Physicochemical changes in whey protein concentrate texturized by reactive supercritical fluid extrusion

The mechanisms of interactions in whey protein concentrate (WPC) texturized by reactive supercritical fluid extrusion and pH modifications were evaluated in terms of protein solubility in different extraction buffers, electrophoresis, free sulfhydryl (SH) groups, and apparent viscosity. The soluble protein content and free SH groups of the texturized WPC (tWPC) produced at pH 2.89 decreased by 20% and 16% relative to the unextruded control. It was completely soluble in the presence of urea and SDS, indicating the importance of non-covalent interactions in maintaining the structure of this product. Its dispersion (20% w/w) yielded a creamy texture with a particle size in the micron-range (mean diameter 5 μm) and contributed 258 times higher viscosity compared to the unextruded control. The tWPC produced at pH 8.16 was soluble only in the presence of a reducing agent. It yielded a grainy texture with a high proportion of large particles due to an extensive aggregation via intermolecular disulfide formations.     

Water soluble inner aqueous phase markers as indicators of the encapsulation properties of water-in-oil-in-water emulsions stabilized with sodium caseinate

The aim of this study was to evaluate the suitability of Methylene Blue (MB) and Vitamin B₁₂ (Vit-B₁₂) as water soluble inner aqueous phase (W₁) markers for measuring the encapsulation efficiency and stability of water-in-oil-in-water (W₁/O/W₂) double emulsions stabilized by sodium caseinate (NaCN). The encapsulation efficiency and stability were determined by centrifugation of the double emulsion to separate the cream phase (W₁/O) and the outer aqueous phase (W₂) and measuring the concentration of marker in W₂ by absorbance spectrophotometry. To validate this method the marker concentration measurable and the stability of the marker in W₂ were measured. Both markers could be accurately measured in W₂ and there was no change in the concentration of marker on storage of a W₂ solution for 7 days at 45 °C. The recovery yields of MB and Vit-B₁₂ in the recovered W₂ of an oil-in-water (O/W₂) emulsion, determined using the procedure normally used for measuring encapsulation efficiency and stability, were 78% and 99%, respectively, and 52 and 100%, respectively. Double emulsions had encapsulation efficiency of 61.9 ± 21.4% and 16.6 ± 1.1% and encapsulation stability of 62.0 ± 22.6% and 10.7 ± 0.7% for MB and Vit-B₁₂, respectively. Recovery yield and encapsulation efficiency/stability data for MB indicate that it is not a suitable marker for measuring the encapsulation properties of NaCN stabilized double emulsions while similar data for Vit-B₁₂ indicate that it is a suitable marker for studying the encapsulation properties of double emulsions stabilized with NaCN. Methods used in other studies to measure encapsulation properties of double emulsions are discussed in light of the results obtained in this study.     

The use of various live animal measurements to predict carcass and meat quality in two divergent lamb breeds

Live weight, subjective scores of condition and conformation, live animal video image analysis (LVIA), ultrasound and X-ray computed tomography (CT) scanning were used to investigate the best method or combination of methods for predicting carcass and meat quality traits in live Texel and Scottish Blackface lambs. Predictors derived from CT alone accounted for a high proportion of the variance in dissected fat and muscle weight in Texel lambs (adjusted R² = 0.8), as well as intra-muscular fat content in the loin (0.6), but lower proportions in Blackface lambs (0.7 for fat, 0.4–0.5 for muscle and intra-muscular fat), after adjusting for sire and fixed effects. Adding traits measured by other in vivo methods increased prediction accuracies (adjusted R²) by up to 0.26, depending on trait and data set. Shear force and ultimate pH could not be accurately predicted using the traits considered here (adjusted R² < 0.4). Although the same methods tended to be best for predicting product quality traits between breeds, prediction accuracies differed.     

