Physical Stability of Whey Protein-stabilized Oil-in-water Emulsions at pH 3: Potential ω-3 Fatty Acid Delivery Systems (Part A)

ABSTRACT: The oxidative stability of polyunsaturated lipids can be improved by incorporating them in oil droplets surrounded by positively charged whey protein isolate (WPI) membranes. This study dealt with the factors that influence the physical properties of WPI-stabilized oil-in-water emulsions at pH 3. Emulsions containing 5 to 50 wt% corn oil and 0.5 to 5.0 wt% WPI (protein-to-oil ratio of 1:10) were prepared at pH 3. The apparent viscosity of the emulsions increased appreciably at oil concentrations ≥ 35 wt%; however, the particle size was relatively independent of oil concentration. The influence of NaCl (0 to 250 m M ) on the physical properties of 28 wt% emulsions was examined. Significant increases in mean particle size, apparent viscosity, and creaming instability occurred at ≥150 m M NaCl, which were attributed to flocculation induced by screening of the electrostatic repulsion between droplets. The influence of heat treatment (30°C to 90°C for 30 min) on 28 wt% emulsions was examined in the absence and presence of salt, respectively. At 0 m M NaCl, heating had little effect on the physical properties of the emulsions, presumably because the electrostatic repulsion between the droplets prevented droplet aggregation. At 150 m M NaCl, the mean particle diameter, apparent viscosity, and creaming instability of the emulsions increased considerably when they were heated above a critical temperature, which was 70°C when salt was added before heating and 90°C when salt was added after heating. These results have important implications for the design of WPI-stabilized emulsions that could be used to incorporate functional lipids that are sensitive to oxidation, for example, ω-3 fatty acids.     

Rheological behaviour of emulsions of avocado and watermelon oils during storage

Rheological properties of emulsions made out of avocado pulp and watermelon seed oils with whey protein concentrate were determined during different storage periods. The oils, as well as the emulsions behaved like non-Newtonian liquids, having shear-thinning characteristics. Both oils showed moderate shear-thinning characteristics as the flow behaviour indices were between 0.86 and 0.88. The shear-rate/shear-stress data could be adequately fitted (r = 0.997–0.999) to a common rheological equation, e.g. the power-law model. Avocado pulp oil was markedly more viscous than was watermelon seed oil which was also evident from the higher apparent viscosity and consistency index values.     

Influence of green banana pulp on the rheological behaviour and chemical characteristics of emulsions (mayonnaises)

The influence of green banana pulp (GBP) on rheological behaviour and chemical characteristics of emulsions (mayonnaises) was investigated in this work. Five formulations were developed, using an experimental design for constrained surfaces and mixtures, with the following proportions (water/soybean oil/GBP): F1 (0.10/0.20/0.70), F2 (0.20/0.20/0.60), F3 (0.10/0.25/0.65), F4 (0.20/0.25/0.55) and F5 (0.15/0.225/0.625). Rheological properties of the emulsions were obtained with a rotational Haake Rheostress 600 rheometer and a cone and plate geometry sensor (60 mm diameter, 2° cone angle), with a gap distance of 1 mm. The samples presented high values for mineral salts and low calories. The emulsions showed pseudoplastic behaviour at 10 and 25 °C and rheological data were well described by the Herschel-Bulkley model. Formulations with high GBP content (F1 and F3) presented higher yield stress and apparent viscosity values. The results obtained with the response surface methodology, which were adjusted by the quadratic model, showed that GBP had a significant influence on the increase of yield stress and apparent viscosity. The consistency coefficient increased with an increase in soybean oil concentration and water contributed to high values of flow behaviour index in all emulsions samples.     

PHYSICO-CHEMICAL CHANGES DURING ENZYMATIC LIQUEFACTION of MANGO PULP (cv. Keitt)

Mango pulp from Keitt variety was liquefied with 1.1 mL/kg commercial enzyme mixture preparations for 2 h at 40C. Various physico-chemical characteristics of the mango pulp at different stages of liquefaction were investigated. Apparent viscosity of pulp and serum reduced rapidly to 78% and 93% respectively, in 30 min liquefaction. No marked changes in apparent viscosity of pulp samples and percentage cell wall hydrolysis in the subsequent 60, 90 and 120 min were observed. High correlation coefficient values (R² > 0.99) of the linear regression analysis showed the feasibility of using a power law model for fitting the shear stress-shear rate data of the pulp. the enzymetreated pulp showed 83% and 84% serum yields during 30 and 120 min reaction times respectively against 52% for fresh pulp. Slight increase in TSS (°Brix), acidity, reducing and total sugars, and slight decrease in pH was found in the pulp as well as serum fractions as the incubation continued. No marked change in color (yellowness) was observed in the enzyme-treated pulp, however, the corresponding serum showed less yellowness and color saturation indicating retention of yellow pigments in the pulp fraction. Δ-3-carene was identified as major mono terpenic compound in mango pulp comprising more than 73% of the total aroma compounds. About 9% loss in the total aroma components was observed during the liquefaction process.     

