Surface protein coverage and its implications on spray-drying of model sugar-rich foods: Solubility,powder production and characterisation

We have investigated the amount of protein required to produce amorphous sugar powders through spray-drying. Pea protein isolate was used as a model plant protein and sodium caseinate was used as a model dairy protein. Powder recovery in a laboratory spray dryer was used as a measure of the ease of spray drying for a given formulation. More than 80% of amorphous sucrose and fructose was produced with the addition of sodium caseinate, while the pea protein isolate was able to produce only recoveries of less than 50% of amorphous sucrose. Sensitivity of low molecular weight surfactants has been demonstrated using both ionic (sodium stearoyl lactylate) and non-ionic (polysorbate-80) surfactants. Spray-dried powders were subjected to physico-chemical characterisation and dissolution experiments. The maximum solubility of all powders was obtained after 5 min of dissolution. The solubility of the sodium caseinate increased by 6–7% in the presence of fructose and low molecular weight surfactants. The solubility of the amorphous powders of sucrose–pea protein isolate was found to be lower than amorphous powders of sucrose–sodium caseinate and fructose–sodium caseinate. The addition of sucrose in water increased the solubility of the pea protein isolate from 16.84% to more than 83%. The non-ionic surfactant (Tween-80) has reduced the solubility of sucrose–pea protein isolate–Tween-80 powders significantly (p < 0.05) compared to those of sucrose–pea protein isolate–sodium stearoyl lactylate powders. The solubility of sucrose–sodium caseinate powders was comparable to that of pure sodium caseinate, indicating that addition of sucrose into 0.13% sodium caseinate does not have any significant effect on the solubility of this protein at this concentration.     

Heat-induced aggregation of whey proteins in the presence of κ-casein or sodium caseinate

Aggregates were formed by heating mixtures of whey protein isolate (WPI) and pure κ-casein or sodium caseinate at pH 7 and 0.1 M NaCl. The aggregates were characterized by static and dynamic light scattering and size exclusion chromatography. After extensive heat-treatment at 80 °C for 24 h, almost all whey proteins and κ-casein formed mixed aggregates, but a large proportion of the sodium caseinate did not aggregate. At a given WPI concentration the size of the aggregates decreased with increasing κ-casein or sodium caseinate concentration, but the overall self-similar structure of the aggregates was the same. The presence of κ-casein or caseinate therefore inhibited growth of the heat-induced whey protein aggregates. The results were discussed relative to the reported chaperone-like activity of casein molecules towards heat aggregation of globular proteins.     

Formation and functionality of whey protein isolate–(kappa-, iota-, and lambda-type) carrageenan electrostatic complexes

The formation of electrostatic complexes between whey protein isolate (WPI) and (κ-, ι-, λ-type) carrageenan (CG) was investigated by turbidimetric measurements as a function of pH (1.5–7.0), biopolymer weight-mixing ratio (1:1–75:1 WPI:CG) and NaCl addition (0–500 mM) to better elucidate underlying mechanisms of interaction. Emulsion stabilizing effects of formed complexes was also studied to assess their potential as emulsifiers. Complex formation followed two pH-dependent structure-forming events associated with the formation of soluble (pH_c) and insoluble (pH_?1) complexes. For both the WPI–κ-CG and WPI–ι-CG mixtures, pH_c and pH_?1 occurred at pH 5.5 and 5.3, respectively, whereas in the WPI–λ-CG mixture values were slightly higher (pH_c = 5.7; pH_?1 = 5.5). In all mixtures, maximum turbidity was found to occur near pH 4.5, before declining at lower pHs. Biopolymer mixing ratios corresponding to maximum OD was found to occur at the 12:1 ratio for both the WPI–κ-CG and WPI–λ-CG mixtures, and 20:1 ratio for WPI–ι-CG mixture. The addition of NaCl disrupted complexation within WPI–κ-CG mixtures as levels were raised, whereas when ι-CG and λ-CG was present, complexation was enhanced up to a critical Na⁺ concentration before declining. Adsorption of CG chains to the small WPI–WPI aggregates during complexation was proposed to be related to both the linear charge density and conformation of the CG molecules involved. Emulsion stability in the mixed systems (12:1 mixing ratio), regardless of the CG type (κ, ι, λ), was significantly higher than individual WPI solutions indicating enhanced ability to stabilize the oil-in-water interface.     

