Effects of freezing on composition and fatty acid profiles of sheep milk and cheese

Small Ruminant Research 64 (2006) 203–210

Effects of freezing on composition and fatty acid profiles of sheep milk and cheese R.H. Zhang, A.F. Mustafa ∗ , K.F. Ng-Kwai-Hang, X. Zhao Department of Animal Science, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Que., Canada H9X 3V9 Received 18 August 2004; received in revised form 3 March 2005; accepted 4 April 2005 Available online 9 June 2005

Abstract A study was conducted with sheep milk to determine the effects of freezing temperature and freezing time on milk composition, cheese yield and composition and fatty acid profile of milk and cheese. Bulk tank samples of sheep milk were collected for 4 consecutive weeks and stored at −15 or −25 ◦ C for 1–6 months. Milk samples frozen at the two different temperatures were thawed monthly at 22 ◦ C and milk was used for cheese making. Results showed freezing temperature and freezing time had no effect on concentration of milk total solids, protein, casein, non-protein N, true protein and lactose contents, however, milk fat percentage decreased (P < 0.05) progressively during the 6 months freezing period with less changes (P < 0.05) observed at −25 ◦ C than at −15 ◦ C. Freezing at either temperature for more than 2 months reduced (P < 0.05) actual cheese yield with lowest (P < 0.05) yield observed at 6 months of storage, however, 37% moisture adjusted cheese yield and cheese fat and protein percentages were not affected by freezing treatments. Fatty acid composition of thawed milk and fatty acid profile of cheeses were not affected by freezing temperature and freezing time. It was concluded that freezing sheep milk at −15 and −25 ◦ C for up to 6 months had only minor effects on milk and cheese composition. Despite the fact that freezing reduced actual cheese yield, adjusted cheese yield was similar for all freezing treatments. Freezing had no effect on milk or cheese fatty acid concentrations. Under the conditions of this study, good quality cheese can be produced from ovine milk frozen at −15 and −25 ◦ C for up to 6 months without influencing cheese yield or composition. © 2005 Elsevier B.V. All rights reserved. Keywords: Sheep milk; Freezing; Fatty acids; Cheese

1. Introduction Raising sheep for milk production is a traditional industry in many countries, such as in the Mediter∗ Corresponding author. Tel.: +1 514 3987506; fax: +1 514 398 7964. E-mail address: [email protected] (A.F. Mustafa).

0921-4488/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2005.04.025

ranean region (Bencini and Pulina, 1997). However, the dairy sheep industry in North America only began in the late 1980’s and has been growing steadily in the past decade, driven primarily by the increasing cheese market, small investment, ease of operation and freedom from quota limitation (Haenlein, 2001; Wendoff, 2001). Sheep milk is mainly used for cheese making due to its high fat and total solid contents. It has been

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reported that as much as 70% of sheep milk is used for cheese making (Mann, 1988). Due to seasonality and low production levels, and in order to provide a stable milk supply or to accumulate enough milk for processing, raw sheep milk may be frozen for several weeks or months (Wendoff, 2001). Freezing could have adverse effects on milk quality and stability properties such as fat separation, protein flocculation and development of off-flavor (Muir, 1984; Needs, 1992). These changes not only affect product shelve life, but also the yield and quality of dairy products such as cheese and yogurt (Wendoff, 2001). Preservation of milk by freezing has been a research subject since mid 1930s (Muir, 1984), and most of the work has focused on developing methods by which concentrated and unconcentrated cow milk could be kept for an extended period of time without affecting milk stability and quality. Freezing can have adverse effects on milk fat by destroying milk fat globules which leads to fat separation (Muir, 1984). Furthermore, unsaturated fatty acids in frozen milk are readily oxidized and degraded causing an oxidized off-flavor (Fennema et al., 1973; Needs, 1992). Further changes in fatty acid profile of frozen and thawed milk can occur during cheese making (Ha et al., 1989; Shantha et al., 1992; Garcia-Lopez et al., 1994). Effects of frozen storage on milk fatty acids and on yield and quality of cheese made from thawed sheep milk have not been determined. Therefore, the objectives of this study were: (1) to investigate the effects of freezing on cheese yield and composition of ovine milk, (2) to examine the influence of freezing temperature and freezing time on fatty acid composition in milk and cheese and (3) to determine changes in fatty acid composition related to freezing treatments during the cheese making process.

