The amino acid composition,solubility and emulsifying properties of sweet potato protein

A protein was purified from the high-protein type sweet potato variety 55-2 available in China. The amino acid composition, solubility and emulsifying properties of the sweet potato protein (SPP) were studied. The SPP was rich in aspartic acid (18.5%) and glutamic acid (9.30%) while essential acid amino acids made up approximately 40.7% of the SPP. The SPP was highly soluble in distilled water over a wide range of pH. However, solubility of the SPP in 1.0 M NaCl and 1.0 M CaCl₂ solutions was low especially at pH below the pI of the SPP. The SPP in CaCl₂ demonstrated emulsifying activity index (EAI) and emulsion stability index (ESI) many folds higher than those in distilled water and NaCl solution (P < 0.05).     

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 pH and NaCl/CaCl2 on the solubility and emulsifying properties of sweet potato protein

BACKGROUND: The effects of NaCl and CaCl₂ on the solubility and emulsifying properties, namely emulsifying activity index (EAI) and emulsion stability index (ESI) of sweet potato proteins (SPPs) at pH 1–10, were investigated. RESULTS: At lower NaCl (0.1 mol L^?1) and CaCl₂ (0.05 mol L^?1) concentrations, the solubility profiles of the SPPs were very similar to those in distilled water, and the lowest solubility occurred at pH 4. Increased NaCl and CaCl₂ concentration resulted in lower SPP solubility in most of the pH studied (P < 0.05). At pH < 3, NaCl improved the EAI of SPP while at pH > 7 it reduced the EAI of the SPP (P < 0.05). Moreover, addition of NaCl also resulted in reduction of ESI of the SPP in most of the pH studied (P < 0.05). On the other hand, the presence of 0.2 mol L^?1 CaCl₂ rendered the EAI and ESI of the SPPs independent of the influence of pH. CONCLUSION: The present studies show that pH and salts modified the emulsifying properties of the SPPs, and CaCl₂ at a certain concentration could be used to improve the emulsifying properties of the protein. Copyright © 2008 Society of Chemical Industry     

The effect of sulphuric acid activation on the crystallinity,surface area,porosity, surface acidity,and bleaching power of a bentonite

The Hanç?l? (Keskin, Ankara, Turkey) bentonite was activated with H₂SO₄ by dry method at 97 °C for 6 h to obtain optimum parameters for imparting a maximum bleaching power towards soybean oil. The H₂SO₄ content in dry bentonite-acid mixture was changed between 0% and 70%. The natural and activated samples were examined by X-ray diffraction (XRD), N₂ adsorption–desorption, and n-butylamine adsorption (from the solution in cyclohexane). The specific surface area (S), specific micro–mesopore volume (V), mesopore size distribution (PSD), and surface acidity (n_m) of the samples were determined. The bleaching power (BP) of each sample for alkali-refined soybean oil was determined. The S, V, n_m, and BP increase after activation at various acid contents up to 40% H₂SO₄ without any considerable change in crystal structure of the smectite. The BP is controlled more by the PSD rather than other adsorptive properties of the bleaching earth. The optimum parameters for activation to obtain maximum bleaching power, are H₂SO₄% = 50–60, S = 250–230 m² g⁻¹, V = 0.46–0.47 cm³ g⁻¹, n_m = 9.0 × 10⁻⁴–8.4 × 10⁻⁴ mol g⁻¹ and PSD mainly distributed between 1.4 and 6.0 nm.     

Isolation and properties of AMP deaminase from jumbo squid (Dosidicus gigas) mantle muscle from the Gulf of California,Mexico

Adenosine monophosphate (AMP) deaminase was purified from jumbo squid mantle muscle by chromatography in cellulose phosphate, Q-Fast and 5′-AMP sepharose. Specific activity of 2.5 U/mg protein, 4.5% recovery and 133.68 purification fold were obtained at the end of the experiment. SDS–PAGE showed a single band with 87 kDa molecular mass, native PAGE proved a band of 178 kDa, whereas gel filtration detected a 180 kDa protein, suggesting the homodimeric nature of this enzyme, in which subunits are not linked by covalent forces. Isoelectric focusing of this enzyme showed a pI of 5.76, which agrees with pI values of AMP deaminase from other invertebrate organisms. AMP deaminase presented a kinetic sigmoidal plot with V_max of 1.16 μM/min/mg, K_m of 13 mM, K_cat of 3.48 μM.s⁻¹ and a K_cat/K_m of 267 (mol/L)⁻¹.s⁻¹. The apparent relative low catalytic activity of jumbo squid muscle AMP deaminase in the absence of positive effectors is similar to that reported for homologous enzymes in other invertebrate organisms.     

