Influence of sucrose on cold gelation of heat‐denatured whey protein isolate

A solution of heat‐denatured whey proteins was prepared by heating 100 g kg⁻¹ whey protein isolate (WPI) at pH 7.0 to 75 °C for 15 min in the absence of salt. Heat treatment caused the globular protein molecules to unfold, but electrostatic repulsion opposed strong protein–protein aggregation and so prevented gel formation. When the heat‐denatured whey protein solution was cooled to room temperature and mixed with 15 mM CaCl₂, it formed a gel. We investigated the influence of the presence of sucrose in the protein solutions prior to CaCl₂ addition on the gelation rate. At relatively low concentrations (0–100 g kg⁻¹), sucrose decreased the gelation rate, presumably because sucrose increased the aqueous phase viscosity. At higher concentrations (100–300 g kg⁻¹), sucrose decreased the gelation rate, probably because sugar competes for the water of hydration and therefore increases the attraction between proteins. These data have important implications for the application of cold‐setting WPI ingredients in sweetened food products such as desserts. © 2000 Society of Chemical Industry     

Cold-set whey protein–flaxseed gum gels induced by mono or divalent salt addition

Mixed cold-set whey protein isolate (WPI)–flaxseed gum (FG) gels, induced by the addition of CaCl₂ or NaCl at fixed ionic strength (150 mM), were evaluated with respect to their mechanical properties, water-holding capacity (WHC) and SEM microscopy. They were prepared by mixing FG and thermally denatured (90 °C/30 min) WPI solutions at room temperature, but the gels were formed at 10 °C using two methods of salt incorporation: diffusion through dialysis membranes and direct addition. The mixed systems formed using dialysis membranes showed phase separation with the development of two (axial) layers, and the CaCl₂-induced gels presented radial phase separation. In general the CaCl₂-induced gels were less discontinuous, stronger, and showing lower WHC and deformability than the NaCl-induced gels. An increase in the FG concentration reduced the gel strength and WHC for both systems, which was associated with a prevailing phase separation between the biopolymers over the gelation process. Using direct salt addition, apparently none of the mixed gels showed macroscopic phase separation, but the NaCl-induced gels showed much higher hardness and elasticity than the CaCl₂-induced gels. Since the gelation process occurred more quickly by direct salt addition, and more effectively for the divalent salts, the more fragile structure of the CaCl₂-induced gels was a consequence of disruption of the cross-link interactions of the aggregates during the agitation used to homogenize the salt added.     

Physicochemical Properties of Whey Protein-Stabilized Emulsions as affected by Heating and Ionic Strength

Corn oil-in-water emulsions (19.6 wt%; d₃₂～ 0.6 μm) stabilized by 2 wt% whey protein isolate (WPI) were prepared with a range of pH (3–7) and salt concentrations (0–100 mM NaCl). These emulsions were heated between 30 and 90°C and their particle size distribution, rheological properties and susceptibility to creaming measured. Emulsions had a paste-like texture around the isoelectric point of WPI (～φ 5) at all temperatures, but tended to remain fluid-like at pH >6 or <4. Heating caused flocculation in pH 7 emulsions between 70 and 80°C (especially at high salt concentrations), but had little effect on pH 3 emulsions. Flocculation increased emulsion viscosity and creaming. Results were interpreted in terms of colloidal interactions between droplets.     

Dilute solution properties of wild sage (Salvia macrosiphon) seed gum

In this paper, the effect of salt type (sodium and calcium chlorides), salt concentration (0, 0.5, 20 and 50 mM) and temperature (20, 30 and 40 °C) on the properties of dilute sage seed gum (SSG) solutions were investigated. SSG was evaluated for intrinsic viscosity by various models i.e. Huggins, Kraemer, Higiro and Tanglertpaibul and Rao equations. The results showed that the Tanglertpaibul & Rao and Higiro equations were chosen as the best models for intrinsic viscosity determination of SSG at different temperatures and salts concentrations, respectively. The increase in ionic strength of the NaCl and CaCl₂ from 0 to 0.5 mM caused increase in intrinsic viscosity, but increasing the temperature from 20 to 40 °C and salts concentrations from 0.5 to 50 mM decreased the intrinsic viscosity. Divalent ions from CaCl₂ showed a more pronounced effect on the intrinsic viscosity compared with monovalent ions from NaCl. SSG solutions at all temperatures and salts concentrations were in the dilute domain. The weight-average molecular weight of sage seed gum was obtained as 1.5 × 10⁶ Da.     

