Effects of Reducing Agent Concentration on Soy Protein Fractionation and Functionality

ABSTRACT: The concentration of the reducing agent SO₂ significantly affected fraction yields, purities, and compositions during soy protein fractionation, especially the purity of the glycinin-rich fraction. The optimum amount of reducing agent was 5 m M SO₂ based on protein yields, purities, and functional properties. With no SO₂, the glycinin-rich fraction contained 29% of the total protein with only 63% glycinin, and the β-conglycinin-rich fraction contained 10% of the total protein with 94%β-conglycinin; whereas, by adding 5 m M SO₂, the glycinin-rich fraction contained 23.4% of total protein with 81.5% glycinin, and the β-conglycinin-rich fraction contained 16.8% of the total protein with 83.7%β-conglycinin. Increasing amounts of storage proteins were lost in the whey fraction as SO₂ concentration increased. The functional properties of the 2 major fractions were greatly influenced by the addition of SO₂. The thermal behaviors of the fractions were only slightly affected by using higher amounts of SO₂. The solubility and hydrophobicity of the glycinin-rich fraction decreased with increasing SO₂ concentration, whereas the solubility of the β-conglycinin-rich fraction increased. Emulsification properties of the glycinin-rich fraction were adversely affected by higher SO₂ concentrations, whereas, those of the β-conglycinin-rich fraction were improved. The β-conglycinin-rich fractions had better emulsification properties than did the glycinin-rich fractions. The best foaming properties were achieved at 5 m M SO₂.     

Characterisation of soybean glycinin and β-conglycinin fractionated by using MgCl2 instead of CaCl2

A simple two step precipitation method was used to investigate the effect of MgCl₂ instead of CaCl₂ on fractionation of soybean glycinin and β-conglycinin. Compositional and physicochemical properties of the resulting protein fractions were characterised. The optimised procedure, in terms of protein yield, purity, phytate content and physicochemical properties, was obtained when the addition of 5 m m MgCl₂ was used. After application of 5 m m MgCl₂, the phytate content of the glycinin-rich and β-conglycinin-rich fractions was about 0.4% and 1.3%, respectively, but the addition of 5 m m CaCl₂ increased the phytate content of the glycinin-rich fraction to 1.25% and decreased that of β-conglycinin-rich fraction to 0.67%. Low phytate protein product was suitable for use in infant formula and acidic food. The solubility of the glycinin-rich fractions with MgCl₂ was significantly higher than that with CaCl₂ at pH < 4.5. Application of MgCl₂ improved thermal stability of the β-conglycinin-rich fraction.     

Incorporation of Soymilk Lipid into Soy Protein Coagulum by the Addition of Calcium Chloride

ABSTRACT: The effect of protein composition on the lipid incorporation into protein coagulum (tofu curd) was investigated using soymilk prepared from mixtures of glycinin-rich and β-conglycinin-rich soybeans. The lipid incorporation takes place with the addition of CaCl₂ so that a particulate fraction of the protein is aggregated. The incorporation occurred by less addition of CaCl₂ with increasing glycinin in soymilk. The protein particle content and the glycinin content of the particles increased along with increasing glycinin. The lipid incorporation took place at lower CaCl₂ concentration when the particulate glycinin content was high. The mechanism of the lipid incorporation into soybean curd is discussed from these results.     

Effects of NaCl Concentration on Salting-in and Dilution During Salting-out on Soy Protein Fractionation

ABSTRACT:  Glycinin and β-conglycinin are the main storage proteins in soybeans that can be fractionated by using alkali extraction, SO₂, salting-in with NaCl, salting-out by dilution and pH adjustment to produce a glycinin-rich fraction, a β-conglycinin–rich fraction, and an intermediate fraction, which is a mixture of the two proteins. Two different strategies were employed to optimize the procedure to achieve high efficiency in recovering the β-conglycinin–rich fraction. The first strategy was to optimize salting-in effects of NaCl, and the effects of NaCl concentration on the yields and purities of the protein fractions were investigated. The maximum protein yield of the β-conglycinin–rich fraction was obtained at 500 mM NaCl, but at the expense of purity. The optimum NaCl concentration was 250 mM, at which good protein yield (18.5%) and purity (84.5%) were achieved. At higher NaCl concentrations, the protein yields of the intermediate fractions were significantly lower, and the protein loss in the whey fraction increased. The second strategy was to improve the salting-out step for the β-conglycinin–rich fraction. At 0- and 0.5-fold dilution, the purities and yields of the β-conglycinin–rich fractions were significantly lower than at 1.0- and 2.0-fold dilution. There were no differences in protein yields or purities when using 1.0- or 2.0-fold dilution. According to these results, the recommended NaCl concentration for the salting-in step is 250 mM and the dilution factor for salting-out is 1.0.     