C NMR and electrospray ionization mass spectrometric study of sucrose aqueous solutions at high pH: NMR measurement of sucrose dissociation constant

The ¹³C NMR technique is used for the measurement of the first dissociation constant of sucrose (HL) in highly alkaline solutions. In 1.0 M NaCl/NaOH medium and for 25 °C, the concentration dissociation constant (pK₁) was 13.1 ± 0.3; and, for 60 °C, pK₁ = 12.30 ± 0.05. The β-d-fructofuranosyl ring was found to be responsible for dissociation. The NMR data reveal no clear evidence of the second dissociation step below pH 14, either at 25 °C or at 60 °C. In the solutions with 4–10 mol dm⁻³ NaOH content the ¹³C NMR technique indicated the chemical shift changes, treated as the second dissociation step of sucrose and a sodium complex formation. A very rough estimation, for variable ionic strength, gives the value: pK₂ ∼ 15.8 ± 0.8. The anionic species L⁻ and NaH₋₁L⁻ have been registered by electrospray ionization time-of-flight mass spectrometry (ESI-ToF MS) for 0.01 M sucrose solutions with initial pH 13.     

Effects of ageing and low internal temperature of grilling on the formation of heterocyclic amines in beef Longissimus dorsi muscle

The mutagenic heterocyclic amines (HAs) originate in processed proteinaceous food. The effects of ageing (non-aged - i.e. 24 h post mortem vs. 14 and 28 days post mortem kept at 1 °C) and final internal temperature on cooking (T_i, 65 and 80 °C) on the content of HAs in grilled steaks (two-plated grill, temperature of 220 °C) were studied. HA precursors (creatine, creatinine, and free amino acids) and ageing indicators, such as instrumentally measured colour values, pH_ultimate values and length of myofibrilar fragments on raw and cutting values on grilled beef Longissimus dorsi muscles were determined. The muscles originated from eight commercially slaughtered Simmental bulls, 19-20 months old. The content of HAs was determined by a solid-phase extraction procedure. Meat ageing is accompanied by large changes in the chemical composition and structure of muscle tissues. In general, all the ageing indicators and precursors of HAs were influenced by ageing time at the 5% level or less. Creatine content declined significantly (non-aged: 6.00 mg g⁻¹, 14 days: 5.82 mg g⁻¹, and 28 days: 5.55 mg g⁻¹) and creatinine increased with days of ageing (non-aged: 0.19 mg g⁻¹, 14 days: 0.24 mg g⁻¹, and 28 days: 0.26 mg g⁻¹). Higher contents of total free amino acids were determined after 14 and 28 days of storage (28.18 μmol g⁻¹ and 37.59 μmol g⁻¹) than in non-aged beef (19.00 μmol g⁻¹). In this study, two HAs were determined: MeIQx (2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline) and PhIP (2—amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine). The content of HAs increases with ageing. At lower T_i, more MeIQx was formed; at higher T_i, more PhIP was formed. MeIQx was present in all samples while PhIP was found only in samples grilled to higher T_i. Samples treated to T_i = 80 °C generally contained less HAs (non-aged meat: 0.20 ng g⁻¹, 14 days: 0.26 ng g⁻¹, and 28 days: 0.28 ng g⁻¹) than samples treated to T_i = 65 °C (non-aged meat: 0.19 ng g⁻¹, 14 days: 0.36 ng g⁻¹, and 28 days: 0.39 ng g⁻¹) on account of MeIQx thermolability.     

