Abstract: Nine lactating buffaloes were ranked into three groups (three animals each) using 3x3 Latin square design (with 35 days each period). Experimental rations were: control (concentrate feed mixture (CFM): berseem clover (BC), 2:1 DM basis), low selenized yeast [control ration plus10 g/h/d selenized yeast (2.5 mg Se/h/d)] and high selenized yeast [control ration plus10 g/h/d selenized yeast (4.5 mg Se/h/d)]. At the last 3 days of each period, the collected milk from each group was pooled and used for analysis and manufacturing of Domiati cheese. The obtained results indicated that feeding diets supplemented with low or high selenized yeast improved milk yield and its protein content significantly (p<0.05). Also, both yield and protein recovery of cheese from group fed diet supplemented with low selenized yeast was improved as compared with high selenized yeast and control diets. Feeding diets supplemented with low or high selenized yeast had no effect on chemical, physical and organoleptic properties of Domiati cheese. The increase in total protein, fat and firmness of cheese during storage was correlated with decrease in pH values and moisture content of cheese. Also, the weight loss of cheese was more correlated with increase in soluble nitrogen and decrease of moisture content of cheese.
INTRODUCTION
Milk production and composition in animals are influenced by a number of genetic and non-genetic. The latter include age, stage of lactation, climatic condition and nutritional status and management levels. In order to restore productivity of lactating animals and to optimize milk production, various drugs, hormones and feed additives have been proposed (Lurdi, 1993). The use of live yeasts to supplement diets is one way to achieve this goal (Kholif et al., 2000). Selenium is an essential microelement for animal and man. Its deficiency in nutrition may decrease the productivity of domesticated animals (Foster and Sumer, 1997). El-Batal and Fadel (2002) produced an edible food yeast (S. cerevisiae) having high levels of organically bound intracellular selenium in an assimilable non-toxic form, which is useful as a dietary supplement. Kholif (2005) and European Food Safety Authority (2006) used selenized yeasts as a nutritional additive in ruminant diets, being a source of the essential trace element selenium in an organic form.
Domiati cheese is a most popular cheese variety made in Egypt. The yield and composition of Domiati cheese vary according to the kind of milk used in cheese making, the recovery of milk constituents in the resulting cheese would also vary accordingly (Ibrahim et al., 1974). Therefore, this study was conducted to evaluate the effects of selenized yeast supplemented rations on the milk production and composition and Domiati cheese yield and quality during cold storage period. Also, this study was undertaken to evaluate the relationships among some properties of Domiati cheese as affected by milk composition and storage period.
MATERIALS AND METHODS
Materials
Selenized yeasts (Saccharomyces cerevisiae F-25 with organic selenium)
were obtained from Microbial Chemistry Lab. National Research Centre, Dokki,
Cairo, Egypt. The cultures were maintained on Malt agar medium.
Calf rennet powder (HALA) and mixed strains of Lactococcus lactis sp. Lactis and Lactococcus lactis sp. cremoris were obtained from Chr. Hansen’s Lab Oritorum. A/S Copenhagen, Denmark). Salt was obtained from El-Naser Company of Alexandria.
Animals and Diets
Nine lactating buffaloes (2-4 lactation season and weighting in average
496±4 kg) in mid-lactation were ranked in three groups (three animals
each) according to their milk production and lactation season using 3x3 Latin
square design (with 35 days each period). Experimental rations were as follows:
control (concentrate feed mixture (CFM): berseem clover (BC), 2:1 DM basis),
low selenized yeast [control ration plus10 g/h/d selenized yeast (2.5 mg Se/h/d)]
and high selenized yeast (control ration plus 4.5 mg Se/h/d selenized yeast)
and high selenized yeast [control ration plus10 g/h/d selenized yeast (4.5 mg
Se/h/d)]. Selenized yeasts were top-dressed on the ground CFM. The CFM was consisted
of 35% yellow corn, 25% wheat bran, 22% undecorticated cotton seed meal, 15%
rice bran, 1.5% ground limestone and 1.5% common salt. The chemical composition
of ingredients is show in Table 1. The offered feeds were
assessed to cover the requirements for each animal according to NRC (1988) allowances
for daily cattle. The CFM for each animal was offered individually once daily
at 8.00 am, while berseem clover was offered twice daily at 10.00 am and 4.00
pm Daily milk production was determined.
Methods
Cheese Manufacturing
At the last 3 days of each period, the animals are hand milked (twice/day).
