María J. Martinez

Interactions in the aqueous phase and adsorption at the air–water interface of caseinoglycomacropeptide (GMP) and β-lactoglobulin mixed systems

The aim of this work was to study the interactions and adsorption of caseinoglycomacropeptide (GMP) and GMP:beta-lactoglobulin (beta-lg) mixed system in the aqueous phase and at the air-water interface. The existence of associative interactions between GMP and beta-lg in the aqueous phase was investigated by dynamic light scattering, differential scanning calorimetry (DSC), fluorometry and native PAGE-electrophoresis. The surface pressure isotherm and the static and dynamic surface pressure were determined by tensiometry and surface dilatational properties. The results showed that GMP presented higher surface activity than beta-lg at a concentration of 4%wt but beta-lg showed higher film forming ability. In the mixed systems beta-lg dominated the static and dynamic surface pressure and the rheological properties of interfacial films suggesting that beta-lg hinders GMP adsorption because, in simple competition, GMP should dominate because of its higher surface activity. The surface predominance of beta-lg can be attributed to binding of GMP to beta-lg in the aqueous phase that prevents GMP adsorption on its own.

Interfacial and foaming interactions between casein glycomacropeptide (CMP) and propylene glycol alginate

Proteins and polysaccharides are widely used in food formulation. While most of the proteins are surface active, only few polysaccharides can adsorb at the air-water interface; this is the case of propylene glycol alginates (PGA). It is known that casein glycomacropeptide (CMP), a bioactive polypeptide derived from κ-casein by the action of chymosin, presents a great foaming capacity but provides unstable foams. So, the objective of this work was to analyze the impact of mixing CMP and a commercial variety of PGA, Kelcoloid O (KO), on the interfacial and foaming properties at pH 7.0. It was determined the surface pressure isotherm, the dynamics of adsorption and the foaming properties for CMP, KO and the mixed system CMP-KO. CMP dominated the surface pressure of CMP-KO mixed system. The presence of KO synergistically improved the viscoelastic properties of surface film. The foaming capacity of CMP was altered by KO. KO foam presented a higher stability than CMP foam and it controlled the stability against drainage and the initial collapse in the mixed foam.

Interactions between β-lactoglobulin and casein glycomacropeptide on foaming

The aim of this work was to study the effect of interactions between casein glycomacropeptide (CMP) and β-lactoglobulin (β-lg) at pH 6.5 and 3.5 on the foaming properties of the mixed systems with different CMP:β-lg ratios. The foaming properties were determined by the bubbling method with a Foamscan instrument. A highest overall foam capacity (OFC), foaming capacity (FC) and mainly stability of mixed foams at pH 3.5, as compared to the mixed foams at pH 6.5 or the foams of CMP and β-lg was observed. At pH 6.5, the stability of mixed foams decreased with increasing the CMP content, while OFC and FC values were similar to β-lg foam. The performance of the mixed systems was discussed in relation with the interactions between CMP and β-lg in the aqueous phase (as observed by dynamic light scattering and differential scanning calorimetry in previous works).

Reduced β-lactoglobulin IgE binding upon in vitro digestion as a result of the interaction of the protein with casein glycomacropeptide

The aim of this work was to evaluate the effect of the presence of casein glycomacropeptide (CMP) on the in vitro digestibility and potential allergenicity of β-lactoglobulin (β-lg)-CMP mixtures. The digestion products were analyzed by RP-HPLC and RP-HPLC-ESI-MS/MS. The potential allergenicity of the digestion products was studied by human IgE binding by inhibition ELISA with serum samples from children with clinical allergic symptoms to β-lg. No differences were observed by HPLC in the mixtures hydrolysates due to CMP-β-lg interactions. RP-HPLC-ESI-MS/MS results showed different peptides occurring in the mixtures hydrolysates. Additionally, it was observed a significant reduction of β-lg IgE binding in the presence of CMP. The disappearance of epitopes in the digested mixtures could explain the lower IgE binding observed in these systems compared to β-lg. It can be concluded that the presence of CMP in products containing β-lg may modify the digestion products that may reduce the potential allergenicity of β-lg.