Effect of phosphorus on the fruit yield and food value of two landraces of Trichosanthes cucumerina L.- Cucurbitaceae

Studies were conducted in the early season of 2002 and 2003 at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Nigeria to evaluate the effect of phosphorus (P) on fruit yield and chemical composition of two landraces of Trichosanthes cucumerina L. For the purpose of the study, two landraces of T. cucumerina named Landrace I and Landrace II were used. The five levels of phosphorus evaluated were 0, 30, 60, 90 and 120 kg P₂O₅ ha⁻¹ using single super phosphate fertilizer (8% P). Statistical analysis showed that 90 kg P₂O₅ ha⁻¹ gave statistically significant higher fruit yield (16.4 tons ha⁻¹) compared to other P levels. The fruit yield of the two Landraces did not differ significantly. Except for crude protein content, the 90 kg P₂O₅ ha⁻¹ produced significantly higher ether extract (1.22 g 100 g⁻¹), crude fibre (1.93 g 100 g⁻¹), moisture content (90.5 g 100 g⁻¹), ash (0.90 g 100 g⁻¹), total sugars (0.81 g 100 g⁻¹) and ascorbic acid (28.7 mg 100 g⁻¹) than other P levels. The essential amino acids compositions were also significantly higher at 90 g 100 g⁻¹ compared to other lower P levels. Landrace I had significantly higher ether extract (0.90 g 100 g⁻¹) content than Landrace II (0.62 g 100 g⁻¹) while Landrace II in turn had significantly higher total sugar (0.76 g 100 g⁻¹) compared to Landrace I (0.61 g 100 g⁻¹). The essential amino acids composition is high and the oxalate composition is low. The high ascorbic acid and amino acid content together with a low oxalate composition suggested a strong basis for encouraging the cultivation of this indigenous fruit vegetable to augment nutrient requirement, improve diet and consequently alleviate poverty, preserve the biodiversity and increase the gene bank of neglected wild species of high quality nutrient sources.     

Functional and structural properties and in vitro digestibility of acylated hemp (Cannabis sativa L.) protein isolates

The effects of succinylation and acetylation on some functional, structural properties and in vitro trypsin digestibility of hemp protein isolate (HPI) were investigated. The extent of acylation gradually increased from 0 to 60–70%, with the anhydride‐to‐protein ratio increasing from 0 to 1.0 g g^?1. Size exclusion chromatography showed that succinylation led to formation of more soluble protein aggregate than acetylation, especially at anhydride levels higher than 0.1 g g^?1. Succinylation led to gradual increase in protein solubility (PS) from 30 to 85–90%, while in the acetylation case, the PS was improved only at low anhydride levels, increasing from 30 to about 50% with anhydride‐to‐protein ratio increasing from 0 to 0.2 g g^?1. At neutral pH, the emulsifying activity indexes (EAI) of HPI was 22.1 m² g^?1, and the EAI linearly and significantly increased with the extent of acylation. The EAIs of succinylated and acetylated HPI (1.0 g g^?1) were 119.0 and 54.4 m² g^?1, respectively. Differential scanning calorimetry (DSC) and intrinsic fluorescence spectrum analyses indicated gradual structural unfolding of proteins, or exposure of hydrophobic clusters to the solvent, especially at higher anhydride levels. Additionally, the in vitro trypsin digestibility was significantly improved by the succinylation. The results indicated that the chemical acylation treatment (especially succinylation) could be applied to modify some selected functional properties of hemp proteins, especially PS and emulsifying ability.     

Neriifolin S, a dimeric serine protease from Euphorbia neriifolia Linn.: Purification and biochemical characterisation

A dimeric serine protease Neriifolin S of molecular mass 94 kDa with milk clotting activity has been purified from the latex of Euphorbia neriifolia by anion exchange and size-exclusion chromatography. It hydrolyses peptidyl substrates l-Ala-pNA with highest affinity (K_m of 0.195 mM) and physiological efficiency (K_cat/K_m of 144.5 mM s). Enzyme belongs to the class of neutral proteases with pI value of 6.8, optimal proteolytic activity displayed at pH 9.5 and temperature 45 °C. Its proteolytic activity is strongly stimulated in the presence of Ca⁺² ions and exclusively inhibited by serine protease inhibitors. Enzyme is fairly stable toward chemical denaturants, pH and temperature. The apparent T_m, was found to be 65 °C. Thermal inactivation follow first order kinetics with activation energy (Ea), activation enthalpy (ΔH∗), free energy change (ΔG∗) and entropy (ΔS∗) of 27.54 kJ mol⁻¹, 24.89 kJ mol⁻¹, −82.34 kJ mol⁻¹ and 337.20 J mol⁻¹ K⁻¹.     

