Fatty acid profile and cholesterol content of Ghezel sheep milk during lactation period
Summary (2 min read)
- Iran (received: 3 December 2016; accepted: 23 January 2017).
- The effect of lactation period on milk composition in different sheep breeds have been studied by several authors (KUCHTIK et al., 2008), but the results do not support each other probably because of different factors that may change sheep milk composition (NUDDA et al., 2002) According to the FAO (2014) reports, Iran ranks eighth in the world for sheep milk production, which is about 5% of the total milk production by country.
- 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).
- 1.3. 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).
- The column was capillary TRB sterol (30 m × 0.22 mm × 0.22 μm) (Teknokroma, Italy).
- 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.
- Medium-chain fatty acids 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%.
- 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.
- Considering the average fat content of the milk (5.25 g/100 g milk), the cholesterol content could be reported as 283.43 mg/100 g fat.
- GOUDJIL and co-workers (2003) have reported a range between 15–30 mg/100 ml milk and 288 mg/100 g fat.
- WOJTOWSKI and co-workers (2001) reported 26.11 mg/100 ml milk for sheep milk, as well.
- Regression analysis of cholesterol content during the lactation period showed a signifi cant increase (P<0.05).
- 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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