Ovalbumin thermal Gelation Prediction by Application of Temperature-Time History

A model for characterizing changes in viscosity of soy protein during extrusion was adapted to predict apparent viscosity ratio of gelling ovalbumin. For ovalbumin (87% purity) the temperature time histories of 3,5, and 7% gel formation were determined at 85, 90 and 95°C. A back-extrusion method was used to determine apparent viscosity ratios during gelation. Activation energy for denaturation/gelation was estimated at 159 kJ/mol. The model parameter a (degree of molecular entanglement) was 0.75, 0.75, and 1.0 for 3, 5, and 7% gels, respectively. Reaction rate constants were similar for samples with different protein concentrations. Maximum apparent viscosity ratio increased as protein concentrations increased. The mathematical model was verified by determining apparent viscosity ratios at 86 and 93°C and water holding at 90°C, resulting in R²-0.93. This model may be useful in predicting ovalbumin thermal gelation apparent viscosity ratios.     

Lipid oxidation in salted-dried fish: II. The effect of photosensitisers on the rate of oxidation of a fish oil

The contribution of photosensitised oxidation to the extent of lipid oxidation of a model fish oil system has been considered using a number of methods of measurement, namely peroxide value, polyene index and the initial rate of oxygen uptake. This represents the initial stages of the development of a model system which will eventually simulate the processing and storage of salted, sun-dried fish. The effects of the photosensitisers, protoporphyrin IX, riboflavin and myoglobin on the rate of oxidation of a highly unsaturated fish oil in a model system, have been studied under dark or photosynthetic light conditions at 30°C. As has previously been established, the initial rate of oxygen uptake proved to be a more reliable method than the peroxide value or the polyene index in determining the extent of lipid oxidation of the oil in the model system. Protoporphyrin IX, riboflavin and myoglobin all increased the rate of oxygen uptake significantly in photosynthetic light at 30°C, from a rate of 0–158 μl O₂g^?1for the control to 0.335 μl O₂g^?1min^?1, 0.308 μl O₂ g^?1min^?1 and 0.461 μl O₂g^?1min^?1, respectively. However, in the dark at 30°C their addition had no effect on the initial rate of oxygen uptake, showing that these components increased the rate via a photosensitised oxidation mechanism rather than by autoxidation. The addition of β-carotene, a well-established singlet oxygen quencher, to the systems containing the photosensitisers at 30°C in the light significantly reduced the rate of oxygen uptake, but not to the same rate as in the control. Photosensitised oxidation has been classified as Type I or Type II; the reduction observed in oxygen uptake rate in the presence of β-carotene shows the Type II mechanism involving singled oxygen to be important. Studying β-carotene on its own in the model system at 30°C showed an unexpected increase in the rate of oxygen uptake both in the light and in the dark.     

Rheological behaviour and colour changes of ginger paste during storage

Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high‐density‐polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20–80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s^?1 in 3 min, followed by a steady shear at 200 s^?1 for 3 min and finally decreasing linearly from 200 to 0 s^?1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel–Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol^?1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers.     

Steady and dynamic shear rheology of glutinous rice flour dispersions

The steady and dynamic shear rheological properties of Korean glutinous rice flour dispersions were evaluated at different concentrations (4, 5, 6, 7 and 8%). Glutinous rice flour dispersions at 25 °C showed a shear‐thinning behaviour (n = 0.487–0.522) with low magnitudes of Casson yield stresses (σ_oc = 0.056–0.339 Pa). The magnitudes of σ_oc, consistency index (K) and apparent viscosity (η_a,100) increased with the increase in concentration. The power law model was found to be more suitable than the exponential model in expressing the relationship between concentration and apparent viscosity. The apparent viscosity over the temperature range of 25–70 °C obeyed the Arrhenius temperature relationship, with high determination coefficients (R² = 0.982–0.998), indicating that the magnitudes of activation energies (E_a) were in the range of 9.05–11.89 kJ mol^?1. A single equation, combining the effects of temperature and concentration on η_a,100, was used to describe the flow behaviour of glutinous rice flour dispersions. Magnitudes of storage (G′) and loss (G′′) moduli increased with the increase in concentration and frequency. Magnitudes of G′ were higher than those of G′′ over most of the frequency range.     

