Effects of transglutaminase treatment on the thermal properties of soy protein isolates

The effects of covalent cross-linking of microbial transglutaminase (MTGase) on the thermal properties of soy protein isolates (SPI), including the thermal denaturation and glass transition were investigated by conventional and modulated differential scanning calorimetry (DSC). The MTGase treatment significantly increased the thermal denaturation temperatures (including the on-set temperature of denaturation, T_m and the peak temperature of denaturation, T_d) of glycinin and β-conglycinin components of SPI (P ⩽ 0.05), and the thermal pretreatment of SPI further increased the extent of this improvement. The MTGase treatment also improved the ability of SPI to resist the urea-induced denaturation. Modulated DSC analysis showed that there were two glass transition temperatures (T_g) in the reversible heat flow signals of native SPI (about 5% moisture content), approximately corresponding to 45 and 180 °C, respectively. These T_g values of SPI were significantly decreased by the MTGase treatment (at 37 °C for more than 2 h) (P ⩽ 0.05). The improvement in the hydration ability of protein and the formation of high molecular biopolymers may account for the changes of thermal properties of soy proteins caused by the MTGase cross-linking.     

Functional and molecular properties of calcium precipitated soy glycinin and the effect of glycation with κ-carrageenan

This study describes an extraction process for the preparation of highly purified calcium precipitated glycinin (11S). Initial extraction of soy proteins using isoelectric precipitation at pH 6.8 followed by cryo-precipitation yielded 4.2% product (11S) recovery with 98% protein purity for the control extracted with NaOH. Addition of calcium chloride (CaCl₂) doubled the extraction yield (9%) compared to the control and when two other salts were used (i.e., sodium (Na₂SO₄) and ammonium (NH₄)₂SO₄ sulfate, average yields of 4.4% and 5.17%, respectively). Thermal and molecular stability under varying conditions (pH, salts, SDS as a protein structure perturbing agent), and effect of glycation on functional and structural properties were investigated. Size exclusion chromatography and electrophoresis confirmed the predominance of a major band with MW of ～342 kDa with 98.4% purity. Differential scanning calorimetry (DSC) yielded one endothermic transition peak at 95.5 °C. Denaturation temperatures were >100 °C for all salt concentrations studied. The pH had a dominant influence on the structural properties of glycinin. In the presence of NaCl and CaCl₂ (0.2–1 M), the protein structure showed very little denaturation and no aggregation bands were observed even on heating to 95 °C. Lower SDS concentrations (0.5–1%) resulted in denaturation and aggregation, while at 2% SDS only denaturation was observed. Glycation did not alter the conformational structure of protein. Improvements in surface properties were observed with moderate degree of glycation (6–24 h).     

High-pressure homogenisation of raw bovine milk. Effects on fat globule size distribution and microbial inactivation

Whole raw milk was processed using a 15 L h⁻¹ homogeniser with a high-pressure (HP) valve immediately followed by a cooling heat exchanger. The influence of homogenisation pressure (100–300 MPa) and milk inlet temperature T_in (4°C, 14°C or 24°C) on milk temperature T₂ at the HP valve outlet, on fat globule size distribution and on the reduction of the endogenous flora were investigated. The T_in values of 4–24°C led to milk temperatures of 14–33°C before the HP valve, mainly because of compression heating. High T_in and/or homogenisation pressure decreased the fat globule size. At 200 MPa, the d_4.3 diameter of fat globules decreased from 3.8±0.2 (control milk) to 0.80±0.08 μm, 0.65±0.10 or 0.37±0.07 μm at T_in=4, 14°C or 24°C, respectively. A second homogenisation pass at 200 MPa (T_in=4°C, 14°C or 24°C) further decreased d_4.3 diameters to about 0.2 μm and narrowed the size distribution. At all T_in tested, an homogenisation pressure of 300 MPa induced clusters of fat globules, easily dissociated with SDS, and probably formed by sharing protein constituents adsorbed at the fat globule surface. The total endogenous flora of raw milk was reduced by more than 1 log cycle, provided homogenisation pressure was ⩾200 MPa at T_in=24°C (T₂∼60°C), 250 MPa at T_in=14°C (T₂∼62°C), or 300 MPa at T_in=4°C (T₂∼65°C). At all T_in tested, a second pass through the HP valve (200 MPa) doubled the inactivation ratio of the total flora. Microbial patterns of raw milk were also affected; Gram-negative bacteria were less resistant than Gram-positive bacteria.     