Pineapple fruit bromelain affinity to different protein substrates

Optimal pH and temperature conditions for proteolytic activity of pineapple fruit bromelain were determined using five different substrates: azocasein and azoalbumin (pH 3–10 at 20–70 °C), casein and sodium caseinate (pH 2–10 at 20–70 °C), and haemoglobin (pH 2–6.5 at 30–60 °C). Fruit bromelain has shown optimum activity at pH 7.5 for azoalbumin and at 6.5 for azocasein, all at 55 °C. Fruit bromelain activity determined with casein and sodium caseinate has shown optimum activity at 59 °C, while the optimum pH was 7.7 for casein and 6.5 for sodium caseinate. Optimum hydrolysis conditions of fruit bromelain towards haemoglobin showed a sharp peak at an acidic pH 2.9 at 37 °C. The lowest results of K_m and the highest results of V_max/K_m were found for azocasein and azoalbumin. These substrates are highly recommended for fruit bromelain activity determination.     

Effect of thermal treatments on the properties of coconut milk emulsions prepared with surface-active stabilizers

Previously we have demonstrated improved stability of coconut milk emulsions homogenized with various surface-active stabilizers, i.e., 1 wt% sodium caseinate, whey protein isolate (WPI), sodium dodecyl sulfate (SDS), or polyoxyethylene sorbitan monolaurate (Tween 20) [Tangsuphoom, N., & Coupland, J. N. (2008). Effect of surface-active stabilizers on the microstructure and stability of coconut milk emulsions. Food Hydrocolloids, 22(7), 1233–1242]. This study examines the changes in bulk and microstructural properties of those emulsions following thermal treatments normally used to preserve coconut milk products (i.e., −20 °C, −10 °C, 5 °C, 70 °C, 90 °C, and 120 °C). Calorimetric methods were used to determine the destabilization of emulsions and the denaturation of coconut and surface-active proteins. Homogenized coconut milk prepared without additives was destabilized by freeze–thaw, (−20 °C and −10 °C) but not by chilling (5 °C). Samples homogenized with proteins were not affected by low temperature treatments while those prepared with surfactants were stable to chilling but partially or fully coalesced following freeze–thaw. Homogenized coconut milk prepared without additives coalesced and flocculated after being heated at 90 °C or 120 °C for 1 h in due to the denaturation and subsequent aggregation of coconut proteins. Samples emulsified with caseinate were not affected by heat treatments while those prepared with WPI showed extensive coalescence and phase separation after being treated at 90 °C or 120 °C. Samples prepared with SDS were stable to heating but those prepared with Tween 20 completely destabilized by heating at 120 °C.     

Monitoring air/liquid partition of mastic gum oil volatiles in model alcoholic beverage emulsions: Effect of emulsion composition and oil droplet size