Emulsifying properties of proteins extracted from Australian canola meal

Canola protein albumin fraction, globulin fraction, and canola protein isolate (CPI) were compared to commercial soy protein isolate (SPI) in terms of their emulsifying properties at various pH values. The globulin fraction had higher emulsifying capacity (EC), higher emulsifying activity index (EAI), and the droplet size of emulsions it stabilized was consistently smaller irrespective of pH compared to albumin fraction or CPI. In comparison to SPI, globulin fractions also had higher EC at all pH values tested, higher EAI at acidic pH, and smaller or comparable average emulsion droplet size at both pH 4 and 7. The stability of canola protein based emulsions were comparable to those of SPI based emulsions at most pH values (except the emulsion stabilized by the CPI at pH 4), with no significant (p > 0.05) changes in droplet size during storage for up to 7 days at room temperature. These emulsions, however, experienced separation into the emulsion and serum phases after 24 h storage at room temperature with the exception of CPI- and SPI-stabilized emulsions at pH 9. This study demonstrates the comparable emulsifying properties (forming or stabilizing) of some canola proteins to commercially available SPI, suggesting the potential use of canola proteins in food applications.     

Effect of flaxseed meal on the dynamic mechanical properties of starch-based films

Starch (S)–flaxseed meal (FM) biofilms were prepared from potato and maize starch by incorporating FM up to 15% (dry solid basis) and using glycerol as plasticizer. The dynamic mechanical properties, tensile properties and water vapor permeability (WVP) of these films were measured. The storage modulus of both the starch (control) and starch–FM films decreased as temperature increased. Tan δ increased initially in all the films with increase in temperature until a peak value was reached which allowed the determination of glass transition temperature (T_g). Both tensile strength and Young’s modulus of the starch–FM films increased with increase in the FM content. The WVP of the potato starch–FM films first increased to 2.261 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) when FM content increased to 5% and decreased down to 1.832 (×10⁵ g m⁻² h⁻¹ Pa⁻¹) with further increase in the FM content to 15%. While the WVP values of the cornstarch and corn starch–FM films were not significantly (p > 0.05) different. The incorporation of FM increased the tensile strength, decreased the % elongation at break and increased the T_g.     

Application of acetylacetone chelation solid-phase extraction to GFAAS measurements of trace amounts of beryllium in livers and muscles of poultry and livestock

Trace amounts (0.004–0.55 ng) of beryllium (Be) in a dried bovine liver sample (20 mg) can be accurately determined by graphite-furnace atomic absorption spectrophotometry (GFAAS) after treating with microwave digestion (HNO₃/H₂O₂) at 85 °C for 10 min and using acetylacetone as a chelating agent in the presence of an acetate buffer (pH 6.0). The method detection limit (MDL, 3σ) for Be was found to be 0.18 ng g⁻¹ and the limit of quantification (LOQ, 10σ) was found to be 0.60 ng g⁻¹; the calibration graph was linear up to 27 ng g⁻¹. The Be contents measured in four liver and four muscle samples (BCR CRM-185R bovine liver, BCR CRM-384 pork muscle, and six samples collected in Kaohsiung, Taiwan, ROC) were between 2.3 and 4.7 ng g⁻¹. Good spiked recoveries (96.0–103.0%) were obtained for these eight samples with a relative standard deviation (RSD, n = 3) ?3.0%. The method could be applied to measurements of Be in livers and muscles of poultry and livestock.     

Nutrient contents of kale (Brassica oleraceae L. var. acephala DC.)

Fructose, glucose and sucrose, as the major soluble sugars and citric and malic acids, as the major organic acids, were identified and determined in kale (Brassica oleraceae L. var. acephala DC., black cabbage) leaves. Fructose was the predominant sugar (2011 mg 100 g⁻¹ dry wt) identified, followed by glucose (1056 mg 100 g⁻¹ dry wt) and sucrose (894 mg 100 g⁻¹ dry wt). The contents of citric and malic acids were at 2213 and 151 mg 100 g⁻¹ dry wt in the leaves. The 16:0, 18:2n − 6 and 18:3n − 3 fatty acids were the most abundant fatty acids in the leaves. Considering the level of these fatty acids, 18:3n − 3 was found to be the highest (85.3 μg g⁻¹ dry wt), contributing 54.0% of the total fatty acid content. Linoleic acid (18:2n − 6), being the second most abundant fatty acid was present at 18.6 μg g⁻¹ dry wt, contributing 11.8% of the total fatty acid content. In the seed oil of kale, 22:1n − 9 was the most abundant fatty acid (4198 μg g⁻¹ dry wt, 45.7%), with 18:2n − 6 (1199 μg g⁻¹ dry wt, 12.3%) and 18:1n − 9 (1408 μg g⁻¹ dry wt, 14.8%) being the second next most abundant fatty acids. The most abundant amino acid was glutamic acid (Glu) which was present at 33.2 mg g⁻¹ dry wt. Aspartic acid, which was the second most abundant amino acid, was present at 27.6 mg g⁻¹ dry wt and accounted for 10.2% of the total amino acid content of kale leaf. The amino acid content was assessed by comparing the percentages of the essential amino acids in kale leaf versus those of a World Health Organization (WHO) standard protein. The protein of kale leaf compares well with that of the WHO standard. Only one amino acid, lysine, had a score that fell below 100%; the lysine score of kale leaf was 95%. This study attempts to contribute to knowledge of the nutritional properties of the plant. These results may be useful for the evaluation of dietary information.     

