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Methods to evaluate egg freshness in research and industry: A review

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Abstract

The modern poultry industry is not satisfied with the traditional system of the handling and processing of eggs which is based on candling and visual inspection of the eggs. Currently, the operator of the conveyer does not have the opportunity to inspect 120 000 eggs per hour and to estimate the freshness, weight, bacterial infection, presence of technical spoilage, eggshell defects without elimination of subjectivity, fatigability and destruction. That is why the problem of automatization of egg quality control is rather difficult. In order to assure a high and consistent egg quality, an attractive and alternative strategy for determining the state of egg freshness can be achieved by sensors technologies. These techniques (e.g., near-infrared, mid-infrared, fluorescence spectroscopies, etc.) appear to be very promising for non-destructively determining egg freshness because they are relatively not expensive. Such methods cannot eliminate the need for more detailed physico-chemical analyses, but they may help to screen samples that require further examination.
Eur Food Res Technol (2006) 222: 727–732
DOI 10.1007/s00217-005-0145-4
REVIEW ARTICLE
Romdhane Karoui ·Bart Kemps ·Flip Bamelis ·
Bart De Ketelaere ·Eddy Decuypere ·
Josse De Baerdemaeker
Methods to evaluate egg freshness in research
and industry: A review
Received: 10 June 2005 / Revised: 15 August 2005 / Accepted: 20 August 2005 / Published online: 13 December 2005
C
Springer-Verlag 2005
Abstract The modern poultry industry is not satisfied
with the traditional system of the handling and processing
of eggs which is based on candling and visual inspection of
the eggs. Currently, the operator of the conveyer does not
have the opportunity to inspect 120 000 eggs per hour and to
estimate the freshness, weight, bacterial infection, presence
of technical spoilage, eggshell defects without elimination
of subjectivity, fatigability and destruction. That is why the
problem of automatization of egg quality control is rather
difficult. In order to assure a high and consistent egg qual-
ity, an attractive and alternative strategy for determining the
state of egg freshness can be achieved by sensors technolo-
gies. These techniques (e.g., near-infrared, mid-infrared,
fluorescence spectroscopies, etc.) appear to be very promis-
ing for non-destructively determining egg freshness be-
cause they are relatively not expensive. Such methods can-
not eliminate the need for more detailed physico-chemical
analyses, but they may help to screen samples that require
further examination.
Keywords Egg quality .Egg freshness .Non-destructive
techniques
Introduction
Freshness makes a major contribution to the quality of egg
and egg products. One of the most important objective in
the food industry is that of achieving a uniform quality
both of raw materials and of the final product. One of the
main concerns of the egg industry is the systematic determi-
nation of egg freshness, because consumers may perceive
variability in freshness as lack of quality. Egg white and egg
yolk are extensively utilised as ingredients because of their
R. Karoui ()·B. Kemps ·F. Bamelis ·B. De Ketelaere ·
E. Decuypere ·J. De Baerdemaeker
Egg Quality and Incubation Research Group,
K.U. Leuven Kasteelpark Arenberg 30,
3001 Leuven, Belgium
e-mail: Romdhane.Karoui@biw.kuleuven.be
Tel.: +32(0)16321470
Fax: +32(0)16328590
unique functional properties, such as gelling and foaming.
Foams are used in the food industry for the manufacture of
bread, cakes, crackers, ice creams, etc. Hen egg yolk has
good emulsifying properties. The foaming and emulsifying
properties of albumen and yolk respectively are affected by
protein concentration, pH, ionic strength. The changes that
occur in egg during storage are many and complex and af-
fect the functional properties of egg yolk and egg albumen.
These changes includes: thinning of albumen, increase of
pH, weakening and stretching of the vitelline membrane
and increase in water content of the yolk.
