Dielectric properties of egg whites and whole eggs as influenced by thermal treatments

Effects of cooking on dielectric properties of liquid whole eggs and liquid egg whites were studied in connection with radio frequency and microwave heating processes to preserve shelf-stable products. Dielectric measurements were made using an open-ended coaxial probe method over a temperature range of 20 and 120 °C at radio frequencies 27 and 40 MHz, and microwave frequencies 915 and 1800 MHz. Thermal denaturation of liquid egg whites and whole eggs influenced the dielectric constants and dipole loss component of eggs, as reflected by changes in loss factors above 60 °C. In addition, loss factor of liquid whole eggs was generally smaller than that of egg whites and larger than the loss factor of egg yolk. Ionic conductivity was a dominant factor determining the dielectric loss behavior of egg products at radio frequencies, whereas dipole water molecules played an increasing role with an increase in microwave frequencies.     

Dielectric properties of chestnut flour relevant to drying with radio-frequency and microwave energy

Dielectric properties of compressed chestnut flour samples with 11.6–48.0% w.b. moisture content were determined with a network analyzer and an open-ended coaxial-line probe over a frequency range from 10 to 4500 MHz and a temperature range from 20 to 60 °C. The results showed that the permittivities of chestnut flour were a function of frequency, moisture content and temperature. Both dielectric constant and loss factor decreased with increasing frequency but increased with increasing moisture content and temperature. The relationship between permittivities and moisture content and temperature at 27, 40, 915 and 2450 MHz could be described by second- or third-degree polynomial models, with the coefficients of determination higher than 0.993. The analysis of variance showed that moisture content and temperature had strong significant effects on permittivity values. The penetration depth decreased with increasing frequency, moisture content and temperature. Large penetration depth at radio frequencies below 100 MHz may provide practical large-scale dielectric drying of chestnut.     

Dielectric properties of ground almond shells in the development of radio frequency and microwave pasteurization

To develop pasteurization treatments based on radio frequency (RF) or microwave energy, dielectric properties of almond shells were determined using an open-ended coaxial-probe with an impedance analyzer over a frequency range of 10–1800 MHz. Both the dielectric constant and loss factor of almond shells decreased with increasing frequency, but increased with increasing temperature and moisture content. The absolute value of the slopes of log–log plots between loss factor and frequency increased with increasing temperature at low frequencies, especially at high temperatures and moisture contents. The effective electrical conductivity of shell samples was close to zero at the lowest moisture content (6% w.b.) and 3–9 times larger at 90 °C than 20 °C for the highest moisture content (36% w.b.). A good linear relationship was observed between permittivity and density at 1800 MHz. The power penetration depths at RF range (27 and 40 MHz) were about 6–24 times as deep as those for microwave frequencies (915 and 1800 MHz) at each corresponding temperature and moisture content. It is likely that RF energy may provide uniform heating and high throughput treatments for controlling Salmonella in in-shell almonds after washing.     

Water holding capacity,dielectric properties and light microscopy of conventionally and ohmically cooked meat emulsion batter

Samples of meat emulsion batter were steam- or ohmically cooked (at voltage densities ranging from 3 to 7 V cm^–1) to target end-point temperatures and compared using expressible fluids (EFs), dielectric properties and light microscopic techniques. EF testing revealed higher levels of expressible moisture in steam-cooked samples (P<0.05) and greater amounts of expressible suspended solids in the highest voltage density ohmically cooked samples (i.e. 7 V cm^–1) (P<0.05). (dielectric constant) and (loss factor) dielectric values at 300 and 3,000 MHz were higher for steam-cooked samples, suggesting greater amounts of loosely bound water. Subsequent light microscopic evaluation of samples suggested slightly greater levels of physical disruption in ohmically cooked samples, which could have affected the ability of the emulsion to bind water and fat.     

