Fresh Hen Research Articles

Evaluation of some heavy metal residues content in hen’s table eggs marketed in Egypt

In the present study, 120 fresh hen’s egg samples (Balady and farm) were randomly collected from supermarkets of Alexandria and El-Behera Governorates, Egypt and analyzed for lead and Cadmium residues expressed in (µg kg-1) in egg content using atomic absorption Spectrophotometer device. Results revealed that the total mean concentrations of Cd was 0.23± 0.0122 (µg kg-1) and the total mean concentration of lead was 123.45 ± 14.597(µg kg-1). Results also revealed that the residues of Cadmium in all examined samples were within the permissible limit (0.05mg kg-1) and lead (Pb) concentrations exceeded the MRL value of (0.1 mg kg-1) in 7/120 (5.83%) of the total examined eggs. Lead contamination of hen’s eggs represents a potential public health hazard, especially to children repeatedly consuming eggs from contaminated hen’s eggs. The public health hazard and adverse outcomes of the examined toxic heavy metals on human consumers were discussed. Appropriate precautions are warranted to minimize the heavy metal consumption contamination especially of lead.

Acidic and Heat Processing of Egg Yolk Dispersions

Egg yolk is a multifunctional ingredient widely used in many food products, wherein proteins are the dominant component contributing to this functionality. However, the potential risk of foodborne illness associated with egg use forces us to ensure that foodstuffs based on egg yolk are managed in a safe and sanitary manner. Lowering the pH under a certain value by adding acids could serve this purpose, but it can also greatly modify the rheological and functional properties of egg yolk. This research aims to assess the influence of citric acid on the rheological properties and microstructure of chicken egg yolk dispersions and their heat-set gels. The dispersions were prepared from fresh hen’s eggs yolks by adding water or citric acid to obtain a technical yolk (45 wt.% in solids) at the desired pH value. Viscoelastic measurements were carried out using a control stress rheometer, and microstructure was evaluated by cryo-scanning electronic microscopy (CryoSEM). An evolution of the viscoelastic properties of egg yolk dispersions from fluid to gel behavior was observed as the pH decreased until 2 but showing a predominantly fluid behavior at pH 3. The profile of viscoelastic properties along the thermal cycle applied is modified to a great extent, also showing a strong dependence on pH. Thus, the sol–gel transition can be modulated by the pH value.

Hyperbaric storage of egg white at room temperature: Effects on hygienic properties, protein structure and technological functionality

Fresh hen (Gallus gallus domesticus) egg white was submitted to hyperbaric storage at 200 MPa at room temperature for up to 28 days. Control samples were stored at 4 °C and 0.1 MPa. Storage conditions were compared for antimicrobial capacity towards inoculated (circa 4 log CFU g−1) Staphylococcus aureus and Salmonella enterica, and changes in physical, structural and functional properties. S. enterica was completely inactivated within 3 h of hyperbaric storage. Prolonged hyperbaric storage promoted slight egg white yellowing, probably due to non-enzymatic browning or riboflavin-protein decomplexation, and induced minor changes in egg white protein structure. Partial conversion of ovalbumin into S-ovalbumin led to slightly decreased gelling capacity. Pressurized egg white proteins also resulted slightly compressed and electrically stabilized, becoming more prone to solvent interactions. Based on these effects, viscosity of egg white increased almost 4-fold and foaming capacity increased by circa 35%. Our work demonstrated for the first time that hyperbaric storage guarantees safety and hygiene of egg white without detriment to its technological functionality. Industrial relevanceHyperbaric storage could represent an interesting alternative to refrigeration due to its capability to preserve food hygienic properties. Concomitantly, it could be used to pasteurize and even enhance technological functionality of protein-rich food ingredients. These goals could be achieved with negligible energetic consumption if working units were made viable for industrial application.