Freshness can be explained to some extent by some objec-
tive sensory, (bio)-chemical, microbial and physical param-
eters and can therefore be defined as an objective attribute
[1]. Knowledge of the various descriptors of properties
that are encountered in egg immediately after lay must be
known as well as the changes in properties that take place
over time. This information can be gained by performing
controlled storage experiments that extend from the time
after lay, loss in freshness and spoilage can thus be moni-
tored; once dynamics and the rate of various changes that
occur have been measured, the next step is to try to develop
a model in order to determine age of commercial shell eggs
in terms of equivalent egg age or predicted the remain-
ing shelf life of an unknown sample. To achieve this aim,
it is useful to combine several measurements obtained by
different methodologies and correlate them with sensory
assessments, which are used to evaluate egg freshness. The
aim of this article is to review the potential of both destruc-
tive and non-destructive techniques for the evaluation of
egg freshness. Another goal is the development and appli-
cation of spectroscopic techniques as research tools for egg
products and sensors for on-line measurements.
Destructives egg freshness determination
Sensory evaluation
Sensory evaluation is defined as the scientific disci-
pline used to evoke, measure, analyse and interpret
728
characteristics of food as perceived by the senses of sight,
smell, taste, touch and hearing. Sensory tests can be di-
vided into three groups: discriminative test, which indicates
whether there is a difference between samples; descriptive
tests and affective tests [2]. Descriptive and discriminative
tests are objective analytical tests in which a trained panel
is used. Affective tests are subjective consumer tests that
are based on a measure of preference or acceptance. The
choice of method depends on the purpose of the applica-
tion of the sensory evaluation and whether it is used in
product development, quality control, consumer studies or
research.
Characteristic sensory changes occur in the appearance,
odour, taste and texture of egg during aging. Only few pa-
pers have underlined the effect of storage and temperature
on the sensory attributes of eggs. Campo et al. [3]have
used panellists to express their acceptability of the white,
yolk and whole raw egg on the visual appreciation, in a 0–
100 scale. In this research, the eggs were stored at different
temperatures (e.g., 4, 18 and 32 C) and at different days
of storage (e.g., 0, 7, 14 and 21 days).
For visual appreciation yolk acceptability, the researchers
reported that temperature was the main factor with influ-
ence on the evaluation of each parameter. Storage time has
also an effect but appeared less significant than temperature.
Indeed, panellists were able to appreciate clear differences
between, on the one hand, fresh egg yolks (68.9±7.3) and
those stored during 21 days at 18 C (45.6±8.5) and, on
the other hand, between fresh eggs yolks and those stored
during 7 days at 32 C. The appreciation of the yolk visual
aspect of eggs stored during 3 weeks at 18 C was signif-
icantly better (P<0.5) than those of eggs kept 7 days at
32 C[3]. However, panellists were unable to differenti-
ate the new-laid eggs from the eggs stored at 4C for any
length of time, which maintained its good yolk appearance.
Concerning albumen acceptability, the panellists were able
to differentiate between new-laid eggs and those stored at
18 and 32 C whatever the storage time (7, 14 or 21 days).
In a second step, the panellists were asked to evaluate
texture, white flavour intensity, white favour acceptability,
yolk aroma, yolk flavour intensity and yolk favour accept-
ability in a 0–100 scale. Regarding yolk texture, no dif-
ference were found between treatments in yolk aroma and
yolk flavour intensity attributes, while yolk favour accept-
ability attribute depend from the storage temperature and
storage time [3]; indeed, a significant difference were found
between new-laid egg from those stored during 18 days at
whatever the storage temperature (4 or 18 C).
Regarding albumen texture, significant difference were
found (P<0.5) between eggs stored for 21 days at 4 C
which had a high albumen consistency, and those stored
for 14 days at 18 C. Acceptability of white flavour was
better judged in new-laid eggs and those stored at 4 C
for 7 days than eggs stored 21 days at 18 C[3]. This
difference has been attributed to the degradation of suphur-
containing volatiles which are the main factor influencing
on the acceptability of albumen [4].
From the above study, the researchers concluded that
storage temperature had a higher effect on the acceptability
of eggs by a trained panel than the duration of its storage
especially for egg visual appreciation. However, the texture
of such eggs found to be dependent by both temperature and
time. Indeed, eggs stored under refrigeration can maintain
their sensory quality almost invariably up to 3 weeks from
date of lay, while those stored at 18 C lose a part of their
sensory quality after 2 weeks.