The LonB protease controls membrane lipids composition and is essential for viability in the extremophilic haloarchaeon Haloferax volcanii

Although homologs of the ATP-dependent Lon protease exist in all domains of life, the relevance of this protease in archaeal physiology remains a mystery. In this study, we have constructed and phenotypically characterized deletion and conditional lon mutants in the model haloarchaeon Haloferax volcanii to elucidate the role of the unusual membrane-bound LonB protease in archaea. Hvlon could be deleted from the chromosome only when a copy of the wild type gene was provided in trans suggesting that Lon is essential for survival in this archaeon. Successful complementation of the lethal phenotype of ΔHvlon was attained by expression of the heterologous protease gene Nmlon from the haloalkaliphilic archaeon Natrialba magadii, meaning that the biological function of Lon is conserved in these organisms. Suboptimal cellular levels of Lon protein affected growth rate, cell shape, cell pigmentation, lipid composition and sensitivity to various antibiotics. The contents of bacterioruberins and some polar lipids were increased in the lon mutants suggesting that Lon is linked to maintenance of membrane lipid balance which likely affects cell viability in this archaeon. The phenotypes associated to a membrane-bound LonB protease mutant were examined for the first time providing insight on the relevance of this protease in archaeal physiology.

Affinity chromatography matrices for depletion and purification of casein glycomacropeptide from bovine whey

Casein glycomacropeptide (CMP) is a 64‐ amino acid peptide found in cheese whey, which is released after κ‐casein specific cleavage by chymosin. CMP lacks aromatic amino acids, a characteristic that makes it usable as a nutritional supplement for people with phenylketonuria. CMP consists of two nonglycosylated isoforms (aCMP A and aCMP B) and its different glycosylated forms (gCMP A and gCMP B). The most predominant carbohydrate of gCMP is N‐acetylneuraminic acid (sialic acid). Here, we developed a CMP purification process based on the affinity of sialic acid for wheat germ agglutinin (WGA). After formation of chitosan beads and adsorption of WGA, the agglutinin was covalently attached with glutaraldehyde. Two matrices with different WGA density were assayed for CMP adsorption. Maximum adsorption capacities were calculated according to the Langmuir model from adsorption isotherms developed at pH 7.0, being 137.0 mg/g for the matrix with the best performance. In CMP reduction from whey, maximum removal percentage was 79% (specifically 33.7% of gCMP A and B, 75.8% of aCMP A, and 93.9% of aCMP B). The CMP was recovered as an aggregate with an overall yield of 64%. Therefore, the matrices developed are promising for CMP purification from cheese whey.

Synergistic effect of casein glycomacropeptide on sodium caseinate foaming properties

Several strategies to improve the interfacial properties and foaming properties of proteins may be developed; among them, the use of mixtures of biopolymers that exhibit synergistic interactions. The aim of the present work was to evaluate the effect of casein glycomacropeptide (CMP) on foaming and surface properties of sodium caseinate (NaCas) and to establish the role of protein interactions in the aqueous phase. To this end particles size, interfacial and foaming properties of CMP, NaCas and NaCas-CMP mixtures at pH 5.5 and 7 were determined. At both pH, the interaction between CMP and NaCas induced a decrease in the aggregation state of NaCas. Single CMP foams showed the highest and NaCas the lowest foam overrun (FO) and the mixture exhibited intermediate values. CMP foam quickly drained. The drainage profile of mixed foams was closer to NaCas foams; at pH 5.5, mixed foams drained even slower than NaCas foam, exhibiting a synergistic performance. Additionally, a strong synergism was observed on the collapse of mixed foams at pH 5.5. Finally, a model to explain the synergistic effect observed on foaming properties in CMP-NaCas mixtures has been proposed; the reduced aggregation state of NaCas in the presence of CMP, made it more efficient for foam stabilization.