates was determined by high‐performance size‐exclusion chromatography (HPSEC); the weight‐average molecular weights and the intrinsic viscosities ranged between 0.45 × 10⁶ and 1.32 × 10⁶ and 2.77 and 4.11 dl g^?1, respectively. Structural features of barley β‐glucans were revealed by ¹³C NMR spectroscopy and high‐performance anion‐exchange chromatography (HPAEC) of the oligomers released by the hydrolytic action of lichenase. Lichenase degradation showed that β‐glucans from all barley cultivars consisted of blocks of cellotriosyl and cellotetraosyl units, accounting for 90.6–92.3% of the total oligomers released, with a molar proportion of these units between 2.31 and 2.77. Rheological measurements of aqueous solutions/dispersions of β‐glucans showed the behaviour of non‐interacting polysaccharides and a transition from the typical viscoelastic response to gel‐like properties after a time period that depended on the molecular size of the polysaccharide. The lowest molecular size β‐glucans from the Triptolemos cultivar showed shorter gelation times than their higher molecular weight counterparts. The effect of sugar incorporation (glucose, fructose, sucrose, xylose and ribose), at a concentration of 30% (w/v), to the β‐glucans gels (6% w/v) on compression parameters seemed to be related to the type of sugar used; the pentose sugars substantially reduced gel firming. Copyright © 2004 Society of Chemical Industry     

Purification and physicochemical characterization of ovine β‐lactoglobulin and α‐lactalbumin

Ovine whey proteins were fractionated and studied by using different analytical techniques. Anion‐exchange chromatography and reversed‐phase high‐performance liquid chromatography (HPLC) showed the presence of two fractions of β‐lactoglobulin but only one of α‐lactalbumin. Gel permeation and sodium dodecyl sulfate (SDS)‐polyacrylamide gel electrophoresis allowed the calculation of the apparent molecular mass of each component, while HPLC coupled to electrospray ionisation‐mass spectrometry (ESI‐MS) technique, giving the exact molecular masses, demonstrated the presence of two variants A and B of ovine β‐lactoglobulin. Amino acid compositions of the two variants of β‐lactoglobulin differed only in their His and Tyr contents. Circular dichroism spectroscopy profiles showed pH conformation changes of each component. The thermograms of the different whey protein components showed a higher heat resistance of β‐lactoglobulin A compared to β‐lactoglobulin B at pH 2, and indicated high instability of ovine α‐lactalbumin at this pH.     

Deterioration of β-carotene in certain hydrogenated fats. III.—Factors affecting the rate at which green discoloration occurs

The influence of a variety of additives and thermal treatments upon the rate at which green discoloration develops in β-carotene-hydrogenated fat systems is reported. The observed effects are discussed in relation to the hypothesis that the colour change is associated with the production of β-carotene epoxides from the oxidation of β-carotene by peroxy acids which are formed by the interaction of aldehydoglycerides with dissolved oxygen. Possible methods which might be employed in avoiding the incidence of the discoloration include suitable choice of oil, the use of certain additives, notably commercial lecithin (for food uses), adequate ‘tempering’ of the finished fat, and care in the use of cool (and cold) storage.     

Endosperm α 1,4—α 1,6 Glucopolysaccharides Utilization During Germination of Sweet Corn and Other Maize Genotypes

The quantity variations and the structural changes of the α 1,4 —α 1,6 glucopolysaccharides contained in the endosperm of sweet corn, waxy and amylose extender maize genotypes, were studied during early germination. The α 1,4 —α 1,6 glucopolysaccharides were fractionated according to their branching degree. The results obtained showed that: the degradation pattern of the α 1,4 —α 1,6 glucopolysaccharides was similar for the different corn genotypes studied. In addition, soluble dextrins or partial degradation products were not detected, but reducing sugars were accumulated. Furthermore, the structure of the remaining polysaccharides was similar to those present in the non germinating seed. These results led us to propose that once a polysaccharide molecule was used as the substrate by degradative enzymes during germination, that molecule was totally degraded.     