Physico-chemical methods
The characteristic of fresh eggs change during aging, being
influenced by both storage temperature and environmental
conditions (concentrations of O2and CO2, relative humid-
ity). The albumen has a major influence on overall interior
egg quality. Thinning of the albumen is a sign of qual-
ity loss. When a fresh egg is carefully broken out onto a
smooth flat surface, the round yolk is in a central position
surrounded by thick albumen. When a stale egg is broken
out, the yolk is flattened and often displaced to one side
and the surrounding thick albumen has become thinner, re-
sulting in a large area of albumen collapsed and flattened to
produce a wide arc of liquid. The most widely method used
for the determination of albumen quality is the Haugh Units
[5] which is based on determining both the weight on the
intact weight and the albumen height of a broken egg. The
Haugh Units has been reviewed extensively by Williams
[6], although many authors have criticised it [710] and
have shown that the adjustment of egg weight implied by
the Haugh Units is incorrect except possibly in the sample
of eggs determined by Haugh [5]. Indeed, Williams [6]re-
ported that the strain and age have an effect on the height
of albumen: the albumen height decreases when the age of
hen increases, even as the egg weight and the total amount
of albumen increase [11,12].
Another indices used to evaluate egg freshness is air cell
height which is affected by egg weight and storage relative
humidity [13,14]. Air cell height, the only quantitative egg
freshness parameter considered by the European Union reg-
ulation depends on the egg weight. Theoretically, a grade A
egg at packaging has to keep the characteristics of its grade
(air cell height <6 mm) up to expiring date. However, the
strong dependence of the air cell height from environmen-
tal relative humidity and temperature makes it difficulty to
guaranty the quality without a strict control of these two
variables throughout the whole egg marketing cycle.
The pH has been used to determine the egg freshness.
Hence, the pH of albumen from a newly laid egg is between
7.6 and 8.5 [15]. During the storage of shell eggs, the pH
of albumen increases at a temperature-dependent rate to a
maximum value of about 9.7 [16]. The rise in the albumen
pH is caused by a loss of carbon dioxide from the egg
through the pores in the shell. Indeed, the pH of albumen
is dependant on the equilibrium between dissolved carbon
dioxide, bicarbonates ions, carbonate ions and proteins.
Albumen refraction index, which consist to measure the
liquid concentration of albumen (index of refraction) by
utilizing the refraction phenomenon of light at the bound-
ary plane between the lane of a small prism exposed at a
729
part of the detection section of the refractometer and the
liquid to be measured, has also been used as an indicator of
egg freshness by Stanescu et al. [17]. However, this tech-
nique is too laborious and need a long time compared to
the measurements determined by pH and Haugh Units. Re-
cently, new chemical indices that increase both in albumen
and yolk during the storage of eggs (e.g., uridine and pyrog-
lutamic acid) have been considered as descriptors of shell
egg freshness [14]. Furosine, ε-N-(2-furoylmethl-l-lysine),
produced by acid hydrolysis of the Amadori compounds,
is a promising shell egg freshness index when determined
in albumen [18,19]. This index shows high repeatability
and low natural variability in fresh eggs and moreover, is
independent from egg weight, hen age and storage relative
humidity. Recently, Hidalgo et al. [20] have confirmed the
possibility of expressing shell egg freshness as equivalent
egg age, using furosine as a reference index.
Non-destructives egg freshness determination
Nowadays, the modern poultry industry is not satisfied
with the traditional system of the handling and process-
ing of eggs which is based on candling. That is why the
problem of automatization of egg quality control is rather
difficult. To reply to this request, non-destructive methods
for determining egg freshness have been proposed. Results
published in the last years showed that spectroscopic tech-
niques in combination with multivariate statistical methods
have broad application in the determination of egg fresh-
ness.
Infrared spectroscopy
Infrared radiation (IR) or the term infrared alone refers
to energy in the region of the electromagnetic radiation
spectrum at wavelengths longer than those of visible light,
but shorter than those of radio waves. The applications
of this technique for animal nutrition, agricultural and food
sciences have increased considerably in the last decade [21,
22].
