Effect of pasteurisation on the chemical composition of liquid whole egg. II.—Comparison of the protein fractionation patterns of raw and pasteurised liquid whole egg

Samples of commercial raw and pasteurised whole egg were re-examined after 41 weeks' storage under frozen conditions. As well as differences between the two samples, the protein fractionation patterns revealed marked differences from the original unstored material. A second comparison of commercial raw and pasteurised egg indicated that considerable differences could occur in the protein fractionation patterns of raw egg. This was confirmed in subsequent experiments. Two experiments on egg white showed that pasteurisation for 2 1/2 min at 135°F caused no change in the fractionation pattern of the proteins, and provided sound evidence for the reproducibility of the fractionation procedure. The separate influences of time and temperature of heating on liquid whole egg were studied in a series of laboratory-scale pasteurisation experiments. It appeared that time was a more important factor than temperature and that a heating time of 5 minutes, which is approximately the time that the bulk of the egg is held at the pasteurising temperature in commercial plants, caused significant changes in the fractionation patterns of both soluble and insoluble proteins. When pasteurisation was carried out for 2 1/2 min at 148–152°F, and also when time was varied at 150°F, the thiol and disulphide concentrations of the soluble proteins were not altered by any of the pasteurisation conditions studied. A short study was made of the distribution of α-amylase activity during the fractionation of the soluble proteins of raw whole egg. Preliminary experiments on gel filtration of the insoluble protein portions indicated that this technique is capable of revealing changes in molecular weight distribution resulting from pasteurisation and gave support to the view that heat treatment of whole egg results in aggregation or association of some of the proteins.     

Effect of pasteurisation on the chemical composition of liquid whole egg IV.—Further resolution of certain fractions of the soluble proteins

Amino acid analyses confirmed previous electrophoretic evidence that two particular chromatographic fractions from the soluble proteins of liquid whole egg were mixtures of proteins. Further resolution of these fractions has been effected by ion-exchange chromatography on carboxymethyl cellulose, using sodium acetate buffer solutions containing increasing concentrations of sodium chloride followed by certain alkaline solutions. Some distinctions between sub-fractions obtained from raw and pasteurised egg have been noted.     

Statistical analysis of effects of industrial processing steps on functional properties of pasteurised liquid egg white

Egg white is widely used as an ingredient in the food industry owing to its excellent functional properties. The transformation of shell eggs into safe liquid, frozen, or spray‐dried egg white with extended shelf life requires many technological operations that result in modifications to the egg white's functional properties. The present study highlights the critical steps affecting foaming and gelling properties during a classical pasteurised liquid egg white process. The main source of variation in functional properties was raw material quality, accounting for 70% of the variability. Part of the remaining 30% was explained by mechanical egg white–yolk separation, tank storage, pasteurisation and homogenisation that resulted in damage to the functional properties, whereas initial flow through pipes and pumping resulted in their improvement. The effects of these steps could be grouped according to the type of treatment undertaken. Dry matter content, pH and treatment intensity at each step contributed about 30% of the variability in functional properties due to processing steps. Relationships between the modifications of egg white functional properties and protein conformation were established. Between 46 and 78% of the variability in functional properties can be explained by protein denaturation, temperature and enthalpy changes. Copyright © 2004 Society of Chemical Industry     

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.     

The significance of critical processing steps in the production of dried egg albumen powder on gel textural and foaming properties

The purpose of the present work was to study the variation in egg albumen functional properties as a function of seven selected processing steps from the initially raw liquid albumen to the final dried egg albumen powder. Albumen samples in six replicates were analysed for dry matter, pH, glucose, triglycerides, albumen gel properties (ie textural stress and Hencky strain, water‐ and protein‐binding capacity and gel colour L*, a*, b*), foaming properties (ie overrun, stability against drainage and bubble breakdown) and surface tension. The gel texture and water‐holding capacity significantly decreased during the processing steps from raw albumen through storage, centrifugation and ion exchange, whereas the final dry‐pasteurisation resulted in increased gel properties. Covalently linked protein polymers formed during the dry‐pasteurisation, as revealed by SDS‐PAGE, may explain this improvement. The foam overrun increased twofold during the three final steps of ultrafiltration, spray‐drying and dry‐pasteurisation compared with the raw albumen; however, the foam stability decreased, ie drainage and foam volume breakdown rates increased. The surface pressure increase was positively correlated with the foam overrun. This paper reveals at which processing steps the control of functional properties of egg albumen powder can take place. Copyright © 2004 Society of Chemical Industry     