The purpose of this work was to study the impact of the structure and composition of hydroalcoholic emulsions on the air–liquid partition of aroma compounds of the essential oil of Pistacia lentiscus var. chia, commonly known as mastic gum oil (mainly consists of terpenes). Oil-in-water emulsions (φ = 0.17), containing 15% (v/v) ethanol, stabilized by three different emulsifiers (sodium caseinate, whey protein isolate and Tween 40), were prepared by using two different lipid phases (sunflower oil and anhydrous butter fat). The homogenization conditions were varied to obtain emulsions with different volume–surface mean diameters. The partition of the volatile compounds between air phase and emulsions at three different temperatures (25, 37 and 50 °C) was monitored by applying the Headspace Solid Phase Microextraction technique, followed by gas chromatography–mass spectrometry (GC–MS) analysis. In general, the results obtained showed that sodium caseinate was the most effective in retaining mastic aroma compounds, while WPI was the least effective. This could partly be explained by the different structure of the two proteins which, when adsorbed at the interface, form a membrane that acts as a barrier and influences the partition of the aroma compounds between the air and the liquid. At the same time interactions of aroma compounds with the two proteins in the bulk phase may also play a role. The retention of the aroma compounds depended on the oil droplet size only in the case of sodium caseinate containing emulsions at 37 and 50 °C. This behaviour could be due to the substantial increase in the thickness of the adsorbed casein layer when moving from a fine sized emulsion to one with a much larger size as well as to differences in the ratio of free to adsorbed emulsifier. The composition of the lipid phase also appeared to have a significant impact on the concentration of volatile compounds in the headspace of mastic gum oil containing emulsions stabilized by proteins. This was lower in the case of butter fat probably due to differences in composition with regard to fatty acid degree of saturation as well as to volatile absorption by the liquid lipid at 40 °C and subsequent entrapment in the semisolid fat at 25 °C.     

Interfacial and emulsifying properties of lentil protein isolate

The dynamic interfacial tension (DIFT) at oil–water interface, diffusion coefficients, surface hydrophobicity, zeta potential and emulsifying properties, including emulsion activity index (EAI), emulsion stability index (ESI) and droplet size of lentil protein isolate (LPI), were measured at different pH and LPI concentration, in order to elucidate its emulsifying behaviour. Sodium caseinate (NaCas), whey protein isolate (WPI), bovine serum albumin (BSA) and lysozyme (Lys) were used as benchmark proteins and their emulsifying property was compared with that of LPI. The speed of diffusion-controlled migration of these proteins to the oil/water interface, was in the following order: NaCas > LPI > WPI > BSA > Lys, while their surface hydrophobicity was in the following order: BSA > LPI > NaCas > WPI > Lys. The EAI of emulsions stabilised by the above proteins ranged from 90.3 to 123.3 m²/g and it was 93.3 ± 0.2 m²/g in LPI-stabilised emulsion. However, the stability of LPI-stabilised emulsions was slightly lower compared to that of WPI and NaCas-stabilised emulsions at the same protein concentration at pH 7.0. The ESI of LPI emulsions improved substantially with decrease in droplet size when protein concentration was increased (20–30 mg/ml). Reduction of disulphide bonds enhanced both the EAI and ESI compared to untreated samples. Heat treatment of LPI dispersions resulted in poor emulsion stability due to molecular aggregation. The stability of LPI-stabilised emulsions was found to decrease in the presence of NaCl. This study showed that LPI can be as effective emulsifiers of oil-in-water emulsions as are WPI and NaCas at ?20 mg/ml concentrations both at low and neutral pH. The emulsifying property of LPI can be improved by reducing the intra and inter-disulphide bond by using appropriate reducing agents.     

Effect of microbial transglutaminase treatment on thermal stability and pH-solubility of heat-shocked whey protein isolate

Whey protein isolate (WPI) dispersions (5% protein, pH 7.0) were subjected to heat-shock at 70 °C for 1, 5 and 10 min. The heat-shocked WPI dispersions were treated with microbial transglutaminase (MTGase) enzyme, and thermal properties and pH-solubility of the treated proteins were investigated. Heat-shocking of WPI for 10 min at 70 °C increased the thermal denaturation temperature (T_d) of β-lactoglobulin in WPI by about 1.5 °C. MTGase treatment (30 h, 37 °C) of the heat-shocked WPI significantly increased the T_d of β-lactoglobulin by about 6.3–7.3 °C when compared with heat-shocked only WPI at pH 7.0. The T_d increased by about 13–15 °C following pH adjustment to 2.5; however, the T_d of heat-shocked WPI was not substantially different from heat-shocked and MTGase-treated WPI at pH 2.5. Both the heat-shocked and the heat-shocked-MTGase-treated WPI exhibited U-shaped pH-solubility profiles with minimum solubility at pH 4.0–5.0. However, the extent of precipitation of MTGase-treated WPI samples at pH 4.0–5.0 was much greater than all heat-shocked and native WPI samples. The study revealed that while MTGase cross-linking significantly enhanced the thermal stability of β-lactoglobulin in heat-shocked WPI, it caused pronounced precipitation at pH 4.0–5.0 via decreasing the hydrophilic/hydrophobic ratio of the water-accessible protein surface.     