Effect of pre-incubation conditions on growth and survival of Staphylococcus aureus in sliced cooked chicken breast

In this work, the effect of pre-incubation conditions (temperature: 10, 15, 37 °C; pH 5.5, 6.5 and water activity, a_w: 0.997, 0.960) was evaluated on the subsequent growth, survival and enterotoxin production (SE) of Staphylococcus aureus in cooked chicken breast incubated at 10 and 20 °C. Results showed the ability of S. aureus to survive at 10 °C when pre-incubated at low a_w (0.960) what could constitute a food risk if osmotic stressed cells of S. aureus which form biofilms survive on dried surfaces, and they are transferred to cooked meat products by cross-contamination. Regarding growth at 20 °C, cells pre-incubated at pH 5.5 and a_w 0.960 had a longer lag phase and a slower maximum growth rate. On the contrary, it was highlighted that pre-incubation at optimal conditions (37 °C/pH 6.5/a_w 0.997) produced a better adaptation and a faster growth in meat products what would lead to a higher SE production. These findings can support the adoption of management strategies and preventive measures in food industries leading to avoid growth and SE production in meat products.     

Effect of thermal treatment on the activation of bovine plasminogen

The effect of heat on plasminogen (PG) was studied in both buffer and milk. The denaturation temperature for bovine PG was determined. Kinetic analysis of heated PG was conducted using a coupled assay and Spectrozyme^®PL. The effect of heat on PG activation was studied in milk samples with and without addition of PG activator. The temperature range for denaturation of PG was between 50.1 and 61.6 °C. The overall catalytic efficiency increased for PG heated to 60 °C and above, as indicated by the significant increase in k_cat/K_M. In a milk system, a significant increase in activation of PG was measured at 57 °C. A drop in activation of PG was observed at higher temperatures, suggesting counteracting effects of other milk components that were affected by heat. Results indicated that the increased activation of heated bovine PG observed in buffer and milk systems was probably due to the unfolding of PG as a result of thermal denaturation.     

Radio-sensitivity of pathogens in inoculated prepared foods of animal origin

The effectiveness of irradiation for inactivating Staphylococcus aureus, Listeria ivanovii, Salmonella Typhimurium, and Escherichia coli in the prepared foods of animal origin was investigated. Commercially available seasoned and cooked beef, fried egg, and ham were purchased, radiation-sterilized, and inoculated at 10⁶–10⁷ CFU/g with each of the four pathogens and stored at three storage conditions at 10 °C, 20 °C, and 30 °C. D₁₀-values of S. aureus, L. ivanovii, Salmonella Typhimurium, and E. coli were 0.34±0.01, 0.24±0.02, 0.24±0.01, and 0.27±0.01 kGy, respectively. No viable cells were detected at 3 kGy of irradiation. Salmonella mutagenicity assay (Ames test) indicated that the 10 kGy irradiated samples were statistically similar to non-irradiated control samples in the Salmonella mutagenicity assay (Ames test). These studies demonstrate that irradiation can be used as an additional safety tool to produce microbiologically safe and wholesome prepared foods of animal origin.     

Effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel

To elucidate the effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel, Ca²⁺ induced gelation of soybean protein were investigated by rheological approaches, electrophoresis analysis, confocal scanning laser microscopy (CSLM) and surface hydrophobicity (S₀). The results showed that, both CaCl₂ concentration (20–40 mM) and preheating temperature (80–120 °C) took significant influence on the dynamic viscoelasticity of the gel samples. The bands distribution of samples preheated at 120 °C were different from the bands distribution of samples preheated below 100 °C in denature and native electrophoresis. The CSLM analysis showed that the gel became coarser as the Ca²⁺ increased. On the other hand, two different kinds of gel were shown under the same Ca²⁺ concentration: a bead-like structure (below 100 °C) and a filamentous structure (above 100 °C). According to fractal theory, weak-linked gel (α was >0.8) was formed when preheating below 100 °C, while a transition gel (α = 0.52–0.62) was obtained when preheating over 100 °C. All these results suggested that the preheating temperature influence the type of cold-set gel.     