RELATIONSHIP BETWEEN THE BOSTWICK MEASUREMENT AND FLUID PROPERTIES

Consistency of tomato concentrates was evaluated in a Bostwick consistometer. The concentrates were produced in a semibatch evaporator at soluble solids content from 5.3 to 24.0°Brix. The apparent viscosity, yield stress and density were measured at 20C. With respect to the gravity current analysis, the Bostwick measurement correlated well with the theoretical ratio of the apparent viscosity to density (R² = 0.96). For the concentrates with yield stress values in the range of 60–200 Pa, the predicted extent of flow based on the slump analysis was within 2% of the measured extent of flow in the Bostwick consistometer.     

Effect of tertiarybutylhydroquinone on lipid oxidation in fish crackers

The effect of tertiarybutylhydroquinone (TBHQ) in retarding lipid oxidation in fish crackers fried in refined, bleached and deodorised palm olein (RBD olein) during storage was evaluated. The indices of lipid oxidation used were the peroxide and p-anisidine values and u.v. absorbances at 232 and 268 nm of oil extracted from fish crackers stored at 60°C. Two methods for TBHQ incorporation into the fish crackers were used. Fish crackers that were prepared by frying of fish chips in RBD olein containing TBHQ were more stable towards oxidative rancidity than control fish crackers prepared with RBD olein without TBHQ. The rate of lipid oxidation in fish crackers prepared from fish chips that were made with TBHQ in the dough formulation and fried in RBD olein without TBHQ was slightly higher than in control fish crackers. A storage study carried out at room temperature (30°C) showed the same trend in relative rates of lipid oxidation. The study showed that the incorporation of TBHQ into the frying medium was an effective means of retarding the onset of rancidity in fried fish crackers while the incorporation of TBHQ into the dough mixture made the fish cracker slightly more susceptible towards lipid oxidative reactions.     

Lipid oxidation in salted-dried fish: The effect of temperature and light on the rate of oxidation of a fish oil

In relation to studies of lipid oxidation during the processing and storage of salted sun-dried fish, the measurement of the initial rate of oxygen uptake has been studied on a model system consisting of a highly polyunsaturated fish oil. This parameter has been used for assessing the effects of temperature and light conditions on the model system and has been compared to changes in the peroxide value and the polyene index. Assessment of oxygen uptake using a Gilson respirometer was found to give a clearer indication than other methods of assessment of the effect of different conditions on fish oil oxidation. At 30°C the initial rate of oxygen uptake increased from 0-103 μl O₂, g^?1 miir^?1 to 0-158 μl O₂, g^?1 min^?1 with a change in light conditions from dark to photosynthesis light. At 40°C, the rate of oxygen uptake was fester than at 30 °C, and the effect of light was more pronounced, giving values of 0.188 μl O₂, g^?1 min^?1 and 0.483 μ O₂, g^?1 min^?1, for dark and photosynthesis light, respectively. The observed results for the measurement of the initial rate of oxygen uptake suggest its use as a sensitive and reliable method for the investigation of the contribution of the many components in salted sun-dried fish towards the rate of oxidation and subsequent rancidity.     

Furcellaran Gel Creep Study

Consideration has been given to the creep of furcellaran gels concentrated to 0.5-2.0% at temperatures of 25 to 50 °C in the region of linear viscoelasticity. The gel shear modulus (G) corresponding to reversible strain decreases with temperature. The dependence of the shear modulus on concentration at 25 C has the form G ∞ c2.7. The gel irreversible strain is observed in the entire temperature interval studied. The dependence of the largest NEWTONian viscosity on temperature is described by De Guzman-Arrhenius' equation. The apparent activation energy of viscous flow for a 1.25%-gel is 63 ± 5 kJ/mole. The dependence of the largest NEWTONian viscosity (ηN) on oncentration at 25 °C has the form ηN ∞ c^3.1 The break-down enthalpy of the gel cross-link is relatively small (18-25 kJ/mole).     