Dielectric properties of salmon (Oncorhynchus keta) and sturgeon (Acipenser transmontanus) caviar at radio frequency (RF) and microwave (MW) pasteurization frequencies

Radio frequency (RF) and microwave (MW) heating provide an important advantage of more rapid heat penetration in pasteurization processes for heat labile high value foods, which to date, have only been pasteurized by conductive heating. The objectives of this work were to determine the dielectric constant, loss factor and power penetration depth for salmon (0.8% and 2.3% total salt) and sturgeon (0.20 and 3.3% salt) caviars at RF frequency of 27 MHz and MW frequency of 915 MHz (20–80 °C). The dielectric constant (ε′) and dielectric loss factor (ε″) for salmon and sturgeon caviar increased markedly with increasing temperature at 27 MHz but not at 915 MHz. Power penetration depth was higher at 27 MHz compared to 915 MHz, and in unsalted compared to salted roe. Power penetration depth tended to decrease as temperature increased.     

Physicochemical and functional properties of whole legume flour

The physicochemical, functional and pasting properties of whole flours from pinto bean, lima bean, red kidney bean, black bean, navy bean, small red bean, black eye bean, mung bean, lentil and chickpea were investigated. Significant differences in physicochemical characteristics and functional properties were observed (P < 0.05). Bulk densities, water absorption indices, water solubility indices, oil absorption capacities, emulsion activities, and emulsion stabilities ranged from 0.543 g/mL to 0.816 g/mL, 4.09 g/g to 6.13 g/g, 19.44 g/100 g to 29.14 g/100 g, 0.93 g/g to 1.38 g/g, 61.14%–92.20%, and 84.15%–96.90%, respectively. Phaseolus legume flour exhibited higher water absorption capacity, oil absorption capacity, emulsion activity, and emulsion stability compared with other kinds of legume flour. Pasting properties were significantly different (P < 0.05). Pasting temperatures and the peak, final, and setback viscosities of the flours ranged from 73.2 °C to 83.0 °C, 96.2 RVU to 216.8 RVU, 118.5 RVU to 243.8 RVU, and 28.3 RVU to 103.2 RVU, respectively.     

Functional properties of pasteurised liquid whole egg products as affected by the hygienic quality of the raw eggs

The viscosity, foaming and baking performances of pasteurised liquid whole egg products were investigated to study the influence of raw egg hygienic quality on egg product functional performances. Uracil, lactic acid and 3OH-butyric acid measured in the pasteurised egg products were taken as chemical indices of the hygienic quality of the raw material. A high variability in the functional properties was observed, especially for overrun and foam stability, as well as in the chemical indices of hygiene. Many interesting correlations were found between variables, for example between overrun and cake volume (p < 0.001). Instead, no significant correlations were found between the chemical indices and the different functional properties. However, the application of Principal Component Analysis demonstrated that a good hygienic quality of the raw material used to prepare the liquid whole egg products is a prerequisite needed to develop good functional performances, although other factors pertaining to composition or processing also have a role.     

磷酸盐单体与微波处理对鲢鱼鱼糜凝胶特性的影响

研究了在水浴和微波两种加热方式下,焦磷酸钠(SPP)、三聚磷酸钠(STPP)和六偏磷酸钠(SHMP)对鲢鱼鱼糜凝胶强度和保水性的影响。结果表明,采用7.5W/g功率、40s/周期(连续5次处理)的微波加热处理后,鱼糜的凝胶强度显著升高,但其整体变化趋势与对照组(即水浴加热)相似;分别添加SPP和STPP的鱼糜凝胶强度均在0.2%时达到最大值,与对照组差异显著;而SHMP在添加量为0.4%时,凝胶强度达到最大值,但与对照组差异不显著;分别添加三种磷酸盐单体的鱼糜经微波加热处理后,其凝胶保水性变化趋势明显不同于各自对照组的变化趋势;微波加热组除添加SHMP后的保水性下降外,其余处理组的鱼糜保水性均有提高;经微波加热处理的SPP组和STPP组保水性也明显优于对照组。此外,微波加热处理也可以大大缩短鱼糜凝胶化的时间。     