Influence of interfacial composition on oxidative stability of oil-in-water emulsions stabilized by biopolymer emulsifiers

The objective of this research was to evaluate the influence of storage pH (3 and 7) and biopolymer emulsifier type (Whey protein isolate (WPI), Modified starch (MS) and Gum arabic (GA)) on the physical and oxidative stability of rice bran oil-in-water emulsions. All three emulsifiers formed small emulsion droplets (d₃₂ < 0.5 μm) when used at sufficiently high levels: 0.45%, 1% and 10% for WPI, MS and GA, respectively. The droplets were relatively stable to droplet growth throughout storage (d₃₂ < 0.6 μm after 20 days), although there was some evidence of droplet aggregation particularly in the MS-stabilized emulsions. The electrical charge on the biopolymer-coated lipid droplets depended on pH and biopolymer type: −13 and −27 mV at pH 3 and 7 for GA; −2 and −3 mV at pH 3 and 7 for MS; +37 and −38 mV at pH 3 and 7 for WPI. The oxidative stability of the emulsions was monitored by measuring peroxide (primary products) and hexanal (secondary products) formation during storage at 37 °C, for up to 20 days, in the presence of a pro-oxidant (iron/EDTA). Rice bran oil emulsions containing MS- and WPI-coated lipid droplets were relatively stable to lipid oxidation, but those containing GA-coated droplets were highly unstable to oxidation at both pH 3 and 7. The results are interpreted in terms of the impact of the electrical characteristics of the biopolymers on the ability of cationic iron ions to interact with emulsified lipids. These results have important implications for utilizing rice bran oil, and other oxidatively unstable oils, in commercial food and beverage products.     

Lipid and water crystallization in protein-stabilised oil-in-water emulsions

Phase and state transitions occurring during freezing and thawing of oil-in-water emulsions with different water phase formulations, interfacial compositions and two lipid types were studied as crucial factors affecting emulsion stability. Emulsions containing 0–40% (w/w) sucrose in the water phase at pH 7, and 10, 20, 30, 40% (w/w) dispersed lipid phase (sunflower oil, SO or hydrogenated palm kernel oil, HPKO) with whey protein isolate, WPI, or sodium caseinate, NaCAS, (protein:lipid = 1:10 and 2:10) as emulsifier were prepared. Phase/state behaviour of the continuous and dispersed phases was determined by differential scanning calorimetry (DSC). Emulsion stability and morphology were derived from DSC data, gravitational separation and particle size analysis during 4 freeze-thaw cycles. Systems were stable when only lipid crystallization occurred. DSC data showed that lipid crystallization prior to water crystallization (i.e. emulsions containing HPKO) caused destabilisation at low sucrose concentrations (0, 2.5 and 5% w/w). Emulsions were stable if the dispersed oil phase crystallized after the dispersing water phase (i.e. emulsions containing SO). A concentration of sucrose ≥10% (w/w) in the aqueous phase gave stable emulsions. At 10:1 lipid to protein ratio, WPI showed better stabilising properties than NaCAS at 2.5 and 5% (w/w) sucrose. Double concentration of WPI (lipid:protein = 10:2) at 0% (w/w) sucrose significantly improved systems stability, whereas no positive effect was observed when the concentration of NaCAS was increased. From morphology study, in addition to lipid destabilisation, thickening and flocculation caused instability of the systems. These were extensive in systems containing WPI and were ascribed to interactions between whey proteins during thermal cycling.     

