An assessment of the texture of acidified sodium caseinate gels with added inulin using response surface methodology

This work evaluated the effect of inulin concentration (0–6.0% w/w) on the mechanical properties and microstructure of gels composed of sodium caseinate (CN) (1.5–6.5% w/w) at pH 4.6. Inulin did not statistically affect the elastic modulus and rupture properties of the studied gels but affected the nonlinear mechanical behaviour. Samples with higher inulin concentrations (6% w/w) presented strain‐weakening deformation behaviour, whilst gels with lower inulin concentrations were strain hardening. The presence of inulin resulted in a more closed‐pores network. Gel deformability increased as CN concentration was enhanced, reaching a maximum of 0.60 at 5.58% (w/w) CN, but was not affected by inulin concentration.     

Interference of sodium caseinate in the TBARS assay

One of the most common methods of measuring lipid oxidation in foods is the quantification of malonaldehyde by reaction with 2-thiobarbituric acid (TBA) in the so called TBA-reactive substances (TBARS) assay. Different variants of the TBARS assay include those in which the food sample reacts directly with the TBA reagent and those that involve collection of a distillate from the food before reaction with TBA. Interference of sodium caseinate (NaCas) in a TBARS assay involving direct reaction of TBA with a food sample was observed while exploring the possible retardation of lipid oxidation in sliced turkey meat coated with a NaCas-containing edible film. This short report shows the extent of interference encountered and illustrates the importance of validating the TBA method for particular applications.     

Physical properties of edible films made from mixtures of sodium caseinate and WPI

The physical properties of thin films (25–30 μm) made from mixtures of sodium caseinate (NaCas) and whey protein isolate (WPI) were investigated. Films were formed by mixing solutions of NaCas (2.5% w/w protein), plasticised with glycerol (NaCas–gly) at a glycerol:protein ratio of 0.32, with WPI solutions (2.3% w/w protein), plasticised (WPI-gly) at a glycerol:protein ratio 0.37. Tensile and water barrier properties of films formed from mixtures of NaCas–gly and WPI-gly were similar to films containing NaCas–gly only. Films containing only WPI-gly had higher maximum load and elastic modulus values than the mixed films. Increasing the NaCas–gly content of the films from 25 to 100% greatly increased solubility. This increased film solubility may increase the number of food applications for protein-based films.     

Use of sodium caseinate/glycerol edible films to reduce lipid oxidation in sliced turkey meat

The objective of this study was to investigate the influence of sodium caseinate films containing glycerol [glycerol:protein ratio 0.32 (w/w)] on lipid oxidation in cooked turkey breast meat slices. Slices were wrapped in films of different thickness (22, 42, and 58 μm) and were stored at 4 °C for 1, 2, 3 and 4 days. Lipid oxidation was measured using TBARS and hexanal assays on each day of storage while an olfactory sensory analysis was carried out on all the samples after 4 days of storage. TBARS values and hexanal levels of unwrapped samples (~6.0 mg MDA/kg and ~8.0 mg hexanal/kg) were significantly (P ≤ 0.05) higher than those of the casein film wrapped samples (~3.0 mg MDA/kg and ~3.0 mg hexanal/kg). Sensory analysis also showed significant (P ≤ 0.05) differences between wrapped samples and unwrapped samples, the former being perceived as less rancid. Thus wrapping in caseinate films may help reduce lipid oxidation in cooked turkey meat.     

Encapsulation of bixin in sodium caseinate to deliver the colorant in transparent dispersions

Bixin, the major colorant component of annatto, is water insoluble and sensitive to degradation by temperature, pH, and light stresses. In this work, we studied an encapsulation process by spray drying warm 40% v/v aqueous ethanol solution with dissociated sodium caseinate (NaCas) and dissolved bixin. Upon hydration of spray-dried powder, transparent dispersions were observed at a wide pH range away from the isoelectric point (pI) of NaCas. The stability of bixin was much improved and the consistent yellow color was obtained. The volume–length mean particle diameters of capsules were around 250 nm in dispersions, slightly bigger than that of NaCas, based on dynamic light scattering, but the difference was not observed based on atomic force microscopy. Capsules and the mixture of NaCas and bixin showed different fluorescence and FTIR spectra. At pH near the pI of casein, soluble soybean polysaccharides adsorbed strongly onto capsules and stabilized them from aggregation. The simple encapsulation approach studied in the present work showed a promising process to enhance the stability and dispersibility of carotenoids using NaCas as a carrier, especially in transparent dispersions.     

Interactions between pig gastric mucin and sodium caseinate in solutions and in emulsions

The interactions between pig gastric mucin (PGM) and sodium caseinate (Cas) were studied in solutions and in Cas-stabilized emulsions with respect to the ratio of the two components and the pH (1–7) with an emphasis on pH cycling, using absorbance, zeta potential, light scattering, creaming and microscopy measurements. In solutions, pH-reversible interactions were observed at pH 3 or lower, down to pH 1. Zeta potential measurements suggest that interactions are electrostatic in nature at pH 3, while the negligible charge of PGM allows for some attractive interactions with positively charged Cas at pH 1. Caseinate-stabilized oil-in-water emulsions are stable toward coalescence at pH 1 and pH 7; some coalescence is observed at pH 3. Addition of PGM results in flocculation, either due to depletion (pH 7), or due to bridging flocculation and Cas–PGM interactions similar to those observed in solution (pH 1 and pH 3). The flocculation is reversible, as is shown in pH cycling at pH 1 to pH 7, then to pH 1. Overall, the above can be of interest as an examination of the fate of emulsions in pH transitions and cycling in the human gastrointestinal tract.     

