biochemical characteristics of ewe and goat milk (2011)
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Small Ruminant Research 101 (2011) 3340
Contents lists available at SciVerse ScienceDirect
Small Ruminant Research
j ourna l homepage: www.e lsev ier .com/locate /smal l rumres
Biochemical characteristics ofewe and goat milk: Effect on the qualityofdairy products
Marzia Albenzio , Antonella Santillo
Department of Production and Innovation inMediterraneanAgriculture and Food Systems, University of Foggia, ViaNapoli, 25, 71100, Foggia, Italy
a r t i c l e i n f o
Article history:
Available online 2 October 2011
Keywords:
Milk technological properties
Cheese quality
Texture
Flavour
Biofuncional molecules
a b s t r a c t
The objective ofthis review paper is to report research findings on the role ofmilk protein
and indigenous enzymes on the ability ofewe and goat milk to be processed and on the
quality ofdairy products. Emphasis is placed on the role ofcasein characteristics and of
indigenous enzymes on flavour, rheology, texture, and biofuncionality of ewe and goat
cheese.
Finally, the review highlights that further study is needed on milk protein genetic vari-
ants in ovine species, and on the role ofindigenous enzymes, especiallyminor proteolytic
enzyme systems, on the quality ofsmall ruminantsmilk and dairy products.
2011 Elsevier B.V. All rights reserved.
1. Introduction
Milk protein and indigenous enzymes impact directly
on the ability ofmilk to be processed and on the quality of
dairyproducts.Thecharacteristics ofcaseinin eweandgoat
milk are of particular interest due to the high number of
polymorphism thatare related to cheesemakingproperties
of milk. Indigenous enzymes in small ruminant milk have
receivedminor attention than bovinemilk and focused on
the principal enzyme complex as plasmin and lipoprotein
lipase. Ewe and goat milk is mainly processed to cheese,
which are in increasing demand, therefore there is a need
of knowledge on the role of indigenous proteoliytic and
lipolyticenzymes on thecheesemakingability andon their
effects onripeningprocess.Biofuncionalityin eweandgoatmilk and dairy products is a new and much unexplored
research field which could be of particular significance for
the exploitation of small ruminant production.
The purpose of the present review is to report the role
of casein characteristics and indigenous enzymes on (i)
This paper is part of the special issue entitled Products from Small
Ruminants, Guest Editedby A. Govaris andG.Moatsou. Corresponding author. Tel.: +390881 589327; fax: +390881 589301.
E-mail address:[email protected] (M. Albenzio).
cheesemaking properties of ewe and goat milk; (ii) the
quality of cheesewitha particular reference toflavour, rhe-ology, and texture.Moreover, recent research are reported
on biofunctional compounds in ewe and goat milk and
dairy products.
2. Influence of casein polymorphismon
cheesemakingproperties of ewe and goatmilk
The genetic polymorphisms of milk proteins are of
importance as they areassociated toquantitativeandqual-
itative parameters in milk. Protein composition affects
technological properties of milk especially in cattle and
goatswhile in sheep theresults arecontroversial (Giambra
et al., 2010). Genetic polymorphisms of milk proteins alsoplay an importantrole inelicitingdifferent degreesofaller-
gic reaction (El-Agamy, 2007; Park, 1994; Saini and Gill,
1991). Some studies revealed that goat milk (Bevilacqua
et al., 2001; Slacanac et al., 2010) can be considered as a
proper alternative to human milk due to hypoallergenic
properties of its proteins.
Extensive investigation in goat milk revealed the pres-
ence of high numbers of alleles at the four casein loci
(Albenzio et al., 2009a; Kpper et al., 2010; Moioli et al.,
2007; Sacchi et al., 2005; Roncada et al., 2002): the
casein polymorphism is associated with different casein
0921-4488/$ see frontmatter 2011 Elsevier B.V. All rights reserved.doi:10.1016/j.smallrumres.2011.09.023
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34 M. Albenzio, A. Santillo / Small Ruminant Research 101 (2011) 3340
synthesis levels and different rate of phosphorylation of
the peptide chain (Albenzio et al., 2009a; Grosclaude et al.,
1994; Martin, 1993; Park et al., 2007). Goat milk from
animals with strong alleles have been associated with
higher cheeses yields and firmer curds thanmilk fromani-
mals with weak alleles (Albenzio et al., 2009a; Clark and
Sherbon, 2000; Tziboula-Clarke, 2003). Also -CN poly-morphisms i.e. levelsof glycosylationandphosphorylation
affects the susceptibility of goat milk to clotting enzymes
(Amigo et al., 2000) with important technological impli-
cation by influencing the coagulation stages of renneting.
