Characterization of Apple Juice Foams for Foam-mat Drying Prepared with Egg White Protein and Methylcellulose

ABSTRACT: Intrinsic stability and rheological properties of apple juice foams for foam mat drying were studied. Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less stable but showed a higher degree of solidity (stronger structures), higher foaming capacity, and smaller bubble average diameter than methylcellulose foams. Foam stability increased with increasing concentrations of either methylcellulose or egg white. Increasing whipping times increased the stability of egg white foams only. Stability parameters (maximum drainage and drainage half-time) were correlated in terms of rheological parameters of the continuous phase (consistency index and apparent viscosity at 30/s, respectively). The correlations ( R ²= 0.766 and 0.951, respectively) were considered acceptable because they were independent of whipping time and foaming agent nature and concentration. Results on foam rheology obtained by dynamic and vane tests were in agreement, but the latter method was more sensitive. Optimal concentrations to obtain the most solid foams (0.2% methylcellulose and 2% to 3% egg white, respectively) were the same concentrations required for maximum foaming capacity. Based on this observation and previous models, an empirical expression was proposed to predict the degree of solidity (in terms of inverse phase angle and yield stress) only as a function of foam structural properties (air volume fraction and average bubble size). The model proved to be satisfactory to fit experimental results ( R ²= 0.848 and 0.975, respectively), independently of whipping time, foaming agent nature and concentration.     

Image Analysis of Representative Food Structures: Application of the Bootstrap Method

ABSTRACT:  Images (for example, photomicrographs) are routinely used as qualitative evidence of the microstructure of foods. In quantitative image analysis it is important to estimate the area (or volume) to be sampled, the field of view, and the resolution. The bootstrap method is proposed to estimate the size of the sampling area as a function of the coefficient of variation (CV _Bn ) and standard error (SE _Bn ) of the bootstrap taking sub-areas of different sizes. The bootstrap method was applied to simulated and real structures (apple tissue). For simulated structures, 10 computer-generated images were constructed containing 225 black circles (elements) and different coefficient of variation (CV _image ). For apple tissue, 8 images of apple tissue containing cellular cavities with different CV _image  were analyzed. Results confirmed that for simulated and real structures, increasing the size of the sampling area decreased the CV _Bn  and SE _Bn . Furthermore, there was a linear relationship between the CV _image  and CV _{Bn .} For example, to obtain a CV _Bn  = 0.10 in an image with CV _image  = 0.60, a sampling area of 400 × 400 pixels (11% of whole image) was required, whereas if CV _image  = 1.46, a sampling area of 1000 × 100 pixels (69% of whole image) became necessary. This suggests that a large-size dispersion of element sizes in an image requires increasingly larger sampling areas or a larger number of images.     

Factors Determining Yield Stress and Overrun of Whey Protein Foams

ABSTRACT: Foams were formed by whipping whey protein solutions (15% w/v protein) containing NaCl, CaCl₂, lactose, or glycine. Foam overrun and yield stress were determined. Foams made from whey protein ingredients have greater overrun and yield stress if the concentration of β-lactoglobulin is high relative to a-lactalbumin. The presence of 0.4 M CaCl₂ in the foaming solution increases overrun and yield stress for β-lactoglobulin and a-lactalbumin. The high yield stress of β-lactoglobulin and a-lactalbumin foams made from solutions containing CaCl₂ suggests that CaCl₂ is altering rheological properties of the interfacial protein film and/or contributing to protein aggregation or network formation in the lamellae.     

Artificial neural network modeling for temperature and moisture content prediction in tomato slices undergoing microwave-vacuum drying

ABSTRACT:  Inputs for ANN (multihidden-layer feed-forward artificial neural network) models were drying time ( t _{i + 1}), initial temperature ( T ₀), moisture content ( MC ₀), microwave power, and vacuum pressure. The outputs were temperature ( T _{i + 1}) and moisture content ( MC _{i + 1}) at a given t _{i + 1}. After training the ANN models with experimental data using the Levenberg-Marquardt algorithm, a two-hidden-layer model (25-25) was determined to be the most appropriate model. The mean relative error (MRE) and mean absolute error (MAE) of this model for T _{i + 1} were 1.53% and 0.77 °C, respectively. In the case of MC _{i + 1}, the MRE and MAE were 11.48% and 0.04 kg_water/kg_dry, respectively. Using temperature ( T _i ) and moisture content ( MC _i ) values at t _i in the input layer significantly reduced the computation errors such that MRE and MAE for T _{i + 1} were 0.35% and 0.18 °C, respectively. In contrast, these error values for MC _{i + 1} were 1.78% (MRE) and 0.01 kg_water/kg_dry (MAE). These results indicate that ANN models were able to recognize relationships between process parameters and product conditions. The model may provide information regarding microwave power and vacuum pressure to prevent thermal damage and improve drying efficiencies.     