Assessment of physical and mechanical properties of sodium caseinate and stearic acid based film-forming emulsions and edible films

Edible films were prepared using sodium caseinate (6–8 g/100 g) and stearic acid (0–2 g/100 g). Effects of the ratio of stearic acid and sodium caseinate to water on the water vapor permeability (WVP) and mechanical properties of the prepared films were evaluated. Film-forming emulsions were also tested for rheological properties and surface tension. Changes in the ratios of sodium caseinate and stearic acid to water had significant effects on WVP (p < 0.05) and surface tension (p < 0.01). Higher values of consistency coefficient and elastic modulus were obtained in the presence of higher stearic acid. In addition, increase in stearic acid content increased the rate of water loss and gain of elastic modulus at the early stage of drying and resulted in production of less flexible film. The resultant edible film prepared with 6 g/100 g sodium caseinate and 2 g/100 g stearic acid showed the lowest WVP of 1.368 (g mm/m² h kPa).     

In vitro binding of bile salts by lentil flours, lentil protein concentrates and lentil protein hydrolysates

The binding capacity of bile salts by lentil flours produced from two varieties, Blaze and Laird and their protein concentrates and hydrolysates were studied. Sodium cholate, sodium deoxycholate, sodium taurocholate, sodium glycocholate and sodium chenodeoxycholate were tested individually, and their binding interactions with the lentil products were analyzed using the Trinity Biotech Bile Acids Kit 450-10 and compared to cholestyramine. All tested samples bound the bile salts investigated, and the amount of bile salts bound (> 70%) was sometimes greater than that bound by cholestyramine. Overall, there were no major differences in the bile salt binding capacities of similar samples prepared from the two varieties of lentil. In vitro digestion of the lentil proteins by pepsin/trypsin/??-chymotrypsin, alcalase/flavourzyme and papain significantly reduced the bile salt binding capacity compared to the undigested samples except in the case of sodium deoxycholate where no significant differences in bile salt binding were observed before and after hydrolysis. Binding of bile salts has been linked to cholesterol reduction, thus, the ability of the lentil products to bind bile salts is of interest as it may suggest that lentils could potentially have cholesterol-reducing properties.     

Oxidation promotes cross-linking but impairs film-forming properties of whey proteins

The objective of the study was to investigate the impact of oxidation on the film-forming properties of whey protein isolate (WPI). Sequential heating (70–90 °C) then oxidation (0.1 mM FeCl₃/1 mM ascorbate/0–20 mM H₂O₂) (H → O) or vice versa (O → H) were conducted to oxidize/unfold WPI at pH 6.8 and 8.0 before casting. The resulting films were characterized through mechanical, microstructural, and protein electrophoretic analyses. Oxidation promoted protein cross-linking mainly through disulfide bonds. Tensile strength (TS) and elongation at break (EAB) of films decreased for WPI oxidized by higher concentrations of H₂O₂. Film solubility (protein leachability) at pH 3–7, ranging from 20 to 40%, was unaffected by H₂O₂ up to 5 mM but reached almost 100% at above 5 mM H₂O₂ except at pH 4–5. β-Lactoglobulin dimers and its complex with α-lactalbumin were abundant in O → H WPI films and polymers of WPI dominated in H → O films. Microstructural images confirmed that oxidation promoted crumbly structures thereby explaining the reduced film-forming capability.     

Impact of surface deposition of lactoferrin on physical and chemical stability of omega-3 rich lipid droplets stabilised by caseinate

There is considerable interest in developing delivery systems to encapsulate and protect chemically labile lipophilic food components, such as omega-3 rich oils. In this study, multilayer emulsion-based delivery systems were prepared consisting of omega-3 rich oil droplets coated by either caseinate (Cas) or lactoferrin–caseinate (LF–Cas). Surface deposition of LF onto Cas-coated oil droplets was confirmed by ζ-potential measurements. Emulsions containing lactoferrin and caseinate had better physical stability to pH changes and salt addition (pH 3–7, 0–50 mM CaCl₂ at pH 7) than those containing only caseinate (pH 5–7, 0–2 mM CaCl₂ at pH 7). The addition of LF also retarded the formation of lipid oxidation markers (hydroperoxides and thiobarbituric acid reactive substances) in the emulsions. The ability of LF to enhance both the physical and chemical stability of protein-stabilised emulsions is useful for the fabrication of delivery systems designed for utilisation within the drug and food industries.     