2. Materials and methods 2.1. Milk collection and storage Bulk tank milk samples were collected from a collaborating farm in Quebec for 4 consecutive weeks in February 2003. The milking ewes (average days in milk 25 ± 5.7) were crossbred East Friesian with Lacaune and were receiving 600 g of concentrate mix (per animal per day, as fed) consisting of corn, wheat bran and soybean meal, and 2.5 kg alfalfa hay (as fed). During

the first 2 weeks of milk collection, ewes were separated from their lambs for 12 h during the evening, machine milked once daily in the morning and their lambs allowed to suckle for 12 h during the day. At the end of the first 2 weeks, lambs were weaned and ewes were machine milked twice daily during the last 2 weeks of milk collection. The animals were kept in barn during the sampling period. Each week, milk samples (30 l) were collected and transported to the laboratory within 2 h. Once in the laboratory, milk samples were thoroughly mixed and packaged in 12 freezer bags (2.5 kg milk each). The freezer bags were then randomly placed in two freezers set at −15 and −25 ◦ C (each with six bags) and stored for 1–6 months. Sub-samples of fresh milk were retained for compositional analyses and cheese making. The frozen milk samples from each week were removed from freezers monthly and thawed quickly at 22 ◦ C. Each time the thawed samples were used for compositional analyses and cheese making. Visual examination was also made for the thawed milk samples to exam the stability and homogeneity of milk. 2.2. Cheese making A laboratory cheese making procedure (Marziali, 1985) was used to make cheddar-type cheese from fresh and thawed milk samples. Briefly, 2 kg milk was put into a square plastic container, followed by pasteurizing milk for 30 min at 65 ◦ C. Pasteurized milk was cooled down to 30 ◦ C and maintained at that temperature for 30 min in a water bath, followed by addition of 40 ml lactic acid culture (Agropur Coop´erative Agro-Alimentaire, Granby, Que., Canada). After 1 h incubation, calf rennet (Agropur Coop´erative AgroAlimentaire, Granby, Que., Canada) was added to the milk at a rate of 200 ␮l/kg milk, and thoroughly mixed using a wire whisk. After 30 min, the formed coagulum was cut horizontally and vertically to facilitate the drainage of whey, the whey was drained every 30 min for 3 h and collected into flasks for compositional analyses. Milk and whey pH (after coagulation and cutting) were measured every 30 min during the cheese making process. When pH dropped to 5.75, all whey was removed, and the curd was weighed and cut into approximately 2.5 cm cubes to which an amount of salt equivalent to 1.5% of the coagulum’s weight was added and well mixed. The curd was then collected into a cir-

R.H. Zhang et al. / Small Ruminant Research 64 (2006) 203–210

cular plastic mold lined with cheesecloth with a mesh size of 0.8 mm, and pressed overnight at room temperature under a 2 kg weight. The following morning, the cheese was weighed, hermetically sealed in a plastic bag and refrigerated for later analysis. Actual cheese yield was expressed as gram of cheese per 100 g of milk while theoretical cheese yield was calculated according to the formula (Van Slyke and Price, 1949): Yield =

{0.93 fat + (casein − 0.1)} × 1.09 100 − moisture in cheese (%)

Fat and casein in the formula represent percentage of these components in milk. Adjusted yield was expressed as gram of 37% moisture cheese per 100 g of milk. 2.3. Compositional analysis Fresh milk, thawed milk and whey samples were analyzed for fat, protein, lactose and somatic cell count by infrared analysis (Programme d’Analyse des Troupeaux Laitiers du Qu´ebec) using a Milko Scan (model: Foss 4000, Foss Food Technology, Denmark) calibrated for sheep milk. The fat content of milk and whey was verified using the Mojonnier method according to AOAC (1999) while protein content was verified using a N Determinator System (model: 601-700-500 FP428, Leco Corporation, St. Joseph, MI, USA). Dry matter in milk, cheese and whey were determined by the oven method (AOAC, 1999). Casein and non-protein nitrogen in milk were analyzed according to the procedure of AOAC (1999). Fat and protein in cheese were analyzed as previously described. For milk fatty acids analysis, 300–500 mg of fat was collected by centrifuging 10 ml of milk at 2000 × g for 15 min, while fat from cheese (300–500 mg) was extracted with a mixture of methanol and methylene chloride as described by Garcia-Lopez et al. (1994). Milk and cheese fat was methylated according to the procedure of Sukhija and Palmquist (1988) using hexane instead of benzene. Fatty acid methyl esters were analyzed using a gas chromatograph (Hewlett-Packard model 5890 series II, equipped with flame ionization detector at 250 ◦ C and model 7673 auto injector; Hewlett-Packard, Palo Alto, CA, USA) fitted with a fused silica capillary column (SP-2380, 100 m × 0.25 mm; Supelco Inc., Bellefonte,