Near infrared (NIR) spectroscopy is widely used for
the determination of organic constituents in feeds, foods,
pharmaceutical products and related materials. The tech-
nique is advantageous for many applications because it can
provide rapid, non-destructive and multi-parametric mea-
surements. The technique is also suitable for at-line and
on-/in-line process control. The NIR is based on the ab-
sorption of electromagnetic radiation at wavelength in the
range 800–2500 nm. NIR spectra of food absorption corre-
spond mainly to overtones and combinations of vibrational
modes involving C–H, N–H and O–H chemical bonds. At
present time, there are two technological ways to use NIR
technology: Near-Infrared Reflectance (NIRR) and Near-
Infrared Transmittance (NIRT). NIRR normally requires
sample grinding to obtain a uniform surface for measure-
ment of reflectance, while NIRT requires little or no sample
preparation. Consequently, NIRT is a faster and more re-
producible technique than NIRR. But NIRT is less sensitive
than NIRR. One of the strength of NIRR technology is that
it allows several constituents to be measured concurrently
[23].
In the sector of egg, the application of NIR for the deter-
mination of egg freshness is rather limited. Only a few stud-
ies have been published about the potential of this technique
to determine the egg freshness. The first publication on
measuring eggs by NIR addressed an early stage of Norri’s
work [24]. However, these measurements of freshness cov-
ered only a few hours of egg storage. The feasibility of
evaluating freshness of intact eggs in the course of 28 days
in storage was recently proved by Schmilovitch et al. [1].
The spectral region of wavelengths below 1100 nm is of-
ten called near-NIR. Usually, diode array spectrophotome-
ters cover the spectrum range below 1100 nm. Schmilovitch
et al. [1] have used near-NIRT to determine the freshness
of eggs. The results obtained from the Partial Least Square
(PLS) showed that the variables, days after hatching, air
chamber size, weight loss and pH could be predicted by
near-NIRT with a correlation coefficient varying between
0.9 and 0.92. However, these high correlation coefficients
refer to group means rather than to individual egg. Bamelis
[25] has used visible (VIS) in the range of 300–750 nm,
and NIR (in the range of 750–2500 nm) spectral analysis,
to monitor the freshness of eggs during storage; this author
showed a large variation between the spectra of individual
eggs in a batch. This variation depends on both internal
egg characteristics and shell characteristics. In addition, a
difference between time-dependent and time-independent
variability of the transmission spectra has been found be-
cause shell conductance, shell thickness and shape index
are correlated significantly with the time-independent vari-
ability [25].
Recently, Kemps et al. [26] assessed the potential of
VIS-NIRT spectroscopy to determine the internal quality
of eggs. A total of 600 eggs were monitored during storage
at 0, 2, 4, 6, 8, 10, 12, 14, 16 and 18 days. On the same
eggs and for the different storage time, Haugh Units and
pH were also measured. Using PLS, the correlation coeffi-
cients for the prediction of the Haugh Units and pH were
0.82 and 0.86, respectively. The obtained results show bet-
ter prediction of pH than Haugh Units. This could be due
as explained here above by the low exactitude to determine
the Haugh Units compared to the measurement of the pH.
The superposition of many different overtone and combi-
nation bands in the NIR region causes a very low structural
selectivity for NIR spectra compared to the mid infrared
(MIR) where many fundamentals can usually be observed
in isolated positions. Many overlapping signals is the NIR
give rise to a spectrum with broad peaks, making it difficult
to interpret compared to the conventional MIR spectrum
[27]. Starting from these explanations, it appears very dif-
ficult to study the secondary structure of egg proteins using
NIR.
MIR represents the spectrum of the absorption of all the
chemical bonds having an infrared activity between 4000
and 400 cm1. The acyl-chain is mainly responsible for
the absorption observed between 3000 and 2800 cm1,
730
whereas the peptidic bound C–NH is mainly responsible
of the absorption occurring between 1700 and 1500 cm1
[28]. Most of the absorption bands in the MIR region, but
not in the NIR region, have been identified and attributed
to chemical groups [27]. The triacylglycerols ester linkage
C–O (1175 cm1), C=O(1750 cm1) group and acyl
chain C–H (3000–2800 cm1) stretch wavenumbers are
commonly used to determine fat [29]. The infrared bands
appearing in the 3000–2800 cm1region are particularly
useful because they are sensitive to the conformation and
the packing of the phospholipid acyl chains [27,28,30,
31]. For example, the phase transition of phospholipids
(sol-to-gel state transition) can be followed by the MIR
spectroscopy [29]. Indeed, increasing temperature results
in a shift of the bands associated with C–H (2850, 2880,
2935 and 2960 cm1) and carbonyl stretching mode of the
phospholipids [29].