Physical and thermo-mechanical properties of whey protein isolate films containing antimicrobials, and their effect against spoilage flora of fresh beef

The effectiveness of antimicrobial films against beef's spoilage flora during storage at 5 °C and the impact of the antimicrobial agents on the mechanical and physical properties of the films were examined. Antimicrobial films were prepared by incorporating different levels of sodium lactate (NaL) and -polylysine (-PL) into sorbitol-plasticized whey protein isolate (WPI) films. The moisture uptake behavior and the water vapor permeability (WVP) were affected only by the addition of NaL at all concentrations used since an increased water uptake and permeability were observed with the addition of NaL into the protein matrix. An increase of the glass transition temperature (5–15 °C) of the sorbitol region, as determined by Dynamic Mechanical Thermal Analysis (DMTA), was caused by the addition of -PL into the WPI specimens. Instead, incorporation of NaL into the protein matrix did not alter its thermo-mechanical behavior. The addition of NaL at concentrations of 1.0% and 1.5% w/w in the film-forming solution resulted in a decline of maximum tensile strength (σ_max) and Young modulus (E). A decrease of E and σ_max, accompanied with an increase in elongation at break (%EB), was also observed with increasing -PL concentration, at moisture contents higher that 10% (w/w). The antimicrobial activity of the composite WPI films was tested on fresh beef cut portions. The maximum specific growth rate (μ_max) of total flora (total viable count, TVC) was significantly reduced with the use of antimicrobial films made from 0.75% w/w -PL in film-forming solutions (p < 0.05), while the growth of Lactic Acid Bacteria was completely inhibited. Significant inhibition of growth of the total flora and pseudomonads was also observed with the use of films made with protein solutions containing 2.0% w/w NaL. These results pointed to the effectiveness of the antimicrobial whey protein films to extend the shelf life of fresh beef.     

Kinetics of phase separation during pressure-induced gelation of a whey protein isolate

The kinetic process of pressure-induced gelation of whey protein isolate (WPI) solutions (20–28%, w/v) was studied using in situ light scattering. The gelation of WPI solutions could be induced by pressurization at 250 MPa, a pressure lower than that reported in other studies. The gelation time decreased with increasing WPI concentration and followed an exponential rule. The relationship of the logarithm of scattered light intensity (I) versus time (t) was linear after the induced time and could be described by the Cahn–Hilliard linear theory. With increasing time, the scattered intensity deviated from the exponential relationship, and the time evolution of the scattered light intensity maximum I_m and the corresponding wavenumber q_m could be described in terms of the power-law relationship as I_m  t^β and q_m  t^−α, respectively. These results indicated that phase separation occurred during the gelation of WPI solutions under high pressure.     

Thermal degradation kinetics of aqueous anthocyanins and visual color of purple corn (Zea mays L.) cob

Purple corn cob was the byproduct during the corn processing. Thermal degradation kinetics and Hunter color parameters (a, b, C, h° and ΔE) of aqueous anthocyanins from purple corn cob were studied at selected temperatures (70 °C, 80 °C and 90 °C) at pH 4.0. The results indicated that the thermal degradation of anthocyanin and Hunter color C, a and ΔE parameters followed the first-order reaction kinetics, while Hunter color h° and b parameters followed zero-order reaction kinetics. The calculated values of activation energies (Ea) were 18.3, 35.9, 37.1, 31.6, 34.9 and 30.0 kJ/mol for anthocyanins, C, a, ΔE, h° and b parameters, respectively. The higher Ea indicated that greater temperature sensitivity of visual color as compared to anthocyanins content. The degradation of anthocyanins showed positive correlation with C (R² > 0.909), a (R² > 0.860) and ΔE (R² > 0.940), while the degradation of anthocyanins showed negative correlation with h° (R² > 0.828) and b (R² > 0.735) during heating.

Industrial relevance

Purple corn cob was the byproduct during the corn processing. Purple corn cob is dark purple to almost black color due to its high content of anthocyanins, which makes this byproduct a good source of anthocyanins. In this study, the excellent linear correlation between Hunter color parameters (a, b, C, h° and ΔE) and content of anthocyanins showed that the Hunter color parameters may also be used instead of anthocyanins content during heating. The advantage of using the visual Hunter color parameters may be measured as on-line quality control parameters during thermal processing of food industry.     