205

PA, USA). Helium was used as a carrier gas. Injector and detector temperature was 250 ◦ C. The oven temperature was programmed as follows: initial temperature of 140 ◦ C maintained for 1.0 min; the temperature was then increased to 240 ◦ C at 5 ◦ C/min. The temperature was maintained for 10 min. The total run time was 31 min. The internal standard used was heptadecanoic acid (C17:0 ; Nu Check Prep Inc., Elysian, MN, USA). A standard fatty acid mixture containing 50 fatty acids and purified known individual fatty acids were used to provide standard retention times. Fatty acids were identified by comparing with the retention times of fatty acids in standard samples. 2.4. Statistical analysis Data were analyzed as a repeated measures in a randomized complete block design using the mixed model procedure of SAS (1989) with the following model: Yijk = µ + wki + Tj + Mk + Tj × Mk + eijk where Yijk represents the observations for the dependent variables, µ the least-square mean average, wki the random effect of week i (block i), Tj the fixed effect of freezing temperature j, Mk the fixed effect of freezing time k (month k), Tj × Mk the effect of interaction between freezing temperature j and freezing time k and eijk is the residual error. Differences were considered significant when P ≤ 0.05.

3. Results and discussion 3.1. Milk composition and cheese yield The average composition of the four milk batches used in this study was 15.2 ± 1.91% (13.99–17.05%) total solids, 4.8 ± 1.62% (3.16–6.22%) fat, 4.4 ± 0.26% (4.03–4.63%) protein and 4.8 ± 0.19% (4.57– 5.01%) lactose. Due to low fat, protein and total solid percentages for the first two batches, the four batch averages for these components were lower than those reported in the literature for sheep milk (Ploumi et al., 1998; Wendoff, 2001). This is likely due to the fact that ewes were suckled during the first 2 weeks of the collection period. Low milk fat and protein percentages for suckled ewes have also been reported by Fuertes et al. (1998) and McKusick et al. (2001). Differences in milk

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Table 1 Sheep milk composition as affected by freezing temperature and time Freezing time (months) 0 Dry matter (%) Fat (%) Lactose (%) Protein (%) Casein (% of protein) Casein (%) Non-protein nitrogen (% of protein) True protein (% of protein) Somatic cell count (×1000)

1

2

Freezing temperature 3

4

5

15.18 15.06 15.05 15.02 15.00 14.99 4.97a 4.97a 4.94b 4.92c 4.89d 4.87de 4.78 4.78 4.77 4.77 4.76 4.75 4.44 4.43 4.42 4.41 4.37 4.34 77.01 76.99 77.58 76.89 76.75 77.25 3.39 3.40 3.37 3.41 3.32 3.41 4.08 4.10 4.02 4.11 4.00 4.08 95.92 95.90 95.98 95.89 96.00 95.92 271.5 229.8 272.6 242.6 287.6 258.4

S.E.M

−15 ◦ C

−25 ◦ C

14.92 0.89 4.85e 0.77 4.74 0.10 4.33 0.14 77.02 0.70 3.37 0.12 4.07 0.08 95.93 0.09 294.1 52.40

14.97 4.88a 4.76 4.38 76.95 3.38 4.05 95.96 250.6

15.05 0.89 4.94b 0.77 4.76 0.10 4.39 0.13 77.20 0.43 3.38 0.11 4.07 0.07 95.94 0.08 251.1 31.85

6

S.E.M

Means in the same row with different superscripts (a–e) within freezing time or freezing temperature differ (P < 0.05).