Optimization of dry heat treatment of egg white in relation to foam and interfacial properties

The properties of foams processed with reconstituted egg white were investigated as a function of the denaturation undergone by the proteins during the pasteurization stage in dry state. Various time-temperature tables were applied on the original egg white powder, ranging from 1 to 7 days, and from 60 to 80 °C. Differential Scanning Calorimetry was used to determine the denaturation degree of each EWP induced by the dry heat treatment. The rheological properties of the interface, using the drop tensiometer method, were shown to be significantly affected by the denaturation and to be a relevant parameter for foamability, stability and foam texture. The bulk properties of the foams were interrelated with interfacial properties by using principal component analysis (PCA) and cluster analysis (HCA). The resulting classification of the heat treatments reveals that mild treatment offers a good compromise between the heating cost and the functional properties of the foams.     

Effect of moisture content on selected physicochemical properties of two commercial hen egg white powders

After short-term storage at 23 °C, selected physicochemical properties of two hen egg white powders (with and without hydrolysis) were studied. Overall, the effect of moisture content on physicochemical properties of Hydrolysed Egg White powder (HEW) was more severe than those of Dried Egg White powder (DEW). The denaturation temperature (T_d) and its enthalpy change (ΔH_d) of ovalbumin in DEW followed an exponential model, as well as the T_d of HEW. The Gordon-Taylor equation modelled well the glass transition temperatures (T_g) of HEW and DEW. The Guggenheim-Anderson-de Boer (GAB) model fitted well to the type II moisture sorption isotherm. At the critical moisture content (12.0%, dry basis), compared with DEW, the colour of HEW began to darken dramatically and its hardness started to change significantly. These changes were closely related to the inherent characteristics of the two products. The mechanisms relevant to these physicochemical changes were discussed.     

Chemical and functional properties of fibre concentrates obtained from by-products of coconut kernel

The coconut kernel residues obtained after extraction of coconut milk (MR) and virgin coconut oil (VOR) were analysed for their potential as dietary fibres. VOR was defatted and treated chemically using three solvent systems to isolate coconut cell wall polysaccharides (CCWP).     

Influence of glycerol and water activity on the properties of compressed egg white-based bioplastics

In this paper, the effects of glycerol (35%, 40% and 45%) and water activity (0.34 and 0.48) on the physical, mechanical and morphological properties of compressed egg white-based bioplastics are investigated. Lighter, more reddish and less yellowish sheets with a decreased thickness and second-order transition temperature, improved mechanical properties (increased flexibility and decreased rigidity and stiffness) and constant moisture content can be obtained by increasing water activity. Increasing the GLY content results in the same type of changes but to a lesser extent and increased moisture content. Increasing both, water activity and GLY, leads to a more pronounced effect for some properties. This study demonstrates that compressed egg white-based bioplastics with desired properties can be obtained by adjusting water activity and GLY content during their synthesis.     

The effect of egg albumen on the viscoelasticity of crab sticks made from Alaska Pollock and Pacific Whiting surimi

The influence of the amount of egg albumen contained as a gelation agent in crab sticks made from Alaska Pollock or Pacific Whiting surimi on their viscoelastic properties was examined. Dynamic oscillatory and transient tests allowed a variety of parameters to be measured in order to establish the intensity of the interactions in the protein network which characterize the gel strength. This physical property is fundamental for the nominal quality texture and eating quality of surimi and surimi-based seafood analog products (surimi seafood). Three different egg albumen contents around the nominal value (2%) were studied, namely: 1.5, 2 and 2.5%. The viscoelastic gel strength (A_n) and gel strength (S) values obtained in the frequency sweep and creep tests, respectively, were quite consistent. Increasing the protein content of the surimi increased the gel strength of both types of crab sticks (p < 0.05). The optimum egg albumen content was found to be about 1.5% for Alaska Pollock and 2% for Pacific Whiting surimi. Based on these results, the industry could use less albumen in making crab sticks from Alaska Pollock surimi, which surpasses Pacific Whiting surimi in quality.     