Edible Coatings to Inhibit Lipid Migration in a Confectionery Product

Coatings containing hydrocolloids and sweetners were tested for lipid barrier and sensory properties, adhesion to chocolate, viscosity, and a_w. A coating containing high methoxyl pectin, acacia gum, high fructose corn syrup, dextrose, fructose, and sucrose was most effective. Coatings (0.5 mm thick, a_w 0.5) showed no detectable oil migration after 47 days at 30 ± l°C, compared to 11.5 mg/cm² trilinolein equivalents migration in 1 day at 21 ± 2°C. Coatings (0.5 mm thick) were applied between chocolate and peanut butter and tested for sensory characteristics. Except for the color of the coating, no significant difference occurred in overall preference compared to control (no coating) samples.     

Rheological and differential scanning calorimetry studies on structural and textural changes in frozen Atlantic mackerel (Scomber scombrus)

The viscoelastic behaviour and thermal stability of Atlantic mackerel fillets stored at ?20 and ?30 °C for up to 2 years were investigated. An increase in elastic (G′) and viscous (G″) modulus values, reflecting protein aggregation, was observed in samples stored at ?20 °C compared with those stored at ?30 °C, as well as with storage time. The results indicate that toughening on frozen storage is not just limited to lean gadoid fish but also occurs in fatty fish, leading to texture deterioration. Differential scanning calorimetry of fillets stored at ?20 °C showed a shift to a lower transition temperature (T_m) and a decrease in enthalpy (ΔH) compared with control fillets stored at ?30 °C; this change was enhanced when fillets were stored for a longer period of time, confirming protein denaturation and the formation of aggregates reported previously by the authors (J Sci Food Agric 82: 579–586 (2002)). The contribution of lipid oxidation to protein aggregation was shown by storing minced mackerel with or without the antioxidant vitamin E at ?10 °C. The G′ and G″ values were higher in samples stored without vitamin E than in samples stored with vitamin E; thus antioxidants may be used to minimise protein aggregation in fatty fish. The role of lipid oxidation in promoting protein aggregation and deterioration in the texture of fatty fish has not been reported hitherto. Antioxidants such as vitamin E may be used not only to prevent lipid oxidation but also to minimise protein damage in order to prolong the shelf‐life of fatty fish. Copyright © 2004 Society of Chemical Industry     

Inhibition of oxidative rancidity in frozen cooked fish flakes by tert-butylhydroquinone and rosemary extract

The antioxidant properties of tert-butylhydroquinone (0·5 g kg^?1 + 20 g kg^?1 ascorbic acid—TBHQ-AS) and an extract of rosemary (2·5 g kg^?1) alone and in combination were determined by their addition as solutions to cooked fish flakes stored at - 20°C. Oxidation was measured by following changes in free fatty acids, thiobarbituric acid number, fatty acid composition and sensory evaluation. The order of effectiveness in inhibiting oxidation was TBHQ-AS > combination > rosemary > untreated control ?70°C > untreated control -20°C. Sensory evaluation indicated that green aroma and flavor notes were associated with the rosemary extract, while fish oil notes were associated with untreated samples.     

Effect of lipid oxidation and frozen storage on muscle proteins of Atlantic mackerel (Scomber scombrus)

The effect of storage on the lipids and proteins in Atlantic mackerel stored for up to 24 months at ?20 and ?30 °C was studied. Traditional methods including the peroxide value, thiobarbituric acid‐reactive substances (TBARS) and a reverse phase HPLC method were used to determine the primary and secondary lipid oxidation products. All tests showed an increase in lipid oxidation products with storage time and at a higher storage temperature of ?20 °C compared with samples stored at ?30 °C. Antioxidants had a significant effect (P < 0.01) on the inhibition of lipid oxidation, as shown by the reduction in peroxide value and hydroxides, and malondialdehyde formation. Similarly, deterioration of protein structure and functionality in mackerel stored for 3, 6, 12 and 24 months was greater at ?20 than ?30 °C. ATPase activity in the myosin extract of Atlantic mackerel showed a significant decrease (P < 0.01) with progressive frozen storage. Protein solubility in high salt concentration (0.6 M NaCl) decreased (P < 0.01) during storage at both ?20 and ?30 °C but was greater at ?20 °C. Interestingly, antioxidants BHT, vitamin C and vitamin E protected the proteins against complete loss of ATPase activity and protein solubility to a significant level (P < 0.01) for up to 1 year at ?20 °C compared with samples stored without antioxidants. This study confirms the deleterious effect of lipid oxidation products on protein structure and function in frozen fatty fish. © 2002 Society of Chemical Industry     