components between the four milk batches should not affect our results, since our main interest was to investigate the effects of freezing temperature and storage time on milk and cheese properties. No interaction of storage duration × storage temperature was noted for all parameters tested in our study. Milk total solids, protein, casein, non-protein N, and lactose percentages were not affected by storage time or freezing temperature (Table 1). Visual examination showed that milk stored at −25 ◦ C had good stability and homogeneity during 6 months of freezing. In contrast, milk stored at −15 ◦ C demonstrated protein flocculation after 3 months, but the homogeneity was restored after pasteurizing the thawed milk at 65 ◦ C for 30 min. Similar phenomenon has been observed by Wendoff (2001). Milk fat percentage progressively declined (P < 0.05) as freezing time increased (Table 1). The decline in milk fat percentage was more significant (P < 0.05) at −15 ◦ C than at −30 ◦ C freezing temperature. Reasons for the reduction in milk fat percentage during freezing storage are not fully understood. It is possible that ice crystals, formed during freezing, might have damaged the fat globules. Milk fat occurs naturally in discrete globules, which are stabilized by a phospholipid and protein rich membrane (Muir, 1984; Keenan and Mather, 2003). During freezing, ice crystals compact entrapped fat globules causing release of lipoproteins from the milk fat globule membrane. This may result in destabilization of the emulsion and coalescence of globules upon subsequent thawing (Fennema et al., 1973). The larger crystals formed at −15 ◦ C are more destructive to fat globules than the

smaller ice crystals formed at −27 ◦ C (Koschak et al., 1981; Needs, 1992). The released fat, primarily triacylglycerols, are subjected to lypolysis by lipoprotein lipase. It has been reported that milk content of free fatty acids increases as storage time increase (Needs, 1992; Wendoff, 2001). However, milk free fatty acids were not determined in the present study. The destruction of fat globules, the enzymatic breakdown of triacylglycerols and the microbial activities may be the reasons for the reduction in milk fat during freezing storage. Somatic cell count values were below the threshold for sub-clinical mastitis in dairy ewes (GonzalezRodriguez et al., 1995) and were not affected by storage duration or temperature (Table 1). Teat dip after milking and culling of ewes with chronic mastitis were routinely applied in the flock used in our study, which would explain the low somatic cell count. Freezing temperature had no effect on actual cheese yield (14.3%, Table 2). Cheese yield was also not affected by freezing time up to 2 months. However, freezing milk for 3 months caused a moderate (4%) reduction (P < 0.05) in cheese yield with no further reduction up to 5 months of storage. A more significant (P < 0.05) reduction in cheese yield (8%) was observed for milk frozen for 6 months. However, adjusted cheese yield (Table 2) was not affected by freezing. These results suggest that water-holding capability of cheese was reduced as a result of freezing. This was supported by the higher (P < 0.05) whey yield from milk stored for 6 months relative to the whey from control milk. Freezing may alter protein structure of milk and cheese by destroying hydrogen bonds of the polypeptides and therefore reduce water-holding capacity (Fontecha et

R.H. Zhang et al. / Small Ruminant Research 64 (2006) 203–210

207

Table 2 Effect of freezing temperature and time on cheese making from sheep milk Freezing time (months) 0 Cheese yield Actual (%) Adjusted (%)

1

Freezing temperature 2

3

4

5

6

S.E.M

−15 ◦ C

−25 ◦ C

S.E.M

14.80a 13.56

14.78a 13.53

14.58ab 13.36

14.35b 13.17

14.23b 13.13

14.13bc 13.12

13.84c 13.28

1.07 1.31

14.20 13.14

14.43 13.37

1.06 1.30

Cheese composition DM (%) 57.28c Fat (%) 27.19 Protein (%) 25.63

57.27c 27.29 25.23

57.42c 26.34 25.99

57.53bc 27.45 25.71

57.81b 27.01 25.04

58.12ab 27.66 25.46

60.35a 28.92 26.43

1.54 2.65 1.06

58.03 27.08 25.85

58.14 27.81 25.44

0.47 2.59 1.04

1640.12c

1638.25c

1684.38a

18.77

1664.96

1658.75

18.18

8.13a 0.81a 1.33 5.29a

8.15a 0.84a 1.33 5.29a

7.84c 0.64c 1.34 5.15c

0.22 0.05 0.05 0.11

Whey yield (g) Whey composition DM (%) Fat (%) Protein (%) Lactose (%)