Functional Properties of Improved Glycinin and β-nglycinin Fractions

ABSTRACT: Glycinin and β-conglycinin have unique functionality characteristics that contribute important properties in soy foods and soy ingredients. Limited functionality data have been published for glycinin and β-conglycinin fractions produced in pilot-scale quantities. Protein extraction conditions were previously optimized for our pilotscale fractionation process to maximize protein solubilization and subsequent product recovery. Glycinin, β-conglycinin, and intermediate (mixture of glycinin and β-conglycinin) fractions were prepared using optimized-process (OP) extraction conditions (10:1 water-to-flake ratio, 45°C) and previous conditions termed Wu process (WP) (15:1, 20°C). Viscosity, solubility, gelling, foaming, emulsification capacity, and emulsification activity and stability of the fractionated proteins, and soy protein isolate (SPI) produced from the same defatted soy white flakes were compared to evaluate functional properties of these different protein fractions. Differential scanning calorimetry, sodium dodecylsulfate-polyacrylamide gel electrophoresis, and surface hydrophobicity data were used to interpret functionality differences. OP β-conglycinin had more glycinin contamination than did the WP β-conglycinin. OP and WP solubility profiles were each similar for respective glycinin and β-conglycinin fractions. Emulsification activities and stabilities were higher for OP β-conglycinin and OP intermediate fractions compared with respective WP fractions. β-Conglycinin and SPI emulsification capacities (ECs) mirrored solubility profile, whereas glycinin ECs did not. OP glycinin had a higher foaming capacity than WP glycinin. OP and WP intermediate fraction apparent viscosities trended higher than those of other protein fractions. β-Conglycinin dispersions at pH 3 and 7 produced firm gels at 80°C, whereas glycinin dispersions formed weaker gels at 99°C and did not gel at 80°C.     

Factors Determining Yield Stress and Overrun of Whey Protein Foams

ABSTRACT: Foams were formed by whipping whey protein solutions (15% w/v protein) containing NaCl, CaCl₂, lactose, or glycine. Foam overrun and yield stress were determined. Foams made from whey protein ingredients have greater overrun and yield stress if the concentration of β-lactoglobulin is high relative to a-lactalbumin. The presence of 0.4 M CaCl₂ in the foaming solution increases overrun and yield stress for β-lactoglobulin and a-lactalbumin. The high yield stress of β-lactoglobulin and a-lactalbumin foams made from solutions containing CaCl₂ suggests that CaCl₂ is altering rheological properties of the interfacial protein film and/or contributing to protein aggregation or network formation in the lamellae.     

Comparison of Gum Arabic, Modified Starch, and Whey Protein Isolate as Emulsifiers: Influence of pH, CaCl2 and Temperature

ABSTRACT: The particle size and zeta potential of model beverage emulsions (0.01 wt% soybean oil-in-water emulsions, d ≅ 1 mm) stabilized by gum arabic, modified starch, or whey protein isolate (WPI) were studied with varying pH (3 to 9), CaCl₂ concentration (0 to 25 mM), and temperature (30 °C to 90 °C). Temperature, pH, CaCl₂ strongly influenced emulsions stabilized by WPI because its stabilizing mechanism was mainly electrostatic repulsion, but not those stabilized by gum arabic or modified starch because their stabilizing modes of action were mainly steric repulsion. This study may have important implications for the application of WPI as an emulsifier in beverage emulsions.     