Albenzio et al. (2009a) set a multiple covariance analy-
sis including casein genotype, SCC, goat milk composition
as factors able to account for milk coagulation properties.
Results evidenced that caseingenotypewas the factor that
accounted for a significant percentage of the total vari-
ability for goat milk renneting parameters (i.e. r, k20 and
a30). The study of goat casein loci permits to differentiate
goat population on the basis of milk utilization: animals
with weak or null casein alleles should be used in breed-
ingprograms aimedatproducingmilkwith hypoallergenic
properties andanimalswith strongalleles to improvequal-
ity and properties of milk and related products (Albenzio
et al., 2009a; Roncada et al., 2002; Sacchi et al., 2005).
The knowledge ofmilk protein genetic variants ismore
fragmentary in ovine species and is still limited to s1-CN and -LG loci, giving less conclusive results than ingoats (Amigo et al., 2000; Barillet et al., 2005; Moioli et al.,
2007). For their low frequency, the effects of casein poly-
morphisms on dairy traits or technological properties of
ewe milk are too inconsistent for implementing selection
(Barillet et al., 2005). The study of ewe casein variants
represent an effective approach to identify association to
economic traits to improve sheep breeds for specific milk
protein production (Barillet, 2007; Giambra et al., 2010).
3. Role of indigenous enzymes on cheesemaking
properties of ewe and goatmilk
Recent reviewreportedfindingsaboutindigenousenzy-
matic activity in ovine and caprine milks in relation to
equivalent bovine milk enzyme (Moatsou, 2010). Indige-
nous enzymes ineweandgoatmilk aremainlyrepresented
by plasmin system, cathepsin D, elastase, and lipase. The
study of plasmin system and lipase is well documented
(Albenzioet al., 2004a,2005a,2009b;Battaconeet al., 2005;
Caroprese et al., 2007; Chvarri et al., 1998; Chilliard et al.,
2003; Cortellino et al., 2006; Fantuz et al., 2001) whereas
cathepsins and elastase in small ruminant have received
attention recently (Albenzio et al., 2009b; Moatsou et al.,
2008; Santillo et al., 2009b).
Indigenous proteolytic enzymes are mainly associ-
ated to leukocyte cells: polymorphonuclear neutrophilic
leukocyte (PMNL), macrophages, lymphocytes which are
groupedtogetherwithmammary epithelial cells and iden-
tified assomatic cells (SC). Plasmin activity isunder control
of a complex enzymatic system in which one of the plas-
minogen activators results associated with somatic cells
(Politis et al., 1991); somatic cells contain lysosomes that
release active proteloytic enzymes i.e. elastase, cathep-
sin and collagenase (Kelly andMcSweeney, 2002). Several
authors have reported that an increase in bovine milk
somatic cell count (SCC) causes an increase in the amount
ofmilk proteolytic activitywhich in turn reduces the yield
and quality of cheese (Ali et al., 1980; Grandison and Ford,
1986; Verdi and Barbano, 1991). It is worth to note that
milk from small ruminants is characterized by different
levels of total somatic cells and distribution of leuko-
cyte cell type than bovine milk (Albenzio et al., 2004a,
2009b; Caroprese et al., 2007; Chen et al., 2010; Cuccuru
et al., 1997; Morgante et al., 1996). Recently Albenzio and
Caroprese (2011) reported thatpolymorphonuclear leuko-
cytes (PMNLs) represent the main population detected in
ewe milk with high somatic cell count (>1106 cells/mL)
andthat this leukocyteclasscouldbeuseful todifferentiate
ewe milk cell count being strictly responsible for the SCC
increase.