Fermentation of Cucumbers Brined with Calcium Chloride Instead of Sodium Chloride

ABSTRACT: Waste water containing high levels of NaCl from cucumber fermentation tank yards is a continuing problem for the pickled vegetable industry. A major reduction in waste salt could be achieved if NaCl were eliminated from the cucumber fermentation process. The objectives of this project were to ferment cucumbers in brine containing CaCl₂ as the only salt, to determine the course of fermentation metabolism in the absence of NaCl, and to compare firmness retention of cucumbers fermented in CaCl₂ brine during subsequent storage compared to cucumbers fermented in brines containing both NaCl and CaCl₂ at concentrations typically used in commercial fermentations. The major metabolite changes during fermentation without NaCl were conversion of sugars in the fresh cucumbers primarily to lactic acid which caused pH to decrease to less than 3.5. This is the same pattern that occurs when cucumbers are fermented with NaCl as the major brining salt. Lactic acid concentration and pH were stable during storage and there was no detectable production of propionic acid or butyric acid that would indicate growth of spoilage bacteria. Firmness retention in cucumbers fermented with 100 to 300 mM CaCl₂ during storage at a high temperature (45 °C) was not significantly different from that obtained in fermented cucumbers with 1.03 M NaCl and 40 mM CaCl₂. In closed jars, cucumber fermentations with and without NaCl in the fermentation brine were similar both in the chemical changes caused by the fermentative microorganisms and in the retention of firmness in the fermented cucumbers.     

Ca2+-Induced Gelation of Pre-heated Whey Protein Isolate

Addition of CaCl₂ to pre-heated whey protein isolate (WPI) suspensions caused an increase in turbidity when pre-heating temperatures were ≥ 64°C. Pre-heating to ≥ 70°C was required for gelation. WPI suspensions which contained CaCl₂ became turbid at 45°C and formed thermally induced gels at 66°C. Thermally and Ca²⁺-induced gels showed significant time/temperature effects but the penetration force values in the Ca²⁺-induced gels were always lower. However, Ca²⁺-induced gels were higher in shear stress at fracture. The Ca²⁺-induced gels had a fine-stranded protein matrix that was more transparent than the thermally induced gels, which showed a particulate microstructure.     

Comparison of properties of oil-in-water emulsions stabilized by coconut cream proteins with those stabilized by whey protein isolate

Coconut cream protein (CCP) fractions were isolated from coconuts using two different isolation procedures: isoelectric precipitation (CCP1-fraction) and freeze–thaw treatment (CCP2-fraction). The ability of these protein fractions to form and stabilize oil-in-water emulsions was compared with that of whey protein isolate (WPI). Protein solubility was a minimum at ∼pH 4, 4.5 and 5 for CCP1, CCP2, and WPI, respectively, and decreased with increasing salt concentration (0–200 mM NaCl) for the coconut proteins. All of the proteins studied were surface active, but WPI was more surface active than the two coconut cream proteins. The two coconut cream proteins were used to prepare 10 wt% corn oil-in-water emulsions (pH 6.2, 5 mM phosphate buffer). CCP2 emulsions had smaller mean droplet diameters (d₃₂ ≈ 2 μm) than CCP1 emulsions (d₃₂ ≈ 5 μm). Corn oil-in-water emulsions (10 wt%) stabilized by 0.2 wt% CCP2 and WPI were prepared with different pH values (3–8), salt concentrations (0–500 mM NaCl) and thermal treatments (50–90 °C for 30 min). Considerable droplet flocculation occurred in the emulsions near the isoelectric point of the proteins: CCP2 (pH ∼ 4.3); WPI (pH ∼ 4.8). Emulsions with monomodal particle size distributions, small mean droplet diameters, and good creaming stability could be produced at pH 7 for WPI, but CCP2 produced bimodal distributions at this pH. The CCP2 and WPI emulsions remained relatively stable to droplet aggregation and creaming at NaCl concentrations ⩽50 and ⩽100 mM, respectively. In the absence of salt, both CCP2 and WPI emulsions were quite stable to thermal treatments (50–90 °C for 30 min).     