Effect of pan-frying in extra-virgin olive oil on odour profile, volatile compounds and vitamins

Changes in odour of Arauco (ARA) and Arbequina (ARB) extra-virgin olive oil (OO) were monitored during frying by electronic nose (EN) and solid-phase microextraction–gas chromatography methodologies. Degradation of α- and γ-tocopherols was monitored by HPLC. Electronic nose data and volatile compounds were analysed at intervals of 15 min ( t ₁₅) during 60 min of frying ( t ₆₀). α- and γ-tocopherols were determined at intervals of 5 min ( t ₅) during 30 min of frying ( t ₃₀). Principal components analysis applied to EN data showed one component, PC₁ which accounted 96.6% of the total odour variation. SnO₂ sensors had a positive correlation with PC₁. ARA variety corresponding to frying t ₆₀ had the highest positive correlation with PC_1. Analysis of variance results for volatile compounds showed an increase on production for: 3-methyl butanal, n -pentanal, n -hexanal, n -heptanal and n -nonanal at 15 min of frying for ARB OO and at 30 min for ARA OO. α-tocopherol and γ-tocopherol showed an important decrease after the first 5 min of frying for ARB OO and at 15 min for ARA OO.     

RHEOLOGICAL INDICES OF FRUIT CONTENT IN JAMS: EFFECT OF FORMULATION ON FLOW PLASTICITY OF SHEARED STRAWBERRY AND PEACH JAMS

The effect of formulation factors on Casson yield values measured at low shear rates (0.08 ≤γ≤ 1.01s^-1) (σ₀₁) and at medium shear rates (2.58 ≤γ≤ 387.30s^-1) (σ₀₂) was analyzed in previously sheared strawberry and peach jams. Twenty three samples of each fruit jam were prepared according to a second order composite rotatable design. Composition ranges were: fruit content, 25–55%; soluble solids content, 60–70° Brix; added pectin in strawberry jams, 0.3–0.7% and in peach jams, 0.1–0.5%. Variation of σ₀₁ values in strawberry jams depended mainly on the interactions between fruit and soluble solids and between fruit and pectin, while in peach jams, it depended on fruit-soluble solids and soluble solids-pectin interactions. Patterns of change of σ₀₂ values with composition were similar to those observed for σ₀₁ in both strawberry and peach jams. Predictive power of σ₀₁ and σ₀₂ values for estimation of fruit content was low, but taken in conjunction with soluble solids content and total pectin values, 79.5% of the variability of fruit content in strawberry jams and 91.1% of same in peach jams could be explained.     

Influence of vitamin E supplementation on spontaneous oxidized flavour of milk in dairy buffaloes

Twenty-four Murrah buffaloes (60 days pre-partum) were divided into four equal groups (T ₁ , T ₂ , T ₃ and T ₄ ) and were supplemented with 0, 1000, 1500 and 2000 IU α-tocopheryl acetate per day up to 30 days of lactation, and half of these doses from 30 to 60 days of lactation. Milk samples collected fortnightly were analysed for vitamin E, fat, and development of oxidized flavour, with and without copper addition by a panel of judges, and chemically by the thiobarbituric acid test. Scores for oxidized flavour ranged from 0 to 10 with 0–4 as definite, 5–7 as light and 8–10 having no defect. The α-tocopherol content in milk fat (µg/g) averaged 20.55, 25.56, 29.98 and 31.38 in T ₁ , T ₂ , T ₃ and T ₄ groups, respectively. The addition of Cu in the milk significantly increased milk fat oxidation. Better stability of milk in T ₃ and T ₄ groups was observed, which might be due to a higher level of milk α-tocopherol. Addition of 1500 IU α-tocopheryl acetate in the diet of buffaloes helped in improving the oxidative stability of milk.     

Low resolution pulse nuclear magnetic resonance study of water equilibration in dried carrots

Samples taken during air drying of carrots were analysed after different equilibration times. Low resolution NMR measurements were made and the longitudinal ( T ₁) and the transverse ( T ₂) relaxation times calculated. Both T ₁ and T ₂ decreased with the equilibration time for water contents above 0.30 and 0.47 kg water kg^-1 dry matter, respectively. The decrease in relaxation time increased with the water content. For the same water contents, grated carrots gave lower T ₁ values and smaller T ₁ decreases with equilibration time than 3-mm cubes. Low resolution NMR is a technique which is well suited to the monitoring of the tempering phases of industrial drying cycles.     