Physical and rheological properties of liquid whole egg after treatment of concentrated microwave field (CMF)

The influence of selected physical and rheological properties of the egg mass after the treatment of concentrated microwave field (CMF) was analysed in the study. CMF treatment can be generated in the continuous or pulsed way where microwave field is concentrated by a special waveguide. The raw material for the research was fresh hen eggs obtained from Leghorn Brown laying hens at the age of 30-50 weeks. The study investigated the effect of CMF pulses on the raw material, where the variable parameters were intervals between single pulses of 0.5 s, 1.0 s or 1.5 s, as well as 3 different numbers of CMF pulse packets for each of these intervals (5, 7 or 9). In this way, 9 research variants were obtained, not counting the control sample. After completion of the CMF treatment, the temperature of the samples was measured, and then they were cooled down to the temperature of 20 °C, where the analysis of active acidity (pH), color measurements expressed as L*a*b* and viscosity was performed. The results were statistically processed using the analysis of variations, Duncan’s test and the so-called “Response Surface Methodology” with corresponding Pareto charts showing the significance of the analyzed variables and their interactions. It was found that both the amount of energy supplied to the system and the intervals between the CMF pulses for most of the analyzed parameters had a statistically significant effect. The “response surface” models may have practical application, eg in industrial conditions, in determining the impact of individual technological parameters on the final quality of food products, including physical and rheological characteristics.

Single step separation and concentration of biomarker proteins using agarose based miniaturized isoelectric gates for point of care diagnostics

Bedside diagnostics using protein biomarkers requires rapid concentration, isolation and measurement of these specific biomarkers from a complex matrix in a low cost and portable manner. Traditional separation using gel electrophoresis separates the sample into all its constituent elements and requires high voltages and/or long runtime which is often unnecessary for diagnostics where only a specific biomarker needs to be quantified. Digital isoelectric trapping can be used to isolate and concentrate proteins but requires UV cured immobiline gels that have defined pH values and are not tunable to target specific proteins. Here, we have developed miniaturized isoelectric gates to separate, concentrate and quantify a targeted biomarker based on its isoelectric point, from a complex matrix in under 20 min. We designed specific isoelectric gates to concentrate and quantify bovine serum albumin (BSA) at a concentration of 1−5 mg/mL with a peak concentration of over 300 mg/mL, while maintaining its solubility. Next, we have demonstrated isolation of human protein C from a mixture with 1000-fold higher concentration of BSA with no additional processing. Finally, we have demonstrated rapid (< 20 min) separation, concentration and quantification of ovomucoid in a fresh hen egg using dual isoelectric gates at pH 3.9 and 4.3 to trap ovomucoid with an isoelectric point of 4.1 using a low applied voltage of only 15 V. By using low cost agarose gels instead of expensive immobilines, this device reduced the cost and complexity of separation. The combination of low-cost, tunability, fast-runtime, low-operating voltage makes this technique attractive for use in point-of-care biomarker detection without specific antibody tags.

A first approach using micellar electrokinetic capillary chromatography for the determination of fipronil and fipronil-sulfone in eggs.

Fipronil is an insecticide that is not approved in the European Union in food. In 2017, fipronil was involved in a European health alert due to its presence in fresh hen eggs because of an illicit use in poultry farms, so reliable methods are needed to determine fipronil and its main metabolites in these matrixes. In this work, we report the first approach to the study of fipronil and two metabolites, fipronil-sulfone and fipronil-sulfide by CE. MEKC mode was employed using a solution of 50mM ammonium perfluorooctanoate pH 9.0 with 10% (v/v) methanol as background electrolyte. The proposed method was combined with a simple sample treatment based on salting-out assisted LLE (SALLE) using acetonitrile as extraction solvent and ammonium sulfate as salt. The SALLE-MEKC-UV method allowed the simultaneous quantification of fipronil and fipronil-sulfone. Validation parameters yielded satisfactory results, with precision, expressed as relative SD, below 14% and recoveries higher than 83%. Limits of detection were 90µg/kg for fipronil and 150µg/kg for fipronil-sulfone, so in terms of sensitivity further studies of sample treatments allowing extra preconcentration or the use of more sensitive detection, such as MS, would be needed.