Influence of CaCl2 and NaCl injections on the texture and flavour of beef

The present study compares the effects of pre− and post-rigor injections of 0.1 m CaCl₂ or 0.15 m NaCl on sensory characteristics (appearance, texture and flavour) and on physical measurements (sarcomere length, drip loss and mechanical resistance of raw myofibres) of beef meat at 2, 6 and 14 days of ageing. An injection of CaCl₂ 1 h post-mortem (pH ≈6.8) greatly decreased sarcomere length and myofibrillar resistance, increased drip loss, contracted appearance and brightness, and induced abnormal flavour, mainly bitterness, whatever the ageing time. CaCl₂-treatment 1 h post-mortem produced little effect on tenderness during ageing; it was slightly higher at day 2 and lower at day 14 than controls. CaCl₂-injection at 24 h post-mortem did not change the sarcomere length but produced a smaller increase in drip loss and a decrease in the resistance of raw myofibres. Improved meat tenderness compared to controls occurred mainly at days 2 and 6 but, during ageing, abnormal flavour appeared by day 6. NaCl-injection had no effect on either sarcomere length or resistance of raw myofibres, but produced higher drip loss and saltier taste at day 14 only. Thus pre-rigor injection of CaCl₂ is not recommended because of adverse effects on flavour and appearance of meat. Post-rigor injection of CaCl₂ has a beneficial effect on tenderness in the first part of the ageing period, but after complete ageing, the only overall benefit is a decrease in the variability between animals.     

Formation of Soy Protein Isolate Cold-set Gels: Protein and Salt Effects

ABSTRACT: The influence of protein and calcium concentration on soy protein cold-set gel formation and rheology has been investigated. Cold-set gels can be formed at soy protein concentrations from 6% to 9% and calcium concentrations from 10 to 20 mM. Gel properties can be modulated by changing the protein and/or CaCl₂ concentrations. An increase in CaCl₂ concentration from 10 to 20 mM increased gel opacity while an increase in protein concentration from 6% to 9% decreased opacity. Water-holding capacity improved with increasing protein concentration and decreasing CaCl₂ concentration. The elastic modulus (G') increased with protein and calcium chloride concentrations. Microscopy revealed an increase in the diameters of aggregates and pores as CaCl₂ concentration increased and as protein concentration decreased. Cold-set gels with a broad range of characteristics can be obtained from soy protein.     

Effect of CaCl2 and KCl on Physiochemical Properties of Model Nutritional Beverages Based on Whey Protein Stabilized Oil-in-Water Emulsions

ABSTRACT: Calcium chloride (0 to 10 mM) and potassium chloride (0 to 600 mM) were added into model nutritional beverage emulsions containing 7% (w/w) soybean oil droplets and 0.35% (w/w) whey protein isolate (pH 6.7). The particle size, surface charge, viscosity, and creaming stability of the emulsions then were measured. The surface charge decreased with increasing mineral ion concentration. The particle size, viscosity, and creaming instability of the emulsions increased appreciably above critical CaCl₂ (3 mM) and KCl (200 mM) concentrations because of droplet flocculation. The origin of this effect was attributed to reduction of the electrostatic repulsion between droplets due to electrostatic screening and ion binding. CaCl₂ promoted emulsion instability more efficiently than KCl because Ca²⁺ ions are more effective at reducing electrostatic repulsion than K⁺ ions.     

MEASURING THE WATER HOLDING CAPACITY OF NATURAL ACTOMYOSIN FROM CHICKEN BREAST MUSCLE IN THE PRESENCE OF PYROPHOSPHATE AND DIVALENT CATIONS

The water holding capacity (WHC) of natural actomyosin (NAM) extracted at pH 9.2 in 0.6M KCl was measured in the presence and absence of various combination of sodium pyrophosphate (PP_i), MgCl₂ and CaCl₂ using a modification of the classical centrifugation technique. Samples, in the presence of 0.15M NaCl and 20 mM sodium phosphate buffer pH 6, were spun at 30,900 X G (as measured at the bottom of the centrifuge tube) for 15 min at 2–4C. The results show that between 17 and 20 g water/g protein were bound over a wide range of NAM concentrations. In each case the amount of water held by the experimental sample was equal to or less than the amount held by a control run at the same time: 5 mM PP_i= 100%; 5 mM PP_i+ 5 mM MgCl₂= 58%; 5 mM MgCl₂= 85%; 5 mM PP_i+ 5 mM CaCl₂= 68% and 5 mM CaCl₂= 92% of the control. Thus polyphosphate addition in the presence of divalent cations lowers the WHC of NAM. The absence of the organized structure of muscle in NAM is postulated to be the reason that polyphosphate plus divalent cation reduced WHC in these samples. A series of preliminary experiments were run in order to determine the effect of experimental parameters on WHC.     