Changes in somatic cell count in ewes and goats milk
are associated with breed, parity, stage of lactation, type
of birth, estrus, diurnal, monthly and seasonal varia-
tion (Gonzalo et al., 2005, 2006; Raynal-Ljutovac et al.,
2007). When stage of lactation and level of SCC (
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M. Albenzio, A. Santillo / Small Ruminant Research 101 (2011) 3340 35
Lipoprotein lipase (LPL) has an important role in milk
production in themammary gland. Indigenous LPL cataly-
sesthe hydrolysis of triglycerides producingfree fattyacids
(FFA). Chandan et al. (1968) reported that lipase activity in
ovinemilkis about one-tenth and ingoatmilk isabout one-
third than that of bovine milk. The hydrolysis pattern of
ovinemilk fat byovine LPL exhibits a higher rate of hydrol-
ysis towards triglycerides containing medium-chain fatty
acids than towards those containing long chain fatty acids
(Chvarri et al., 1998). Lipolysis in caprine milk results in
the characteristic goat flavour due to the strong presence
of C6:0, C8:0, and C10:0 free fatty acids esterified on car-
bon 3, which are abundant in caprine milk fat (Ha and
Lindsay, 1993). Goat milk lipolysis and LPL activity vary
considerable and in parallel across goat breeds and geno-
types (Chilliardet al., 2003); Delacroix-Buchet et al. (1996)
report thatLPL activity ishigher ingoatmilkwith theweak
s1-CN FF genotype than in the goatmilk with the strongAA genotype.
4. Characteristics of cheese quality
The objective of cheese ripening is to convert the fresh
curd to one of the many cheese varieties with various
appearance, taste, flavour, texture, and functionality char-
acteristics.All theseare involved in thedefinitionof cheese
quality and are related to the intensity of the ripening pro-
cess in terms of proteolysis, lipolysis, and glycolysis.
Raw milk compositional and biochemical characteris-
tics, milk technological treatment and renneting process,
curd production, ripening of mature cheese represent a
multiplicityof factors that impact, directly or indirectly, on
the quality of dairy products. Each factor of this complex
system is affected by the activity of enzymes originated
frommilk (i.e. indigenous enzymes and microflora), coag-
ulants, and starter andnon starter microflora.
The coagulants used for cheesemaking hydrolyses
casein producing the initial breakdown products from
s- and -CNs at different rate depending on the coag-ulant used. Regarding indigenous proteolytic enzymes it
has been reported that plasmin acts on -CN and -CNleading to the formation of the polypeptides 12 3-CN andproteose-peptone, and-CN degradationproducts(Albenzio et al., 2010). However, the hydrolyses of princi-
pal caseins proceeds differently along with ripening time
with-CNproducts being releasedwithinthe first phaseofripeningwhereas thecleavageof-CNstarts less readily asan outcome of the different specificity of protolytic agents
towards caseins (Albenzioet al., 2010; Irigoyenet al., 2000;
Revilla et al., 2007).
Casein degradation and casein degradation products
represent an important index of cheese ripening and
describe, together with changes in proteolytic enzyme
activity, a complex pattern of events occurring during
cheese ripening. However, all these parameters are influ-
enced by several factors therefore they are not easily
related. Albenzio et al. (2004a) found that in ovine fresh
cheese curd the decrease of plasmin (PL) and plasmino-
gen derived (PG) activities coincided with an increase in
nonprotein nitrogen (NPN) suggesting that NPNmolecules
derived from CN hydrolysis may be involved in the
regulation of PLPG enzyme system. Furthermore, as
reported in previous studies (Albenzio et al., 2005b, 2010;
Santillo and Albenzio, 2008) changes in the formation of
-CN mainly derived from plasmin activity were not syn-chronized with the changes in PL activity in the cheese
during ripening.