Galactomannan esters—A simple, cost-effective method of preparation and characterization

Acetate, succinate and octenylsuccinate derivatives of galactomannans were prepared in anhydrous reaction conditions carried out at slightly elevated temperature (40–60 °C) using solid NaHCO₃ as a mild base catalyst. Prior surface wetting of the reactants with 5% absolute ethyl alcohol gave derivatives with a higher degree of substitution, although it decreased the slurry viscosity. Use of NaHCO₃ significantly minimized high pH-induced degradative reactions, and its quantitative removal later was easily accomplished by repeated washings with aqueous ethyl alcohol. FT-IR, ¹³C-NMR, HPSEC and SEM data provided additional structural information. These derivatives are useful as functional food ingredients.     

Impact of cooling rates on the staling behavior of cooked rice during storage

The impact of cooling rates (0.40, 1.11, 1.42, 1.64, 2.47 and 3.36 °C/min) on starch retrogradation and textural properties of cooked rice was evaluated. The relationship between cooling rates and different properties were determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry, and textural properties were determined by a Texture Analyser. This study showed that the ΔH_r value and hardness value had a negative correlation with cooling rate during storage, −0.963  r  −0.716, P < 0.01; −0.826  r  −0.706, P < 0.05, respectively. However, a positive correlation was found between adhesiveness and cooling rate (0.237  r  0.882, P < 0.05). These results indicated that the cooked rice chilled with slower cooling rate retrograded faster than chilled with rapid cooling rate. Therefore, high quality cooked rice can be produced by rapid cooling process.     

Ultrasonic spectrometry study of the influence of temperature on whey protein aggregation

Ultrasonic attenuation spectroscopy was used to investigate the influence of pre-treatment temperature on the formation of pH-induced particulate aggregates in aqueous native and alkaline-denatured whey protein solutions. Ultrasonic attenuation spectra (1–150 MHz) of 2.5 wt.% whey protein solutions were measured over a pH range of 2–12 using whey solutions, which were previously heated at temperatures ranging from 30 to 90°C. There was a large temperature dependent increase in attenuation around the isoelectric point of the proteins (pH 3–5.5), which was caused by scattering of ultrasound by increased protein aggregation. A maximum in attenuation was observed at 80°C. The particle size distribution and concentration of the aggregates was determined using ultrasonic scattering theory. A loss of large particles (10 μm) was detected upon heating. Ultrasonic spectroscopy was shown to be a valuable tool for studying aggregation of proteins in solution.     

Quality evaluation of raw ground almond kernels (Prunus dulcis): Effect of active and modified atmosphere packaging, container oxygen barrier and storage conditions

The present study investigated the effect of active and modified atmosphere packaging, container oxygen barrier and storage conditions on quality retention of raw ground almonds. Ground almond kernels were packaged in: a) polyethylene terephthalate//low density polyethylene (PET//LDPE), and b) low density polyethylene/ethylene vinyl alcohol/low density polyethylene (LDPE/EVOH/LDPE), under N₂ or with an oxygen absorber and stored either under fluorescent light or in the dark at 4 or 20 °C for a period of 12 months. Quality parameters monitored were: peroxide value (PV), hexanal content, color, fatty acid composition and volatile compounds. Of the sensory attributes color, texture, odor and taste were evaluated. PV ranged between 0.26 for fresh almonds and 19.98 meq O₂/kg oil for almonds packaged in PET//LDPE pouches under N₂ exposed to light at 20 °C after 12 months of storage. Respective values for hexanal were < 28.5 µg/kg and 9.38 mg/kg. Polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA) increased with a parallel decrease of monounsaturated fatty acids (MFA) after 12 months of storage in samples stored with the oxygen absorber while in samples packaged in PET//LDPE under N₂, a decrease in PUFA and MUFA with a parallel increase in SFA was recorded. Likewise, volatile compounds such as aldehydes, ketones, alcohols, acids, alkanes and aromatic hydrocarbons increased during storage indicating enhanced lipid oxidation. Color parameters L, a and b remained unaffected in all treatments including the oxygen absorber while under a N₂ atmosphere L parameter showed a small but statistically significant (p < 0.05) decrease with a parallel increase (p < 0.05) of a and b values after 12 months of storage. The most pronounced color changes occurred for samples in PET//LDPE pouches irrespective of lighting conditions at 20 °C. Raw ground almonds retained acceptable quality for ca. 6–7 months packaged in PET//LDPE and ca. 8 months packaged in LDPE/EVOH/LDPE pouches under N₂ irrespective of lighting conditions at 20 °C while at 4 °C shelf life was extended by an additional month as compared to storage at 20 °C. Use of the oxygen absorber provided a shelf life of at least 12 months for all samples irrespective of container oxygen barrier, lighting conditions and storage temperature.