Controlling denaturation and aggregation of whey proteins during thermal processing by modifying temperature and calcium concentration

Whey protein isolate solutions (8.00 g protein/100 g; pH 6.8) were treated for 2 min at 72, 85 or 85 °C with 2.2 mM added calcium Ca to produce four whey protein systems: unheated control (WPI‐UH), heated at 72 °C (WPI‐H72), heated at 85 °C (WPI‐H85) or heated at 85 °C with added Ca (WPI‐H85Ca). Total levels of whey protein denaturation increased with increasing temperature, while the extent of aggregation increased with the addition of Ca, contributing to differences in viscosity. Significant changes in Ca ion concentration, turbidity and colour on heating of WPI‐H85Ca, compared to WPI‐UH, demonstrated the role of Ca in whey protein aggregation.     

Thermal and Calcium Pretreatment Affects Texture, Pectinesterase and Pectic Substances of Frozen Sweet Cherries

Freezing causes loss of turgidity and firmness in sweet cherries. Thermal pretreatment at 50°C for 10 min followed by immersion in 100 mM CaCl₂ and thermal pretreatment at 70°C/2 min with or without immersion in 100 mM CaCl₂ prevented freezing-induced loss of firmness. Thermal pretreatments increased the pectin fraction soluble in EDTA, reduced the degree of pectin esterification, and increased both the concentration of divalent cations in the cell wall and the pectinesterase activity bounded to the cell wall. Immersion in CaCl₂ increased the concentration of Ca²⁺ cations in the cell wall and enhanced the effect of thermal pretreatments on pectinesterase activity.     

Calcium Treatment to Maintain Quality of Zucchini Squash Slices

Zucchini squash slices dipped in solutions of CaCl₂ alone or with chlorine were stored at 0°C, 5°C, and 10°C. Slices developed water soaked areas (chilling injury) at 0°C and brown discoloration at 5°C and 10°C, which increased with storage. The amount and severity of chilling injury/browning/decay of water-dipped controls were least at 5°C. Calcium treatments helped in reducing development of decay, rate of total microbial growth, ascorbic acid loss, and shear force decrease of slices stored at 0°C and 10°C but not at 5°C. Addition of chlorine to CaCl₂ seemed to have some benefits at 0°C or 10°C.     

The emulsifying properties of Persian gum (Amygdalus scoparia Spach) as compared with gum Arabic

The current study compares the emulsifying properties of Persian gum (PG) and gum Arabic (GA) in emulsions. The effects of concentration (0.5–3% w/v PG, 2.5–15% w/v PG), pH (2–7), ionic strength [NaCl, CaCl₂ (0–300 mM)], and temperature (40–90°C) were investigated. The surface–volume mean diameter (D₃₂) of the emulsions showed that the minimum values were 9.89 ± 0.68 and 4.52 ± 0.03 µm for emulsions containing 1.5% w/v PG and 15% w/v GA, respectively. In addition, the zeta potential of PG and GA emulsion changed from ?23.5 to ?39.5 and ?30.5 to ?46.0 mV, respectively. The interfacial tensions of PG and GA emulsions were varied in the ranges of 34.0–15.0 and 29.0–9.0 mN/m, respectively. Changes in the D₃₂ value of GA emulsions showed were not significantly different (p > 0.05) with respect to the effects of pH, NaCl, CaCl_2, and temperature. The NaCl concentration had no significant effect on D₃₂; but its value decreased from 13.11 to 5.70 µm as the CaCl₂ concentration increased. The interfacial tension of PG significantly increased with decreasing pH 7–2 and increasing 0–300 mM salts. After heating (25–90°C), the D₃₂ values of PG and GA emulsions changed to 11.04–14.54 and 4.21–4.21 μm, respectively. The results of this study can be useful for the application of PG as an emulsifier in beverage emulsions.     

