| Abstract | Lećevački sir je sir pastirske tradicije koji pripada skupini tvrdih dalmatinskih i
primorskih sireva. U prošlosti se proizvodio na gospodarstvima lećevačkog kraja od
punomasnog ovčjeg, kravljeg ili miješanog ovčjeg i kravljeg mlijeka, ovisno o dobu godine
i sastavu stada. Danas se proizvodi od miješanog ovčjeg i kravljeg mlijeka.
Cilj ovog rada je utvrditi utjecaj udjela i sastava ovčjeg mlijeka na randman,
proteolitičke promjene i promjene teksture lećevačkog sira tijekom zrenja te utjecaj
sezone, godine i stada na kemijski sastav, posebice na udio dušičnih sastojaka, fizikalna
svojstva i higijensku kvalitetu mlijeka dalmatinske pramenke.
Proizvelo se 15 šarži lećevačkog sira miješanjem različitog udjela ovčjeg i kravljeg
mlijeka, pri čemu je udio ovčjeg mlijeka bio kako slijedi: od 35 % do 39 %, od 40 % do 44
% i od 45 % do 50 %. Uzorci su uzimani na početku zrenja, 30., 60. i 90. dan zrenja.
Uzorci ovčjeg mlijeka prikupljeni su sa šest farmi u submediteranskom području Hrvatske
koje na prirodnim pašnjacima uzgajaju autohtonu pasminu ovaca ‒ dalmatinsku
pramenku. Analiza fizikalno-kemijskog sastava mlijeka i sira provedena je standardnim
metodama. Proteolitičke promjene tijekom zrenja lećevačkog sira utvrđene su
standardnim metodama, dok su svojstva teksture utvrđena metodom testa kompresije.
Trajanje zrenja uzrokovalo je značajno (P<0,01) povećanje udjela mliječne masti,
proteina i suhe tvari lećevačkog sira. Također je utvrđen značajan (P<0,01) porast svih
pokazatelja zrenja sira (indeks alfa i indeks beta, udio dušika topljivog u vodi i 12-
postotnoj trikloroctenoj kiselini u odnosu na ukupni dušik). Povrh toga, trajanje zrenje
uzrokovalo je značajno (P<0,01) povećanje napona puknuća (kPa), značajno (P<0,01)
smanjenje deformacije do točke puknuća (%) i elastičnosti (mm).
Veći udio ovčjeg mlijeka u miješanom mlijeku (od 45 % do 50 %) uzrokovao je
značajno (P<0,01) smanjenje udjela suhe tvari i mliječne masti te značajno (P<0,05)
povećanje udjela proteina u lećevačkom siru. Različit udio ovčjeg mlijeka u miješanom
mlijeku nije imao utjecaja na prethodno spomenute pokazatelje zrenja lećevačkog sira.
Veći udio ovčjeg mlijeka u miješanom mlijeku pokazao je trend smanjenja vrijednosti
stvarnog randmana (P = 0,11) i iskoristivost masti (P = 0,074) u proizvodnji lećevačkog
sira. Također, veći udio ovčjeg mlijeka u miješanom mlijeku pokazao je trend (P = 0,088)
porasta napona puknuća (kPa), značajan (P<0,05) porast deformacije do točke puknuća
(%) i elastičnosti (mm).
Iz rezultata ovih istraživanja može se zaključiti da udio ovčjeg mlijeka u miješanom
mlijeku u proizvodnji lećevačkog sira ne treba biti veći od 39 %, s obzirom na to da veći
udio ovčjeg mlijeka ima nepovoljan utjecaj na stvarni randman i iskoristivost masti u
proizvodnji lećevačkog sira. Povrh toga, lećevački sir s većim udjelom ovčjeg mlijeka ima
manji udio suhe tvari i mliječne masti. Napon puknuća (kPa), deformacija u točki puknuća
(%) i elastičnost (mm) bili su veći zbog smanjenog sadržaja masti i istodobno povećanog
sadržaja proteina u lećevačkom siru. |
| Abstract (english) | Introduction
Milk and dary products produced from cows, sheep, goats and buffalos are
important part of Mediterranean nutrition. However, production of cheese from mixed milk
from different dairy animals is common habits in Mediterranean countries. There are
examples of cheeses produced from mixed milk, which belong to the groups of fresh, soft,
albumin, semi hard, hard cheeses, as well as, cheeses that belong to the group of pasta
filata type. Lećevački cheese is pastoral and traditional cheese, which belong to the group
of hard Dalmatian and coastal cheeses. In the past, this cheese was produced on the
family farms of the area of Lećevica from full fat sheep's milk, cow's milk, or mixed milk,
depending on the season and herd composition. Nowadays, it is produced from mixed
sheep's and cow's milk. Milk composition of mixed milk depend on many different
variability of milk, in fact on composition and physico-chemical properties of different milk
types which are used in the production of the cheese.
Hypothesis and aims of the research
The hypothesis of the thesis are:
Higher ratio of sheep's milk in mixed milk during the production of
Lećevački cheese would effect:
o Higher yield
o More intensive proteolysis, which would change the stage of casein
particles and texture of the cheese during ripening.