Giant Amazonian fish pirarucu (Arapaima gigas): Its viscera as a source of thermostable trypsin

A trypsin was purified from pyloric caeca of pirarucu (Arapaima gigas). The effect of metal ions and protease inhibitors on its activity and its physicochemical and kinetic properties, as well its N-terminal sequence, were determined. A single band (28.0 kDa) was observed by SDS–PAGE. Optimum pH and temperature were 9.0 and 65 °C, respectively. The enzyme was stable after incubation for 30 min in a wide pH range (6.0–11.5) and at 55 °C. The kinetic parameters K_m, k_cat and k_cat/K_m were 0.47 ± 0.042 mM, 1.33 s⁻¹ and 2.82 s⁻¹ mM⁻¹, respectively, using BApNA as substrate. This activity was shown to be very sensitive to some metal ions, such as Fe²⁺, Hg²⁺, Zn²⁺, Al³⁺, Pb²⁺, and was highly inhibited by trypsin inhibitors. The trypsin N-terminal sequence IVGGYECPRNSVPYQ was found. The features of this alkaline peptidase suggest that it may have potential for industrial applications (e.g. food and detergent industries).     

Emulsifying characteristics of commercial canola protein–hydrocolloid systems

Emulsifying properties of commercial canola protein isolate (CPI)–hydrocolloid-stabilized emulsions were evaluated under varied conditions (CPI, salt and hydrocolloid concentrations; pH, denaturants). Emulsifying activity index (EAI) and emulsion stability (ES) were determined by turbidimetric testing. The results showed that under complexing conditions (at pH 6), the addition of 1% (w/v) κ-carrageenan (κ-CAR) increased the EAI of CPI-stabilized emulsions from 162 to 201 m²/g and ES from 68% to 95%. Under conditions promoting incompatibility (at pH 10), the use of 1% (w/v) guar gum increased the EAI of CPI-stabilized emulsions from 68 to 177 m²/g and ES from 66% to 100%. The lower EAI and ES values observed in CPI–hydrocolloid-stabilized emulsions treated with sodium salts and denaturants support the involvement of hydrophobic interactions, hydrogen bonds and disulfide linkages in the emulsification of these systems. Interfacial properties of CPI–hydrocolloid mixtures were improved by electrostatic complexing and incompatibility, making these systems suitable for stabilizing food emulsions.     

Isolation and properties of 5′-nucleotidase isolated from jumbo squid (Dosidicus gigas) mantle muscle from the Gulf of California,Mexico

The enzyme 5′-nucleotidase of jumbo squid (Dosidicus gigas) mantle was purified and its SDS–PAGE showed a single band of 33 kDa, whereas a protein with a molecular mass of 107 kDa was detected by gel filtration suggesting a homotrimeric nature of this enzyme. Subunits of the named enzyme were not linked by covalent bonds. Isoelectric focusing of this enzyme showed a pI of 3.6–3.8 and presented a hyperbolic kinetics with V_max of 1.16 μM/min/mg of protein, K_m of 1.49 mM, K_cat of 3.48 μM of P_ι s⁻¹ and K_cat/K_m relation of 356.52 ((mol/L)⁻¹ s⁻¹). Purified enzyme preferred AMP as substrate (by 6.7-folds) than IMP, showing a K_m of 6.34 mM, V_max of 0.19 μM/min/mg of protein a K_cat of 0.3388 mol of P_ι s⁻¹ and K_cat/K_m relation of 53.44 ((mol/L)⁻¹ s⁻¹). The low K_m in relation to purified AMP deaminase of the same organism suggested a high contribution of 5′-nucleotidase in AMP degradation in jumbo squid mantle.     