Purification of pectin from apple pomace juice by using sodium caseinate and characterisation of their binding by isothermal titration calorimetry

The binding of sodium caseinate to pectin using Isothermal Titration Calorimetry (ITC) under different pH values (2, 3, 3.5), and comparison of two purification processes (sodium caseinate or ethanol), based on the physicochemical characteristics of purified pectin was evaluated. The results indicated that ITC titration confirmed the existence of interactions between caseinates and pectin at pH 3 and 3.5. The interaction depicts two interdependent steps, one attributed to an electrostatic interaction and another related to a co-acervation mechanism. The chemical characteristics of pectins are strongly dependent on the purification process. Under some extraction conditions, ethanol is not specific to the recovery of pectin since it causes the precipitation of other compounds together with this polysaccharide.     

Phase behaviour of oat β-glucan/sodium caseinate mixtures varying in molecular weight

The isothermal phase behaviour at 5 °C of mixtures of sodium caseinate and oat β-glucan isolates varying in molecular weight (MW) was investigated by means of phase diagram construction, rheometry, fluorescence microscopy and electrophoresis. Phase diagrams indicated that the compatibility of the β-glucan/sodium caseinate system increases as β-glucan MW decreases. Images of mixtures taken at various biopolymer concentrations revealed phase separated domains. Results also revealed that at the state of thermodynamic equilibrium, lower MW samples yielded considerable viscosity in the mixture. At equivalent hydrodynamic volume of β-glucan in the mixtures, samples varying in molecular weight exhibited similar flow behaviour. A deviation dependent on the protein concentration was observed for the high MW sample in the concentrated regime due to the size of β-glucan aggregates formed. Results demonstrate that by controlling the structural features of β-glucan in mixtures with sodium caseinate, informed manipulation of rheological properties in these systems can be achieved.     

Potential of nisin-incorporated sodium caseinate films to control Listeria in artificially contaminated cheese

A sodium caseinate film containing nisin (1000 IU/cm²) was produced and used to control Listeria innocua in an artificially contaminated cheese. Mini red Babybel^® cheese was chosen as a model semi-soft cheese. L. innocua was both surface- and in-depth inoculated to investigate the effectiveness of the antimicrobial film as a function of the distance from the surface in contact with the film. The presence of the active film resulted in a 1.1 log CFU/g reduction in L. innocua counts in surface-inoculated cheese samples after one week of storage at 4 °C as compared to control samples. With regard to in-depth inoculated cheese samples, antimicrobial efficiency was found to be dependent on the distance from the surface in contact with the active films to the cheese matrix. The inactivation rates obtained were 1.1, 0.9 and 0.25 log CFU/g for distances from the contact surface of 1 mm, 2 mm and 3 mm, respectively. Our study demonstrates the potential application of sodium caseinate films containing nisin as a promising method to overcome problems associated with post-process contamination, thereby extending the shelf life and possibly enhancing the microbial safety of cheeses.     

Stability of sunflower protein hydrolysates in simulated gastric and intestinal fluids and Caco-2 cell extracts

The in vitro stability of bioactive properties in sunflower protein hydrolysates and purified peptides was studied by using simulated gastric fluid, simulated intestinal fluid, and Caco-2 cells extracts. Protein hydrolysates that inhibit the angiotensin converting enzyme and copper chelating peptides produced by hydrolysis with the microbial protease alcalase were partially resistant to incubation with simulated gastric and intestinal fluids. These hydrolysates and others produced by hydrolysis using pepsin plus pancreatin were also partially resistant to incubation with Caco-2 cells extracts. In addition, the ACE inhibitory peptide FVNPQAGS that is generated by extensive hydrolysis using pepsin and pancreatin, was found to be resistant to hydrolysis by Caco-2 cells extracts. These results suggest that stability in the digestive tract should not be a problem for the bioavailability of these bioactive peptides.     

NMR studies of the gelation mechanism and molecular dynamics in agar solutions

Changes in the molecular mobility of agar were measured by pulsed-field-gradient stimulated echo (PFG-STE) ¹H NMR at various temperatures in order to elucidate the mechanism of gelation in solutions. The echo signal intensity of agar decreased steeply and the diffusion coefficient D of agar increased near the sol-to-gel transition temperature T_s-g, and D decreased with further cooling. These results suggested that the polysaccharide chains in agar aggregated in bundles to form a network at around T_s-g. High molecular weight chains aggregated preferentially in agar, with the soluble, non-aggregated agar (“solute agar”) left in the network forming loose aggregates upon further cooling. Evidence for this behavior was obtained from GPC measurements on the solute agar squeezed from the gel. These loose aggregates readily disassociated on reheating, whereas the aggregated bundles were quite thermally stable, which corresponded well with the thermal stability of the gel strength. The changes in the restrictions on molecular mobility in these solutions were evaluated from measurements of D of a dendrimer added as a probe molecule, which was sensitive to the dilution of the solute agar accompanying gelation. The hydrodynamic shielding length ξ, which was considered to represent the hydrodynamic mesh size created by the solute agar, was calculated from D of the dendrimer, shedding light on the changes in the microscopic environment during gelation.