Season, year and flock would effect chemical composition, particularly the
ratio of nitrogen compounds, physical properties and hygienic characteristic
of sheep milk of Dalmatian Pramenka.
Therefore, the aim of this thesis was to determine the influence of ratio of sheep's
milk in mixed milk on cheese yield, proteolytic changes and textural properties of
Lećevački cheese during ripening, as well as, influence of season, year and flock on
chemical composition, especially on the ratio of nitrogen compounds, physical properties
and hygienic quality of sheep's milk of Dalmatian Pramenka.
Materials and methods
It was produced 15 batches of Lećevaćki cheese with different ratio of sheep's and
cow's milk. Ratio of sheep's milk was as follow: from 35 % fo 39 %, from 40 % to 44 %
and from 45 % to 50 %. Sample of cheeses were taken from the begining, 30., 60. and 90.
days of ripening. Sheep's milks were obtained from six family farms in sub-Mediterranean
area of Croatia where Dalmatian Pramenka is reared on natural pastures. All farms
included in this research breed Dalmatian Pramenka and they were located in the hilly
area of Dalmatian hinterland on the altitude between 200 m and 500 m. Milk was analysed
by standard methods for physical and chemical properties. Cheese was analysed by
standard method for physical and chemical properties. Cheese yield of Lećevački cheese
was determined by VanSkyke formula. Proteolytic changes during ripening of Lećevaćki
cheese were followed by standard methods that included four indicators of ripening as
follow:
Σγ-CN/β-CN (total relative ratio of γ-CN in β-CN),
αs1I-CN/( αs1I-CN + αs1-CN) (relative ratio of degraded fragments of αs1-I-CN in sum
of αs1-CN i αs1I-CN).
Percentage of water soluble nitrogen fraction in total nitrogen (WSN/TN)
Percentage of 12 % three clorine aceticacid soluble nitrogen fraction in total
nitrogen (TCASN/TN).
Textural properties were determine by the method of compression test by using
textural analyser (TA Plus Lloyd Instruments, UK), which was equiped by 500 N
mesearing unit, as a tool surounded probe was used with dyameter of 50 mm. Cheese
samples were used through out whole cut surphace cheese zone by spetial auger.
Analysis were perfomed by software program Nexygen plus from which figures
following parameters were calculated:
Fracture stress (kPa)
Percentage strain at fracture
Elasticity (mm).
Statistical analysis were conducted by using statistic program SAS (2001). For
description of analysed variables, method of descriptive statistics were used (PROC
UNIVARIATE). The effect of different ratio of sheep's milk in mixed milk on physicochemical
compositon, proteolysis and textural properties of Lećevački cheese, as well as,
the effect of season, year and flock on chemical composition, physical properties and
hygienic qualty of milk of Dalmatian Pramenka were tested by analysis of variance (PROC
GLM).
Results and conclusions
Higher ratio of sheep's milk (from 40 % to 44 %) increased ratio of fat, protein,
casein, lactose and total solids non-fat and total solids, while decreased the ratio of nonprotein
nitrogen in mixed milk.
Ripening time significantly (P<0.01) increased the ratio of milk fat, protein and total
dry metter of Lećevački cheese. Moreover, it was found that all ripening indicators (index
alpha and beta, water soluble nitrogen and 12% three clorine aceticacid soluble nitrogen
in total nitrogen) significantly (P<0.01) increased too. Simillarly, ripening time caused
significantly (P<0.01) increasing of fracture stress (kPa), significant decreasing of
percentage strain at break and elasticity (mm).
Higher percentage of sheep's milk in mixed milk (from 45 % fo 50 %) caused
significant (P<0.01) decreasing of total dry metter and milk fat content, as well as,
significant (P<0.05) increasing of protein content in Lećevački cheese. Different ratio of
sheep's milk in mixed milk did not effect any, previously mentioned, ripening indicators.
Higher ratio of sheep's milk in mixed milk decreased actual yield (P = 0.11) and fat
recovery (P = 0.074) in the production of Lećevački cheese. Moreover, higher ratio of
sheep's milk in mixed milk increased fracture stress (kPa; P = 0.088) and significanlty
decreased (P<0.05) percentage strain at break and elasticity (mm).
Significant effects were observed for season (P<0.001) and flock (P<0.05) on all
analyzed chemical components of milk. Significan effect of the year was observed on
lactose, casein, non-protein nitrogen (NPN; P<0.01), protein (P<0.05) and somatic cell
count (SCC) and bacterial count values (TB; P<0.05).
Acording to the results of this investigations it could be concluded that it is not
reasonlable to produce Lećevački cheese with sheep's milk in mixed milk in ratio higher
then 39 % taking into consideration that higher ratio of sheep's milk in mixed milk
decreased actual yield and fat recovery in the production of Lećevački cheese. Moreover,
Lećevački cheese with higher ratio fo sheep's milk contained lower total dry metter and
milk fat. Fracture stress (kPa), percentage strain at break and elasticity (mm) were higher
as a consequence of decreasing of fat content and simultaneously increasing of protein
content in Lećevački cheese. |