The development of Fourier transform infrared (FTIR)
spectroscopy in recent years also affords the possibility
of obtaining unique information about protein structure
and protein–protein and protein–lipid interactions without
introducing perturbing probe molecules [32]. The Amide I
and II bands (1700–1500 cm1) are known to be sensitive
to the conformation adopted by the protein backbone. The
secondary structures of proteins can be deduced from their
FTIR spectra since there are good correlations between the
Amide I band (1700–1600 cm1) and the levels of α-helix,
β-sheet and unordered structure in proteins [31].
Although the peptide bonds are essentially responsible
for the absorbance of proteins in the 1700–1500 cm1re-
gion, the side chains of several amino acids (glutamic acid,
aspartic acid, glutamine, asparagine, lysine, arginine and
tyrosine) can contribute to the signal in the Amide II region
[33]. The carboxylate groups of the side chains of aspartic
and glutamic acids absorb between 1580 and 1520 cm1.
However, as the whole fresh egg contained a considerable
amount of water, the water is absorbed in this region and
may affect the interpretation of the spectra. Water is a very
strong infrared absorber with prominent bands centred at
3360 cm1(H–O stretching band), at 2130 cm1(water
association band) and at 1640 cm1(the H–O–H bend-
ing vibration) [34]. Infrared spectroscopy can be used with
proteins in aqueous solution. Precise subtractions of the
H2O band are possible because of the frequency precision
achievable with FTIR. The subtraction of a large H2O band
from a large absorbance spectrum of protein in H2Otoget
a small spectrum of protein was difficult considering older
dispersive infrared spectrometers [35]. In addition, the de-
velopment of the attenuated total reflectance (ATR) device
allows the sampling problems encountered when collecting
spectra from opaque and viscous samples to be overcome.
It can be concluded that the MIR could be a suitable tech-
nique for monitoring the changes that occurred during the
storage of eggs.
Despite the advantage of MIR to study the secondary
structure of proteins, this technique was seldom used to
study the egg freshness. To our knowledge, only Narushin
et al. [36] have used diffuse infrared spectroscopy (5000–
640 cm1) to predict egg shell quality (e.g., shell thick-
ness, shell weight, shell fracture force, maximal deforma-
tion and shell stiffness). Among these parameters, shell
thickness was the best predicted parameter by MIR since
the correlation coefficient was 0.52. Accuracy of the pre-
diction of the shell maximum deformation (r=0.35–0.42),
the shell weight to surface area ratio (r=0.40–0.45), and
the shell stiffness (r=0.24–0.29) was slightly improved but
the difference between the correlation coefficients were not
significant.
Front-face fluorescence spectroscopy
Absorption of light by molecule causes the excitation of
an electron moving from a ground state to an excited state.
After the electron has been excited, it rapidly relaxes from
the higher vibrational states to the lowest vibrational state
of the excited electronic state. After reaching the lowest
vibrational state of the excited electronic state, the excited
state may decay to the ground state by the emission of a
photon (fluorescence). Due to energy losses, the emitted
fluorescence photon always carries less energy than the
absorbed photon [37,38].
Fluorescence spectroscopy offers several inherent advan-
tages for the characterization of molecular interactions and
reactions. First, it is 100–1000 times more sensitive than
other spectrophotometric techniques [39]. Second, fluores-
cent compounds are extremely sensitive to their environ-
ment. For example, tryptophan residues that are buried in
the hydrophobic interior of a protein have different fluo-
rescent properties than residues that are on a hydrophilic
surface [40]. This environmental sensitivity enables to char-
acterize conformational changes such as those attributable
to the thermal, solvent or surface denaturation of proteins,
as well as the interactions of proteins with other food com-
ponents. Third, most fluorescence methods are relatively
rapid.
If absorbance is less than 0.1, the intensity of the emitted
light is proportional to fluorophore concentration and exci-
tation and emission spectra are accurately recorded by clas-
sical right-angle fluorescence device. When the absorbance
of the sample exceeds 0.1, emission and excitation spectra
are both decreased and excitation spectra are distorted [40].