Selective Proteolysis of the Glycinin and β-Conglycinin Fractions in a Soy Protein Isolate by Pepsin and Papain with Controlled pH and Temperature

ABSTRACT: Proteolysis of soy protein isolates (SPI) was investigated by using pepsin with a pH of 1.5 to 4.0 at 37°C and papain at a temperature of 37°C to 80°C with pH 7.0. The glycinin fraction in native SPI was selectively hydrolyzed by pepsin in the pH 1.5 to 2.5 range. On the other hand, the p-conglycinin fraction in native SPI was selectively hydrolyzed by papain at 70°C. This selective proteolysis would be significantly correlated with the denaturation of glycinin and β-conglycinin in SPI. A protocol for preparing hydrolysates selectively enriched with glycinin or β-conglycinin was proposed.     

EFFECT of HONEY AS an ANTIBROWNING AGENT IN LIGHT RAISIN PROCESSING

Various process methods were evaluated for the production the light Thompson Seedless raisins. Treatments included: control, commercial (sulfur gas treated), 20% honey solution pressure dip, 10% honey solution pressure dip, 5000 ppm sulfite solution pressure dip, 5000 ppm sulfite solution nonpressure dip, Erthorbic Acid/Citric Acid/CaCl₂ solution pressure dip, blanch treatment and a Natick solution. Measured variables included Hunter Colorimeter tristimulus characteristics, visual assessment and rank comparison using Friedman Rank Analysis. the Hunter L, a, b results indicated the honey solution treatments produced lighter and yellower raisins than the commercial and pressure infused sulfite solution treatments. the Erthorbic Acid/Citric Acid/CaCl₂ pressure dip treatment resulted in the darkest product. Based on results of the Friedman Rank Analysis, raisins produced using honey with no added SO₂ were ranked highest by each of the 18 untrained panelists.     

Ultrastructural and Changes in Pectin Composition of Sweet Cherry from the Application of Prefreezing Treatments

ABSTRACT: Thermal and calcium pretreatments applied to preserve the sweet cherry texture by the freezing/thawing process produced biochemical changes in the pectic substances and ultrastructural alterations to the cells and tissues, which were visible under scanning electron microscopy. Partial dehydration of the epidermic tissue caused by calcium (100 m M CaCl₂) and thermal (50 °C/10 min) pretreatment attenuated the surface damage produced by freezing. However, pretreatment at 70 °C/2 min caused partial destruction of the epidermic tissue and plasmolysis of the parenchymatic cells. After freezing, the cell walls in the parenchymatic tissue of the fruits pretreated with 100 m M CaCl₂ exhibited swelling as a result of gelling of the cell-wall pectic material. Thermal pretreatments increased the ethylenediaminetetraacetic acid (EDTA)-soluble pectin fraction and reduced the degree of pectin esterification. Thermal treatments at 70 °C, without immersion in calcium, reduced the water- and pectinase-soluble pectin fractions, whereas immersion in calcium prevented depolymerization of these fractions. Immersion in 100 m M CaCl₂ increased the water-soluble pectin fraction.     

Physical loss and chemical reactions of SO2 in strawberry jam production

Strawberries for jam production frequently undergo extended storage in sulphite liquor before conversion into jam. Using ³⁵S-labelled sulphite an extensive equilibration of ³⁵S-labelled species between the fruit and the liquor has been demonstrated. Most of the loss of measurable SO₂ was accounted for in terms of (i) the chemical reactions during storage and (ii) the physical losses during jam production. In this work approximately 78% of the liquor sulphite was taken up by the fruit; 98.5% of this either reacted chemically or was boiled off, viz. 38% was converted to non-volatile compounds during storage, a further 11% reacted during jam making, 50% was boiled off and 1.5% remained measurable in the jam.     