Effects of ohmic heating on technological properties of whole egg

The aim of this work was to study the effects of different ohmic heating conditions on color, rheology, foaming, and gelling properties of whole egg. Industrial products treated by conventional heat pasteurization and the corresponding raw materials were also evaluated. Ohmic treatments accomplished in a static cell (65.5 °C × 3 min, 70 °C × 1 min, and 67 °C × 4.5 min) increased whole egg apparent viscosity (up to 190%), but also foam overrun (up to 28%) and gel hardness (up to 15%). The performance improvement was confirmed by treatments carried out in a continuous pilot plant (71 °C × 0.6 min, 68 °C × 1.4 min) and the products resulted stable during storage at 4 °C for 30 days. In conclusion, this study demonstrated that ohmic heating is a suitable alternative to conventional pasteurization. Low temperature treatments are preferable to avoid possible rheological issues due to protein denaturation.Industrial relevanceWhole egg is a protein ingredient with multiple technological properties, used in many foods. Due to safety reasons, food manufacturers often use pasteurized liquid egg products, microbiologically safer and easier to handle with respect to shell eggs. In order to satisfy the required sanitary levels for liquid egg products, thermal pasteurization treatments are needed. However, since egg proteins are very sensitive to high temperatures, attention must be paid to avoid coagulation entailing deleterious effects against egg quality. In this study, different ohmic heating treatments were evaluated as milder alternatives to conventional pasteurization. The lab- and pilot-scale experiments and the subsequent statistical analyses of the obtained results contributed to assess the effects of the different ohmic treatments on technological features (e.g. color, rheology, foaming, and gelling properties) of liquid whole egg. This study demonstrated that ohmic heating is a suitable technology for whole egg treatment, paving the way for new opportunities in order to produce safe food ingredients with improved technological functionalities.     

Effects of spray-drying and freezing on the proteins of liquid whole egg

Commercial pasteurised liquid whole egg was spray-dried, both alone and mixed with liquid milk, and some of it was frozen. Paper electrophoresis revealed that lipoprotein fractions from the pasteurised liquid egg were mainly immobile, in contrast to unpasteurised new-laid egg which contained both mobile and immobile lipoprotein fractions. The major difference between the soluble proteins of the commercial chilled pasteurised liquid egg and those of the same egg after freezing and thawing was the presence, in the former, of an inert lipoprotein fraction, amounting to 3.6% of the total egg solids and containing 88% lipid. The “soluble” proteins of spray-dried egg and egg-milk mixture also included large “inert” lipoprotein fractions eluted with the void volume. They contained 72–81% of lipid and accounted for 7–13% of the total egg solids. Larger fractions were eluted by the stronger salt buffer solutions and by hydrochloric acid from the dried egg-milk mixture than from the dried egg, and these were probably derived from the milk. All the spray-dried samples possessed the “inert insoluble” protein fraction characteristic of liquid egg, and the presence of a high molecular weight lipoprotein fraction was confirmed in each case. The “insoluble proteins” of the spray-dried samples had higher protein contents than those from the original chilled liquid egg and the thawed frozen egg.     

Functional egg white–pectin conjugates prepared by controlled Maillard reaction

Changes in the functional properties of egg white (EW) protein/pectin mixtures and their chemical conjugation via the Maillard reaction were investigated. Pectin with high degrees of esterification was conjugated to EW protein at 60 °C and 79% relative humidity for 0, 6, 12, 24 and 48 h. The conjugates were compared with a physical mixture of the two components. There was a significant decrease in the available lysine (free amino groups) of the conjugated protein during incubation with the polysaccharides, negatively correlated to the emulsification properties. Oil–water emulsions prepared using the EW–pectin conjugates showed good stability, with oil droplet mean volume diameters of 0.29–1.2 μm. The conjugates showed higher emulsion viscosity and stability than the raw materials at ambient temperature. Addition of pectin (0.05–0.5% w/v) to EW at concentrations of 1% and 5% w/v had a significant effect on foam volume and stability.     

Rheological properties of foams generated from egg albumin after pH treatment

Rheological properties of foams at pH 4.5 and 8.5 made from egg albumin proteins after pH-induced unfolding and refolding treatments were investigated. The foams behaved as highly elastic materials. Static and dynamic yield stress was investigated using small, steady shear experiments. Yield stress was measured also in oscillation mode and high correlation was found between dynamic yield stress and critical stress amplitude. All pH treatments led to firmer foams than untreated foams at pH 8.5. At pH 8.5 the control foam had a very weak structure (static yield stress at 3.4 Pa and dynamic yield stress at 5.5 Pa for the fresh made foams), while pH-treated foams at pH 8.5 had values (static yield stress up to 39.2 Pa and dynamic yield stress up to 47.1 Pa for the fresh made foams) that were even higher than the values for the control at pH 4.5 (static yield stress at 22.4 Pa and dynamic yield stress at 25.4 Pa for the fresh made foams, which is a good foaming pH for egg albumin). It was shown that an increase in yield stress of foams after drainage is related to foam stability and liquid drainage. This study demonstrated that unfolding egg albumin at low or high pH followed by refolding leads to a substantial increase in foam firmness and gives the foam different properties than foams from untreated egg albumin.     