Cheesemakingtechnology isoneofthemainfactorsable
to affect indigenous enzyme level and activity. In Canes-
trato pugliese ovine cheese, production protocol includes
heating the curd in hot whey: the rise of temperature can
promote syneresisandinactivationofheat-labileinhibitors
of PL and of PG activators (Albenzio et al., 2007). The influ-
ence of cheesemaking technology on PL and PG activities
in fresh acid cheeses Caprino and Chevre and in semi-hard
cheeses (Tronchetto, Caciotta, and Fiore Sardo) evidenced
that the acid curds had lower PL and PG derived activities
than semi-hard cheeses. Cortellino et al. (2006) ascribed
this result to the effect of the thermal inactivation of the
cooking step on PL inhibitors in semi-hard cheese. Heat-
ing of milk at 90 C (whey protein precipitation) removes
inhibitors of PG activators leading to higher levels of PL
activity in Cacioricotta goat cheese (Albenzio et al., 2006).
Salting of fresh curd is a further step able to influence
enzymatic activity in cheese during ripening; in fact, salt-
ingdepressestheactivityofmost of theenzymes in cheese,
including indigenous milk proteinases such as plasmin
(Sutherland,2003). Fox (2003) reportsthat hydrolysis of-CN is strongly inhibited by a NaCl content in the cheese of
5%. In Canestrato pugliese cheese from ewemilka salt con-
centration of about 4%was able to inhibit -CN hydrolysisas indicated by the limited accumulationof small peptides
ascribed to -CNs over 45d of ripening (Albenzio et al.,2004b, 2005b). Also lipolytic activity appears to be limited
at NaCl> 13g/kg of cheese in Idiazabal cheese made from
raw ewes milk and natural rennet (Njera et al., 1994).
Level of FFA in cheese are an outcome of the lipolytic pro-
cessoccurring inewe and goat cheeses and depends on the
length of ripening time. Traditional ewe and goat cheeses
are manufactured using lamb and kid rennet paste which
contains lipolytic enzymes that comprise pregastric and
gastric esterases responsible for the liberation of short and
mediumchain FFA in the cheesematrix (Jacob et al., 2010).
The balance of different lipases in rennet paste influences
thelipolytic pattern ofcheeseduring ripening,withamajor
content of short chain fatty acids in correspondence to
highcontent ofPGE (Collins et al., 2003). Furthermore,sev-
eral studies (Albenzio et al., 2001; Gobbetti and Di Cagno,
2003) have reported a higher level of FFA in cheeses made
from raw milk compared to pasteurized or thermal milk.
Besidemilk indigenous LPL such differences are attributed
to lipaseandesteraseactivities of themilkmicrofloraespe-
cially non starter lactic acid bacteria (NSLAB).
5. Cheese flavour
Flavour of cheese is determined by its taste and aroma
and results from the correct balance and concentration of
numerous sapid and aromatic compounds perceived dur-
ing cheese consumption. Proteolysis and lipolysis are of
great importance in the development of cheese flavour
and are ruled by the residual milk clotting enzyme, milk
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proteinase and lipase, proteolytic and lipolytic enzymes
from starter and non starter bacteria, and lipases asso-
ciated to certain coagulants (Collins et al., 2003; Visser,
1993). However, excessive proteolysis and lipolysis could
result in off-flavours because high concentrations of bit-
terpeptides andvolatileFFA, respectively, influencecheese
flavoureitherdirectlyor asprecursorsof other compounds
(Broadbent et al., 2002; Pinho et al., 2004). Theamino acids
liberatedin thecheesematrixduringsecondaryproteolysis
undergo further catabolic reactions which involve decar-
boxylation, deamination, transammination, desulfuration
leading to the production of compounds such as amines,
acids, and thiols. It is accepted that FFA, especially short
chain FFA, have a direct impactoncheeseflavour, FFAs also
act as precursor molecules which lead to the production of
other flavour compounds, such as methylketones, esters,
fatty acids lactones and alcohols (McSweeney and Sousa,
2000; Tziboula-Clarke, 2003). Diet is a main factor affect-
ing the odorof freshmilkbecause odorous substancesmay
be transferred to themilk (i) directly to inhaled air into the
blood and from there to the milk and (ii) by direct absorp-
tion from the digestive tract; and (iii) via rumen gases
to the blood and milk. Moio et al. (1996) identified two
sesquiterpenes in milk and cheese produced from sheep
fed on a natural pasture being these constituent of signifi-
cance for their role in determiningmilk and cheese flavour
and as chemicalmarkers of the milk used tomake cheese.