Enhancement of the functional properties of whey protein by conjugation with maltodextrin under dry‐heating conditions

Conjugation of whey protein isolate (WPI) and maltodextrin (MD, dextrose equivalent of 6) was achieved by dry‐heating at an initial pH of 7.0, at 60 °C and 79% relative humidity, with WPI: MD6 ratio of 1:1, for up to 24 h. Conjugation was achieved with limited development of colour and advanced Maillard products on 24 h of heating. Conjugation increased the protein solubility at pH 4.5, by 7.1–8.5%, compared to the unheated and heated WPI controls. Conjugation of WPI with MD6 enhanced the stability and retention of clarity in protein solutions heated at 85 °C for 10 min with 50 mM added NaCl.     

Chemical and physico-chemical characterisation of fibres from Laminaria digitata (kombu breton): A physiological approach

The content and chemical composition of soluble and insoluble dietary fibres from the brown marine alga Laminaria digitata (kombu breton) were determined. Two enzymic-gravimetric methods were used to determine (1) the content of soluble and insoluble fibres according to a modification of the AOAC procedure, and (2) the distribution of the soluble fibres in saline buffer at 37°C and at pH 2·0 and 7·5 used to simulate the gastric and intestinal phases of digestion, respectively. The total dietary fibre contents obtained by the two methods were similar (37·3 and 40·0%) and of these 84·8–87·4% was soluble. A partitioning of soluble fibres may occur during digestion since 49·3% was recovered in saline buffer at pH 2·0 whereas 50·7% was recovered in saline buffer at pH 7·5. Solubility of dietary fibres was related to the chemistry of brown algal polysaccharides. Fucans and laminarans were essentially soluble at pH 2·0 and alginate at pH 7·5, and insoluble fibres consisted primarily of cellulose. Oil adsorption and hydration properties (uptake, retention and swelling) in water, 154 mM NaCl, and 38 mM CaCl₂ at 20 and 37°C of three particle sizes of L digitata were measured. Oil adsorption was low (0·16–0·41 g g^?1) and was related to the particle size of the fibres. Hydration properties were more important with small particles except in CaCl₂ solution and followed the order water > NaCl > CaCl₂. Water uptake and swelling were greater at 37°C than at 20°C. The overall decrease in hydration properties observed with solutions of ionic strength ～0·15 was interpreted as reflecting the decrease in the electrostatic repulsion between charged polysaccharides. The lowest water uptake, water retention and swelling were obtained with solutions of CaCl₂, and were related to the known selective afinity of alginate for calcium. Thus, L digitata is especially rich in soluble dietaryfibres, and these have physico-chemical properties characteristic of the polysaccharides present. Water absorption and uptake and swelling can be modulated according lovarious physical and chemical parameters.     

Crystallization Kinetics of Concentrated α,α-Trehalose and α,α-Trehalose/Salt Solutions Studied by Low-resolution 1H-Pulsed NMR

Crystallization kinetics of concentrated trehalose and trehalose/salt solutions were followed by proton ¹H) pulsed nuclear magnetic resonance (¹H p‐NMR). Three concentrations (66,70, and 72.5%) of trehalose and with the addition of ZnCl₂.2H₂O, CaCl₂.2H₂O, and MgCl₂.2H₂O were crystallized at 5,10,15,20, and 25 °C. Supercooling and molecular diffusion determined the crystallization rates. The highest rate of crystallization of 66,70, and 72.5% trehalose occurred at 20 °C, whereas the lowest rate occurred at 25 °C. The maximum solid content was higher at lower temperatures, as expected based on the higher supercooling values. Crystallization was delayed by the addition of salts and especially of CaCl₂.2H₂O.     