Vascular effects and antihypertensive properties of κ-casein macropeptide

The blood-pressure-lowering effect of bovine κ-casein macropeptide (CMP), previously reported to exhibit a modest angiotensin-converting enzyme (ACE)-inhibitory activity in vitro, was evaluated in spontaneously hypertensive rats (SHR). The oral administration of CMP (150 mg kg⁻¹) significantly reduced the systolic blood pressure (SBP) of SHR. The antihypertensive action was more pronounced when CMP was treated with trypsin. The sequence MAIPPKK, identified in the tryptic hydrolysate of bovine CMP, significantly reduced blood pressure at a dose of 10 mg kg⁻¹. The CMP and its tryptic peptides induced relaxation of endothelium-intact aortic rings. The sequence MAIPPKK also evoked a significant relaxation effect; however, the shorter sequence MAIPPK and the strong ACE-inhibitory tripeptide IPP exhibited a vascular relaxing effect lower than 10%. The implications of vascular relaxing mechanisms, as well as the possibility that the tripeptide IPP is at least partially responsible for the antihypertensive effects of CMP, are discussed.     

Bioequivalence of β‐carotene and retinol

For many years it was accepted that 6 mg of β‐carotene were required to produce 1 mg of vitamin A in the form of retinol. The equivalence was based on the assumptions that two‐thirds of dietary β‐carotene are not absorbed, while in the metabolism of the remaining third 1 mol of β‐carotene is converted to 1 mol retinol. Recently, the bioequivalence was raised to 12 mg β‐carotene and 1 mg retinol. The objective of this review was to re‐examine the data that were used to support the new equivalence ratio, especially since some of these data were obtained in developing countries where infestation with gut parasites and exposure to other infections is common, yet the influence of inflammation on plasma carotenoid and retinol concentrations is frequently ignored. Bioequivalence studies examined in this review include those done in developing and developed countries, depletion and repletion studies, feeding with vegetable sources of β‐carotene or pure supplements, influence of helminths, carotenoid interactions and matrix effects and studies using stable isotopes (SI). SI studies show the bioefficacy of β‐carotene conversion to retinol is generally poor even for pure β‐carotene unless the dose is small and fed regularly until equilibration is reached. Retinol formation appears to be inversely influenced by previous vitamin A intake, the amount of material given and current vitamin A status. In spite of technical complexities, more SI studies where liver reserves of vitamin A are determined pre and post intervention are needed to evaluate β‐carotene bioefficacy of different vegetable sources. Copyright © 2006 Society of Chemical Industry     

Competitive adsorption of α-lactalbumin in the molten globule state

The molten globule state of α-lactalbumin is a partially denatured form with native-like secondary structure and disordered tertiary structure. Using circular dichroism measurements, it was demonstrated that the molten globule state was produced by decreasing the pH to 2.0 at 25°C or by removing bound Ca²⁺ by treatment with ethylenediamine—tetraacetic acid (EDTA) at pH 7.5 and 40°C. Tension measurements showed that α-lactalbumin in the molten globule state is more easily unfolded at liquid interfaces than is the native protein. Results of competitive adsorption experiments involving α-lactalbumin and β-lactoglobulin at the oil droplet surface in emulsions are consistent with preferential adsorption of α-lactalbumin during emulsification when it is in the molten globule state. In contrast to the difficulty of exchange between α-lactalbumin and β-lactoglobulin at the oil-water interface in emulsions at 25°C, it has been found that the two whey proteins are able partially to displace one another from the oil—water interface at 40°C. While native α-lactalbumin was found to be readily displaced from the oil—water interface by β-lactoglobulin at 40°C, it was found that α-lactalbumin in the molten globule state in the presence of EDTA at 40°C had itself the capacity for displacing β-lactoglobulin from the interface.