Segregative interactions and competitive binding of Ca in gelling mixtures of whey protein isolate with Naκ-carrageenan

Gelling mixtures of Na⁺κ-carrageenan with whey protein isolate (WPI) at pH 7.0 have been studied rheologically and by differential scanning calorimetry (DSC), with comparative measurements for the individual constituents of the mixtures. The concentration of WPI was held fixed at 10.0 wt% and carrageenan concentration was varied in the range 0.05–3.0 wt%. Ca²⁺ cations, which have been shown previously to be particularly effective in inducing gelation of κ-carrageenan, were introduced as CaCl₂. The concentration of CaCl₂ used in most of the experiments was 8 mM, but other concentrations were also studied. Mixtures were prepared in the solution state at 45 °C, and showed no evidence of either phase separation or complex formation. Rheological changes were monitored by low-amplitude oscillatory measurements of storage modulus, G′, during (i) cooling (1 °C/min) and holding at 5 °C, to induce gelation of the carrageenan in the presence of non-gelled WPI; (ii) heating and holding at 80 °C to dissociate the carrageenan network and induce gelation of WPI; (iii) cooling and holding again at 5 °C, to give composite networks with both components gelled; and (iv) re-heating to 80 °C to dissociate the carrageenan network. Gel structure was characterised further by creep–recovery measurements at the end of each holding period, and by torsion measurements at 5 °C, before and after thermal gelation of WPI.     

Direct nanoHPLC-ESI-QTOF MS/MS analysis of tryptic caseinophosphopeptides

Caseinophosphopeptides (CPPs) were generated following tryptic hydrolysis of sodium caseinate. Hydrolysate peptides were separated and identified using nano-HPLC ESI-QTOF MS/MS. Sequence coverage in the 3 h hydrolysate was 79.4%, 55.6%, 80.9% and 68.1% for α_s1-, α_s2-, β- and κ-casein (CN), respectively. Variable levels of serine phosphorylation in β-CN f1–25 were observed in the 3 h hydrolysate. Analysis of β-CN f1–25 4P demonstrated that this peptide was stable during the course of hydrolysis. The effect of heat treatment (75 °C, 45 min) at pH 6.0, 7.0 and 8.0 on the peptide profile of the 3 h hydrolysate was studied. Compared to pH 6.0 and 8.0, least modification in phosphopeptide profiles was observed for the hydrolysate sample heated at pH 7.0. Different dephosphorylation and oxidation patterns were also observed following heat treatment at the three pH values. These results demonstrate that heat treatment, in addition to pH, has a major effect on both the phosphorylated and non-phosphorylated peptide profiles of CN hydrolysates.     

Physical assessment of composite biodegradable films manufactured using whey protein isolate,gelatin and sodium alginate

Composite films were manufactured using whey protein isolate (WPI), gelatin (G) and sodium alginate (SA) using a simplex centroid design. Tensile strength (TS), puncture strength (PT), percentage elongation at break point (E), tear strength (TT), water vapour permeability (WVP) and oxygen permeability (OP) of films were evaluated. The interactions between biopolymers showed quadratic effects (P < 0.01) on TS, E, PT, TT and WVP values. Scanning electron microscopy (SEM) was performed to investigate the microstructures of composite films. The proportion of ingredients required to produce the optimum composite films was determined to be: WPI (g):G (g):SA (g) = 8.0:12.0:5.0. Overall, films (WPIGSA-9) produced using the combination of WPI (g):G (g):SA (g) = 10.0:16.0:14.0 demonstrated the best barrier to oxygen (8.00 cm³ μm/m² d kPa); while films (WPIGSA-1) showed the best barrier to water vapour (48.04 g mm/kPa d m²); films (WPIGSA-6) using the combination of WPI (g):G (g):SA (g) = 10.0:17.5:22.5 had the best mechanical properties of all of the experimental composite films tested.     

