Colour and pigments in Milk and Dairy

Abstract

This chapter surveyed different aspects related to milk and dairy colour characteristics. Appearance of dairy products is a complex topic involving many factors related to primary and transformation processing and storage conditions. As an aspect of the appearance of food, consumers are sensitive to product colour. In this context, colour measurement has become a useful tool for quality product and process management in the dairy industry. Several dietary factors have been identified as being responsible for the characteristics of the raw milk obtained. Milk contains different amounts of carotenoids that contribute to the nutritional and sensory properties of dairy products. Therefore, carotenoids are relevant in determining the colour of dairy products. In processed milk, raw milk characteristics are overlapped with processing parameters affecting colour stability as consequences of several reactions that occurred during the transformation process. In dehydrated diary products, the storage conditions determine the stage reached by the Maillard reaction and, therefore, the induced variations in colour. Emerging processing technology in food production is a growing field. Within these technologies, high pressure is the most developed and different types of devices are commercially available. Even though, high pressure technology is still not widely adopted by the industry sector. Dairy products treated with high pressure exhibit changes in colour characteristics that depend on both the pressure exerted and the time of exposure.

Full text

Milk and Dairy Products
Chapter XI
Colour and Pigments
Gabriela Grigionia,b,c, Andrea Biolattod, Leandro Langmana,c, Adriana
Descalzoa,c, Martín Iruruetaa, Roxana Páeze and Miguel Tavernae
aInstituto Tecnología de Alimentos, Centro de Investigación de Agroindustria, Instituto
Nacional de Tecnología Agropecuaria INTA, CC 77 (B1708WAB) Morón, Buenos Aires,
Argentina, ggrigioni@cnia.inta.gov.ar
bConsejo Nacional de Investigaciones Científicas y Técnicas CONICET, Av. Rivadavia 1917
(C1053AAY) Buenos Aires, Argentina
cFacultad de Agronomía y Ciencias Agroalimentarias, Universidad de Morón, Cabildo 134
(B1708JPD) Morón, Argentina
dEEA Concepción del Uruguay, Instituto Nacional de Tecnología Agropecuaria INTA Ruta
Provincial 39 Km 143,5 (3260) Concepción del Uruguay, Entre Ríos, Argentina
eEEA Rafaela, Instituto Nacional de Tecnología Agropecuaria INTA, Ruta Nacional 34 Km
27, CC 22 (2300), Rafaela, Santa Fe, Argentina

ABSTRACT
This chapter surveyed different aspects related to milk and dairy colour
characteristics.
Appearance of dairy products is a complex topic involving many factors
related to primary and transformation processing and storage conditions. As an
aspect of the appearance of food, consumers are sensitive to product colour.
In this context, colour measurement has become a useful tool for quality
product and process management in the dairy industry.
Several dietary factors have been identified as being responsible for the
characteristics of the raw milk obtained. Milk contains different amounts of
carotenoids that contribute to the nutritional and sensory properties of dairy
products. Therefore, carotenoids are relevant in determining the colour of
dairy products.
In processed milk, raw milk characteristics are overlapped with processing
parameters affecting colour stability as consequences of several reactions that
occurred during the transformation process. In dehydrated diary products, the
storage conditions determine the stage reached by the Maillard reaction and,
therefore, the induced variations in colour.
Emerging processing technology in food production is a growing field. Within
these technologies, high pressure is the most developed and different types of
devices are commercially available. Even though, high pressure technology is
still not widely adopted by the industry sector. Dairy products treated with
high pressure exhibit changes in colour characteristics that depend on both the
pressure exerted and the time of exposure.