1640.75bc 1656.88b 8.07ab 0.80ab 1.33 5.23b

1669.38ab 1681.50a

8.02bc 0.78b 1.33 5.26ab

7.92c 0.63c 1.32 5.24ab

7.91c 0.6c 1.34 5.23b

8.02a 0.76a 1.33 5.23

7.95b 0.67b 1.33 5.23

0.21 0.05 0.06 0.11

Means in the same row with different superscript (a–c) within freezing time or freezing temperature differ (P < 0.05).

al., 1993). Data on the effects of freezing of sheep milk on cheese yield are not available. However, Wendoff (2001) suggested that sheep milk should be stored at −27 ◦ C or below to maximize the yield of processed products such as cheese and yogurt. Whey yield was not influenced by freezing temperature, while the effects of freezing time on whey yield were opposite to those reported for cheese yield (Table 2). Cheese composition was not affected by storage temperature (Table 2). Freezing time had no effect on cheese fat and protein percentages. However, cheese made from milk frozen for 4 months had more (P < 0.05) DM content than cheeses made from milk frozen for 0, 1 or 2 months. Dry matter content was also higher (P < 0.05) for cheese made from milk frozen for 6 months, than for cheeses made from milk frozen for less than 5 months. Differences in cheese DM content may explain the lack of differences in adjusted cheese yield between the various freezing times. Freezing time and freezing temperature affected whey composition (Table 2). Whey from milk stored for 5 months or more contained lower (P < 0.05) DM and fat percentages than whey from milk stored for less than 5 months (Table 2). Whey DM and fat percentage were higher (P < 0.05) when milk was stored at −15 ◦ C than at −25 ◦ C. However, fat content of all

wheys was less than 1% suggesting efficient retention of fat in cheese. Differences in whey DM content are likely a result of increasing whey yield as freezing time increased (Table 2). Whey protein percentage was not affected by freezing temperature or freezing time. Differences in whey lactose percentage were minimal despite some statistical differences (Table 2). Percentage and total output of fat in whey from 2000 g milk were decreased (P < 0.05) as freezing time increased (data not shown), which probably resulted from the decreasing fat content in milk and retaining of this milk constituent in cheese. Composition of sheep whey reported in our study is in good agreement with that reported by Wendoff (2001). 3.2. Fatty acid composition in milk and cheese Freezing temperature and freezing time had no effect on fatty acid composition of thawed milk, suggesting the absence of auto-oxidation of PUFA during freezing (Table 3). Fennema et al. (1973) showed that unsaturated fatty acids in cow’s milk and cream are readily oxidized and degraded during freezing and an off-flavor may be apparent in the thawed milk and cream. The lack of freezing effects on PUFA in our study suggests that the two freezing temperatures used did not compromise the nutritional value of sheep milk

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R.H. Zhang et al. / Small Ruminant Research 64 (2006) 203–210

Table 3 Effects of freezing temperature and time on sheep milk fatty acid composition (% of total fatty acids) Freezing time (months)

Freezing temperature

0

1

2

3

4

5

6

S.E.M

−15 ◦ C

−25 ◦ C

S.E.M

C4:0 C6:0 C8:0 C10:0 C12:0 C14:0 C14:1 C15:0 C16:0 C16:1 trans C16:1 cis C17:1 C18:0 C18:1 trans11 C18:1 cis9 C18:2 cis C18:2 trans C18:3 n6 C18:3 n3 Others SCFAa MCFAb LCFAc PUFAd MUFAe SFAf CLAg

2.8 2.7 2.5 6.8 3.9 10.1 0.4 1.5 22.1 1.1 0.9 0.7 12.2 2.4 17.7 2.3 0.7 1.1 1.9 5.2 18.7 36.7 39.4 7.1 23.2 64.6 1.1

2.9 2.7 2.5 6.8 3.9 10.2 0.4 1.5 22.2 1.1 0.9 0.7 12.1 2.4 17.5 2.3 0.6 1.1 1.9 5.2 18.8 36.9 39.1 7.0 23.0 64.8 1.1