Rheological study of cowpea puree ‘adowè’ and the influence of saliva on the puree viscosity

The traditional preparation of adowè is laborious, time, water, and fuel consuming and this has resulted in a decline in its consumption. We investigated the characteristics of adowè where powder-based products were used to formulate the traditional puree as a means of reducing the cost of the dish. In the absence of additional salt, the cooking of cowpea seeds was characterised by two activation energy domains from the swelling kinetics below and above 60 °C ± 5 °C of ≈15.30 and ≈28.35 kJ mol⁻¹, respectively. Decorticated seeds were completely cooked after ≈60 min at 95 °C and the puree of 31% ± 2% (w/w) exhibited an apparent viscosity of ≈6 kPa s at ≈0.1 s⁻¹ and 23 °C, as determined by the back extrusion method. The purees exhibited a shear-thinning flow, time decreasing viscosity at constant shear rate, and a partially recoverable capacity. At a shear rate of 50 s⁻¹ and for a shearing time of 80 s, the viscosity increased sharply by a factor 200 as the concentration was increased from 12% to 20% (w/w) by a factor 1.67. In the presence of saliva, the viscosity was shown to remarkably decline with a greater impact for concentrations ≈15% (w/w).     

Urea and Heat Unfolding of Cold-Adapted Atlantic Cod(Gadusmorhua)Trypsin and Bovine Trypsin

The reversible unfolding reactions for phenylmethylsulphonyl fluoride (PMSF)-modified trypins from Atlantic cod (cod PMS-trypsin) and cattle (bovine PMS-trypsin) were monitored by fluorescence spectrophotometry as a function of urea concentration and temperature. For urea unfolding at 25°C, the free energy change at zero concentration of urea (ΔG(H₂O)) for cod PMS-trypsin was 11(±4·4) kJ mol⁻¹ compared with 18(±1·14) kJ mol⁻¹ for bovine PMS-trypsin, while the mid-point concentration for urea unfolding curve ([urea]_1/2) was 3·0(±0·57) M and 4·1(±0·16) M, respectively. From studies of enzyme heat unfolding, the mid point temperature of the thermal unfolding curve ( T _m ) was 46(±1·4)°C for cod PMS-trypsin compared with 57(±2)°C for bovine PMS-trypsin. The standard free energy change (Δ G° ) for reversible thermal unfolding of cod PMS-trypsin was 9(±1) kJ mol⁻¹ compared with 19(±1) kJ mol⁻¹ for bovine PMS-trypsin. Values for the enthalpy (Δ H _m ), entropy (Δ S _m ) and heat capacity (Δ C _p ) for heat unfolding are compared. Results from urea and thermal unfolding studies show that cod PMS-trypsin has a significantly lower conformational stability than bovine PMS-trypsin.     

Oxidation Kinetics of Menhaden Oil with TBHQ

The oxidation kinetics of menhaden oil containing 0% to 0.02% tertbutylhydroquinone (TBHQ) were evaluated at 37°C. Induction periods, and monomolecular and bimolecular oxidation rates were determined from thiobarbituric acid analysis. The disappearance rates of several fatty acids were determined from GC analysis. Free fatty acid and viscosity changes were evaluated. Induction periods were directly related to TBHQ concentration. Monomolecular rates decreased with increasing TBHQ concentration, but bimolecular rates did not change. The rate of disappearance of unsaturated fatty acids was proportional to their degree of unsaturation, but not related to TBHQ concentration. Free fatty acid content and viscosity increased rapidly after the monomolecular period.     

A Kinetic Study of Furan Formation in Wheat Flour‐Based Model Systems during Frying