Effect of preheating and other process parameters on whey protein reactions during skim milk powder manufacture

Skim milk powder was manufactured in a milk powder plant using different preheating temperatures, concentrate heating temperatures and spray drying temperatures. Varying the preheating conditions from 70 °C for 52 s to 120 °C for 52 s had a marked effect on the denaturation of $\beta$-lactoglobulin A, $\beta$-lactoglobulin B, $\alpha$-lactalbumin, bovine serum albumin (BSA), and immunoglobulin G. In contrast, varying concentrate heating temperature (65–74 °C) and inlet/outlet air dryer temperature (200/101 °C–160/89 °C) had a minimal effect on whey protein denaturation. Most of the whey protein denaturation and association with the casein micelle occurred in the preheating section of the powder plant. Aggregation of β-lactoglobulin (β-lg) and BSA predominantly involved disulphide bonds. Although, greater than 90% of the β-lg and BSA was denatured after preheating at 120 °C for 52 s, the extent of association with the casein micelle was lower, 50% for β-lg and 75% for BSA.     

Adsorption of FD&C Red No. 40 by chitosan: Isotherms analysis

The adsorption of azobenzene FD&C Red No. 40 (C.I. 16035) from aqueous solutions by chitosan was studied through adsorption isotherms. The effects of pH (5.7, 6.6 and 7.5), particle size ranges (0.10 ± 0.02, 0.18 ± 0.02 and 0.26 ± 0.02 mm), deacetylation degree (42 ± 5%, 64 ± 3% and 84 ± 3%) and temperature (25, 35 and 45 °C) were investigated. Langmuir, Freundlich and Redlich–Peterson (R–P) adsorption models were applied in order to describe the experimental isotherms and isotherm constants. Coefficients of determination (R² > 0.95) and mean relative error (MRE < 0.10) values showed that Langmuir and R–P models presented better fit with the experimental data. The maximum monolayer adsorption value has been found to be 529 mg g^?1, at pH 6.6, temperature 35 °C, particle size range 0.10 ± 0.02 mm, and deacetylation degree 84 ± 3%.     

Destruction of Salmonella Enteriditis inoculated onto raw almonds by high hydrostatic pressure

The effects of continuous (50,000, 60,000 and 70,000 psi with holding times of 5 and 10 min) and discontinuous (oscillatory) (six cycles at 60,000 psi with a holding time of 20 s) high hydrostatic pressure (HHP) treatments on the viability of two Salmonella Enteriditis strains (FDA and PT30) inoculated onto raw almonds were evaluated at 25, 50, and 55 °C. Complete inactivation of the S. Enteriditis was achieved in 0.1% peptone water after continuous pressurization at 60,000 psi and 25 °C for 5 min. Continuous pressurization of raw almonds inoculated with S. Enteriditis at 60,000 psi and 50 °C for 5 min resulted in less than a log reduction (log₁₀ 0.83) of vegetative cells. The decimal reduction time using the continuous pressurization parameters was determined to be 9.78 min. A discontinuous process consisting of six cycles of pressurization at 60,000 psi and 50 °C for 20 s provided greater than a one log reduction (log₁₀ 1.27 for FDA and log₁₀ 1.16 for PT30) of the S. Enteriditis concentration. The low water activity (a_w) of the almonds was found to impart baroprotective attributes on the S. Enteriditis cells. When the almonds were directly suspended in water and then pressurized, a log₁₀ reduction of 3.37 was achieved. HHP of certain dry foods appears to be feasible if the food is directly suspended in the pressurizing medium (water).     