11.1 INTRODUCTION
Colour is one of the attributes that affect consumer perception of quality. As
well as flavour and texture, they are considered to be major attributes that
contribute to the overall quality products. Hence, in the food industry, the
assessment of the colour has become an important part of quality product and
process management (Burrows, 2009).
In some foods, colour is the first criterion to be perceived by the consumer. As
stated by Burrows (2009), the repeated recognition of a particular brand of a
food commodity largely depends on its typical colour.
As an aspect of the appearance of food, consumers are sensitive to product
colour. Even though, preferences differ among and within countries. In many
European countries, a yellow colour in milk is associated with pasture,
bringing connotations of “natural” feeding (Prache et al., 2003 a or b). In
contrast, it is considered negative for certain colour-sensitive markets of the
Middle-East (Houssin et al., 2002 missing in refs list).
Food colour is the result of natural products associated with the raw material
from which it is processed and / or coloured compounds generated as a result
of processing (Morales and von Boekel, 1998). It is influenced by how the
food matrix interacts with light, regarding as its reflecting, absorbing or
transmitting characteristics, which in turn is related to its physical structure
and chemical nature (Kaya, 2002).
Colour measurements to characterize dairy products have been employed by
Rhim et. al. (1988 missing in refs list), Pagliarini et. al. (1990 missing in refs
list), Kneifel et al. (1992), Nielsen et al. (1997a, 1997b), Celestino et al.

(1997a, 1997b), Morales and van Boekel (1998), Priolo et. al (2003) and
Grigioni et. al. (2009 2009 is missing in refs list) to cite few examples.
In the following sections several aspects of colour characteristics in milk and
dairy product are screened. In the first one, some basic definitions are given.
In the second section, the relevance of colour pigment is presented. In the
third, the colour stability due to processing by conventional and emerging
technology is discussed. Finally, some conclusions are pointed out.
11.2 MEASUREMENT TECHNIQUES
The procedures used to describe colour are based on the specification of the
three stimuli. Due to the phenomenon of trichromacy, any colour stimulus can
be matched by a mixture of three primary stimuli in adequate amounts
(Guirao, 1980). This involves a process of integration. Clarity, tone and
saturation can be discriminated by an observer when seeing a colour. But in
contrast, the observer can not detail the spectral composition of the stimulus.
A colorimeter is used to evaluate in physical terms psychological feelings.
When a colour is described, the observer usually refers to attributes of
chromatic sensation as hue, lightness and saturation. In colorimetry these three
aspects are considered psychological correlates of the physical dimensions of
the stimulus.
Besides the reflectance spectrum, each colour can be identified by certain
independent coordinates. Using these coordinates it is possible to build colour-
spaces where each colour is represented by a point in that space.

CIE (Comission Internationale de l´Eclairage) is devoted to the world wide
cooperation and the exchange of information relating to the science and art of
light and lighting, colour and vision, photobiology and image technology
(http://www.cie.co.at). CIE derived the most used systems for colour
determination which are based on the use of standard illuminate and observer.
Among the several existing colour scales (Hunter Lab, XYZ system, etc.) CIE
recommended the CIELAB colour space that is a three-dimensional spherical
system defined by three colorimetric coordinates. The coordinate L* is called
the lightness. The coordinates a* and b* form a plane perpendicular to the
lightness. The coordinate a* defines the deviation from the achromatic point
corresponding to lightness, to red when it is positive and toward the green if
negative. Similarly, the coordinate b* defines the turning to yellow if positive
and to blue if negative (Perez Alvarez, 2006 missing in refs list).
11.3 IMPORTANT PIGMENTS IN MILK AND DAIRY PRODUCTS
Several dietary factors have been identified as being responsible for the
obtained raw milk characteristics. These factors include those associated
with the diet fed to animals. Among these, the nature and stage of maturity of
forage, the pasture system in use, the supplements given, the adaptation
periods and the energy balance have special significance.
Carotenoids are a family of more than 600 molecules that are synthesized by
higher plants and algae. They form the main group of natural pigments and are
natural pigment precursors of the yellow to red colour range in vegetal and
animal tissues. Plant carotenoids are transferred into animal products. As