The collected milk from each group was pooled and used for analysis and manufacturing
of Domiati cheese according to Fahmi and Sharara (1950). All milk batches were
heated to 75°C/15 sec. and then cooled to 38°C. The starter culture
(1% w/w) and salt (5%w/w) were added to cheese milk and appropriate amount of
rennet was added to achieve coagulation in 150 min. The resultant cheeses were
separately pickled in their whey and stored at 6±2°C for 3 month.
The samples were analyzed fresh and every month of storage.
Analysis of Samples
Samples of ingredients and rations were analyzed for dry matter, ash, crud
fiber, organic matter and ether extract according to methods of AOAC (1995).
Nitrogen-free extract was calculated.
Moisture and ash contents in milk and cheese samples were determined according
to AOAC (2000). Fat content was determined by the Gerber method. Total nitrogen
content (TN) of the samples was determined by Kjeldahl method.
| Table 1: | Chemical composition of concentrate feed mixture (CFM) and berseem clover (BC) (% Dry matter basis) |
The protein content was obtained by multiplying the percentage of total nitrogen content by 6.38. pH value was measured using digital pH meter (HANNA, Instrument, Italy) with glass electrode. Salt contents of Domiati cheeses were estimated using Volhard method according to Richardson (1985). Water soluble nitrogen (WSN) of cheese samples was extracted according to Coskun and Tuncturk (2000) as follow: 20 g cheese was homogenized with distilled water (2:8), hold at 40°C for 1 h and then centrifuged at 3000 x g for 30 min. The extraction was filtered and used for determination of nitrogen content.
Penetration using Koehler K 19500, Penetrometer (Sycamore AVE, USA) as described by Kammerlehner and Kessler (1980) was measured as an indicator for cheese firmness (0.1 mm = penetrometer unit, PE).
Cheese yield was calculated as the weight of finished cheese divided by the weight of milk used. The recovery percentage of fat and protein were calculated according to Mahran et al. (1999). The weight loss was calculated relative to fresh cheese weight.
Domiati cheese was judged at fresh and every month of storage for organoleptic properties by 11 staff numbers of dairy department according to Pappas et al. (1996).
Statistical Analysis
Data obtained were statistically analyzed according to procedures outlined
by Snedecor and Cochran (1982). The Duncan's multiple range tests was used to
test the significance between means (Duncan, 1955).
RESULTS AND DISCUSSION
Milk Yield and Composition
Milk yield was significantly (p<0.05) higher in selenized yeasts supplemented
groups representing an increase of about 15.22 and 18.12% for buffaloes fed
low and high selenized yeast diets, respectively than buffaloes received the
control diet (Table 2). Also, milk protein was higher (p<0.05)
in milk from animals fed low selenized yeast diets followed by animals fed high
selenized yeast diets and then animals fed control ration. From these data we
can conclude that there was a positive effect of selenium and yeast on the digestibility
of organic matter and/or metabolic process in the mammary gland, which led to
the increase of milk yield and protein synthesis. However, milk fat, total solids
and solids-not-fat contents were insignificantly (p>0.05) increased with
low selenized yeast treated group compared with high selenized or control groups.
However, milk pH showed an opposite trend. These results with the animals fed
selenized yeasts supplemented diets agreed with those reported by Kholif et
al. (2000, 2005) with yeast or with selenized yeast (Kholif, 2005).
| Table 2: | Effect of supplementing buffalo’s diets with selenized yeast (low or high) on the yield and composition of buffalo’s milk |
| Means in the treatments with different superscripts are significant (p<0.05), Means each value obtained from 9 animals.Control = Concentrates: berseem clover, 2: 1, SNF = Solid Not Fat | |
Cheese Yield and Recovery
Supplementing buffalo’s diets with low selenized yeast increased cheese
yield and protein recovery comparable to control, but the treatments effects
were not statistically significant (Table 3). However, milk
produced from buffaloes fed diets supplemented with high selenized yeast had
lower cheese yield and protein recovery than low level selenized yeast (p<0.05)
and control (p>0.05). The reasons here are not clear. Cheese yield was correlated
with milk solids (r = +0.75**), especially protein and fat (r = +0.93**)
contents (Table 7), although, no much differences were observed
in fat recovery among all treatments.