2.8 2.7 2.5 6.8 3.9 10.0 0.4 1.5 22.4 1.0 0.9 0.7 12.2 2.5 17.6 2.3 0.6 1.1 1.9 5.1 18.7 37.0 39.2 7.0 23.1 64.8 1.1

2.9 2.7 2.6 6.9 4.0 10.2 0.5 1.5 22.4 1.1 0.9 0.7 12.2 2.5 17.6 2.3 0.6 1.1 1.9 4.7 19.0 37.0 39.3 7.1 23.1 65.1 1.1

2.8 2.7 2.5 6.9 3.9 10.1 0.5 1.5 22.0 1.1 0.9 0.7 12.1 2.5 17.5 2.4 0.7 1.1 1.9 5.1 18.8 36.8 39.3 7.2 23.1 64.7 1.2

2.8 2.7 2.4 6.7 3.8 10.1 0.4 1.5 22.4 1.1 0.9 0.7 12.1 2.4 17.5 2.3 0.6 1.2 1.9 5.4 18.4 37.0 39.2 7.1 23.0 64.5 1.1

2.7 2.7 2.5 6.8 3.9 10.1 0.4 1.5 22.2 1.1 0.9 0.7 12.1 2.5 17.5 2.3 0.6 1.1 1.9 5.4 18.5 37.0 39.1 7.0 23.1 64.5 1.1

0.09 0.14 0.10 0.43 0.22 0.53 0.08 0.12 0.96 0.02 0.03 0.02 0.69 0.07 1.13 0.12 0.02 0.05 0.04 0.77 0.96 1.49 1.98 0.17 1.22 1.78 0.02

2.8 2.7 2.5 6.8 3.9 10.1 0.5 1.5 22.4 1.1 0.9 0.7 12.1 2.5 17.5 2.3 0.6 1.1 1.9 5.1 18.7 37.0 39.2 7.1 23.1 64.9 1.1

2.8 2.7 2.5 6.8 3.9 10.1 0.4 1.5 22.1 1.1 0.9 0.7 12.2 2.5 17.5 2.3 0.6 1.1 1.9 5.3 18.7 36.8 39.3 7.0 23.0 64.6 1.1

0.06 0.13 0.1 0.45 0.22 0.52 0.08 0.12 0.93 0.01 0.02 0.01 0.67 0.04 1.11 0.11 0.02 0.04 0.03 0.63 0.93 1.46 1.96 0.16 1.20 1.80 0.02

Total fatty acidsh

95.0

95.0

94.7

95.4

94.9

94.5

94.5

0.76

94.9

94.8

0.63

a b c d e f g h

Short-chain fatty acid: (C4:0 –C12:0 ). Medium-chain fatty acid: (C14:0 –C17:1 ). Long-chain fatty acid: (≥C18:0 ). Poly-unsaturated fatty acid. Mono-unsaturated fatty acid. Saturated fatty acid. Conjugated linoleic acid. Percentage of total fat.

particularly the PUFA content. Unsaturated fatty acids are perceived to be healthier than saturated fatty acids (Kennelly, 1996). Fatty acid profile of sheep milk in our study is in good agreement with the values reported by Baldi et al. (1992) and Rotunno et al. (1998). Similar to the thawed milk, fatty acid profiles of the cheeses was similar for all freezing treatments (Table 4), suggesting that the cheese making was not affected. Our results confirm those of Baer et al. (1996) and Dhiman et al. (1999), who also did not find significant alterations in fatty acid composition during cheese

making. In contrast, other researchers reported increase in concentrations of PUFA during cheese making, particularly conjugated linoleic acid (Garcia-Lopez et al., 1994; Lin et al., 1998). However, these increases were only reported for processed cheeses and were attributed mainly to changes during cooking and ripening of cheeses. The proposed mechanism was, that conjugated linoleic acid could be produced by the auto-oxidation of linoleic acid under anaerobic conditions (Ha et al., 1989), which could be generated during the heating step.