stated by Noziére et.al. (2006b), carotenoids are involved in the nutritional and
sensory characteristics of dairy products, either indirectly through their
antioxidant properties or directly through their yellowing properties. Several
articles in the literature considered their potential as biomarkers for
traceability of products associated to feeding conditions. As a result, the
colour of dairy products highly depends on their carotenoid concentration.
Forages represent the main source of carotenoids for ruminants, where they
develop several functions including provitamin A function, antioxidant
function, cell communication, enhancement of immune function, and UV skin
and macula protection. Nearly 10 carotenoids have been identified in forages:
lutein, epilutein, antheraxanthin, zeaxanthin, neoxanthin and violaxanthin for
xanthophylls, all-trans ß-carotene, 13-cis ß-carotene and α-carotene (Calderón
et al., 2005 2005 or 2007), being the most quantitatively important ß-carotene
and lutein. Differences in the numbers of carotenoids described in forages
could arise from the variety of molecules in natural grasslands (Noziére et.al.,
2006b why b).
In cows’ milk, carotenoids principally consist of all-trans- ß-carotene and, to a
lesser extent, lutein, zeaxanthin, ß-cryptoxanthin (Noziére et al., 2006b). Since
the amount of ß-carotene deposited in adipose tissue and/or secreted in milk
fat varies widely according to the carotenoid content in the feed, it plays a key
role in the sensorial and nutritional value of the final carcass and dairy
products.
Carotenoids are found in higher concentrations in milk produced through
grass-based diets, specially pasture. In grazing systems, a change in

carotenoids in milk in the course of time may depend on both the amount of
carotenoid intake and milk yield. (Calderón et al., 2005 or 2007).
In this context, diets based on grass, mainly pastures, lead to a higher
concentration of β-carotene in milk as compared to diets rich in corn silage or
concentrates (Havemose et. al., 2004; Martin et. al., 2004), since processing
greatly reduces their concentration (Reynoso et. al., 2004; Park et. al., 1983).
11.3.1 Milk colour
As reviewed by Chatelain et al. (2003 missing in refs list), milk colour
characterization is mainly applied to identify technological parameters such as
homogenisation, thermal treatment (including Maillard reactions), fat
concentration, photo-degradation, storage conditions or additives.
The white appearance of milk is the result of its physical structure.
The casein micelles and fat globules disperse the incident light and,
consequently, milk exhibit a high value of parameter L* (lightness).
Technological treatments that influence the physical structure of milk, also
have an effect on L*. The other colour components (parameters a* and b*) are
influenced by factors related to natural pigment concentration of milk.
Several studies concerning the instrumental measurement of colour in milk
and dairy products have been conducted. Some of them (Biolatto et. al., 2007;
Grigioni et. al., 2007) focused on the evaluation of the effect of the milking
season, obtaining a seasonal effect that was evidenced by the variations
observed in the levels of L* (lightness) and b* (blue-yellow component)
colour parameters.

Through a study by Prache and Theriez (1999), based on the
spectrophotometric properties of carotenoids accumulated in sheep milk and
plasma, the effect of diet on the concentration of β-carotene was shown. Thus,
it was possible to differentiate milk obtained from animals fed on diets
containing different levels of carotenoids.
Fijate esta conclusion de los franceses!!!! Si te parece incorporala
Noziere et al. 2006, obtained a weak relationship between milk carotenoids
and its yellow milk coloration. In a study using individual milk samples
analysed immediately after milking, milk carotenoids were responsible for
49% of the variability in the blue-yellow axis (‘b’). This relationship is similar
(R2 = 0.50) in the case of color measurements 2–3 days after the sampling of
bulk milks collected over a 1 year period in industrial dairy plants in the
Massif Central of France. This weak relationship demonstrates that a simple
color measurement cannot be accurately used to determine milk carotenoid
concentration.
As compared to diets consisting of silage, alfalfa-based diets provide a
substantially higher supply of -carotene, an effect that is entirely attributed to
the contribution of alfalfa pasture. Among carotenoid pigments, the β-carotene
and lutein provide the yellow colour. On this account, carotenoids could be
used as indicators of pasture production systems (Prache et al., 2003a, b).
Langman et al. (2009) reported changes in the colour of raw milk in a trial
which compared alfalfa- and silage-based diets fed to Holstein milk cows.
Briefly, the experiment was conducted during spring (October to December) at
the National Institute of Agricultural Technology in Rafaela (province of Santa