Luna et al. (2005) reported that the organoleptic charac-
teristics of cheeses made from CLA-enriched milk, from
ewes fed linseed supplements, did not differ from control
cheeses.
Processing milk with high SCC is associated with an
increase intheproteolysisrateanda modificationofcheese
proteolytic pattern (Coulon et al., 2004). The contribution
of indigenous proteinases in the development of cheese
flavour have a possible negative implication for the accu-
mulation of bitter peptides which are gradually formed
by further degradation of-CN compounds (Visser, 1993).Revilla et al. (2007) reported a lower overall acceptance of
ewe hard cheese made with high SCC milk compared to
medium and low SCC finding that the formerwas judge as
weaklybonded, very grainy, andcrumbly. On thecontrary,
Pirisi et al. (1996, 2000) did not found significant differ-
encesin sensorycharacteristicsand lipolyiscomparingewe
cheeses made from milk with low and high somatic cell
count. Accordingly, also in goat milkJaubert et al. (1996)
andMorganandGaspard (1999) founda minor effectof SCC
on the goatish flavour that is instead mainly influenced by
cheesemaking technology, in particular ripening methods.
Lamb rennet paste contains lipolytic enzymes which
initiate free fatty acid formation (Bustamante et al., 2000;
Santillo et al., 2007b; Virto et al., 2003) thus giving the
cheeses a sharp, piquant aroma; in particular butyric acid
contributes to the cheesy lipolyzed aroma (Pinho et al.,
2004). Agboola et al. (2004) investigated the formation
of bitter peptides, defined as peptides with a molecular
mass of 1656500g/mol, in semi hard ovine cheese: the
results showed that cheese made with Rhizomucor miehei
developedmore bitterpeptides compared to calf rennet. In
general, the coagulant also influences the development of
bitterness by an excessively high activity which depends
on its level and retention in cheese curd; in addition the
presence of certain starter i.e. lactococci have a propensity
to cause bitterness (Fox et al., 2000).
In ovine and caprine cheese the addition of starter and
probiotic cultures (Albenzio et al., 2001, 2010; Corbo et al.,
2001; Kalavrouzioti et al., 2005; Santillo and Albenzio,
2008; Santillo et al., 2007a, 2009a) has been associated
with an increased proteolysis and lipolysis. These cheeses
were tested for sensory attributesbya panel of non trained
consumers. Theresultshowedanabsenceofperceivedsen-
sory attributes inovinecheesewhereasflavourandgeneral
acceptance of caprine cheese had higher scores than the
control cheese.
High pressure treatmentof goatmilk destined to cheese
production (Saldo et al., 2003) had no negligible changes
on the volatile composition therefore pressure can be
regarded as a safe technology not producing unexpected
compounds inmilk and cheese.
6. Cheese rheology and texture
Cheese texture may be defined as a composite sen-
sory attribute resulting from a combination of physical
properties and perceived by the senses of sight, touch,
and hearing (Pinho et al., 2004). While these attributes
are manifested during cheese consumption, mechanical
properties of cheese are determined by the application
of a fixed stress or strain (i.e. compression, shearing,
or cutting) to a sample of cheese under defined exper-
imental conditions. These properties are related to the
composition, microstructure (i.e. the structural arrange-
ment of its components), the physico-chemical state of
its components, and itsmacrostructure, which reflects the
presence of heterogeneities such as curd granule junction,
cracks andfissures, level of fat coalescence, solid fat:liquid
ratio, degree of hydrolysis and hydration of the paraca-
seinmatrix, andlevel of intermolecularattraction between
paracasein molecules (Fox et al., 2000).