Nitrogen extractability and functional properties of defatted Erythrina variegata flour

Defatted Erythrina variegata flour was prepared from dehusked seed meal by hexane extraction of residual oil. The resulting flour had 403 g kg⁻¹ of protein as compared to 282 g kg⁻¹ in the whole seed-defatted meal. Nitrogen extractability of the defatted flour in water was not much influenced by the length of extraction period above 40 min, but an increased extraction was observed at a higher liquid to solid ratio up to a studied limit of 1:60; the optimal ratio was found to be 1:30. The minimum of 26.9% nitrogen was extracted in the pH range 3.0–4.0 and maximum of 94.8% at pH 12. Addition of sodium chloride (0.1 or 0.5 M) broadened the pH range of minimum nitrogen extractability and shifted it toward a lower pH region. At both concentrations of sodium chloride, a marked increase in nitrogen extractability, in the pH range 3.0–7.0, was observed. Precipitation of protein from an extract of pH 10.0 was maximum (85.3%) at pH 4.75. A higher buffer capacity of the flour was observed in the acidic medium (0.195 mmol HCl g⁻¹ flour) than in alkaline medium (0.093 mmol NaOH g⁻¹). Water absorption and oil absorption values for the whole E. variegata seed flour and the dehusked, defatted flour were 1.81, 1.43 and 1.02, 1.52 kg kg⁻¹, respectively.     

Fabrication of viscous and paste-like materials by controlled heteroaggregation of oppositely charged lipid droplets

This study describes the formation of materials with novel textural characteristics by controlled heteroaggregation of oppositely charged protein-coated lipid droplets. Heteroaggregation was induced by mixing a suspension of β-lactoglobulin (β-Lg)-coated lipid droplets (ζ = −51 mV, d₄₃ ∼ 0.35 μm, 20 wt.%) with a suspension of lactoferrin (LF)-coated lipid droplets (ζ = +32 mV, d₄₃ ∼ 0.35 μm, 20 wt.%) under conditions where the two proteins had opposite charges (pH 7). The mean particle size, flow behaviour, and shear modulus of the materials depended on positive-to-negative particle ratio (0–100%), pH (3–9), ionic strength (0–400 mM), and temperature (30–90 °C). The largest particle sizes, highest viscosities, and largest gel strengths were observed at intermediate particle ratios (40% LF:60% β-Lg), which was attributed to a strong electrostatic attraction between oppositely charged droplets (0 mM NaCl, pH 7, 25 °C). A reduction in particle aggregation, viscosity, and gel strength occurred at intermediate ionic strengths due to screening of the electrostatic attraction between oppositely charged droplets. However, increased aggregation, thickening, and gelation occurred at higher ionic strengths due to screening in electrostatic repulsion between similarly charged droplets. Thermal treatment of the samples (90 °C) promoted a substantial increase in gel strength due to protein denaturation and increased droplet attraction. This study has important implications for the utilisation of controlled particle aggregation to create novel structures in foods, cosmetics, personal care, and other products.     

Immobilization of pepsin on chitosan beads

In this study, chitosan beads were prepared by using a cross-linking agent and the resulting beads were employed in immobilization process. Studies on free and immobilized pepsin systems for determination of optimum temperature, optimum pH, thermal stability, pH stability, operational stability, storage stability and kinetic parameters were carried out. The optimum temperature interval for free pepsin and immobilized pepsin were 30–40 and 40–50 °C, respectively. Free and immobilized pepsin showed higher activity at pH 2.0–4.0. Apparent K_m = 12.0 g L⁻¹ haemoglobin (1.56 mM tyrosine) and V_max = 5220 μmol (mg protein min)⁻¹ values were obtained for free pepsin, while apparent K_m = 20.0 g L⁻¹ haemoglobin (2.16 mM tyrosine) and V_max = 2780 μmol (mg protein min)⁻¹ values were obtained for immobilized pepsin. Thermal stability and storage stability of immobilized pepsin were higher than that of free pepsin. Milk clotting activity was used for evaluation of the applicability of pepsin immobilization to industrial process. Optimum milk clotting temperature was found as 40 °C for free pepsin and 50 °C for immobilized pepsin.