Fe, Argentina: 31º11’S; 61º30’W). During a first four-week pre-experimental
period, ten Holstein cows were fed on a silage-only diet with at least 50% of
forage; this diet also contained soy expeller and sunflower pellets (3.5 and 1.1
kg/d per cow, respectively) and hay (1.5 kg/d per cow). Thereafter, five cows
were randomly assigned to an alfalfa diet (at least 60% alfalfa of dry matter on
dietary basis) while another group remained as control, during 60
experimental days.
A significant increase of the -carotene content was observed after 20 days, a
tendency that was maintained at least up to 60 days after the change of diet
(Table 11.1), with dissimilar values in the range of 5-6 μg/g of fat (in milk
obtained from animals fed on alfalfa) vs. 1-1.4 μg/g of fat (in milk obtained
from animals fed on silage). These data are consistent with the results reported
by Calderón et al. (2007) where similar values of -carotene concentration
were observed in milk obtained from Montbéliarde dairy cows fed on diets
rich in carotenoids (67% on dry basis of grass-based silage).
Table 11.1- Effect of day of pasture in raw milk -carotene content. Means
plus standard deviations.
-carotene (g/g milk fat)
Days
0 20 40 60
Silage diet 2,4  0,4 1,1  0,2 0,9  0,3 1,4  0,4
Alfalfa diet 2,9  1,1 5,8  0,9 5,0  0,8 5,6  0,9
As regards the study of the b* colour component, raw milk corresponding to
the alfalfa-based diet showed significant differences only 60 days after

implementing the diet. These samples presented higher b* values, which
indicates a more yellow colour.
In order to summarize spectral results obtained from milk samples, several
authors use indexes that involve the study of the main pigments of milk. The
Integral Value (IV), as proposed by Prache and Theriez (1999), is a widely
used index that allows characterizing milk according to the diet fed to
animals based on the study of spectra in the wavelength range between 450
and 530 nm, corresponding to carotenoids absorption.
This index allowed a clear differentiation between milk obtained from cows
fed on silage and those fed on alfalfa pasture 20 days after changing their diet.
In contrast, the differentiation of milk obtained from animals fed on different
types of silage – when comparing, for example, sorghum-based and corn-
based diets- was not possible using IV. Figure 11.1 illustrates percentage
distributions after applying defined ranges. In the range of integral values
between 450 and 550, milk obtained from silage-fed cows accounted for 100%
of the cases. Also, milk obtained from fresh alfalfa-fed cows accounted for
100% of the cases in the range between 651 and 850. The only range of IV
values within which there was an overlapping between milk obtained from
both diets was that between 551 and 650.
Thus, it was observed that milk samples obtained from silage-fed cows
presented lower IV (450-550), while those from the diet based on alfalfa
pasture presented higher values (651-850).

0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
450-500 501-550 551-600 601-650 651-700 701-750 751-800 801-850
IV values
Alfalfa diet
Silage diet
Figure 11.1- Cumulative relative histogram of Integral Value (IV) determined
in raw milk under different feeding systems.
The results of this research match those obtained by Prache and Theriez or
Thierez (1999). These authors established that the IV was useful to
differentiate milk obtained from animals fed on diets with various carotenoid
levels. In this case, the IV index proved to be useful to distinguish between
milk from a hay- and concentrate-based diet (low in carotenoids) and milk
from a pasture-based diet (rich in carotenoids) 36 days after implementing the
diet. In contrast, after replacing a diet rich in carotenoids (grass-based silage)
with a diet low in carotenoids (hay-based diet), both b* component and IV of
milk did not allow to differentiate milk, even after 50 days.
In addition, a significant correlation of the IV was established with milk -
carotene content. Thus, this index also allowed differentiating milk rich in
carotenoids, such as -carotene, from milk with a low carotenoid content.