Industrial relevance

The use of oxygen absorbers is very effective in extending the shelf life of ground almonds commercially for at least 12 months irrespective of packaging material barrier to O₂, lighting conditions and storage temperature.     

Effect of ultrasonication on the properties of skim milk used in the formation of acid gels

Skim milk was ultrasonicated for times up to 30 min either with or without temperature control. Ultrasonication (US) without temperature control resulted in the generation of considerable heat, with the milk reaching  95 °C within 15 min of treatment. The whey proteins were denatured. Changes to the casein micelle size were observed, with decreases during the early stages of US and increases (because of aggregation) on prolonged treatment. Significant κ-casein dissociated from the micelles. Acid gels prepared from these ultrasonicated samples increased in firmness (final G′) up to a maximum final G′ after  15 min of US, followed by a decrease from this maximum on prolonged treatment. US with temperature control demonstrated that the denaturation of the whey proteins was entirely due to the heat generated during US, although the casein micelle size was still reduced. Acid gels prepared from ultrasonicated skim milk in which the temperature remained below the denaturation temperature of the whey proteins had low final G′, although a small increase was observed with increasing US time. Acid gels prepared from the samples that were ultrasonicated at temperatures above the denaturation temperature of the whey proteins had higher final G′, which could reach values similar to those obtained by the conventional heating of milk. The results of this study indicate that, in skim milk, most of the effect of US can be related to the heat generated from the treatment, with US itself having only a small effect on the milk when the temperatures are controlled.

Industrial relevance

The control and the manipulation of the firmness of acid skim milk gels are important in many dairy food applications such as yoghurts and some types of cheese. US is an emerging technology that could be used to process skim milk for use in acid gelled products. This study has demonstrated that acid gel firmness can be substantially manipulated when skim milk is ultrasonically treated before acidification; however, most of the effect is due to the heat generated during US treatment. As the effects of US are similar to those obtained through conventional heating processes, and as US can control spoilage microorganisms, using US under controlled temperature conditions could be an alternative to conventional heating to give desired functional properties and storage stability to milk products. However, the temperature/denaturation/aggregation would need to be carefully controlled to minimize the detrimental effects of excessive heating.     

A novel global hydrodynamic analysis of the molecular flexibility of the dietary fibre polysaccharide konjac glucomannan

Konjac glucomannans have been widely considered in health food products although their hydrodynamic properties have been poorly understood. The weight-average molecular weight (M_w); sedimentation coefficient (s⁰_20,w) and intrinsic viscosities ([η]) have been estimated for five different preparations. The decrease in both intrinsic viscosity and sedimentation coefficient with molecular weight enables the estimation of molecular flexibility in terms of persistence length (L_p) using the traditional Bohdanecky–Bushin and Yamakawa–Fujii analyses for intrinsic viscosity and sedimentation data respectively. However, this requires an assumption of the mass per unit length M_L. Advantage can now be taken of a recent development in data interpretation which allows the estimation of L_p from combined intrinsic viscosity and sedimentation coefficient data and also an estimate for M_L. Using this “global” procedure an estimate of (13 ± 1) nm is found for L_p and a value of (330 ± 10) g mol⁻¹ nm⁻¹ for M_L.The value for L_p suggests a molecule of considerable flexibility, comparable to galactomannans (L_p  8–10 nm) but not as flexible as pullulan (L_p  1–2 nm).     

The influence of phospholipids and food proteins on the size and stability of model sub-micron emulsions