To avoid these problems, a dilution of samples is currently
performed so that their total absorbance would be less than
0.1. However, the results obtained on diluted solutions of
food samples cannot be extrapolated to native concentrated
samples as the organisation of the food matrix is lost [38].
To avoid these problems, the method of front-face fluores-
cence spectroscopy can be used.
Fluorescence probes or fluorophores represent the most
important area of fluorescence spectroscopy. Intrinsic flu-
orophores include the aromatic amino-acids—tryptophan,
tyrosine and phenylalanine in proteins, vitamin A and B2,
NADH derivatives of pyridoxal and chlorophyll, some nu-
cleotide, and numerous other compounds that can be found
at low or very low concentration in food [41,42]. The flu-
orescent properties of aromatic amino acids of proteins
[40,43,44] can be used to study protein structure or
731
protein-hydrophobic molecule interactions [44]. The major
proteins of egg contain at least one tryptophan residue, the
fluorescence of which allows the monitoring of the struc-
tural modifications of proteins during aging.
As mentioned above, fluorescent molecules are extremely
sensitive to their environment. For example, the emission
of tryptophan is highly sensitive to its local environment,
and is thus often used as a reporter group for protein confor-
mational changes [43]. Spectral shifts have been observed
as a result of several phenomena, such as tertiary structure
change, binding of ligands and protein–protein associa-
tion. In addition, the emission maxima of proteins reflect
the average exposure of their tryptophan residues to the
aqueous phase [43]. The fluorescence properties of trypto-
phan, along with its chromophore moiety-indol ring, have
been studied extensively due to its use as a standard optical
probe for protein structure and dynamics [45].
Vitamin A in egg yolk can be a good fluorescent probe
for the determination of protein–lipid interaction during the
storage of eggs. Indeed, in cheese, it has been reported that
the excitation spectra of vitamin A recorded between 250
and 350 nm with the emission wavelength set at 410 nm
[46] provide information on development of protein–fat
globule interactions during milk coagulation. In addition,
the shape of the vitamin A excitation spectrum is correlated
with the physical state of the triglycerides in the fat globule
[47].
Front-face fluorescence spectroscopy has been used ex-
tensively in the field of dairy products. However, in the liter-
ature, only preliminary studies explored the application of
front-face fluorescence for the determination of egg fresh-
ness [48]. This may be explained by the fact that eggs are
complex products containing numerous fluorescent com-
pounds, which makes it difficult to derive molecular infor-
mation from their spectra. Posudin [48] has assessed the
potential of front-face fluorescence spectroscopy to deter-
mine the freshness of egg. This author has used ultraviolet
radiation for the quality evaluation of eggs with different
level of pigmentation. The emission spectra of different
eggs showed two maxima located at 635 and 672 nm after
excitation at 405, 510, 540 and 557 nm. These excitation
wavelengths are related to the pigments of porphyrin nature
and porphyrin derivatives of florin and oxoflorin. The ob-
tained results showed that the intensity at 672 nm depends
on the egg freshness. Indeed, an egg shell emits vivid red
autofluorescence by ultraviolet radiation, because of the
presence of porphyrin on it. The autofluorescence of a fresh
egg is stronger than that of an old one because the intensity
of autofluorescence depends on the amount of porphyrin on
the shell surface. From these results, it was concluded that
fluorescence spectroscopy could be a promising approach
for quantitative estimation of porphyrin in eggs and thus to
determine the egg freshness.
Other techniques
Besides the above-mentioned techniques, other non-
destructive measurements have been investigated to deter-
mine the egg freshness. V¨
olgyi [49] has used microwave
sensors to determine the freshness of eggs and reported that
the microwave attenuation (water content) and the bistatic
radar cross section (dimensions) of eggs change during 30
days of storage. Their future plan will be the development
of a microwave device for the automatic selection of old
eggs. Using this equipment the quality control of eggs will
be very quick in contrast to the traditional method.