Integral value emerges like a promising tool in feed system traceability. Even
though, more research is needed in order to explore and explain its response
under different feeding conditions.
11.3.2 Dairy products colour
Milk carotenoids are transferred to butter and cheese with minimal losses and
hence contribute to their yellow colour. Since carotenoids and retinol are
soluble in fat, they mainly behave as milk fat. Nevertheless, a small proportion
of retinol and carotenoids are related with whey protein and / or concentrated
in the membrane of fat globules in milk. As a result, a certain amount of these
micronutrients may be lost to whey during cheese and butter processing
(Nozière et. al., 2006).
In addition, process-related factors are involved in the colour of butter and
cheese, such as ripening and storage environment (length, temperature, display
conditions, etc) or contamination by pigment-producing microorganisms.
Hurtaud et al. (2007) characterized the effect of hay and maize silage on the
sensory properties of butter. Physical measurements were done 14 days after
manufacture and the colour of the butter was measured with a Minolta
chromameter. The assay consisted of two trials in order to compare hay and
maize silages during winter of 2001 and 2002. Authors reported that hay diet
had little effect on butter colour and they observed that the dietary effect
differed between trials. This difference was detected instrumentally and
assessed by a sensory panel. Authors related the differences between the
butters from hay, elaborated in successive winter, with a greater loss of

pigments in one of the trial resulting from prolonged weather exposure and
greater loss of carotenoid pigments.
Kneifel et al. (1992) studied colour characteristics in butter samples that were
purchased from local retail outlets. These authors used a microcolor
tristimulus colorimeter with a 10° standard observer and D65 standard
illuminant (Dr Bruno Lange GmbH, Berlin, Germany). Colour differences
between summer and winter butter were reported and authors associated these
variations to differences in -carotene contents. Also, it was pointed out that
L*, a*, b* parameters were strongly influenced by the sample temperature due
to the temperature-dependent extent of fat crystallization.
In the literature several articles investigate the relationships between milk
characteristics and the sensory properties of cheese, especially those related to
animal feeding. As pointed out by Verdier-Metz et al. (2005), the effect of
upstream factors on cheese sensory properties depends on cheese varieties and
cheese making parameters such as partial skimming, pasteurization,
acidification kinetics or ripening time.
Cheese colour is dependent on forage composition. Milk contains variable
amounts of pigments and the variability in milk explains a high proportion of
the variability in dairy products. Feeding system has a marked effect on
carotene content in milk and therefore on the colour of cheeses (Coulon et al.,
2004).
Carpino et al. (2004) studied whether inclusion of native pastures in the diet of
dairy cows changes the colour, odour, taste, consistency, or mouth structure of

Ragusano cheese. Ragusano is a Protected Denomination of Origin cheese
produced in the Hyblean area of Sicily. Authors compared two different
feeding systems (pasture and total mixed ration, TMR) after 4 and 7 moths of
aging. A Macbeth Color-Eye Spectrophotometer (model 2020; Kollmorgen
Instruments Corp., Newburgh, NY) was used to measure the color of cheeses
using Hunter Lab scale and illuminate A. As result of the assay, cheeses made
from milk produced by cows that consumed native pasture were more yellow
than cheeses produced from TMR fed cows. Authors related this difference to
compounds transfer from pasture plants to cheese. Also, the reflectance spectra
were recorded. Significant differences in the amount of reflected light at 460,
480, and 500 nm were observed between pasture and TMR samples. The
absorbance maximum for β-carotene and related carotenoids are in this range.
11.4 COLOUR STABILITY DURING MILK AND DAIRY PRODUCTS
PROCESSING
11.4.1 Conventional treatments
Thermal treatments of milk have been successfully applied in industrial
practice, ranging from mild to severe ones. As expected, the more severe the
heat treatment, the more extensive the damage (Pereira et. al., 2009).
Dairy powders are sensitive to the Maillard reaction as they contain high
concentration of lactose and proteins with high lysine level (Palombo et. al.,
1984). In addition, relatively high temperature and water content during
processing and prolonged storage are the major factors involved in the high

