Fatty acid profile and cholesterol content of Ghezel sheep milk during lactation period
Summary (2 min read)
Introduction
- The sheep in the region are mostly, more than 95%, of the Ghezel breed, which has been noted as one of the two distinctive milk type breeds in Iran (VALIZADEH, 2010).
- Therefore, the aim of the present study is to evaluate the major chemical components, fatty acid profi le, and cholesterol content of sheep milk throughout the lactation period in order to report an average for the content and needed changes in the procedure during the lactation period to help dairy technologists, cheese producers, nutritionists, and physicians.
1.1. Animals feeding and sampling
- The study was carried out on thirty Iranian Ghezel sheep, maintained in the most experienced and biggest traditional farm of the region, Eidi.
- The manuscript contains experimental animals, the study was conducted in accordance with the internationally accepted principles for laboratory animal use and care, and their ethical committee on animal care approved the protocol.
- All of the selected animals were in good condition and clinically healthy.
- They were numbered and fed the same diet as all cattle, a prevalent way of feeding in the region.
- Milk samples were gathered from each encoded sheep every month from two weeks of parturition after the colostrum stage to the end of lactation lasting about six months.
1.2. Chemical composition analysis
- Milk samples were analysed for fat, protein, lactose, and total solids (TS) contents using MilkoScan (Minor 78100, FOSS, Denmark), which was calibrated each month before the tests.
- Soluble nitrogen content was detected by the standard Kjeldahl method according to the AOAC 16.041 (1990).
- 3. Fatty acid profi le Fatty acid composition of the frozen milk samples was determined with the direct transesterifi cation method as proposed by LEPAGE and ROY (1986).
- The injection volume was 1 μl and the split ratio was set at 1:100.
- Injection and detection temperatures were 240 °C and 260 °C, respectively.
1.4. Cholesterol analysis
- After centrifugation at 2000 g, the upper phase was separated for injection to GC (FLETOURIS et al., 1998).
- Oven temperature was set at 285 °C, while injection temperature was 300 °C.
- Equal concentrations of standard cholesterol and alphacholestane (as internal standard) were prepared and injected to GC.
- The resulted peak areas were divided to reach a factor (F).
1.5. Statistical analysis
- One-way analysis of variance and subsequent comparison of means by the least signifi cant difference (LSD) method at 5% probability level was carried out.
- Chemical composition was assessed by regression model.
- Software including SAS and SPSS were used for statistical calculations.
2.1. Milk composition
- Chemical composition of milk samples from thirty sheep (Ghezel breed) gathered during the six months of the lactation period is shown in Table 1.
- Breed could also be an important factor that identifi es sheep milk composition (BOCQUIER & CAJA, 1999).
- It can be concluded that fat, protein, and TS contents increased, while lactose content decreased during the lactation period.
- Milk is an important source of CLA that could respond to more than 75% of human Acta Alimentaria 46, 2017 nutritional demands.
2.3. Cholesterol content
- The cholesterol content of the sheep milk was obtained as 14.88 mg/100 ml milk as an average for the whole period.
- Regression analysis of cholesterol content during the lactation period showed a signifi cant increase (P<0.05).
3. Conclusions
- It can be concluded that with the progress of lactation, the fat, protein, and total solids content of sheep milk increased, while lactose content decreased signifi cantly.
- Furthermore, the sheep milk of the region had a high protein and low fat content compared to other reports.
- Fatty acid profi le analysis showed palmitic acid to be dominant, with permanent content during lactation period.
- The cholesterol content of the sheep milk increased towards the end of lactation independent of fat content.
- The authors kindly acknowledge supports from the Tabriz Branch, Islamic Azad University, Tabriz, Iran.
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Frequently Asked Questions (12)
Q2. What is the significance of the higher protein content in sheep milk?
Higher protein content could be related to nutrition, in that a high level of nutrition and energy balance will decrease fat content and increase protein content in sheep milk (BOCQUIER & CAJA, 1999).
Q3. How was the feeding of the goats?
For the fi rst three months of lactation (February–April), feeding was with dry hay in caves, but throughout the second three months (May–July), hay was substituted with free fresh grazing.
Q4. How was the methanolised milk sample prepared?
The methanolised sample was kept at 45 °C for 1 h, 5 ml K2CO3 was added to cooled vials, and fi nally it was centrifuged at 2000 g.
Q5. What was the fatty acid content of the milk samples?
Medium-chain fatty acids (MCFAs) of C10:0, C12:0, C14:0, and C16:0 contributed to 62% of the total in this study, while the short-chain fatty acid (SCFA) content of C4:0, C6:0, and C8:0 was 4.05%.
Q6. What was the purpose of the study?
The manuscript contains experimental animals, the study was conducted in accordance with the internationally accepted principles for laboratory animal use and care, and their ethical committee on animal care approved the protocol.
Q7. What is the reason for the increase in cholesterol content of sheep milk?
It can be concluded that with the progress of lactation, the fat, protein, and total solids content of sheep milk increased, while lactose content decreased signifi cantly.
Q8. What was the effect of the lower milk yield?
It was obvious in their study that at the fi rst half of lactation lactose synthesis was high, but it decreased towards the end, because of the lower milk yield.
Q9. What was the average chemical composition of the samples?
Total average chemical composition was obtained as: fat=5.41±1.48, protein=6.58±0.78, lactose=4.79±0.80, and total solids 17.52±2.03 (% w/w) (mean ± SD).
Q10. How was the temperature of the milk sample determined?
The initial temperature of the oven was set at 190 °C for eight min, and then increased with a rate of 1 °C min–1 to reach 260 °C.
Q11. How was the cholesterol concentration quantifi ed?
The fi nal concentration of cholesterol was quantifi ed by multiplying 50 F and cholesterol peak area, which accordingly divided by internal standard peak area.
Q12. What is the reason for the increase in fat content of sheep milk?
Increase in fat content during this period could be a reason for the cholesterol content increase as discussed by WOJTOWSKI and co-workers (2001) for an increase from 23.5 to 30 mg/100 ml milk.