Dutta et al. [50] have used an electronic nose-based sys-
tem, which employs an array of four inexpensive commer-
cial tin-oxide odour sensors to analyse the state of the egg
freshness stored over a period of 20–40 days. These au-
thors have applied multivariate statistical analysis to define
regions of clustering in the multi-sensor space according to
the state of the freshness of eggs. Their results suggest that
it is possible to predict egg freshness into one of three states
with up to 95% accuracy. However, no explanation about
the chemical compounds that are involved in determining
the egg freshness was given.
The aging process of eggs implies many modifications of
high complexity, which take place simultaneously or suc-
cessively. As the whole fresh egg contains a considerable
amount of water; water plays an essential role in determin-
ing the structure of proteins. It is important to study the
dynamic properties of water and its interactions with other
components in the egg matrix. NMR relaxation and diffu-
sions measurements have been shown to give detailed infor-
mation on the state of water and to provide insight into the
dimensions and geometries of diffusive domains. Recently,
Dutta et al. [50] have investigated changes in molecular mo-
bility of water in eggs stored at different conditions varying
in combination of temperature (e.g., 5, 20 and 25 C), at-
mosphere (air, CO2) and lighting (dark, artificial light) at a
constant relative humidity of 60% by using nuclear mag-
netic resonance (NMR). During the first week of storage, an
exponential decrease in the transversal relaxation time has
been observed; afterwards, this parameter decreased lin-
early, especially at high temperatures [50]. The observed
modifications have been attributed to the changes in the
physico-chemical environments due to the structural rear-
rangements of protein matrix, contributing to the change
of water mobility during aging. These modifications were
found to be due to the increasing liquefaction of albumen
during storage [5052].
Conclusion
During the past few years, spectroscopic methods have
gained importance in the evaluation of food quality param-
eters. The advantages of spectroscopic methods are their
ability to provide rapid analysis and simultaneous evalua-
tion of several parameters, and their potential for on-line or
at-line. Although, fluorescence and infrared spectroscopies
are techniques whose theory and methodology have
been extensively exploited for studies of both chemistry
and biochemistry, the utility of these spectroscopies for
molecular studies has not been yet fully recognized in
food science and especially in the field of egg products.
732
Fluorescence and infrared spectroscopies have the same
potential to address molecular problems in food science
as in biochemical science field, because the scientific
questions that need to be answered are closely related.
The future aim of our group will be to assess the potential
of these two spectroscopic techniques (e.g., infrared and
fluorescence) for the evaluation of egg freshness. Then a
mathematical model for predicting the freshness, egg age
or remaining shelf life of an unknown egg sample will be
built. Such a model could complement both sensory and
physico-chemical analyses for egg freshness evaluation in
the near future. However, more research is needed; this
should include controlled storage experiments of different
strains of hen eggs to obtain valid parameters for use in
mathematical models.
The development of spectroscopic and microscopic
methods should also increase our understanding of the
determinants of food-texture and may allow to devise a
structure engineering of egg products.
Acknowledgements The authors acknowledge the financial support
of the research council of K.U. Leuven.
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... The variation of external environmental conditions (such as temperature, which is one of the most important factors in cold chain) is dynamic and unpredictable which will lead to various damages to perishable food [3]. However, during the transportation of eggs after laying, the egg aging process changes the physiological, chemical, nutritional and functional features of eggs, for instance, the loss of moisture evaporated through the shell pores and the escape of CO2 from albumen, which decreases the quality of egg during storage [4,5]. Therefore, it is important to monitor the condition of egg quality during the cold chain process to preserve the optimal condition of perishable food throughout the entire logistics process for the safety of the consumer [6]. ...
... Previous research reported that the HU is the index commonly used to evaluate egg freshness [13,16]. Most previous studies predicted that the HU value used temperature data since the freshness or quality of food is highly influenced by the storage time and conditions [5,35,36]. Akter et al. reported that the storage condition fluctuates by a variation of external factors, mainly temperature, humidity and time, which affect the HU of the egg [36]. In this study, we demonstrated that the weight loss has the potential to predict HU value instead of temperature. ...
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... Freshness Test of The egg(Karoui et al., 2006) ...