susceptibility of dehydrated dairy products, as they are favorable conditions
for the Maillard reaction (Labuza, 1972).
During the manufacture process of milk powder, the heat treatment applied
prior to the concentration is very important because many of the physical,
chemical and functional properties of the powder for particular end-uses are
determined by the processing conditions used. Many physical and chemical
reactions occur at this stage (Singh and Newstead, 1998 missing in refs list).
For example, lactose can interact with many components of milk during heat
treatments, and most of the changes associated with lactose involve the
Maillard reaction.
Changes in the colour of whole milk powder (WMP), as regards the type of
thermal treatment applied to raw milk before drying, were objectively
evaluated by Grigioni et al. (2007). In this study, it was reported that WMP
obtained under indirect heat treatment (90-93 °C; 180 s = IHT) had
significantly lower L* values as compared to the values of WMP obtained
under direct heat treatment (105 °C; 30 s = DHT). The L* parameter indicates
the brightness of samples and depicts the capacity of an object to reflect or
transmit light. Furthermore, the authors showed that reflectance, the amount of
light reflected by a surface (Guirao, 1980) measured at 450 nm (r450),
followed the same behaviour as L*. The researchers pointed out that the
decrease in brightness may be due to the formation of brown pigments in
casein-sugar mixtures as a consequence of the Maillard reaction. In contrast,
as regards the application of thermal treatments, the b* parameter was found
to have an opposite behaviour to that of L* and r450. It was observed that

WMP obtained under IHT was prone to show higher b* values than WMP
obtained under DHT. The authors concluded that the combined action of
temperature and time during IHT contributed to the most noticeable changes
in colour since the Maillard reaction had reached a more advanced stage.
Ordóñez et al. (1998) reported that the greater the intensity of the thermal
treatment applied, the greater the chemical changes occurred, mainly
regarding the sensory quality and nutritive value. It is known that direct
heating processes usually result in less browning than indirect heating. This
occurs because indirect processes need a longer residence time in order to
reach working temperature, being the amount of heat applied on milk higher in
this type of treatments (Celestino et al., 1997b).
The storage conditions of dehydrated diary products determine the stage
reached by the Maillard reaction and consequently the shift of colour in
products (Labuza, 1972; Stapelfeldt et al., 1997).
Biolatto (2005) studied the shift of colour in WMP processed under indirect
high heat treatment (90-93 ºC; 180 s; denatured whey protein nitrogen index =
WPNI = 0.72 mg/g), packed in 400 g polyethylene bags contained in
cardboard boxes, and stored at 20 ºC ± 0.5 ºC during 6 months. This study
showed that, in general, the L* parameter of WMP processed from raw milk
produced in different seasons was not significantly affected during storage.
The exception was whole milk powder manufactured in spring which
presented a significant decrease (92.7 vs. 91.4; P < 0.05) of L* parameter
during storage. In addition, the b* parameter of WMP manufactured in autumn
and winter showed a decrease during storage (autumn: 21.5 vs. 19.6; P < 0.05

– winter: 21.4 vs. 18.4; P < 0.05). Contrary to autumn and winter WMPs,
WMPs manufactured in spring and summer were prone to show an increase in
b* value between the start and end of storage (spring: 18.3 vs. 21.2; P < 0.05 –
summer: 20.0 vs. 20.8). As regards the value of r450, autumn and winter
WMPs showed a statistically higher value by the end of storage as compared
to the start of storage. While for WMPs manufactured in spring and summer,
the r450 value at the end of storage was lower than that at the start of storage,
the difference between the start and end of storage was statistically significant
in spring WMPs. According to Kwok et. al. (1999), the measure of r450 may
be used to indicate brown pigment concentration. Renner (1988) pointed out
that during prolonged storage, the Maillard reaction occurs in a detectable
degree only when storage temperature is above 20 ºC.
In the same study, Biolatto (2005) evaluated the shift of colour in WMP
obtained under direct high heat treatment (105 ºC; 30 s; denatured whey
protein nitrogen index = WPNI = 1.16 mg/g), packed in 800 g aluminium cans
under an inert nitrogen atmosphere and stored at 20 ºC ± 0.5 ºC during 12
months. The results showed that although the value of L* parameter at the end
of storage was lower than the value at the start of storage, the differences were
not statistically significant (autumn: 93.3 vs. 93.2; winter: 92.7 vs. 92.6;
spring: 93.5 vs. 93.1; summer: 92.3 vs. 91.7). As regards the b* parameter,
although values corresponding to WMPs manufactured in autumn (18.4 vs.
19.3), winter (18.7 vs. 19.3) and spring (18.5 vs. 18.6) by the end of storage
were higher than those at the start of storage, such differences were not
statistically significant. Summer WMP, in turn, showed a significant decrease