Influence of ultra-high pressure homogenisation on antioxidant capacity,polyphenol and vitamin content of clear apple juice

Ultra-high pressure homogenisation (UHPH) is a recently developed technology and is still under study to evaluate its effect on different aspects of its application to food products. The aim of this research work was to evaluate the effect of UHPH treatments on quality characteristics of apple juice such as antioxidant capacity, polyphenol composition, vitamin C and provitamin A contents, in comparison with raw (R) and pasteurised (PA) apple juice. Several UHPH treatments that include combinations of pressure (100, 200 and 300 MPa) and inlet temperatures (4 and 20 °C) were assayed. Apple juice was pasteurised at 90 °C for 4 min. Antioxidant capacity was analysed using the oxygen radical antioxidant capacity (ORAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH), trolox equivalent antioxidant capacity (TEAC), ferric reducing antioxidant power (FRAP) assay while total phenolic content was determined by the Folin–Ciocalteau assay. According to the FRAP and DPPH assays, UHPH processing did not change apple juice antioxidant capacity. However, significant differences were detected between samples analysed by TEAC and ORAC assays. In spite of these differences, high correlation values were found between the four antioxidant capacity assays, and also with total polyphenol content. The analysis and quantification of individual phenols by HPLC/DAD analytical technique reflects that UHPH-treatment prevented degradation of these compounds. Vitamin C concentrations did not change in UHPH treated samples, retaining the same value as in raw juice. However, significant losses were observed for provitamin A content, but lower than in PA samples.     

The effect of pasteurisation and freezing on the low density lipoproteins of egg.

The low density fraction of egg yolk was separated by gel filtration into two groups of lipoproteins. One group (1) had an extremely high molecular weight and was probably formed by aggregation of the second group (2), which itself had a high molecular weight. In liquid egg the ratio of group 1 to group 2 was increased by pasteurisation for 5 min at 65°C and also by freezing and thawing of either raw or pasteurised material. When group 2 was isolated by gel filtration and then frozen and thawed it was converted to group 1.     

Admittance measurements to assess the total solids and fat contents in liquid whole egg products

In the present research, a method based on admittance measurements able to assess total solids and fat contents (%) in nine different liquid whole egg products was set up. By means of a tetrapolar platinum cell connected to a signal conditioning circuit, an alternating current generator and a data acquisition system, the effect of 15 different combinations of frequencies of the oscillating field (10, 100, 500, 1000 and 5000 Hz) and input voltage levels (1, 1.5 and 2 V) on the estimation of the total solids and fat contents were analyzed. The influence of the temperature solution on the electrical measurements was also assessed. The best estimations were obtained at 1000 Hz and 1 V (R² = 0.998; SE = 0.14%) for the total solids content and at 5000 Hz and 1 V (R² = 0.995; SE = 0.19%) for the fat content. For both parameters, the measurements conducted at 10 Hz appeared affected by the polarization occurring at the electrodes-solution interface. The admittance of the liquid whole egg products linearly increased with the temperature, and a temperature coefficient θ at 20 °C of about 2.1 was calculated. These excellent results encourage an industrial application of the technique for a rapid and economic assessment of the total solids and fat contents in the liquid egg products.     

A market study on the quality characteristics of eggs from different housing systems

To study the differences among commercial eggs from four housing systems i.e. cage, barn, free range and organic, 41 physical and chemical parameters were evaluated on 28 fresh egg samples from the Italian market. The univariate statistic analysis evidenced that organic eggs had the highest whipping capacity and foam consistency but the lowest freshness (the highest air cell height) and albumen quality (the lowest Haugh Unit); cage eggs presented instead the lowest whipping capacity and the highest shell resistance to breaking. The multivariate technique discriminant partial least-squares regression was unable to correctly classify the eggs from the four housing systems but successfully differentiated cage eggs from alternative (organic + barn + free range) eggs. The variables with the most discriminant power were shell breaking resistance, overrun, protein content, and shell thickness.     

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.     