CHANGES IN APPARENT VISCOSITY AND VITAMIN C RETENTION DURING THERMAL TREATMENT OF BUTTERNUT SQUASH (CUCURBITA MOSCHATA DUCH) PULP: EFFECT OF RIPENING STAGE

ABSTRACT

The effects that ripening stage have on the apparent viscosity and ascorbic acid retention in squash pulp exposed at cooking process were analyzed. Total soluble solids contents were taken as indicative of ripening degree. In the raw material, water contents ranged from 79 to 96%, but no significant differences were observed among samples grouped as unripe, ripe and overripe. The ascorbic acid contents of pulp increase with increases in soluble solids contents. Pulp from unripe and ripe squash had similar apparent viscosity values; however, lower viscosity values were obtained in pulp from overripe squash. During heat treatment, significant changes in the apparent viscosity values of pulp from unripe and ripe squash were observed. Heat penetration properties of squash pulp indicate correlation between the inverse slope of the straight portion in the heat penetration curves on a semilog plot (fh) and thermal diffusivity values (α) with dry matter content, but no correlation was found with squash maturity degree. High ascorbic acid retention (82%) in pulp held for 30 min at 95C was found independently of squash maturation degree.

PRACTICAL APPLICATIONS

Knowing the rheological behaviour and the ascorbic acid retention of butternut squash pulp during cooking process could be used as a valuable information previously to make decisions for use this crop as a food supply.

     

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.     

Mangosteen Oil-In-Water Emulsions: Rheology, Creaming, and Microstructural Characteristics during Storage

The rheological properties and physical stability of mangosteen (Garcinia mangostana L.) extract in oil-in-water (MIO/W) emulsions were investigated. Rheological study on the emulsions exhibited Newtonian flow behavior. The 20?wt.% emulsion showed higher apparent viscosity than 10?wt.% MIO/W sample. The effects of salt (NaCl) concentration (0, 50, 100, and 200?mM) and heat treatment (70?°C) on the stability of the emulsions were also examined. Heat (70?°C)- and NaCl (100 and 200?mM)-treated emulsions showed creaming and droplet aggregation on storage for a period of 60?days. The 10?wt.% MIO/W emulsions stored at 4?°C showed a homogeneous distribution of oil droplets with good stability to creaming and viscosity independent of shear stress (i.e., a Newtonian liquid).     

Rheology and Oxidative Stability of Whey Protein Isolate-Stabilized Menhaden Oil-in-Water Emulsions as a Function of Heat Treatment

ABSTRACT:  Menhaden oil-in-water emulsions (20%, v/v) were stabilized by 2 wt% whey protein isolate (WPI) with 0.2 wt% xanthan gum (XG) in the presence of 10 mM CaCl₂ and 200 μM EDTA at pH 7. Droplet size, lipid oxidation, and rheological properties of the emulsions were investigated as a function of heating temperature and time. During heating, droplet size reached a maximum at 70 °C and then decreased at 90 °C, which can be attributed to both heating effect on increased hydrophobic attractions and the influence of CaCl₂ on decreased electrostatic repulsions. Combination of effects of EDTA and heat treatment contributed to oxidative stability of the heated emulsions. The rheological data indicate that the WPI/XG-stabilized emulsions undergo a state transition from being viscous like to an elastic like upon substantial thermal treatment. Heating below 70 °C or for less than 10 min at 70 °C favors droplet aggregation while heating at 90 °C or for 15 min or longer at 70 °C facilitates WPI adsorption and rearrangement. WPI adsorption leads to the formation of protein network around the droplet surface, which promotes oxidative stability of menhaden oil. Heating also aggravates thermodynamic incompatibility between XG and WPI, which contributes to droplet aggregation and the accumulation of more WPI around the droplet surfaces as well.     