Tuning the properties of β-lactoglobulin nanofibrils with pH,NaCl and CaCl2

We investigated the effects of pH (1.6–2.4), NaCl and CaCl₂ (0–100 mm) on the kinetics of β-lactoglobulin fibril formation during heating at 80 °C. The morphology of fibrils was also examined. At pH 1.8–2.4 fibril formation occurred slightly faster with decreasing pH. At pH 1.6 fibril formation during the growth phase occurred much faster than at any other pH. Fibril morphology was unchanged between pH 1.6 and pH 2.0. Addition of NaCl or CaCl₂ accelerated fibril formation during the growth phase, and CaCl₂ shortened the lag phase as well. Worm-like fibrils were seen at ≥60 mm NaCl or ≥33 mm CaCl₂, and these had a persistence length which was much shorter than the long semi-flexible fibrils formed without salts. The efficiency of fibril formation can be substantially enhanced by varying pH and salt concentration.     

Purification and characterization of lysozyme from filipino venus, Ruditapes philippinarum

Lysozyme from Filipino venus (Ruditapes philippinarum) was purified by ion-exchange and gel filtration chromatography. The purification fold and yield were 3,402 and 32.4%, respectively. The molecular weight was determined to be 13.4 kDa by SDS-PAGE. The specific activity of lysozyme was 3.76×10⁵ units/mg protein with Micrococcus lysodeikticus as a substrate. The optimum temperature and pH of lysozyme were 75°C and 5.5, respectively. Lysozyme activity was decreased with about 45% after heat treatment for 30 min at 80°C, and completely inactivated at 100°C. It was activated by NaCl (10–70 mM), MgCl₂, and CaCl₂ (2–5 mM) whereas it was inhibited by ZnCl₂ (2–30 mM).     

Kinetics and equilibria of tea infusion: Part 7—The effects of salts and of pH on the rate of extraction of caffeine from Kapchorua Pekoe Fannings

The rates of extraction of caffeine from sieved Kapchorua PF (600–710 μm) have been measured at 80°C with a range of aqueous salt and buffer solutions of ionic strength 0·11 mol dm⁻³. The first-order rate constants and the half-times of infusion showed no trend with pH when buffers from pH 3·0 to pH 8·3 were employed. The rate constants decreased on the addition of common salts like NaCl, KCl and CaCl₂ but increased in the presence of electrolytes such as Bu₄NCl that contain large ions. The results cannot be interpreted by changes in osmotic pressure although Donnan effects may be involved. Close parallels were found between the rate constants and the solubilities of caffeine in electrolyte solutions at 25°C. In particular, the values of both properties rise appreciably in the presence of species containing aromatic or other organic rings with which caffeine molecules associate.     

Cold‐set whey protein gels induced by calcium or sodium salt addition

Cold‐set whey protein isolate (WPI) gels formed by sodium or calcium chloride diffusion through dialysis membranes were evaluated by mechanical properties, water‐holding capacity and microscopy. The increase of WPI concentration led to a decrease of porosity of the gels and to an increase of hardness, elasticity and water‐holding capacity for both systems (CaCl₂ and NaCl). WPI gels formed by calcium chloride addition were harder, more elastic and opaque, but less deformable and with decreased ability to hold water in relation to sodium gels. The non linear part of stress–strain data was evaluated by the Blatz, Sharda, and Tschoegl equation and cold‐set gels induced by calcium and sodium chloride addition showed strain‐weakening and strain‐hardening behaviour, respectively. The fractal structure of the gels indicated a weak‐link behaviour. For WPI gels results suggest intrafloc links, formed at heating step, which were more rigid than the interfloc links, promoted by salt addition.     

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.     

Factors Influencing the Heat Resistance of a Heat-Resistant Lipase of Pseudomonas

Pseudomonas spp. MC50 produced an extra-cellular lipase that was extremely heat resistant at 100–150°C when heated in water or emulsions. The D-values ranged from 40 min at 100°C to 84 sec at 150°C. The z_D-vallue was 36°C. When heated in water, the lipase exhibited greatest survival at pH 8.5. Below pH 6.5, survival was less than 10% of that at pH 8.5. Survival of lipase heated in emulsions was affected somewhat by the type of oil, corn oil concentration, and type of emulsifier. Type of stabilizer or stabilizer concentration had little effect on lipase survival. Lipase treated with ethylenediaminetetraacetate (EDTA) was fully heat resistant in water; survival declined when lipase was heated in CaCl₂ solutions of 3–120 mM.