in b* parameter (21.6 vs. 16.6) by the end of storage. The value of r450
showed a decrease when storage times (start and end) were compared in each
season (autumn: 59.8 vs. 59.1; winter: 58.0 vs. 57.6; spring: 60.2 vs. 59.4;
summer: 59.1 vs. 58.6); however, this decrease was not statistically
significant. Considering the general evolution of colour and reflectance
parameters, WMP processed under DHT, packed under a nitrogen atmosphere
and stored during 12 months, seems to have undergone no substantial change
in colour, which indicates that the combination of a less intense thermal
treatment and a nitrogen atmosphere might have contributed to preserve the
colour characteristics of WMP during the storage period. In addition,
according to Celestino et al. (1997a), whole milk powder packed in a vacuum
or inert atmosphere, such as nitrogen, may extend its shelf life over 12 months.
As describe by Schebor et al. (1999), Maillard reaction is one of the reactions
that might be affected by the glass transition phenomenon, since it can be
diffusion-limited. Milk powders may contain amorphous solids that can suffer
glassy-to-rubbery transition when they are stored at temperatures higher than
glass transition temperature (Tg).
Fernandez et al. (2003) analysed the glass transition temperatures of milk
powder with hydrolyzed lactose and regular milk powder. As part of their
study, authors analysed browning development in milk stored during 1 month
at 37 °C at different relative humidity using a spectrophotometer Minolta 508-
d (illuminant D65 and an observation angle of 2°). Authors concluded that Tg
values of the main carbohydrates do not account completely for the behaviour
of flowing characteristics and the development of nonenzymatic browning.

Other components in milk powder, like proteins and fat, may also be important
in the physical and the chemical stability.
Consumer perception of cheese is strongly related to its appearance and
texture, which in turn depends on microbiological, biochemical and
technological parameters that affect microstructure directly or indirectly
(Pereira, 2009).
Processed cheese is produced by heating a mixture of cheese, water,
emulsifying salts and optional ingredients, being its structure and sensory
characteristics determined by ingredients and processing conditions. Changes
with age can be influenced mainly by product composition, processing,
packaging and storage conditions like temperature and duration. In general,
this product is considered to have reasonable shelf life. However, shelf life
should be reduced by non-enzymatic browning or lipid oxidation during
storage at ambient temperature for long periods (Schär et al., 2002; Kristensen
et al., 2001). The relevance of nonenzymatic browning in processed cheese
was discussed by Berger et al. (1989), as cited by Schär et al. (2002). The
extent of the reaction is reduced by a lower lactose content, less severe heating
conditions and a lower storage temperature.
Bley et al. (1985) investigate how manufacturing practises and composition of
stirred-curd Cheddar cheese affect nonenzymatic browning. These authors
found a high correlation between galactose content and the brown colour
intensity and pointed out that faster cooling of processed cheese reduced the
intensity of brown colour.

Kristensen et al. (2001) studied the effect of temperature and light exposure on
the colour stability and lipid oxidation in processed cheese in simulated retail
(dark or under a light intensity of about 2000 lx) in a hot climate (one-year
storage period at 5 °C, 20 °C and 37 °C). Colour was measured by a Minolta
Tristimulus Chromometer CR-300 (Minolta Camera Co. Ltd., Osaka 541,
Japan). Authors pointed out that the most prominent change was browning of
the product, which depend strongly on storage temperature but not on
exposure to light. Each colour parameter changes linearly with time,
indicating a zero-order browning reaction. Lightness decreased while a* and
b* parameters increased during the storage.
11.4.2 Emerging technologies
High pressure (HP), power ultrasonics, and pulsed electric field are non-
thermal processing technologies with promising impact in food processing
(Smithers et. al., 2008). Among these technologies, HP devices are
commercial available since the 90’s while others are still at laboratory or
prototype scale.
Non thermal technologies were though for preservation purposes, enhancing
quality product due to the absence (or low) of thermal stress applied. A range
of other application is appearing in dairy systems, such improving process
effectiveness, ingredients differentiation, preservation of heat-labile bioactive
compounds, improving microstructure through component interaction,
between others (Smithers et al., 2008).