Optimising conditions for enzymatic extraction of edible gelatin from the cattle bones using response surface methodology

This work was initiated to optimise the factors affecting the enzymatic extraction of edible gelatin from the cattle bones using response surface methodology. A central composite rotatable design was used to evaluate the effects of the enzyme concentration, time of enzymatic treatment and extraction temperature on the yield of extraction, gel strength, apparent viscosity and absorption at 420 nm. The R ² values of regression models for all the response variables were higher than 0.9. Data analysis showed that all the process variables significantly ( P  < 0.01) affected the gel strength and apparent viscosity of extracted gelatin, whereas the effect of extraction temperature on both yield of extraction and absorption at 420 nm was not significant ( P  > 0.05). Graphical optimum conditions for the extraction yield, gel strength, apparent viscosity and absorption at 420 nm were determined as 6.1 ppm, 15.6 h, 70 °C; 9.1 ppm, 11.9 h, 70.3 °C; 7.86 ppm, 14.9 h, 77.5 °C and 2.8 ppm, 10 h, 60 °C, respectively. For all the response variables, the experimental values were very close to the predicted values and were not statistically different ( P  < 0.05).     

Comparisons of Chemical and Physical Properties of Catfish Oils Prepared from Different Extracting Processes

ABSTRACT:  Four different catfish oil extraction processes were used to extract oil from catfish viscera: process CF1 involved a mixture of ground catfish viscera and water, no heat treatment, and centrifugation; process CF2 involved ground catfish viscera (no added water), heat treatment, and centrifugation; process CF3 involved a mixture of ground catfish viscera and water, heat treatment, and centrifugation; process CF4 involved ground catfish viscera, enzymatic hydrolysis, and centrifugation. Chemical and physical properties of the resulting of catfish oils were evaluated. The CF4 process recovered significantly higher amounts of crude oil from catfish viscera than the other 3 extraction methods. The CF4 oil contained a higher percent of free fatty acid and peroxide values than CF1, CF2, and CF3 oils. Oleic acid in catfish oil was the predominant fatty acid accounting for about 50% of total fatty acids. Weight loss of oils increased with increasing temperatures between 250 and 500 °C. All the catfish oil samples melted around −32 °C regardless of the extraction methods. The flow behavior index of all the oil samples was less than 1, which indicated that the catfish oils exhibited non-Newtonian fluid behavior. The apparent viscosity at −5 and 0 °C was significantly higher ( P  < 0.05) than those at 5, 10, 15, 20, 25, and 30 °C. The average magnitude of activation energy for apparent viscosity of the oil was higher for CF2 than CF1, CF3, and CF4.     

EFFECT OF UNIMODAL PARTICLE SIZE AND PULP CONTENT ON RHEOLOGICAL PROPERTIES OF TOMATO PUREE

The vane method in controlled shear stress mode was used to determine the yield stress and the shear rate—shear stress data of tomato purees containing 10–35% pulp of two different average particle sizes: 0.34 and 0.71 mm. Consistency index and apparent viscosity increased significantly with pulp content and decreased with average particle size. The effect of pulp weight fraction (P) on relative viscosity (η_r) could be described by the single parameter equation: η_r= [1 – (P/A)]⁻², while the effect of particle diameter on η_r could be described using Peclet number. Magnitudes of yield stress determined directly by the vane method were higher than those obtained by using the Casson model, and were proportional to the square of pulp content. Reduced Casson yield stress—P data on purees of both particle sizes followd a single curve. Effects of pulp content and particle size on vane yield stress and apparent viscosity were evident from the correlation forms with high values of R².     

RHEOLOGICAL BEHAVIOR OF PROCESSED MUSTARD. II. STORAGE EFFECTS

Samples of processed yellow mustard with three different particle size distributions (slightly-coarse, standard, and fine) were prepared according to a standard formulation and pilot-plant replication of the commercial methodology and stored for 3 months at 5°C, 25°C, and 45°C. After 3-month storage at 45°C, all samples showed visible liquid separation (syneresis) and aggregation of colloidal particles, as indicated by increase in d _pop and decrease in % colloids. The fine milled samples exhibited syneresis and an increase in d _pop after 3-month storage even at 25°C. The bimodal distribution did not show significant changes as a result of aggregation. In general, increase in d _pop increased apparent viscosity (η _ap ), flow behavior index (n) from the Herschel-Bulkley model, and exponent n" from the loss modulus (G") power law equation. As d _pop increased, Bingham yield stress _o), plastic apparent viscosity (η _p ), shear stress constant (A) from the Weltman stress decay model, yield stress (_o) and consistency index (m) from the Herschel-Bulkley model, exponent n' from the storage modulus (G') power law equation, and minimum values of loss tangent (tan δ) decreased. In heterodisperse semi-solid foods such as processed mustard, the particle size distribution influences the structure (i.e., packing) and the rheological behavior. Therefore, time and temperature dependent instabilities such as syneresis may be minimized by controlling particle size distribution during processing.     