High pressure processing (HPP) of honey for the improvement of nutritional value

The present study was undertaken to assess the effect of high pressure processing (HPP) on total phenolic content (TPC) in manuka honey. Manuka honey is known for its amazing antimicrobial action and antioxidant properties. The effect of HPP (200, 400 and 600 MPa) at ambient and moderate temperatures (53.41 ± 0.30 °C, 65.29 ± 1.77 °C, 71.92 ± 1.63 °C) and their combination for different processing time (5, 10 and 15 min) was investigated. Conventional thermal processing (51.74 ± 0.03 °C, 61.90 ± 0.10 °C and 71.58 ± 0.04 °C) was also carried out as comparison to HPP. Operating HPP at 600 MPa (26.80 ± 0.95 °C–30.18 ± 2.14 °C) for 10 min was found to be the most effective process with 47.16% increment in TPC as compared to unprocessed honey, whereas no significant increase (p < 0.05) was observed in thermal processing as well as in combined HPP–thermal processing. Therefore, HPP at ambient temperatures could be an appropriate method to produce tastier and more nutritive manuka honey.Industrial relevanceThe preservation of total phenolic content (TPC) as a main phytochemical component in honey is very important with direct impact on nutritional value and antioxidant activity. A significant increase in the TPC was obtained by processing. Results demonstrated the HPP capability to increase TPC in manuka honey by 47%. From a nutritional perspective, this result is associated with the production of a higher antioxidant honey, known to prevent certain diseases such as cancer. The study generates a new approach in honey processing which can guarantee the high nutritional quality of honey and its original natural freshness.     

Application of high power ultrasound in the supercritical carbon dioxide inactivation of Saccharomyces cerevisiae

The objective of the study was to analyze the influence of high power ultrasound (HPU) on the supercritical carbon dioxide (SC-CO₂) inactivation kinetics of Saccharomyces cerevisiae and to determine the effect of the temperature (31–41 °C), pressure (100–350 bar) and composition of the medium (YPD Broth, apple and orange juice) on the process of inactivation. Using a batch-mode SC-CO₂ at 350 bar and 36 °C, a reduction of 6.7 log-cycles was obtained after 140 min of treatment. However, when HPU (40 W ± 5 W and 30 kHz) was applied during the SC-CO₂ treatments, a reduction of 7 log-cycles was achieved after 2 min of treatment for all pressures and temperatures applied. The effect of increasing pressure (from 100 to 350 bar, 36 °C) or temperature (from 31 to 41 °C, 225 bar) did not significantly influence this inactivation level. The application of ultrasound leads to a vigorous agitation and cavitation which could accelerate the SC-CO₂ dissolving in the medium. This accelerates the penetration of CO₂ into cells and its inactivation mechanisms. In batch operations the application of HPU increases the speed of reaching saturation solubility of CO₂ in many liquid media and significantly reduces microbial inactivation times.     

Thermo-mechanical properties of egg albumen–cassava starch composite films containing sunflower-oil droplets as influenced by moisture content

The effect of moisture content on the thermo-mechanical and structural properties of egg albumen–cassava starch composite films containing sunflower oil droplets was studied using dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Composite films were prepared by cold gelation, dried in a moisture controlled incubator (83.5%RH) at 25 °C for 8 days and aged at different relative humidity at room temperature (21 ± 1 °C) for 7 days to obtain composite films with moisture contents of 4%, 7%, 11%, 17% and 46% (dry weight basis). In DMA thermograms the magnitude of G′ and G″ increased with increasing temperature in high-moisture samples, decreased and then again gradually increased for intermediate-moisture samples, and decreased in low moisture samples. DSC thermograms indicated two distinct peaks (at 49–53 °C and 79.8 to 132.4 °C) which were attributed to phase transitions and protein denaturation. SEM images indicated that the microstructure of the composite matrix changed with moisture content and heating temperature. Our study confirms that moisture content plays a key role in the thermo-mechanical properties and microstructure of egg albumen–cassava starch composite films containing sunflower oil.     