The effect of freezing and thawing on the magnetic resonance imaging parameters of water in beef, lamb and pork meat

A new multisample magnetic resonance imaging (MRI) technique has been used to measure the values of T ₁, T ₂, magnetization transfer (MT) rate and liquid proton density ratio ( M ₀%) for water in fresh and frozen–thawed beef, lamb and pork; four samples from the longissimus dorsi muscle of 25 different individuals per species were studied. The effect of two different chilling regimes, standard and tenderloin, were also studied. Standard chilled pork and lamb had a significantly higher M ₀% than tenderloin chilled samples, but there was no correlation between M ₀% and fresh weight; the differences in M ₀% are thought to be due to differences in MR (magnetic resonance)-visible water. There was a significant decrease in water content, T ₁ relaxation time, and a significant increase in MT rate in the frozen–thawed samples when all the data were pooled for each species. However, individual animals differed in the magnitude and direction of the change; this means that because of interanimal variation, measurements of MR parameters from a single sample of meat cannot be used at present to authenticate it.     

不同打发状态蛋清泡沫及其凝胶特性的比较

蛋清具有良好的起泡性和凝胶性,其在充气食品中具有难以取代的地位。为研究不同状态蛋清泡沫凝胶的理化性质,该文在室温条件下以恒定搅拌速率（980 r/min）制备了不同打发状态（打发时间为0、50、70和90 s）的蛋清泡沫,并测定了蛋清泡沫的理化特性。随后将不同打发时间的蛋清泡沫加热固化,制备了蛋清泡沫凝胶,通过显微观察、色度、质构和流变分析考察了蛋清泡沫凝胶的特性。实验结果表明,在恒定的搅拌速率下蛋清泡沫的气泡状态会随打发时间的变化而变化。适当延长打发时间,有利于形成比重较低的（0.16～0.17）、具有高起泡性和泡沫稳定性的固态泡沫。打发70 s的蛋清泡沫（蛋清泡沫呈小弯钩状,比重为0.165）稳定性最佳,且经加热固化后,该蛋清泡沫凝胶的亮度（L*=90.28）显著升高,硬度（27.69 g）和弹性（0.78 mm）显著降低（P<0.05）,凝胶性质优良。结果揭示了蛋清泡沫的流变学性质能显著影响蛋清泡沫及其凝胶的性能,为蛋清泡沫在充气食品中的应用提供了理论参考。     

Foaming Properties of Egg Albumen with a Bubbling Apparatus Compared with Whipping

Neither standard method nor instrument exists to accurately measure foaming properties in food. Usually, whipping methods are used but they are only moderately reproducible. We used an original apparatus in which foam was generated by bubbling and then analyzed by conductimetry (liquid in the foam) and a uniline camera (foam volume). The foaming properties of a series of egg-white powders were studied. Among parameters describing foam formation and destabilization, three were repeatable and discriminating. They were correlated with those obtained with whipping methods. Easy to use and rapid, the bubbling method is an alternative for controlling and measuring the foaming properties of egg-white.     

High hydrostatic pressure modification of whey protein concentrate for use in low-fat whipping cream improves foaming properties

Whey is the inevitable by-product of cheese production. Whey can be incorporated into a variety of foods, but little has been done to investigate its suitability in whipping cream. The objective of this work was to evaluate the foaming properties of selected low-fat whipping cream formulations containing whey protein concentrate (WPC) that did or did not undergo high hydrostatic pressure (HHP) treatment. Fresh whey was concentrated by ultrafiltration, pasteurized, and standardized to 8.23% total solids and treated with HHP at 300 MPa for 15 min. Viscosity, overrun, and foam stability were determined to assess foaming properties. Sensory evaluation was conducted with 57 panelists using a duo-trio difference test. The optimal whipping time for the selected formulations was 3 min. Whipping cream containing untreated WPC and HHP-treated WPC resulted in greater overrun and foam stability than the control whipping cream without WPC. Panelists distinguished a difference between whipping cream containing untreated WPC and whipping cream containing HHP-treated WPC. High hydrostatic pressure-treated WPC can improve the foaming properties of low-fat whipping cream, which may justify expansion of the use of whey in whipping cream and application of HHP technology in the dairy industry.     