Effect of sugar, citric acid and egg white type on the microstructural and mechanical properties of meringues

Meringues are characterized by a predominant air phase and their overall quality is intimately related with microstructure. The formation of meringues microstructure relies on the capacity of egg white (EW) proteins to form voluminous and stable foams and it is ultimately related with the chemical properties of proteins and with the addition of ingredients such as sugars, salts, acids and surfactants.The study aimed at assessing the influence of sugar/EW ratio, citric acid and EW type on the microstructural and mechanical properties of meringues. Meringues prepared with different sugar/EW, citric acid level and different EW type were subjected to microstructural analysis by X-ray microtomography and to mechanical assessment by compression tests.Results demonstrate the ability of X-ray microtomography to reconstruct the 3D microstructure of meringues allowing the measurement of porosity, size, shape and distribution of pores. Citric acid, sugar concentration and EW type play a fundamental role on meringues microstructural parameters and mechanical properties. Low sugar/EW ratios as well as increasing citric acid levels increase the air phase and result in a softer texture of meringues. Moreover, low sugar/EW ratios and increasing citric acid in the meringue result in a reduction of pore size and also influence the shape of pores. Meringues microstructural and mechanical properties are affected by the EW quality: fresh and pasteurized EWs and EWs stored at refrigerated temperatures scored the highest structural and mechanical performances, while powdered and frozen EWs and albumens from old eggs showed the worst results. Not only the balance among ingredients but also the choice of raw materials can strongly affect the final quality of meringues.     

Ion distribution and protein proteolysis affect water holding capacity of Longissimus thoracis et lumborum in meat of lamb subjected to antemortem exercise

Exercise has been shown previously to reduce the water holding capacity (WHC) of meat in lamb. The consequence of changes in the distribution of ions pre- and post-rigor and proteolysis on WHC is relatively unknown. Twelve crossbred lambs were used to investigate the effect of exercise on the meat quality traits of the Longissimus thoracis et lumborum (LTL) muscle. There were no treatment effects on Warner-Bratzler shear force (WBSF), myofibril and sarcoplasmic protein solubility, denaturation or sarcomere length. With exercise the initial pH of the muscle was lower and the rate of pH fall to rigor was faster compared to controls. Exercise caused increased purge and meat fluid had a lower osmolarity, magnesium, potassium and sodium concentration. Proteolysis of desmin occurred after day 3 and vinculin on day 7 of ageing with exercise. It was concluded that exercise caused changes in the distribution of ions and the proteolysis of muscle proteins that reduced the ability of the muscle to bind or hold water.     

The effect of thermosonication of milk on selected physicochemical and microstructural properties of yoghurt gels during fermentation

Yoghurt cultures (0.1, 1.5 and 3.5% fat) were prepared from milk which was preheated to 45 °C and subjected to thermosonication (TS) for 10 min at an ultrasound amplitude of 24 kHz. Compared to conventional yoghurts prepared from preheated (90 °C, 10 min) milk, cultures from TS milk at similar fat contents had higher gelation pH values, greater viscosities and higher water holding capacities (WHC). On average, yoghurts from TS treated milks with 1.5 or 3.5% fat had almost 2 fold greater WHC and 25% higher G’ values than conventionally produced yoghurt. Electron microscopy showed differences in the microstructure, with TS yoghurt having a honeycomb like network and exhibiting a more porous nature. These characteristics are absent in conventional yoghurts. In addition, the average particle size in TS yoghurts was smaller (<1 μm) than in conventional yoghurts.     