Behaviour of soyasapogenol B under optimised hydrolysis and ESI mass spec conditions

Soyasaponins are oleanane triterpenoids found in soy (Glycine max Merr). The analysis of the main aglycone (soyasapogenol B) is hampered by inconsistent ion fragmentation patterns produced during MS analysis. The greatest (p < 0.05) increase in soyasapogenol B during acid hydrolysis HCl (5% (v/v)) was at 100 °C (84.59 ± 4.73 μg/ml), followed by 120 °C (69.82 ± 6.20 μg/ml) and 80 °C (46.54 ± 6.41 μg/ml). The capillary temperature (LC–ESI-MS) of 220 °C produced the greatest (p < 0.05) intensity of soyasapogenol B ion. Temperatures between 200 and 250 °C consisted the optimum temperature range for analysing soyasapogenol B. At low capillary temperatures (<200 °C), the soyasapogenol B ion ([M?H]^? = 457.4) was converted to an ion m/z at 441, while, at temperatures ?250 °C the soyasapogenol B ion produced ions m/z at 440 and 437. We report an analysis procedure for detecting intact soyasapogenol B molecular ion without the typical fragmentation reported in the literature.     

Extraction of boldo (Peumus boldus M.) leaves with supercritical CO2 and hot pressurized water

High-activity fractions in boldo leaves were extracted with supercritical CO₂ (SC-CO₂) and hot pressurized water (HPW). Total yield after 3 h of extraction (0.6–3.5%) in low-pressure SC-CO₂ experiments increased with process pressure (60–150 bar) and decreased with temperature (30–60 °C), as expected. The extract obtained with SC-CO₂ at 50 °C and 90 bar contained approximately 50% of essential oil components. In higher pressure experiments with solvent mixtures, the yield increased with pressure (300–450 bar) and modifier concentration (2–10% ethanol), ranging 0.14–1.95 ppm for the alkaloid boldine and 1.8–4.8% for total solids following 1.5 h treatment at 50 °C. Boldine recovery was solubility-controlled, reaching 7.4 ppm after 7-h extraction at 450 bar and 50 °C using an ethanol–SC-CO₂ mixture (5% co-solvent). Boldine solubility and yield decreased when using pure CO₂ at higher pressure (600 bar, 50 °C). The extract yield after 3 h batch-wise HPW extraction increased from 36.9% at 100 °C to 53.2% at 125 °C, and then decreased as temperature was increased to 175 °C. Boldine yield decreased from 26.8 ppm at 100 °C to 0.7 ppm at 125 °C, and was negligible at ⩾150 °C. The essential oil yield increased to a maximum at 110 °C and was negligible at ⩾150 °C also. The ranking of antioxidant potency of various extracts was as follows: HPW at 110 °C > methanol (soxhlet extraction) ≫ high-pressure SC-CO₂ with or without polar co-solvent > low-pressure SC-CO₂.     

Mechanical and thermal characteristics of amaranth starch isolated by acid wet-milling procedure

Effects of soaking conditions during acid wet-milling of amaranth grain on mechanical and thermal properties of amaranth starch were investigated. A factorial design based on temperature (40–60 °C) and SO₂ concentration (0.1–1.0 g/L) was used. Dynamic oscillatory tests involved heating and cooling cycles (25–90 °C) with tempering at 90 °C followed by a frequency sweep (0.1–20 Hz) at constant temperature. Thermal properties of starch suspensions were based on DSC tests. Viscoelastic modulus and thermal properties were affected by both factors, being significant the interaction effect. Maximum values of viscoelastic modulus at the end of heating and cooling steps were determined for samples corresponding to soaking conditions of 50 °C and 1.0 g/L SO₂. Based on Ross-Murphy index from frequency sweep analysis it was found that paste behavior occurs at 60 °C and 0.1 g/L, while at 47.4 °C and 0.72 g/L starch suspension gave a strong gel. Onset (61.7 °C) and peak (66.2 °C) temperatures showed a minimum at 50 °C and 1.0 g/L. As SO₂ concentration decreased, the end of gelatinization took place at lower temperature. Maximum gelatinization enthalpy (12.7 J/g) was found at 40 °C and 0.1 g/L SO₂.     