Manufacturing process isable to influence cheesestruc-
ture thus it is closely related to the rheological parameters
of cheese. In general, the rheological characteristics differ
markedly with the cheese variety and its age. The changes
occurred in the structural component of cheesematrix are
mediatedby theresidual rennet,microorganisms andtheir
enzymes and changes in mineral equilibria between the
serum andparacasein matrix. Chymosin, the primary pro-
teolytic agent hasbeen associatedwith softeningof cheese
texture via hydrolysis ofs1-I-CN (Albenzio et al., 2010).Semi-hard goat cheese manufactured using artisanal kid
rennet paste was found to have a slightly harder, crumbly
andgritty texture than cheesemade with commercial ren-
net due to the lower proteolysis observed and this was
reflected in less softening of the cheese mass (Fontecha
et al., 2006). Pecorino cheeses produced using traditional
rennet paste or rennet paste containing probiotic dis-
played different rheological parameters as a consequence
of the degree of casein breakdown observed during ripen-
ing(SantilloandAlbenzio,2008). Theuse of selectedstrains
of lactic acid bacteria for cheese production promotes ren-
netactivityby reducingmilkpH,aids theexpulsionofwhey
from the curd thus reducing the moisture content of the
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M. Albenzio, A. Santillo / Small Ruminant Research 101 (2011) 3340 37
cheese(Fox etal.,2000). Level ofpHalso playsan important
role in cheese texture: as the pHof cheese curds decreases,
there is a concomitant loss of colloidal calcium phosphate
fromthecasein submicelleswithaprogressivedissociation
of the submicelles into smaller casein aggregates at a pH
value below 5.5 (Lebecque et al., 2001). Upreti et al. (2006)
found that the disaggregation of caseinmicelles exposes a
larger surface area of proteins to proteinases and leads to
an increase in enzymesubstrate interaction. It has been
shown that high acidity, protein, and total solids contents
generallymake thecheeseharderand less easilydeformed
(Kehagias et al., 1995).
Park et al. (2007) and Revilla et al. (2007) reported
important changes in the textureof cheese frommilkwith
SCC over 2.5106 cells/mL: low WarnerBratzler Shear
Force (WBSF) values in cheese were related to the increase
in proteolysis and to the higher amounts of s1-I-CN.Chen et al. (2010) reported lower hardness and higher
springiness in semi soft goat cheese made frommilk with
SCC
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40 M. Albenzio, A. Santillo / Small Ruminant Research 101 (2011) 3340
Slacanac, V., Bozanic, R., Hardi, J ., Szab, J.R., Lucan, M., Krstanovic, V.,2010. Nutritional and therapeutic value of fermented caprine milk.Int. J. Dairy Technol. 63, 171189.
Smacchi, E., Gobbetti, M., 2000. Bioactive peptides in dairy products:synthesis and interaction with proteolytic enzymes. Food Micr. 17,129141.
Sutherland, B.J., 2003. Salting of cheese. In:Roginski, H.,Fuquay, J.W., Fox,P.F. (Eds.), Encyclopedia of Dairy Sciences. MPG Books Ltd, Bodmin,Cornwall, UK.
Tziboula-Clarke, A., 2003. Goat milk. In: Roginski, H., Fuquay, J.W., Fox,
P.F. (Eds.), Encyclopedia of Dairy Sciences. Cornwall Academic Press,12701279.
Upreti,P.,Metzger,L.E., Haynes,K.D.,2006. Influenceof calciumandphos-phorus, lactose,and salt-to-moistureratio onCheddar cheesequality:proteolysis during ripening. J. Dairy Sci. 89, 444453.
Verdi, R.J.,Barbano,D.M., 1991.Properties of proteases frommilksomaticcells andblood leukocytes. J. of Dairy Sci. 74, 20772081.
Virto, M., Chavarri, F., Bustamante, M.A., Barron, L.J.R., Aramburu, M.,Vicente,M.S.,Perez-Elortondo, F.J.,Albisu,M., de Renobales,M., 2003.Lamb rennetpastein ovine cheesemanufacture.Lypolisis andflavour.Int. Dairy J. 13, 391399.
Visser, S., 1993. Proteolytic enzymes and their relation to cheese ripen-ing and flavour: an overview Symposium: proteolytic enzymes andcheese ripening. J. Dairy Sci. 76, 329350.
Wilson, D.J., Stewart, K.N., Sears, P.M., 1995. Effects of stage of lactation,
production, parity and season on somatic cell counts in infected anduninfected dairy goats. Small Rum. Res. 16, 165169.
Zeng, S.S., Escobar, E.N., Popham, T., 1997. Daily variations in somatic cellcount, composition, and production of Alpine goat milk. Small Rum.Res. 26, 253260.