辐射加工技术在食品生产中的应用研究

本文以大豆蛋白系列产品为例,研究了辐射加工技术在食品生产中的具体应用。研究结果表明,大豆蛋白系列产品经辐射加工技术处理后,产品不仅保持了原有的各项理化指标、良好的功能性,而且产品卫生学质量得到大幅度提高,各项指标均符合企业产品质量标准。该项技术的开发应用,解决了长期困扰我国大豆蛋白企业产品微生物超标的问题,实现了大豆蛋白工业化生产。     

Functionality and Microbial Stability of Ultrapasteurized, Aseptically Packaged Refrigerated Whole Egg

Raw, liquid whole egg was ultrapasteurized and aseptically packaged to extend the refrigerated shelf-life and maintain functional quality. Nine processes ranged from 63.7–72.2°C for 2.7 to 192.2 sec and resulted in shelf-lives ranging from 4 to >24 weeks at 4°C. Egg pasteurized by an essentially conventional process (26.2 set, 63.7°C), aseptically packaged and stored at 4°C spoiled in 4–8 weeks. Overall, little or no change was observed in the chemical (protein and solids contents, soluble protein, pH) and functional properties (performance in cakes and custards) of the ultrapasteurized, aseptically packaged, 4°C refrigerated egg compared to raw egg. Egg of acceptable quality may be produced by this process with a 3–6 months shelf-life at 4°C.     

Synthesis,characterisation and use of 2-tetradecylcyclobutanone together with other cyclobutanones as markers for irradiated liquid whole egg

The synthesis and characterisation of 2-tetradecylcyclobutanone (TCB) is described. Both 2-dodecykyclobutanone and TCB were shown to be present in liquid whole egg irradiated at doses of 2.5 and 10.0 kGy. These compounds were absent from the unirradiated pasteurised samples. Using gas chromatography and infrared spectroscopy, there was also evidence for the presence in irradiated egg of 2-tetradeccnyl- and 2-tetradecadienylyclobutanone which are formed from oleic and linoleic acids, respectively. Authentic standards for these unsaturated cyclobutanones were not available commercially but the presence of 2-tetra-decenylcyclobutanone was substantiated by hydrogenating the egg extracts so converting this unsaturated cyclobutanone to TCB. Saturated and unsaturated cyclobutanones appear to be specific products of irradiation and are potential markers for detection of irradiated liquid egg and probably other fat-containing foods.     

Comparative effect of thermal treatment on the physicochemical properties of whey and egg white protein foams

The optimization of the functionalities of commercial protein ingredients still constitutes a key objective of the food industry. Our aim was therefore to compare the effect of thermal treatments applied in typical industrial conditions on the foaming properties of whey protein isolate (WPI) and egg white proteins (EWP): EWP was pasteurized in dry state from 1 to 5 days and from 60 °C to 80 °C, while WPI was heat-treated between 80 °C and 100 °C under dynamic conditions using a tubular heat exchanger. Typical protein concentrations of the food industry were also used, 2% (w/v) WPI and 10% (w/v) EWP at pH 7, which provided solutions of similar viscosity. Consequently, WPI exhibited a higher foamability than EWP. For WPI, heat treatment induced a slight decrease of overrun when temperature was above 90 °C, i.e. when aggregation reduced too considerably the amount of monomers that played the key role on foam formation; conversely, it increased foamability for EWP due to the lower aggregation degree resulting from dry heating compared to heat-treated WPI solutions. As expected, thermal treatments improved significantly the stability of WPI and EWP foams, but stability always passed through a maximum as a function of the intensity of heat treatment. In both cases, optimum conditions for foam stability that did not impair foamability corresponded to about 20% soluble protein aggregates. A key discrepancy was finally that the dry heat treatment of EWP provided softer foams, despite more rigid than the WPI-based foams, whereas dynamically heat-treated WPI gave firmer foams than native proteins.     

Effect of pasteurisation on the chemical composition of liquid whole egg. I. Development of a scheme for the fractionation of the proteins of whole egg

The proteins of whole egg may be separated into soluble and insoluble portions by dialysis against glycine solution followed by centrifugation at a high speed. The soluble proteins can then be resolved into at least twelve fractions by ion-exchange chromatography on diethylaminoethyl-cellulose, using stepwise elution with dilute glycine-phosphate buffer solutions containing increasing concentrations of sodium chloride. Further examination has shown that most of the fractions contain more than one protein, and some tentative identifications have been made. The insoluble proteins can be dissolved in a relatively strong phosphate buffer and fractionated on diethylaminoethyl-cellulose in a similar way. Separate examinations of white and yolk indicated that the soluble proteins of whole egg are predominantly the same as those of the white, and also showed certain differences between whole egg and the separated white and yolk that could be attributed to some form of protein association in mixed whole egg. An initial experiment has suggested that the method described will reveal differences between raw and pasteurised egg.