Furan is a possible human carcinogen, which is formed in worldwide highly consumed fried starchy foods. In order to elucidate the mechanisms responsible for its occurrence in this food category and propose techniques for its mitigation, the kinetics of furan formation, oil absorption, lipid oxidation, and color change were studied in wheat flour‐based model systems during frying at 160, 170, 180, and 190 °C up to 13 min and data were fitted to mathematical models. Additionally, an Arrhenius‐type dependency with temperature was evaluated for all studied responses. More drastic frying conditions increased significantly (P ≤ 0.05) the furan content of fried samples. Furan formation followed a sigmoid trend with frying time only for frying temperature of 190 °C (RMS_190°C: 7.6%). At lower temperatures, furan generation did not reach the asymptotic concentration level. Color change, lipid oxidation, and oil absorption increased with frying temperature and followed asymptotic relationships with frying time. For all evaluated temperatures, color change (RMS: 4.4% to 12.5%) and polar compound generation (RMS: 2.6% to 7.4%) presented good fit to a first‐order kinetic model. Oil absorption was successfully fit to a mass balance‐based model (RMS: 10.0% to 19.8%). Under the experimental conditions studied, only color change (E_A: 15.47 kJ/mol), lipid oxidation (E_A: 6.67 kJ/mol), and oil absorption (E_A: 76.98 kJ/mol) presented good fit (RMS: 0.7% to 6.3%) to an Arrhenius‐type equation. Based on our results, the keeping of frying temperature below 180 °C and the reduction of the frying time would contribute to reduce not only the final furan occurrence in fried foods but also their oil content.     

Rheological Properties of Cabbage Pulp

The rheological behavior of cabbage pulp was determined using a computer controlled rotational rheometer at a temperature range of 20, 30, 40, and 50°C. The flow behavior of pulp was pseudoplastic and fitted well to the Casson model. In all the cases, the effect of soluble solids on apparent viscosity was more pronounced than the effect of temperature. The combined effect of temperature and soluble solid content on viscosity was also given. The activation energy value of 3–6°Brix cabbage puree varied from 7 to 12.6 kJ/mol when shear rate increased from 1 to 10 s^?1. The exponential model developed had an excellent fit (r² > 0.87) and would be useful for the engineering applications.     

Browning of salted sun-dried fish

The lipid of traditional salted, sun-dried fish is highly susceptible to oxidation during processing and storage at tropical ambient temperatures (25–30°C), leading to browning and potential loss of nutritional and economic value of the product. Determinations of extractable fluorescence and soluble brown colour have been found to be relevant indicators of the high degree of lipid oxidation in such fish. Studies on model systems consisting of aerated fish oil and a range of components natural to fish confirmed that, at 25°C, the products of lipid oxidation reacted with phospholipids and amino acids to produce significant fluorescence. Similarly, proteins and amino acids interacted with lipid oxidation products to produce browning, although at 25°C, this only occurred in the presence of water. Temperatures above 50°C are required for the development of browning of aerated fish oil alone. The level of free amino acids in salted, sun-dried fish was found to decrease during storage which correlates with amino acid involvement in fluorescence and colour production. The fluorescence/colour can be related mechanistically to the development of lipid oxidation products and hence provides a realistic basis for their acting as indicators of extensive lipid oxidation.     

Improving the quality of fried oils by using different filter aids

The present study aimed to improve the quality of fried soybean, sunflower, palm and cottonseed oils. Synthetic (Magnesol XL) and natural (diatomaceous earth and kaolin) filter aids were used at various levels (1, 2 and 4%) to adsorb the secondary oxidation products of the oil. The metal patterns (the cations Si, Mg, Ca, Fe, Na, K, Al, Cu, Mn, Zn and the anions CO₃^2?, HCO₃^?, Cl^?, NO₃^?, NO₂^?, SO₄^2?) of Magnesol XL, diatomaceous earth and kaolin were determined. Some physical and chemical properties (refractive index, viscosity, colour, foam height, acid value, peroxide value, thiobarbituric acid value, iodine value, and conjugated diene and polymer contents) of non‐fried, fried and fried–treated soybean, sunflower, palm and cottonseed oils were determined. The frying process was performed at 180 °C ± 5 °C for 12 h continuous heating. The fried oils were treated with the synthetic and natural filter aids at 105 °C for 15 min. The results indicate that Magnesol XL, diatomaceous earth and kaolin contained Si + Mg, Si + Ca and Si + Al, respectively, as the basic metals. Frying soybean, sunflower, palm and cottonseed oils led to significant increases in refractive index, colour, foam height, viscosity, acid value, peroxide value, TBA value, conjugated diene and polymer contents and decrease in iodine value. Treatment of fried oils with Magnesol XL, diatomaceous earth and kaolin at the 1, 2 and 4% levels greatly improved the quality of fried oils. These findings indicate the high efficiency of the filter aids used in the present study in adsorbing the products of oil degradation. Copyright © 2006 Society of Chemical Industry