Effect of a 10-day ageing at 30 °C on the texture of dry-cured hams processed at temperatures up to 18 °C in relation to raw meat pH and salting time

The aim of this study was to investigate the effect of a 10-day ageing at 30 ± 2 °C on the texture of dry-cured hams processed at temperatures up to 18 ± 2 °C for 12 months in relation with raw ham pH and salting time. Three pH groups (semimembranosus muscle at 24 h post-mortem: Low pH < 5.7, Medium pH = 5.7 ⩽ pH ⩽ 5.9, and High pH > 5.9), three salting times (6 d, 10 d and 14 d) and two ageing temperatures (18 °C and 30 °C) were investigated. Physicochemical characteristics, instrumental and sensory texture and product sliceability were evaluated on biceps femoris and semimembranosus muscles. Hams with pH_SM24 < 5.7 should be avoided in order to reduce the incidence of texture problems in dry-cured ham elaboration. Texture problems are especially important in hams with a reduced salt content that are mechanically sliced (not frozen). A 10-day ageing at 30 °C could be useful for reducing the soft texture problems in dry-cured hams processed at temperatures up to 18 °C for 12 months without affecting the product flavour.     

Stickiness curves of high fat dairy powders using the particle gun

High fat (>42%) dairy powders are inherently sticky due to their high levels of liquid surface fat. Incorrect operating conditions when spray drying these powders can rapidly lead to blockages. The particle gun was used to characterise the stickiness curves of high fat cream and cheese powders. Stickiness was shown to increase with increasing temperature to a maximum at 50 °C after which it decreased until no stickiness was observed above 68 °C. A dramatic increase in stickiness for the powders was found when the relative humidity of the air was increased past a certain critical point for each temperature. This was attributed to the lactose component of the powder exceeding its glass transition temperature by a critical amount. Best estimates of the (T−T_g)_crit. values for White Cheese Powder, Low Fat Cream Powder and High Fat Cream Powder were 28, 37 and 38 °C, respectively.     

Water vapor transport properties during staling of bread crumb and crust as affected by heating rate

In order to develop a mathematical model to simulate mass transfer occurring between the crumb and the crust during bread staling, water vapor sorption properties, i.e., moisture diffusivity, WVP and sorption of bread crumb and crust were investigated at 15 °C. Two types of bread baked with two heating rates (7.39 °C/min and 6.32 °C/min) were considered. Sorption and desorption isotherms were determined using Dynamic Vapor Sorption (DVS) and FF and GAB models were applied in the range of 0–0.95 a_w, to fit isotherm curves. Diffusivity was determined from sorption isotherms by using Fick's law and WVP was measured by two methods (gravimetric and from sorption data). Results exhibited maximum values of D_eff in the range of 0.1 and 0.14 g/g d.b. moisture contents. They varied between 0.88 × 10^? 10 and 0.92 × 10^? 10 m²/s for the crust and between 2.24 × 10^? 10 and 2.64 × 10^? 10 m²/s for the crumb, baked respectively at 220 °C and 240 °C. Results of WVP showed that the crust baked at 240 °C was significantly more permeable than the crust baked at 220 °C. This fact was attributed to the difference in porosity and the molecular structure due to heating effects. Also, the presence of steam in the oven atmosphere enhanced the development of higher porosity in the crust, leading to different structures and properties. Moreover, SEM images showed that starch granules were intact and less swelled in the upper crust when baking at 240 °C, resulting in higher WVP.     

Effect of high pressure,temperature, and storage on the color of porcine longissimus dorsi

The color of pork longissimus dorsi high pressure (HP) treated at 200 to 800 MPa at 5 and 20 °C for 10 min was determined to a high degree by pressure level and to a lesser degree by temperature. Severe color changes appeared up to a threshold pressure at 400 MPa. HP treatment at 20 °C compared to 5 °C resulted in meat, which was less red and slightly lighter. Storage at 2 °C for 6 days had no effect on lightness due to no further protein denaturation, but meat HP treated above 300 MPa became significantly less red and more yellow within the first day of storage. Reflectance spectra showed that a short-lived ferrohemochrome myoglobin species was formed during HP treatment at 300 to 800, but transformed into a brown, ferric form of the pigment within the first day of storage. This explains the observed changes in the redness and yellowness after one day of storage.