The influence of both the nature of the surfactant and surfactant concentration on the processes of droplet breakup and coalescence in the formation of decane in water sub-micron emulsions in a high-pressure homogenizer were investigated. Emulsions were produced using a Microfluidics inc. M110-S microfluidizer with an impinging jet high-shear chamber. For all the food grade emulsifiers studied, the droplet size decreased with increasing concentration (weight %) reaching a limiting droplet size between 0.5 and 1% for the proteins and 1.5% for the Phospholipids. A hydrophobic fluorescent dye (1-undecylpyrene) was used to establish the extent of competition between droplet breakup and coalescence in the emulsification process. For the food proteins and phosphatidylglycerol, droplet coalescence in the process reduced as the amount of emulsifier increased, becoming zero at concentrations of about 0.5–1% i.e. the same concentration as that required to produce the limiting minimum droplet size. For phosphatidylcholine some coalescence in the process was observed up to the highest concentration studied (2%) which is indicative of the fact that it normally stabilises water in oil emulsions so favouring coalescence in the process. The data collected in this study show that in the emulsification process droplet size is determined by both breakup and coalescence events, and that the final droplet size is probably a consequence of multiple breakup events until at higher emulsifier concentrations the droplet size is reached which is limited by the breakup capabilities of the homogenizer. Emulsion stability over 400 h was investigated by measuring changes in the droplet size using dynamic light scattering. For the proteins the increase in droplet volume was shown to be linear with respect to time, indicating an Ostwald ripening process. Although there was coalescence on storage at the lowest concentrations of phospholipid used, there was no observed ripening at any emulsifier concentration showing that phospholipid interfaces are structured in such a way as to resist ripening even though decane has a solubility in water. The ripening rate for whey and β-lactoglobulin were observed to be approximately 10 times higher than the ripening rate calculated using the Lifshitz–Slesov–Wagner (LSW) theory 10–20 nm³ s⁻¹. Ripening rates are explained in terms of the nature of the interface formed.     

Effect of whey protein enzymatic hydrolysis on the rheological properties of acid-induced gels

A protein dispersion blend of β-lactoglobulin and α-lactalbumin was heat-denatured at pH 7.5, hydrolyzed by α-chymotrypsin and then acidified with glucono-δ-lactone to form gels at room temperature. Heat treatment induced the formation of whey protein polymers with high concentration of reactive thiol groups (37 μmol/g). The reactive thiol group concentration was reduced by half after 40 min enzymatic hydrolysis. It was further reduced after enzyme thermal deactivation. During acidification, the first sign of aggregation for hydrolyzed polymers occurred earlier than for non hydrolyzed polymers. Increasing the hydrolysis duration up to 30 min resulted in more turbid gels characterized by an open microstructure. Elastic and viscous moduli were both reduced, while the relaxation coefficient and the stress decay rate constants were increased by increasing the hydrolysis duration. After one week storage at 5 °C, the hardness of gels made from hydrolyzed polymers increased by more than 50%. The effect of polymer hydrolysis on acid-induced gelation is discussed in relation to the availability and reactivity of thiol groups during gel formation and storage.     

Total phenolic compounds and antioxidant capacities of major fruits from Ecuador

Seventeen fruits from Ecuador were analysed for total soluble phenolic compounds content and for antioxidant capacity, using three different methods (DPPH, FRAP and ABTS⁺). For the total phenolic content measured by the Folin–Ciocalteu method, three groups, having <100, 200–500 and >1000 mg GAE/100 g FW, were clearly distinguishable. Andean blackberry, capulí cherry peel and banana passion fruit were classified in the third group, with concentrations of 2167, 1494 and 1010 mg of GAE/100 g FW, respectively. Antioxidant capacity analyses revealed the same classes. FRAP and ABTS⁺ gave comparable results and were highly correlated (y = 0.691x + 6.78; r² = 0.908). Spectrophotometric measurements showed that the Andean blackberry and capulí peel but not banana passion fruit contained high levels of anthocyanins (λ_max = 520 nm).     

Cold-set thickening mechanism of β-lactoglobulin at low pH: Concentration effects