As stated by Pereira et al. (2009), high pressure (HP) has been proposed as a
suitable technology for milk treatment to substitute or in addition to thermal
treatment. This procedure has the advantage to produce minimal food quality
deterioration. However, it must be considered the effect upon milk constituents
and consequently on the final characteristics of dairy product.
In milk, the applied of HP treatment induced changes related to the
physicochemical properties of casein micelles and whey proteins: HP affects
intra molecular bonds either reinforcing or weakening them. HP produces
casein micelles disintegration into casein particles of smaller diameter that
increase the translucence of the milk, consequently a decrease in lightness,
reduce milk turbidity and increase viscosity (Trujillo et al., 2002).
Several authors suggest potential benefits to the dairy industry by HP
technology, especially in cheese manufacture and ripening; even though this
technology it is slowly adopted by the food industry.
Sheehan et al. (2005) investigate the effects of HP treatment on the
appearance, rheological and cooking properties of reduced-fat Mozzarella
cheese. Samples were treated at 400 MPa for 5 min at 21 °C, with rates of
compression and decompression of 300 MPa min-1. Once the HP treatment
was complete, samples were stored at 4 °C. Colour was measured at room
temperature on 2-cm thick, freshly cut cheese slices using a Minolta
Colorimeter CR-300 (Minolta Camera, Osaka, Japan), immediately after HP
treatment and after 75 days storage. Authors reported that HP treatment
resulted in a marked decrease in the L*-value (whiteness of cheese), in small
but significant increase in greenness and reduction in yellowness at the

beginning of storage. While, after 75 days no differences between treated
and no treated cheese were observed.
Rynne et al. (2008) examine the effect of HP treatment (400 MPa for 10 min at
room temperature), applied at 1 day post-manufacture, on a range of ripening
characteristics of full-fat Cheddar cheese. Colour was evaluated on the Hunter
Lab scale using a portable Minolta Colorimeter CR-300 (Minolta Camera Co.,
Osaka, Japan), immediately after HP treatment and after 42, 90 and 180 days
of ripening. Authors reported that HP treatment significantly decreased a
(green-red component) and increased b (blue-yellow component) values of the
cheese; while it had no effect on lightness. These changes in colour parameters
are consistent with the higher pH and lower levels of expressible serum in the
HP-treated cheese observed in the trail, both of which could contribute to
reduce casein hydration and thus altered light-scattering properties of treated
cheese.
Okpala et al. (2010) examine the effects of HP treatment on the physico-
chemical characteristics (colour, pH, fat, lipid oxidation, moisture, protein, and
texture) of a rennet-coagulated fresh Scottish cheese treated at a constant
temperature of 25 °C. Colour measurements were carried out immediately
after high pressurisation of fresh cheese samples using a LUCI™ 100
colorimeter Version 01-08-92 (Dr. Bruno Lange GmbH, D-14163 Berlin,
Germany). As a conclusion of the assay, authors advised that both pressure
applied and exposures influenced colour significantly in the HP fresh cheese.
The b*-parameter increased appreciably with increased pressure, and its
pronounced effect was significantly higher than the effect of the a*-parameter.

11.5 CONCLUSION
Colour of milk and dairy products depend on factors related either to primary
and transformation processes.
Carotenoids play a major role in colour of dairy products. The concentration
of carotenoids and retinol in milk depends on several dietary and non-dietary
factors, like animal breed and feeding management. In this context, feeding
systems are relevant in the nutritional and sensory quality of milk and dairy
products. Spectral characterization of milk using visible reflectance
spectroscopy appears to be a promising tool as a global approach in feed
system traceability.
Process-related factors are relevant in the colour of butter and cheese, such as
ripening and storage. The storage conditions of dehydrated diary products
determine the stage reached by the Maillard reaction, being the development
of brown colour an evident indicator of the extent of the reaction. Among the
emerging technologies, dairy products treated with high pressure exhibit
changes in colour characteristics that depend on both the pressure exerted and
the time of exposure.
Colour assessment yields objective and well-defined physical data on milk and
dairy products, being an important part of the product quality and process
management.
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