Are Consumers’ Egg Preferences Influenced by Animal-Welfare Conditions and Environmental Impacts?

We conducted a labelled discrete choice experiment (DCE) to assess consumers’ preferences and willingness to pay (WTP) for fresh hens’ eggs produced via different production systems (caged, barn, free range, or organic). We estimated purchase intentions and WTP for different possible reductions (0%, 10%, 20%, and 30%) of greenhouse gas (GHG) emissions and water use in the egg production systems. Data were collected using an online open-ended questionnaire completed by a representative sample of 1045 Spanish egg consumers. The results of a random parameter logit (RPL) model showed heterogeneous preferences for different types of eggs with higher marginal utility and WTP for a production system ensuring higher animal welfare level, such as free-range eggs. However, consumers showed a lower preference for organic eggs at the actual market prices since they were unwilling to pay for this category of eggs. Moreover, there were positive marginal WTPs for reductions in GHG emissions and water use, but only for significant reductions (20% or 30%) with respect to the current situation. Potential buyers for free-range eggs were identified to be persons under 40 years old, persons with a monthly income of more than €1500, and persons who were pro-environment. Our findings provide producers, sellers and policy makers with useful information that may guide them in the development of successful communication and pricing strategies.

Detection of Residues of Antimicrobial Compounds in Eggs by the Rapid Screening Methods

Abstract Eggs belong to the most frequently consumed products of animal origin worldwide, and therefore the safety of eggs is a substantiated issue. Conventional poultry rearing involves the use of antimicrobials added to their feed or potable water particularly for disease treatment, however, in some countries also for the prevention of diseases, promotion of growth and better utilisation of the feed. Thus, effective control of residues of such substances in eggs is very important for the protection of the public health. The aim of this study was to detect the potential presence of antimicrobial residues in fresh hen eggs using commercially available rapid screening methods (Premi®Test and EXP Ampulle test) and compare the results of both of these tests. We examined 22 samples randomly selected from among 66 samples purchased in 11 European countries. We respected the procedures as supplied by the manufacturers of the tests together with their respective test kits. The examination of eggs by the Premi®Test did not detect the presence of antimicrobial residues in the samples, while the EXP Ampulle test provided 8 positive and 6 dubious results. Our results allowed us to conclude that the EXP Ampulle appears to be more sensitive and allows one to carry out more effective control of the presence of antimicrobial residues in hen eggs intended for human consumption.

Optimization of analytical strategies by Monte Carlo simulation: A case study in eggs for tracing their geographical origin using stable isotope signatures

Tailoring of an analytical method to make it fit for purpose is a basic philosophy that is now widely recognized in laboratory practice, but the application of fit for purpose principles usually remains vague. Generally, applicable guidelines based on measurement uncertainty are still lacking. Previous attempts to quantitatively assess fitness for purpose are either too complex for routine usage or too narrow in their scope as they neglect sampling uncertainty. In real-world situations, sampling uncertainty may exceed the uncertainty in the actual laboratory measurements substantially. Here, we have chosen the example of using measured natural variations in carbon and nitrogen isotopic composition as a tool to differentiate fresh hen eggs produced in Malaysia (δ15N = 3.52 ± 0.22‰; δ13C = −17.56 ± 0.82‰; n = 48) from eggs produced in Singapore (δ15N = 2.99 ± 0.22‰; δ13C = −17.56 ± 0.82‰; n = 27) to identify misdeclaration of eggs in possible scenarios of fraudulent import into Singapore during outbreaks of foodborne diseases. Monte Carlo simulations using standard spreadsheet software were pioneered for optimization of analytical strategies and to decide about quantitative threshold limits for sampling uncertainty and analytical uncertainty for the purpose of the investigation. Data analysis of simulated data yielded threshold limits for a minimal number of eggs to be analysed at a given precision of isotopic analysis for an intended level of statistical significance. The chosen Monte Carlo approach permits to optimize analytical strategies, in general, by matching restraints in available resources, available number of samples for analysis and target values for measurement precision in a quantitative manner.