There is an interest in developing protein based thickening agents for nutritional considerations. A procedure to convert whey protein concentrates or isolates into a pH modified cold-thickening ingredient was developed. Concentration effects on thickening mechanism of this whey protein ingredient were studied with a β-lactoglobulin model system at the pH of the modification procedure, 3.35. In this study, concentration effects on thermal aggregation of β-lactoglobulin were studied at low pH using capillary and rotational viscometry, transmission electron microscopy (TEM), and high performance liquid chromatography coupled with multi-angle laser light scattering (HPLC-MALS). From the results of capillary viscometry, a critical concentration (C_c  6.9% w/w) was identified below which no significant thickening functionality could be achieved. Microscopy revealed formation of flexible fibrillar network at pH 3.35 during heating at all concentrations. These flexible fibrils had a diameter of about 5 nm and persistence length of about 35 nm as compared to more linear and stiff fibrils formed at pH 2 and low ionic strength conditions. Under similar heating conditions at concentration above C_c, larger aggregates similar to microgels were observed compared to the concentration below C_c, where isolated fibrils with an average contour length of about 130 nm were observed. These microgels and apparently stronger interactions between aggregates at concentrations above C_c were seemingly responsible for thickening functionality of heated β-lactoglobulin solutions and subsequently modified powders. Further investigation of β-lactoglobulin aggregation at this pH may provide capability to mechanistically tailor the functional attributes of modified ingredients.     

Competitive amino acid transport between -tryptophan and other amino acids in Schizophyllum commune

In our study on nutritional requirement for the hyphal growth of Schizophyllum commune, we found that a Trp⁻ mutant could not grow in the -Trp-supplied medium in the presence of -Ser. Further growth studies showed that not only -Ser but also as many as 11 kinds of amino acid including -Ala, -Arg, -Asn, -His, -Leu, -Met, -Phe, -Ser, -Thr, -Tyr and -Val inhibited the growth of the Trp⁻ mutant in the -Trp-supplied medium. However, these amino acids did not inhibit the growth of a Trp⁺ strain. The inhibition of growth of Trp⁺ strain induced by a Trp analogue of 5-fluoro- -tryptophan (5FT), which was usually recovered by -Trp, was rescued by the same amino acids mentioned above. The exceptions were Gly and -Ile, which also recovered the growth inhibition induced by 5FT. These results indicate that the permease responsible for the Trp transport in S. commune might also be active to other amino acids. However, it is considered that the permease shows high affinity to -Trp and low affinity to other amino acids. As a result, the transport of -Trp and 5FT may be counteracted by other amino acids.     

Performance and fat quality of heavy pigs fed maize differing in linoleic acid content

Maize shows wide differences in linoleic acid due both to total lipid content and to fatty acid profile. Therefore, diets containing the same high maize percentage (up to 55%) can differ in linoleic acid content and lead to subcutaneous fats of differing suitability for raw ham curing. Two trials were performed on heavy pigs; in the first, 60 pigs (body weight 48.7 ± 5.1 kg) were fed three diets made using three maize batches differing in linoleic acid due to different total lipid content, in the second trial, 40 pigs (live weight 70.4 ± 3.4 kg) were fed two diets made using two maize batches differing in linoleic acid due to their fatty acid profile. Pigs were slaughtered at 170 kg of live weight. In both trials, the growth and slaughtering performance did not differ. In the first trial the three diets lead to a different content of linoleic acid both in subcutaneous (low linoleic vs medium linoleic vs high linoleic P  0.01) and intramuscular fat (low linoleic vs high linoleic P  0.05). In the second trial different linoleic acid content was observed for subcutaneous fat (P  0.01) but not for intramuscular fat. To formulate diets for heavy pigs, it is crucial to know the linoleic acid content of the maize used, because differences of only 0.3% can lead to significant differences in fatty acids composition of depot fats.     

Marinating as a technology to shift sensory thresholds in ready-to-eat entire male pork meat

This study investigated the effect of marinades in improving the eating quality in ready-to-eat boar meat. Neck chops with fat content below 18.9%, skatole 1.1 ppm (range 0.03–1.1) and androstenone 5.6 ppm (range 0.01–5.6) were used. In a screening experiment different marinades were tested for their ability to mask boar taint (defined as manure and urine odour and flavour). Liquid smoke and oregano extracts appeared to have the best potential for masking, and were studied in detail. Results from the study indicated that marinated chops with skatole content of approximately 0.4 ppm appeared similar to castrates in boar taint. Chops with skatole contents above 0.7 ppm remained unmasked despite the use of strongly flavoured marinades. Unmarinated chops served at 60 °C were more tainted than those served at 15 °C, but scored lower for boar taint when reheated, although the concentrations of androstenone and skatole remained the same. The fat content of the chops was not well correlated to the perception of boar taint. The attributes manure and urine were correlated with the level of skatole, but urine attribute was not a good indicator of the androstenone level.