The influence of pasteurization temperature on the physicochemical composition and colour of Murciano-Granadina goat milk

An evaluation of the physicochemical characteristics and colour in Murciano-Granadina goat milk was carried out on several samples subjected to different pasteurization treatments (72°C/15 s, 76°C/15 s and 80°C/10 s). An apparent increase in the level of caseins was observed along with a decrease in the serum protein contents at pasteurization temperatures of 76 and 80°C. This change can be partly justified by the interactions between β-lactoglobulin and K-casein in pasteurized milk. The fat content, viscosity and density of the milk showed minimal sensitivity to the thermal treatments, but the heat treatment did affect the parameters which defined the colour of the milk, as shown by a decrease in the Yellow Index and an increase in the difference in colour.     

Flow Properties of Low-Pulp Concentrated Orange Juice: Serum Viscosity and Effect of Pulp Content

65° Brix serum samples from four concentrated orange juice (COJ) samples, between -19 and 30°C, were mildy shear-thinning fluids with negligible yield stress. The power law model described well the flow data. For one sample, the Powell-Eyring model also described the data. The activation energy of flow (E_a) for the samples was between 11.2–13.6 kcal/gmole. The power law parameters were determined for a 65°Brix sample as a function of pulp content (0–11%) between −19 and 30°C. At a fixed temperature, the apparent viscosity and the consistency index increased exponentially with pulp content. E_a decreased with increase in pulp content and reached a constant value of about 10.2 kcal/gmole. Data on a high-pulp (21.2%), 65° Brix, sample indicated the presence of yield stress, particularly at low temperatures. The Mizrahi-Berk model predicted reliable values of the yield stress.     

RHEOLOGICAL CHARACTERIZATION OF SALAD DRESSINGS. 1. STEADY SHEAR, THIXOTROPY AND EFFECT OF TEMPERATURE

Shear stress-shear rate data of five commercial salad dressings at 2.0, 10.0, 18.3, 26.7, 32.2 and 43.3°C were obtained using a concentric cylinder viscometer. The power law and Casson equations were applicable for all products (r ≫ 0.98). The Arrhenius equation was applicable for the effect of temperature on the apparent viscosity at 100 s^−l (r ≫ 0.97). Rheological data were obtained at a constant shear rate of 275s^−l at 2.0 and 10.0° C. The results show that the Weltman equation was better than the Hahn equation in describing the thixotropic behavior of the five salad dressings.     

Rheological behaviour of acorn starch dispersions: effects of concentration and temperature

Rheological properties of acorn starch dispersions at different concentrations (4%, 5%, 6% and 7%) were evaluated under steady and dynamic shear conditions. The flow behaviours of the acorn starch dispersions at different temperatures (25, 40, 55 and 70 °C) were determined from the rheological parameters provided by the power law model. The acorn starch dispersions at 25 °C exhibited high shear-thinning fluid characteristics ( n  = 0.23–0.36). Consistency index (K) and apparent viscosity (η_a,100) increased with an increase in starch concentration, and were also reduced with increasing temperature. Within the temperature range of 25–70 °C, the η_a,100 obeyed the Arrhenius temperature relationship with a high determination coefficient ( R ² = 0.97–0.99), with activation energies (E_a) ranging between 16.5 and 19.0 kJ mol⁻¹. Both the power law and exponential type models were employed in order to establish the relationship between concentration and apparent viscosity (η_a,100) in the temperature range of 25–70 °C. Magnitudes of storage ( G' ) and loss ( G ") moduli increased with an increase in the starch concentration and frequency (ω). The magnitudes of G ' were higher than those of G " over most of the frequency range (0.63–62.8 rad s⁻¹). The dynamic (η*) and steady shear (η_a) viscosities of acorn starch dispersion at 7% concentration follow the Cox–Merz superposition rule.     