Determination of Levels of Some Heavy Metals in Fish and Hens Eggs in Sudan

The concentration of the food stuffs by toxic metals is a threat and their exposure for long time has determinate effects on the health tutus of animals. Hen’s eggs and fish are one the main sources of protein but if contaminated by toxic heavy metals will cause a harmful effect on human health. This study aimed to assess the concentration of seven microelements performed by Atomic Absorption Spectrophotometer (AAS). Namely (Cadmium, Cobalt, Copper, Iron, Manganese, Lead, and Zinc) in tow samples of some animal products fresh (fish and hens egg) collected from the district popularly in Merowe-city-North Sudan. Heavy metals in hens eggs and fish samples were analyzed using (AAS) in accordance to standard analytical method data obtained were subjected to statistical analysis (ANOVA). To find out the significant difference of toxic heavy metals in fish sample the obtained results showed the average values Cd and Pb (0.100 and 0.720 mg/kg) respectively in fish sample were higher than permissible limits (p<0.05mg/kg) set by world health organization (WHO). The analysis of heavy metals in fish indicated among seven heavy metals tested, lead showed the highest concentration compered to levels essential elements followed by (0.170 for Co, 0.420 for Cu, 1.910 for Fe, 0.145 for Mn, and 2.685 mg/kg for Zn). Our results also showed that accumulation of heavy metals differed in the hens eggs sample recorded high levels of heavy metals found to Cd and Pb (0.070 and 0.305 mg/kg) respectively. The mean concentrations of essential elements followed (3.335 for Zn, 2.200 for Fe, 0.195 for Cu 0.090 for Co, and 0.070 mg/kg for Mn) respectively. Concentrations in sample of the studied fish showed that there were highly significant different between the Cd and Pb (0.100 and 0.720 m/kg) than hens eggs (0.070 and 0.305mg/kg).

Characterization of Probiotic Lactobacillus plantarum MYS14 Isolated from Sannas, a Traditional Fermented Food for its Therapeutic Potential

Background: Traditional fermented foods are a typical niche for probiotic Lactic Acid Bacteria (LAB) and are involved with many therapeutic attributes. Among LAB, Lactobacillus plantarum is one of the most versatile members. Several L. plantarum strains have been documented for their probiotic attributes. There are limited reports on the evaluation of probiotic potential along with the therapeutic properties such as antioxidative ability. With this background, the present study was carried out to screen ‘Sannas’ which is collected from the Coorg region of Karnataka state, India, in the presence of potential probiotic L. plantarum strains for their therapeutic potential. Methods: Sannas was screened for the potential probiotic strains and identified using physiological, biochemical and molecular methods. A series of probiotic attributes were assessed for the selection of potential probiotic strains. Further, the potential probiotic strains were assessed for the in vitro antibiofilm activity against Pseudomonas aeruginosa MTCC 7903. In addition, the cholesterol lowering ability of the potential probiotic strain using four-percent commercial fresh hen egg yolk as the cholesterol source. On the other hand, the in vitro antioxidant activity was also determined by a series of assays. Furthermore, the toxicity assessment was also done by the mitotic index using onion root tips as the source of chromosomes. Results: L. plantarum MYS14 isolated from an unexploited traditional cereal-based fermented food had good functional probiotic attributes and the antibiotic susceptibility was an intrinsic feature, thus consumption of this strain does not possess any health risk to humans and animals. In addition, the strain exhibited strong radical scavenging activity which might be useful in controlling or slowing the progress of several oxidative stress related disorders. On the other hand, the strain also exhibited better cholesterol assimilation, antibiofilm ability and the mitotic index revealed the non-toxic effect of the CFS. Conclusion: The probiotic therapy is gaining significant research interest in relation to gut microbiota in an attempt to better understand the therapeutic potential of probiotic strains isolated from unexploited traditional cereal based foods. It is confirmed that this L. plantarum MYS14 strain possesses several characteristics suitable for the production of various antioxidant probiotic products. Collectively, the results suggest that L. plantarum MYS14 may be used as probiotic strain for therapeutic applications.