A SIMPLE SOLID-PHASE RADIOIMMUNOASSAY FOR AFLATOXIN B1

A solid-phase radioimmunoassay (RIA) for aflatoxin B₁ (afla B₁) was developed. This method involved the incubation of afla B₁, both labelled and unlabelled, with immunoglobulin (IgG)-sepharose gel which was prepared by conjugation of the IgG highly specific to afla B₁ with CNBr-activated sepharose gel, followed by a filtration step. The binding capacity was determined by counting the radioactivity in the filtrate. Studies with different afla B₁ analogues revealed that the IgG-gel bound most effectively with B₁. Binding of afla B₂, G₁, G₂, and aflatoxicol to the IgG-gel was less effective in comparison with the IgG before coupling. Between 0.5–5.0 ng per assay, the displacement of radioactivity from the gel was directly proportional to the amount of afla B₁ present. Using a simple extraction procedure without clean-up step, the recovery yields for afla B₁ in the contaminated corn or wheat at levels of 5 ppb or above were above 60%.     

Saccharomyces cerevisiae strains AWRI 838, Lalvin EC1118 and Maurivin PDM do not produce excessive sulfur dioxide in white wine fermentations

The formation of sulfur dioxide (SO₂) by the related Saccharomyces cerevisiae strains AWRI 838, Lalvin EC11 18 and Maurivin PDM has been determined in white wines produced by laboratory-scale fermentation. Three different preparations of these strains, available for vinification in 1995, were indistinguishable based on production of SO₂. None of the physico-chemical factors investigated could stimulate an over-production of SO₂, and any changes in its concentration were independent of juice pH, sugar content, exposure to air, clarity, initial concentration of SO₂, and grape variety. Only fermentation without exposure to air could affect the concentration of SO₂, reducing it by 13–15% in the final wines. Under the conditions tested, changes in the concentration of SO₂ in wines produced with AWRI 838 and related strains would not account for wines which resist malolactic fermentation.     

Characterization and Functional Properties of Soy β-Conglycinin and Glycinin of Selected Genotypes

ABSTRACT: The principal soy storage proteins, β-conglycinin and glycinin, may provide valuable functionality as food ingredients. These soy protein fractions were isolated from K1430, Hutcheson, K93-90-29, and KS4997 and characterized for solubility, emulsion and surface properties, water holding capacity, and gel rheology. There were significant differences among genotypes regarding all functional properties. The K93-90-29 β-conglycinin exhibited significantly better functional properties compared to the other genotypes except for foam stability. Regarding glycinin, Hutcheson exhibited significantly better functional properties compared to the other genotypes except for foam stability. Continuous evaluation of soy genotypes in various food systems coupled with genetic manipulation should continue to better assess the potential of soy proteins as food ingredients.     

CALCIUM CHLORIDE EFFECTS ON TBA VALUES OF COOKED MEAT

Ground chicken breast and beef top round (semimembranosus) muscles were treated with CaCl₂ (0.05, 0.10, 0.15, and 0.20% on final sample weight basis) and cooked to an internal temperature of 80C. Cooked samples were aerobically stored at 4C for 0 or 4 days and analyzed for 2-thiobarbituric acid (TBA)-reactive substances. Results indicated that CaCl₂ can either inhibit or accelerate lipid oxidation in cooked meat depending on its concentration/meat animal species. TBA values of chicken samples were decreased by CaCl₂ used at ≥ 0.1% of final weight. However, only beef samples treated with the highest CaCl₂ level (0.20%) tended to have lower TBA values when compared to control samples (treated with deionized water only). CaCl₂ used at low levels (0.05% for chicken and ≤0.15% for beef) tended to elevate cooked meat TBA values.     

SEED LIPIDS OF THE MIRACLE FRUIT (SYNSEPALUM DULCIFICUM)

The lipids from the Miracle Fruit seeds comprised 10.15% of the dry weight. The neutral lipids, phospholipids and glycolipids were separated by silicic acid chromatography and the fatty acid composition of each fraction determined. The non-saponifiable lipids, amounting to 1.6% of the neutral lipids were separated into several fractions by thin-layer chromatography and the components of each analyzed by combined gas chromatography-mass spectrometry. The hydrocarbon fraction contained the n-alkane series from C₁₇ to C₃₂ with the C₂₉ and C₃₁ members present in relatively large quantities.
The major triterpene alcohols were α-and β-amyrin and the major sterol was identified as δ⁷ spinasterol. Two short-chain alchols were also present.