Influence of salt and pH on the solubility and structural characteristics of transglutaminase-treated wheat gluten hydrolysate

Hydrolyzed wheat gluten (GH, 77–85% protein) was prepared by limited chymotrypsin digestion at 37 °C for 4 h (degree of hydrolysis = 6.4%) and 15 h (degree of hydrolysis = 10.3%). Microbial transglutaminase (MTGase) treatment (55 °C for 1 h, or 5 °C for 18 h) effect on the solubility and structural characteristics of GH was examined under selected food processing conditions (pH 4.0–7.0, 0–0.6 M NaCl). The MTGase treatment increased solubility of GH by 3–29-fold (P < 0.05) within pH 4.0–7.0. Addition of 0.6 M NaCl or changing the conditions of MTGase incubation did not significantly alter solubility characteristics of GH. The MTGase treatment decreased surface hydrophobicity, and increased carboxyl groups in GH, suggesting cross-linking and deamidation. Fluorescence and UV spectra attributed the improved GH solubility to MTGase-induced polar environment, and partial masking of some nonpolar aromatic amino acids possibly due to high-molecular-weight polypeptides formed.     

Light scattering study of sodium caseinate + dextran sulfate in aqueous solution: Relationship to emulsion stability

Using combined static and dynamic light scattering, various structural and thermodynamic parameters have been determined for the complex particles formed from sodium caseinate (0.5 wt/v%) + dextran sulfate (0.01, 0.1 or 1.0 wt/v%) in aqueous solution at pH = 6.0. The polysaccharide contents refer, respectively, to three polysaccharide/protein molar ratios (R = 1, 10 and 100) calculated on the basis of the measured values of the weight-average molar masses of sodium caseinate particles and dextran sulfate molecules. The complexes were prepared by mixing together the two biopolymer components in bulk solution or bringing them together at the interface in a protein-stabilized foam. The results indicate dissociation of the original sodium caseinate particles in response to associative interactions with excess amounts of negatively charged polysaccharide. A significant difference was observed between properties of complexes formed in solution and those formed at the interface, especially for R = 100. We identify a possible correlation between the structures of these complexes and the recently reported stability properties of oil-in-water emulsions containing the same biopolymers (Jourdain, L., Leser, M. E., Schmitt, C., Michel, M., & Dickinson, E. (2008). Food Hydrocolloids, 22, 647–659). In particular, we infer that the greater hydrophilicity and the more open/bulky architecture of complexes formed in the bulk aqueous phase are better able to provide effective steric/electrostatic stabilization of the so-called “mixed” emulsions, as compared with the interfacial complexes formed in the so-called “bilayer” emulsions. We also present results on the effect of ionic strength on the structural parameters of the complexes, and we attempt to interpret the data in the context of previously determined stability behaviour of the corresponding emulsions.     

Functional properties of fish protein hydrolysates from Pacific whiting(Merluccius productus) muscle produced by a commercial protease

Pacific whiting (Merluccius productus) muscle was used to produce hydrolysates with 10%, 15% and 20% degree of hydrolysis (DH) using the commercial protease Alcalase^® and were characterized at pH 4.0, 7.0 and 10 according their solubility, emulsifying and foaming properties. Protein recovered in soluble fractions increased proportionally with the hydrolytic process, yielded 48.6 ± 1.9, 58.6 ± 4.1 and 67.8 ± 1.4 of total protein after 10%, 15% and 20% DH, respectively. Freeze-dried hydrolysates presented almost 100% solubility (p > 0.05) at the different pHs evaluated. Emulsifying properties (EC, EAI and ESI) were not affected by DH as most samples showed similar (p > 0.05) results. Higher EC (p ? 0.05) than sodium caseinate, used as control, were obtained at pH 4 for most hydrolysates. Hydrolysates showed very low foaming capacity not affected by pH; but foam stability was equal or even better (p > 0.05) than bovine serum albumin (BSA), except at pH 4.0. Results suggest that hydrolysates from Pacific whiting muscle can be produced with similar or better functional properties than the food ingredients used as standards.