Analysis of radiofrequency lesions in egg whites in vitro produced by application of the Tew electrode for different temperatures and times.

Understanding the size and shape of radiofrequency lesions is important to reduce side effects when applied to patients. To investigate the radiofrequency lesions produced by the application of the Tew electrode for different temperatures and times. The white from a fresh hen's egg was placed in a rectangular glass container and warmed to 37 °C. After immersion of the Tew electrode in the egg white, radiofrequency lesions were produced at 65 °C, 70 °C, 75 °C, 80 °C, 85 °C and 90 °C. For each temperature, photographs were taken at 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s and 120 s. The size of the lesion was measured at each temperature and time. A mixed model was used to analyze the data. The size of the lesion increased with increasing temperature and time. There were statistically significant differences in the size of the internal radius between the 65 °C and 70 °C groups and the 70 °C and 75 °C groups, as well as in the 70 °C and 75 °C groups in the size of the external radius and the 60 °C to 80 °C groups in the size of the distal radius. The maximum lesion size was produced at 90 °C and 120 s, and was 1.06±0.16 mm in internal radius, 0.37±0.15 mm in external radius, 0.39±0.04 mm in distal radius. The Tew electrode produces lesions following the contour of the tip, and the internal radius is larger than the external and distal radius. The best combination of temperature and time for lesioning using the Tew electrode is 80 °C, for 60 s to 90 s.

Photopyroelectric assessment of the thermal effusivity of fresh hen egg and of rehydrated egg powders

The availability of thermo-physical data of foods and their constituents is of general importance to food industry. The thermal effusivity e is one among the relevant thermodynamical quantities. The latter is normally calculated from the relationship e = (κρc)½, where c is specific heat, ρ is the density, and κ is the thermal conductivity. The necessity for performing the time consuming independent measurements of these three quantities is the major reason that the existing database with effusivity of foods is not very wide. This paper describes the application of the inverse photopyroelectric (IPPE) technique that allows the determination of effusivity from a single measurement. This approach was used to directly measure thermal effusivity of fresh egg yolk, egg white, and white/yolk blends. In addition, thermal effusivity of rehydrated egg powders (white, yolk, and the whole egg powder) has been measured and compared to that of the fresh hen egg. In case of the egg white, effusivity of rehydrated egg powders was practically the same as that of the fresh egg. However, the difference in effusivity between fresh egg yolk and rehydrated egg yolk, and between the blend of fresh egg and the rehydrated whole egg power was significant. Finally, thermal effusivity of rehydrated egg yolk, egg white, and the whole egg powder was determined as a function of dilution factor.

Molecular typing of avian pathogenic Escherichia coli colonies originating from outbreaks of E. coli peritonitis syndrome in chicken flocks

Escherichia coli colonies isolated from the bone marrow of fresh dead hens of laying flocks with the E. coli peritonitis syndrome (EPS) were genotyped using pulsed-field gel electrophoresis (PFGE). Typing is important from an epidemiological point of view and also if the use of autogenous (auto)vaccines is considered. Birds with EPS originated from one house of each of three layer farms and one broiler breeder farm. Farms were considered as separate epidemiological units. In total, six flocks were examined including two successive flocks of one layer farm and the broiler breeder farm. E. coli colonies (one per bird) from nine to 16 hens of each flock were genotyped. The clonality of E. coli within birds was studied using five colonies of each of nine to 14 birds per flock. E. coli genotypes, which totalled 15, differed between farms and flocks except for two successive layer flocks that shared three genotypes. One to five genotypes were found per flock with one or two genotypes dominating each outbreak. Within hens, E. coli bacteria were always clonal. Colonies of the same PFGE type always had the same multilocus sequence type. However, four PFGE types shared sequence type 95. Neither PFGE types nor multilocus sequence types were unambiguously related to avian pathogenic E. coli from EPS. In cases where persistence of E. coli strains associated with EPS is found to occur frequently, routine genotyping to select strains for autovaccines should be considered.