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Freshness is an important indicator for evaluating egg quality and is crucial for the food processing industry and consumers. The aim of this study is to non-destructively detect and visualize the freshness of eggs during storage by using hyperspectral imaging (HSI) and multivariate analysis. The hyperspectral images of egg samples with different storage time were collected in the spectral range of 401-1002 nm. A binary competitive adaptive reweighted sampling (BCARS) algorithm considering the synergetic effect among variables was proposed to select feature wavelengths from the whole spectral range and compared with competitive adaptive reweighted sampling (CARS). A slime mould algorithm optimized support vector regression (SMA-SVR) model was proposed to develop calibration models for HU (egg freshness indicator). Statistical analysis results indicated that the proposed BCARS had better feature extraction performance than CARS and the SMA-SVR model outperformed the compared models, in which the BCARS-SMA-SVR model yielded the best performance with a determination coefficient (R²) of 0.946 for calibration set and 0.914 for prediction set. Finally, by transferring the quantitative model to each pixel of hyperspectral image, the visualizing distribution map of HU was generated, providing an intuitive evaluation for egg freshness, which facilitates to the management of storage and marketing. The results provided the possibility of implementing a multispectral imaging for online monitoring of egg quality.
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The Haugh unit (HU) is the measure of albumen quality used by the poultry industry, but its correction for egg weight has been severely criticized. The validity of the correction for egg weight was investigated with an unwashed, unclassified sample of 800 eggs obtained from a commercial egg classification station. This sample was divided into four groups, one for study immediately and the others after storage at room temperature for 1, 2, or 3 wk. After weighing, each egg was broken and the height of the albumen was measured. Weights of the yolk, shell, and albumen were determined for each egg, and albumen pH was determined from pooled samples of three eggs each. Haugh units were calculated using the formula: HU = 100 log[H + 7.57 − 1.7W.37]. Statistical relationships between these variables were investigated. A weak relation (r2 = .04 to .07) between albumen height and egg weight was observed. Haugh unit score was dependent on albumen height (r2 = .88 to .95) but independent of either egg or albumen weight, except after 3 wk of storage and when all data were combined. Time in storage explained 78% of the variation in HU and 77% of the variation in albumen height. A regression model including both week and egg weight did not increase these R2 values. Changes in albumen quality over time in storage were described equally well by albumen height as they were by the HU score, suggesting that the HU correction for egg weight is unnecessary.
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Experiments were conducted to study the movement of water across the vitelline membrane of the hen’s egg during storage. Eggs refrigerated at 6°C. for 7 days had less yolk moisture, lower albumen pH and a higher yolk index than those held at room temperature, 27.5°C. Preventing gas exchange under both refrigerated and room temperature conditions resulted in a decrease in albumen pH and no change in yolk index over a 7-day storage period. When gas exchange was permitted, under these conditions, albumen pH increased and yolk index decreased. Yolk moisture decreased under closed, refrigerated conditions and increased under closed, room temperature conditions. Removing the egg from the shell and separating the yolk from the normal relationship to the albumen produced larger changes than leaving them in the shell. Yolks stored under refrigerated conditions in fresh thick albumen had less moisture than those stored in thin albumen. Aging the albumen at pH 8.9 resulted in yolks stored in thick and thin albumen having the same amount of moisture. No changes in yolk index or albumen pH could be attributed to storing in aged or fresh thick and thin albumen.
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It is frequently advantageous to consider the evolution of ideas and results when surveying a particular area of reseach since the early results often contain the fundamental outlines of a problem which subsequently become obscured by the later accumulation of detailed knowledge. The history of the development of protein fluorescence followed a logical pattern and so is quite suitable to discuss with a linear time scale. Because there are many experimental complications presented to investigators of the luminescence of biological macromolecules, each advance in knowledge was and is intimately associated with technological breakthroughs in measurement rather than with advances in theory. Also, because of considerable inherent difficulties in luminescence measurements, many of the initial observations announced were later shown to be in error. So, with apologies to friends and former colleagues for remembering the errors, it is hoped that a brief account of the development of the field will prove to be of value to those who are tempted to enter this difficult area, which is one so susceptible to serious errors.
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The development of the NIR technology definitely involved a team approach, although we did not really consider it a team when the work was being done. We were very fortunate to work on problems which had solutions, and to assemble enough talent to find some of the solutions, I wish to express my thanks to all who contributed to this effort.