Rheological properties,stability and sensory evaluation of low-cholesterol mayonnaises prepared using egg yolk granules as emulsifying agent

No important practical applications have been developed for egg yolk granules until now. However, as they have low cholesterol content and maintain good emulsifying properties, granules could be employed as a potential ingredient in the food industry. In this work, granules obtained in the laboratory by a simple procedure were used as emulsifying agent in mayonnaise preparation. The aim was to develop a low-cholesterol mayonnaise with properties similar to those of typical mayonnaise. For this purpose, three low-cholesterol formulations prepared in the laboratory were compared with a mayonnaise prepared using yolk and also with a commercial mayonnaise. The rheological characteristics of mayonnaises were evaluated, as well as their microstructure and sensorial properties. In addition, colour and particle size measurements at different times of storage were carried out to assess stability. According to results, the use of granules allows the preparation of a low-cholesterol mayonnaise which shows similar characteristics to those of a typical mayonnaise.     

Dielectric properties of guava,mamey sapote,prickly pears,and Nopal in the microwave range

Dielectric properties (DPs) of selected fruits: guava (Psidium guajava), mamey sapote (Pouteria sapota), red prickly pear (fruit from Opuntia streptacantha), and white prickly pear (fruit from Opuntia ficus-indica), as well as nopal (young cactus pads or cladodes from Opuntia ficus-indica) were studied. DPs were determined using the open-ended coaxial probe method at microwave frequencies (500 MHz–2 GHz) and temperatures of 20, 40, and 60ºC. At 20ºC and 915 MHz for unripe fruits, dielectric constant values ranged from 65.7 to 70.9, while the loss factor had values between 8.4 and 20.7. Both dielectric constant and dielectric loss factor were affected by temperature and frequency (p < 0.05). For example, loss factor for red prickly pear at 2450 MHz decreased from 13.88 at 20ºC to 12.8 at 40ºC and 11.7 at 60ºC. DPs of fruits were also affected by their ripening (quantified through the maturity index). In addition, penetration depth decreased with increasing frequency, ranging from 1.98 to 4.80 cm at 915 MHz and from 0.25 to 0.41 cm at 5800 MHz. Results are valuable to develop further applications with microwave technology for these foods, such as microwave-assisted disinfestation treatments or microwave drying.     

Characteristics and functional properties of gelatin from zebra blenny (Salaria basilisca) skin

Gelatin was extracted from alkali-pretreated skin of zebra blenny (Salaria basilisca) using commercial pepsin with a yield of 18 g/100 g of skin sample. The polypeptides pattern, gel strength, viscosity, textural parameters and functional properties of the zebra blenny skin gelatin (ZBSG) were investigated. Amino acid analysis revealed that ZBSG contained almost all essential amino acids, with glycine being the most predominant one. ZBSG was identified as a type I gelatin, containing α₁ and α₂-chains as the major constituents. Its gel strength and viscosity were 170.2 g and 5.95 cP, respectively. Fourier transformed infrared spectroscopy (FT-IR) spectra showed helical arrangements in its structure. Its solubility and functional properties were concentration-dependent. While foam expansion (FE) and foam stability (FS) increased with the increase of concentration, emulsifying activity index (EAI) and emulsion stability index (ESI) were noted to decrease. ZBSG also showed strong clarification ability particularly for apple juice, without affecting nutritional value.     

The role of salt washing of fish skins in chemical and rheological properties of gelatin extracted

Dover sole (Solea vulgaris) skins were washed with different salt solutions previous to gelatin extraction by a mild acid pre-treatment. The effects of NaCl, KCl, MgCl₂, MgSO₄ and no-salt washing on the mineral content, yield of extraction, molecular weight distribution, gel strength, aggregation phenomena and viscoelastic properties of gelatin newly dissolved and after overnight cold maturation were evaluated. Skin washing with NaCl and KCl induced noticeable changes in molecular weight distribution, and consequently in gel strength and rheological properties, especially when compared with unsalted gelatin preparations. However, salts containing Mg²⁺ gave rise to the retaining of this bivalent cation in the resultant gelatin, which is detrimental to the gelatin quality.