Observation of true and pseudo NOE signals using CEST-MRI and CEST-MRS sequences with and without lipid suppression.

To investigate the characteristics of nuclear Overhauser enhancement (NOE) imaging signals in the brain at 7T. Fresh hen eggs, as well as six healthy, and six C6 glioma-bearing Wistar rats were scanned using chemical exchange saturation transfer-magnetic resonance imaging (CEST-MRI) and chemical exchange saturation transfer-magnetic resonance spectroscopy (CEST-MRS) sequences (saturation duration 3 s, power 1.47 µT) with and without lipid suppression. CEST data were acquired over an offset range of -6 to +6 ppm relative to the water resonance in 0.5 ppm steps. The water signals were not disrupted by other protons during the CEST-MRS sequences, and true NOE signals could be observed. Using the CEST-MRI sequence without lipid suppression, pseudo NOE imaging signals were observed in the lipid-containing regions (egg yolk, scalp, and even white matter). These pseudo NOE signals were almost (but incompletely) removed with the lipid suppression. Egg yolk results indicated the presence of the NOE to olefinic protons overlapping with the water signal. In vivo experiments showed that the amide proton transfer signal was larger in the tumor, whereas the NOE signal was larger in the normal white matter. True NOE signals can be detected using MRS sequences, and considerable pseudo NOE imaging signals may be observed using MRI sequences.

Deliberation and Precipitation

In an issue of Common Knowledge given over to experiments in scholarly form and to the discussion of them, this piece is one of three on the genre of microhistory. The other two (by Natalie Zemon Davis and Sir Keith Thomas) argue the merits and demerits of the genre, while this piece seeks to exemplify both its virtues and its risks. To show how microhistory offers intense deliberation on a narrowly defined topic, yet also a kind of hastiness — an impatience with demands for broader scope — Colin Richmond examines one limited facet of the relationship between two Americans resident in England at the turn of the last century: the novelist Henry James and the painter Edwin Austin Abbey. Detailed evidence is mustered to document James's love of fresh hens' eggs and of the undignified lengths he would go to obtain them through the agency of Abbey and his wife. This short piece is written as if a parable, and while its moral goes unstated, the reader's attention is drawn to the unsettled question of whether James exerted maximal effort for minimal results, or whether he knew something about the value of freshness undreamed of by those more patient and dignified in pursuing their desires.

Purification of Immunoglobulin of Egg Yolk with Hydrophobic Charge Induction Chromatography: Comparison of Operation Modes with Packed Bed and Expanded Bed

Immunoglobulin of egg yolk (IgY) was separated from fresh hen eggs by three steps, water dilution, salt-out precipitation, and hydrophobic charge induction chromatography (HCIC). In the purification step, HCIC was used as a novel technology and two chromatographic operation modes, packed bed and expanded bed, were compared to improve the separation efficiency. For packed bed mode, IgY were separated with the purity of 92% and the recovery of 58.4% at the operation condition of pH 7.5 and sample (total protein concentration of 11.6 mg/mL, IgY purity of 31%) loading of 0.2 mL/mL adsorbent. For expanded bed mode, a similar purity of 90% and the recovery of 59.5% were found at the fluid velocity of 500 cm/h and same sample loading of 0.24 mL/ mL adsorbent at pH 7.5. The results demonstrated that HCIC in expanded bed mode is a potential platform technology for antibody separation both in high efficiency and low cost.