EFFECT OF BREAK TEMPERATURE AND HOLDING TIME ON PECTIN AND PECTIC ENZYMES IN TOMATO PULP

SUMMARY –The effect of break temperature and holding time on chemical and physical properties of canned tomato pulp and on the activity of polygalacturonase (PG) and pectin esterase (PE) was investigated. Samples preheated above 200°F were slightly higher in pH value and lower in titratable acidity than those preheated at 160°F and 140°F. The gross viscosity and serum viscosity of the canned tomato pulp increased as break temperature increased. A slight increase in serum viscosity was also observed when holding time was lengthened. The effect of break temperature on serum viscosity was much greater than that of holding time. The total pectin content of the tomato pulp as well as that of the serum increased as the break temperature increased. The same observation holds true for the effect of holding time on the total pectin content of the tomato pulp and tomato serum. This was explained by the inactivation of pectic enzymes at higher break temperature and longer holding periods. The level of PE and PG activity in the frozen tomato pulp decreased as break temperature and holding time increased. No PE activity was detected in samples preheated at 180°F for 15 sec. Samples preheated at 220°F for 15 sec showed no PG activity, while those preheated at 200°F for 15–87 sec still show some PG activity with a retention of about 3.54–5.68%. PG in tomatoes may be inactivated by giving the macerated fruits a hot break temperature higher than 200°F. The critical conditions for inactivation of PE (180°F for 15 sec) and of PG (220°F for 15 sec) found in the course of this investigation are supported by the data obtained on pectin analysis and serum viscosity.     

Dynamic Crystallization of Dark Chocolate as Affected by Temperature and Lipid Additives

The dynamic crystallization was studied in a lab-scale Scraped Surface Heat Exchanger by following variations with time of torque applied during different isotherms between 24.9°C and 31.0°C. Crystallization was in two steps for T 26.2°C but it was in one step at T<26.2°C. The first step corresponded to crystallization of about 1% solid fat and was related to that of saturated triacylglycerols (SSS) which segregated from other cocoa butter triacylglycerols (TAGs) because of their low solubility in TAGs. The second step, an abrupt increase of apparent viscosity, leading to complete crystallization was attributed mainly to the monounsaturated TAGs in the β form. Different amounts of tristearin increased the apparent viscosity and reduced the latent time preceding the first step, but did not influence the main crystallization. Stearic acid and distearin additions also influenced chocolate crystallization.     

Relationship between the thermal conductivity and rheological behavior of acerola pulp: Effect of concentration and temperature

This study aimed to evaluate the thermal conductivity and rheological behavior of acerola pulp at concentrations of 5.5, 7.5, 9.5, 11.5 and 13.5 °Brix and temperatures of 20, 30, 40, 50 and 60 °C. Among the models used to determine conductivity, Maxwell-Eucken was used for data acquisition. Linear equations were fitted to evaluate the influences of concentration and temperature on the thermal conductivity of the pulp. The pulp structure, particle sizes and relation between insoluble and soluble solids were also discussed. The rheological behavior, specifically apparent viscosity versus shear rate, was influenced by both the soluble solids content and the temperature. Among the mathematical models used to test the fit of the experimental data, the Herschel–Bulkley model provided the best statistical adjustments and was then used to determine the rheological parameters. Apparent viscosity was correlated with temperature by the Arrhenius equation. Acerola pulps were shear thinning and thermal conductivity increases with viscosity decreasing with increasing temperature. The structures and concentrations had an impact upon the effective thermal conductivity. The temperature and concentration values have been fixed and equation expressing conductivity as a function of apparent viscosity was proposed, which enable the evaluation of an existing relationship between the two properties.     

Flow property of globulin from red bean (Phaseolus angularis)

Red bean globulin (RBG) dispersions exhibited pseudoplastic behavior, and the flow data were fitted to the power-law model. With increasing protein concentration, there were progressive increases in consistency coefficient (m), apparent viscosity and yield stress, suggesting protein–protein interactions. The flow behavior index (n) was decreased indicating enhanced pseudoplasticity. Ionic strength affected the flow behavior of RBG, with a reversal in its effect at a specific salt concentration (0.5–1.0 M). Addition of chaotropic salts and protein structure perturbants (urea, sodium dodecyl sulfate and dithiothreitol) caused changes in flow behavior, probably due to dissociation of the oligomers and protein unfolding. Pre-heat treatments at a temperature of 80°C, above the onset temperature of RBG, caused dramatic decreases in n and increases in m and apparent viscosity suggesting protein denaturation/aggregation. When RBG dispersions were heated from 25 to 90°C at a fixed rate (1.7°C/min), there was an initial decrease in apparent viscosity, probably due to a lowering of medium viscosity. The viscosity started to increase at around 78°C, the onset temperature of RBG; and sharp increases were observed from 80 to 90°C. Changes in apparent viscosity with increasing temperature (25–60°C) obeyed the Arrhenius law, with similar E_a values at three different shear rate values, suggesting little temperature dependence of viscosity at lower temperature range.