Chemical Composition of Domaiti Cheese
Table 4 show that no significant differences were observed
in pH values, moisture, total protein, fat, ash and salt contents of fresh Domaiti
cheese among all treatments. However, pH values, moisture and ash contents decreased,
but total protein and fat contents increased through storage period up to 3
month. The chemical changes during cold storage period were insignificant, except
changes in pH values (p<0.05). These results could be attributed to the rearrangements,
within the network produced by attractive forces between individual casein particles
or clusters micelles leading to additional intermolecular bonds and, therefore,
to a contraction of the gel and the expulsion of whey, which was favoured by
change in pH values (Walstra et al., 1985). Statistically, significant
correlations were found between milk fat and cheese fat (r = +0.68**).
Also, cheese moisture was highly correlated with pH values during storage period
(Table 7).
| Table 3: | Effect of supplementing buffalo’s diets with selenized yeast (low or high) on cheese yield and protein and fat recovery of Domiati cheese from buffalo’s milk |
| Means in the treatments with different superscripts are significant (p<0.05), Means each value obtained from 9 animals, Control = concentrates: berseem clover, 2:1 | |
| Table 4: | Chemical composition of Domiati cheese during cold storage period as affected by selenized yeast supplementation (low or high) |
| Means in the treatments with different superscripts are significant (p<0.05) | |
Water Soluble Nitrogen: Total Nitrogen Ratio (WSN/TN)
WSN/TN ratio was studied as indicator for protein proteolysis of cheese
during cold storage period. According to the results in Table
7, WSN/TN ratio of fresh Domiati cheese was lower with feeding by low or
high selenized yeast than control treatment (p>0.05). However, during storage
period, gradual and the same rate nearly increases in WSN/TN ratios were observed
in all cheese treatments (p<0.05). Significant correlation was found between
WSN/TN ratios and pH vales (r = -0.78**) and moisture content (r
= -0.64**) (Table 7).
Cheese Weight Loss
After 1 month pickling, the weight loss was lower in cheese made with feeding
by low selenized yeast than other treatments (Table 5), but
the differences were insignificant (p>0.05). Also the results show that a
marked and progressively increase (p<0.05) in cheese weight loss during cold
storage period. The weight losses of Domiati cheese are usually attributed to
biochemical changes that result in curd condition and exclusion of moisture
and soluble constituents in pickling Brine. Statistically, correlations show
negative correlation between weight loss and moisture content (r = -0.5*),
but positive correlation between weight loss and WSN/TN ratio (r = +0.78**)
(Table 7).
Cheese Firmness
Firmness is not closely related to an elastic modulus but rather to a yield
stress. Its value depends on the method of measurement, especially the time
scale and on several product and process variables.The results in Table
5 showed slight differences were record among all treatments in fresh cheese
firmness (p>0.05). During cold storage, cheese firmness gradually increased
with the time, but this increasing was more pronounced after 2 month in all
treatments (p<0.05). This may be due to rearrangement within the network
produced by attractive forces between individual casein particles leading to
contraction of the milk gel (Walstra et al., 1985). There were significant
correlations between cheese firmness and either pH values or cheese moisture
(Table 7).
Organoleptic Properties
It seems from the data given in Table 6 that the all fresh
Domiati cheese had nearly the same scoring point for flavour, body and texture
and the general appearance. The resultant cheese had a good body and texture
(soft, smooth and lubricity texture) and pleasant creamy flavour. However, a
little change was observed in cheese quality during storage period (2 month),
except the body was firm comparable with fresh cheese.
| Table 5: | Effect of supplementing diets with selenized yeast (low or high) on soluble nitrogen, weight loss and firmness of Domiati cheese produced from buffalo’s milk during cold storage period |
| Means in the treatments with different superscripts are significant (p<0.05), Means each value obtained from 9 animals, SN: Soluble Nitrogen, TN: Total Nitrogen, PE: Penetrometer (the higher PE unit means less firmness) | |
| Table 6: | Effect of supplementing diets with selenized yeast (low or high) on sensory properties of Domiati cheese produced from buffalo’s milk during cold storage period |
| Means in the treatments with different superscripts are significant (p<0.05) | |
| Table 7: | Correlation coefficient between milk composition and/or Domiati cheese characteristics during storage period |
| 1: Milk solids, 2: Milk protein, 3: Milk fat, 4: Cheese yield, 5: Protein recovery, 6: Fat recovery, 7: Body and texture, 8: Flavour, 9: Total score, 10: pH, 11: Cheese moisture, 12: Cheese protein, 13: Cheese fat, 14: SN/TN ratios, 15: Cheese firmness, 16: Weight loss | |
As ripening advanced (3 month), the flavour, body and texture and appearance of cheese were improved. This may be contributed to the high content of soluble nitrogen serve as a precursor of certain flavour compounds.