Inoculating Poultry Manure With Companion Bacteria Influences Growth and Development of Black Soldier Fly (Diptera: Stratiomyidae) Larvae

The growth and development of black soldier fly, Hermetia illucens (L.), larvae fed chicken manure inoculated with bacteria isolated from black soldier fly larvae and associated larval feed was evaluated. Four strains of Bacillus subtilis were evaluated. B. subtilis strains S15, S16, S19, were isolated from the gut of black soldier fly larvae. B. natto strain D1 was isolated from the diet fed to black soldier fly larvae. These bacteria were added individually into nonsterile 200 g fresh hen manure at 10(6) cfu/g and homogenized. Treated manure was then inoculated with 4-d old black soldier fly larvae. Prepupal weight ranged from 0.0606 g in the control to 0.0946 g in manure treated with the S15 strain. Larval survivorship to the prepupal stage in all treatments ranged from 98.00 ± 2.65% to 99.33 ± 1.15%. Prepupal survivorship to the pupal stage ranged from 91.92 ± 1.87% to 97.95 ± 1.03%. Adult emergence from the pupal stage did not significantly (P < 0.05) differ across treatments and ranged from 98.95 ± 1.82% to 100.00 ± 0.00%. Adult body length resulting from the larvae in each of the treatments was significantly greater than those from the control. Longevity of adults did not differ significantly between treatments. Time from hatching to the development of the first pupa did not differ significantly across treatments; however, development time from hatching to 90% reaching the prepupual stage was significantly different between treatments and ranged from 29.00 ± 1.00 d to 34.33 ± 3.51 d. Development time from hatching to 90% reaching the adult stages was significantly different between treatments. Our results demonstrate that inoculating poultry manure with bacteria from black soldier fly larvae influences the growth and development of conspecific larvae feeding on the manure.

A study into measuring the antibacterial activity of lysozyme‐containing foods

PurposeThe purpose of this paper is to provide food science or biology students with a simple and reliable method of determining the antibacterial activity of a range of foods and biological materials that contain lysozyme.Design/methodology/approachThe antibacterial effects of the materials reported to contain lysozyme were assayed by gel‐diffusion using the lysozyme‐sensitive bacterium Micrococcus lysodeikticus. The antibacterial effects of the selected test materials, namely fresh hen egg‐white, human saliva, Brussels sprouts, papaya and figs were compared against standard solutions of proprietary analytical crystalline hen egg‐white lysozyme.FindingsThe antibacterial activity of the test substances was similar to the effects of their lysozyme concentrations as quoted by other workers.Research limitations/implicationsAntibacterial activity was higher in avian egg‐white and human saliva than in the assayed plant material. Measurement of the activity in the plant material was at the limits of the sensitivity of the method.Practical implicationsThe two main practical methods for measuring lysozyme are either a gel‐diffusion assay or a spectrophotometric procedure. Gel‐diffusion assay provides a convenient procedure for student investigative work as it has a limited requirement for method development. Additionally, it is simple, cheap, reproducible and does not require specialist equipment. Further possible investigations for students are suggested.Originality/valueThe paper builds on established techniques to provide a procedure that is appropriate for student use for determining lysozyme activity in a variety of biological materials.

Dielectric characterization of hen eggs during storage

Changes of the dielectric parameters of fresh hen eggs during storage were investigated for the development of a method to assess the main quality indices. Dielectric constant ( ε′) and loss factor ( ε″) were measured in the frequency range 20–1800 MHz using an open-ended coaxial probe on thick albumen and yolk of eggs after 1, 2, 4, 8 and 15 days of storage at room temperature. Tests were also carried out at the 9th day of storage to compare dielectric properties of thick and thin albumen. Statistical analysis was performed at 20, 100, 400, 900 and 1800 MHz. Thick and thin albumen showed slight differences in dielectric properties but significant only for ε″ at 900 MHz. Dielectric constant and loss factor of yolk generally increased with the storage time. The maximum increment from the 1st to the 15th days of storage (22%,) was registered for ε″ at 20 MHz. Methods based on the comparison between the experimental ε″ and calculated values by means of conductivity and frequency can potentially be used in predicting eggs’ age.