Effects of Reducing Agent Concentration on Soy Protein Fractionation and Functionality

ABSTRACT: The concentration of the reducing agent SO₂ significantly affected fraction yields, purities, and compositions during soy protein fractionation, especially the purity of the glycinin-rich fraction. The optimum amount of reducing agent was 5 m M SO₂ based on protein yields, purities, and functional properties. With no SO₂, the glycinin-rich fraction contained 29% of the total protein with only 63% glycinin, and the β-conglycinin-rich fraction contained 10% of the total protein with 94%β-conglycinin; whereas, by adding 5 m M SO₂, the glycinin-rich fraction contained 23.4% of total protein with 81.5% glycinin, and the β-conglycinin-rich fraction contained 16.8% of the total protein with 83.7%β-conglycinin. Increasing amounts of storage proteins were lost in the whey fraction as SO₂ concentration increased. The functional properties of the 2 major fractions were greatly influenced by the addition of SO₂. The thermal behaviors of the fractions were only slightly affected by using higher amounts of SO₂. The solubility and hydrophobicity of the glycinin-rich fraction decreased with increasing SO₂ concentration, whereas the solubility of the β-conglycinin-rich fraction increased. Emulsification properties of the glycinin-rich fraction were adversely affected by higher SO₂ concentrations, whereas, those of the β-conglycinin-rich fraction were improved. The β-conglycinin-rich fractions had better emulsification properties than did the glycinin-rich fractions. The best foaming properties were achieved at 5 m M SO₂.     

Effect of amidation on the foaming and physico-chemical properties of bovine serum albumin

Amidation of bovine serum albumin (BSA) was achieved by a water-soluble carbo-diimide, ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated reaction using ammonium chloride as the nucleophile. Partial and substantial amidation of 0.5% (w/v) BSA in 5.5 m ammonium chloride solution with 1 times 10-²mmol EDC over 120 min and 1 times 10^-1mmol EDC over 10 min respectively was achieved on a large scale using diafiltration for rapid termination of the reaction and purification. Residual ammonium chloride otherwise enhanced foaming properties. The amidated proteins were characterized by isoelectric focusing, electrophoresis and hydrophobicity and disulphide- and sulphydryl-group measurements. Compared with native BSA, partially amidated BSA (PA-BSA) produced enhanced foam expansion and foam stability values. This was attributed to minimal denaturation and to the presence of both acidic and basic components (pI range 5.25–7.50) within the single protein. In contrast, substantially amidated BSA (SA-BSA) (pI range 7–9.1) had similar foaming properties to those of the ultrafiltered BSA control which were slightly lower than those of native BSA. However SA-BSA interacted synergistically with native BSA producing enhanced foaming properties particularly at the 1:1 ratio through electrostatic interactions, conformational changes and increased hydrophobicity.     

New Kinetic Approach to the Evolution of Polygalacturonase (EC 3.2.1.15) Activity in a Commercial Enzyme Preparation Under Pulsed Electric Fields

ABSTRACT:  The effect of pulsed electric fields (PEF) on polygalacturonase (PG) activity in an aqueous solution of a commercial enzyme preparation was studied. Monopolar square wave pulses of 4 μs were delivered to the solution, which circulated through tubular chambers with 2 stainless steel electrodes in continuous operation. The electric field intensities ( E ) and treatment time ( t ) ranged within 15 to 38 kV cm⁻¹ and 300 to 1100 μs, respectively. Although important reduction of the PG activity could be achieved (up to 76.5% at E = 38 kV cm⁻¹ and t = 1100 μs), the experimental data showed certain enhancement of PG activity under soft conditions (up to 110.9% at E = 15 kV cm⁻¹ and t = 300 μs). A kinetic mechanism involving 2 consecutive irreversible first-order steps was developed to describe and explain the experimental data. The tested model exhibited high accuracy in respect of the experimental data and the error of the model was lower than 4.4%. The kinetic rate constant of the first ( k ₁) and second step ( k ₂), ratio between the activities of intermediate and native forms of the enzyme (Λ), and other quantities related to the model, were obtained within a Bayesian framework. k ₁ resulted independent of the E applied and considerably greater in magnitude order ( k ₁ mean = 6 μs⁻¹) with respect to k ₂, which was dependent on the applied E (mean values ranged from 489E-6 μs⁻¹ at E = 38 kV cm⁻¹ to 1215E-6 μs⁻¹ at 38 kV cm⁻¹). The dependency of k ₂ toward E was described using an exponential relationship.     

Relationship between energies of water sorption and diffusion in grains

The relationship between activation energy for diffusion, E _D and the BET heat of sorption, E ₁, was determined from literature data for maize, rice, sorghum, soybean and wheat and gave E _D/ E ₁= 0.5. Given that E _D < E ₁, diffusion was interpreted in terms of a mechanism involving the hopping of water molecules from one adsorption site to another.     