R.H. Zhang et al. / Small Ruminant Research 64 (2006) 203–210

209

Table 4 Effects of freezing temperature and time on fatty acid composition of sheep cheese (% of total fatty acids) Fatty acids

Freezing time (months)

Freezing temperature

0

1

2

3

4

5

6

S.E.M

−15 ◦ C

−25 ◦ C

S.E.M

C4:0 C6:0 C8:0 C10:0 C12:0 C14:0 C14:1 C15:0 C:16:0 C16:1 trans C16:1 cis C17:1 C18:0 C18:1 trans11 C18:1 cis9 C18:2 cis C18:2 trans C18:3 n6 C18:3 n3 Others SCFAa MCFAb LCFAc PUFAd MUFAe SFAf CLAg

2.8 2.7 2.5 6.8 3.9 10.1 0.4 1.5 22.3 1.0 0.7 0.7 12.1 2.4 17.6 2.3 0.6 1.2 1.8 5.4 18.7 36.7 39.1 7.1 22.8 64.7 1.1

2.9 2.6 2.5 7.0 4.0 10.6 0.4 1.4 22.2 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.8 18.9 36.3 39.1 7.0 22.3 65.0 1.1

2.9 2.6 2.5 6.9 4.0 10.6 0.4 1.4 22.5 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.4 18.8 36.6 39.1 7.0 28.3 65.3 1.1

2.7 2.6 2.5 7.0 4.0 10.6 0.4 1.4 22.6 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.5 1.2 1.8 5.4 18.9 36.7 39.1 7.0 22.3 65.4 1.1

2.9 2.6 2.5 7.0 4.0 10.6 0.4 1.4 22.8 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.2 18.9 36.9 39.0 7.0 22.3 65.6 1.1

2.9 2.6 2.5 7.0 4.0 10.6 0.4 1.4 22.6 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.4 18.9 36.7 39.1 7.0 22.3 65.4 1.1

2.9 2.6 2.5 7.0 4.0 10.5 0.4 1.4 22.3 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.7 18.9 36.4 39.0 7.0 22.2 65.1 1.1

0.13 0.07 0.06 0.40 0.22 0.59 0.04 0.07 0.86 0.01 0.02 0.02 0.71 0.08 1.06 0.15 0.05 0.02 0.03 0.61 0.85 1.46 1.95 0.18 1.13 1.65 0.04

2.9 2.6 2.5 6.9 3.9 10.5 0.4 1.4 22.5 1.1 0.7 0.7 12.0 2.3 17.1 2.7 0.6 1.2 1.8 5.6 18.8 36.6 39.0 6.9 22.2 65.2 1.1

2.9 2.6 2.5 7.0 3.9 10.6 0.4 1.4 22.5 1.1 0.7 0.7 12.0 2.3 17.2 2.3 0.6 1.2 1.8 5.3 18.9 36.6 39.1 7.0 22.3 65.4 1.1

0.12 0.05 0.06 0.38 0.22 0.58 0.03 0.05 0.85 0.01 0.02 0.01 0.69 0.07 1.02 0.15 0.04 0.01 0.02 0.42 0.81 1.46 1.92 0.18 1.09 1.60 0.02

Total fatty acidsh

94.8

94.2

94.6

94.7

94.8

94.6

94.3

0.60

94.4

94.7

0.66

a b c d e f g h

Short-chain fatty acid: (C4:0 –C12:0 ). Medium-chain fatty acid: (C14:0 –C17:1 ). Long-chain fatty acid: (≥C18:0 ). Poly-unsaturated fatty acid. Mono-unsaturated fatty acid. Saturated fatty acid. Conjugated linoleic acid. Percentage of total fat.

4. Conclusions Results from the present study showed that freezing sheep milk at −15 and −25 ◦ C for up to 6 months had only minor effects on milk and cheese composition. Despite the fact that freezing reduced actual cheese yield, adjusted cheese yield was similar for all freezing treatments. Freezing had no effect on milk or cheese fatty acid concentrations. Under the conditions of this study, good quality cheese can be produced from ovine

milk frozen at −15 and −25 ◦ C for up to 6 months without influencing cheese yield or composition.

Acknowledgements The authors would like to thank D. Gaulin, M. Malkawi and C. Gonthier for their help with fatty acid analysis. Special thanks to Arlene and Jean-Guy Fillion for their cooperation and assistance in animal care

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and sample collection. This project was sponsored by Conseil de recherches en pˆeche et en agroalimentaire de Qu´ebec (CORPAQ).

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