Microbiological Benefits of Removing Foam Formed After UV-Enhanced Ozonation of Poultry-Processing Chiller Water for Recycling

ABSTRACT: Prior experiments using 250 mL samples of unscreened poultry overflow chiller water evaluated the beneficial bactericidal and oxidative effects of 4 different treatments (namely, O₂/O₃,O₂/UV, O₂/O₃/UV, and O₂ as the control) for improving microbiological safety, turbidity, and water-use efficiency allowing its reconditioning for reuse. When excluding foam as in this present study, synergistic reductions > 1.5 log CFU/mL for aerobic plate counts (APC) were additionally achieved after 4 min for all O₃/UV treatment combinations as compared to serially applied treatments of O₃ and UV acting separately. With foam present, 16-min O₃/UV treatments were required to achieve similar results. We now report these additional benefits achieved by removing the foam formed by the advanced oxidation process of ultraviolet-photon enhanced ozonation. Furthermore, foam microbial and general physical content were analyzed to determine suitability as an additive in rendering-type processes. Treatment of the wastewater resulted in total plate counts between 2 to 4 Log CFU/mL in the foam after 8 min. Fat and protein constituted 89% of the solids collected (384 mg/L or 14% of the foam) with trace amounts of metal elements (for example, Ca, Na, K, Fe, Cu) present. Irradiating had negligible effect on foam characteristics yet decreased the amount of solids collected.     

Gelation mechanism of surimi studied by 1h NMR relaxation measurements

ABSTRACT:  In order to elucidate the gelation mechanism of surimi, the temperature dependence of water proton spin–spin relaxation time (¹H T ₂) has been described by a theoretical approach, in which the exposed protein surface is taken into account. Water ¹H T ₂ measured for horse mackerel surimi in the presence of 2.5% NaCl was analyzed on the basis of the consideration for the denaturation and the aggregation of protein in order to explain the macroscopic structural change during the heating and the cooling processes. The temperature dependence of water ¹H T ₂ and the fraction of rigid component gave a clear explanation for the gelation mechanism of surimi. Differential scanning calorimetry thermogram and dynamic viscoelastic measurements supported the results of nuclear magnetic resonance (NMR) measurements. It has been demonstrated that the measurement of NMR relaxation times is useful to describe the gelation mechanism of surimi.     

Vane Yield Stress of Starch Dispersions

ABSTRACT: Yield stresses of 5% (wt/wt) cross-linked waxy maize, tapioca, and Amioca starch dispersions (SDs) were measured with the vane method at different rotational speeds ( N ). The static (σ_0S) and dynamic (σ_0d) yield stress values of each SD were measured before and after breaking down its structure under continuous shear, respectively. The difference (σ_0S - σ_0d) was associated with the stress required to break the internal bonds (σ_b). Values of total yield stress (σ₀=σ_0S) and σ_b, and shear rate were related by power law relationships. The contribution of viscous and network stresses were estimated from an energy balance model. Textural characteristics of the SDs were analyzed in a texture map.     

Influence of pasteurisation,freezing and storage on properties of egg products made from eggs stored for 7 and for 28 days

The influence of the age of eggs before breaking, pasteurisation, freezing and storage at —17°c and the method of whipping on the foaming power, foam stability and viscosity of liquid egg albumen and liquid whole egg were studied. The foaming power (relative volume of foam) and the foam stability were determined with the aid of a Hobart whipping machine N 50. The viscosity was measured with a Brookfield viscometer type LV. Liquid egg albumen from 28-day-old eggs had a better foaming power with better stability than that from 7-day-old eggs. The viscosity of the liquid egg albumen from 7-day-old eggs was higher than that from 28-day-old eggs. When pasteurised with aluminium sulphate, the foaming power and the foam stability of all liquid egg albumens increased. When pasteurised without aluminium sulphate, both properties increased for liquid egg albumen from 7-day-old eggs and decreased for that from 28-day-old eggs. During the first weeks of storage of the egg white at −17°C, the foaming power, foam stability and viscosity gradually increased. Whipping for 1 min at setting 2 and 2 mill at setting 3 yielded a higher foaming power and a higher stability of the foam than whipping for 1 min at setting 2 and then a few minutes at position 3 until visually the optimum had been reached. These differences were significant (P < 0·01) for the foaming power and foam stability. There was no significant difference between the foaming power and stability of the foam for liquid whole egg prepared from 7-day-old eggs and that from 28-day-old eggs. Pasteurisation (3 min at 65°c) gave a decrease in foaming power and foam stability and an increase in viscosity. These differences were significant (P < 0·07) for the foaming power and viscosity. Storage resulted in lower foaming power and higher foam stability. In this case, higher viscosity values were also obtained. The whipping method did not give any significant differences.