Dairy Sheep Symposium - the Department of Animal Sciences ...

analyzed for titratable acidity, syneresis, water holding capacity and gel strength.
Syneresis and water holding capacity of yogurts made from frozen milk, throughout the 12
mo study, were not significantly different than that of the of yogurt made from the initial fresh
milk. Titratable acidity of the yogurts produced from frozen milk after 3 mo of storage were
significantly lower than yogurt made from fresh milk (Table 4). Since pH values for the yogurts
were similar throughout the study, buffering capacity of the frozen milks was reduced due to loss
of salts or proteins. Visual evidence of protein destabilization was observed after 6 mo of storage
at -12°C. However, the protein could be resuspended and stabilized with the pasteurization
treatment. Gel strength was significantly reduced in yogurts made from milk after 9 mo of
frozen storage at -12°C (Table 4). Destabilized protein, in milk stored at –12°C, apparently
interfered with the binding of milk proteins in the formation of the yogurt gel. Yogurt produced
from milk stored at -27°C for 12 mo was comparable to that produced from fresh milk (Table 5).
Results of this study indicate that good quality yogurt can be produced from frozen ovine
milk if frozen and stored at -27°C for up to 12 months. Antifantakis et al. (1980) and Young
(1987) also obtained acceptable quality yogurt from ovine milk frozen and stored at -20° to -
30°C for up to 11 months. Young (1987) reported an unacceptable clot in yogurt from milk
stored at -12°C for 12 mo. Voutsinas et al. (1996) reported that good quality yogurt could be
produced from whole ovine milk that was concentrated and stored frozen at -20°C for 6-8 mo.
However, yogurts produced from frozen, concentrated ovine skim milk were of inferior quality
compared to the initial fresh milk.
Summary
The future potential for production of high quality specialty products from ovine milk is very
promising. However, proper handling of the milk is critical to the overall quality and yield of
processed products. Ovine milk should be rapidly frozen and stored at -27°C or lower for maximum
protein stability. If limited to frozen storage in home freezers (-12°C), frozen storage
should be limited to 3 mo maximum.
Literature Cited
Antifantakis, E., C. Kehagias, I. Kotouza, and G. Kalatzopoulos. 1980. Frozen stability of
sheeps milk under various conditions. Milchwissenschaft 35: 80-82.
Bastian, E.D. 1994. Sheep milk coagulation: Influence of freezing and thawing. Cultured Dairy
Prod. J. 29 (4): 18-21.
Bell, R.W., and T.J. Mucha. 1951. Means of preventing an oxidized flavor in milk. J. Dairy Sci.
34: 432-437.
Boylan, W.J. 1984. Milk production in the ewe. National Wool Grower 74(4): 6-8.
Boylan, W.J. 1986. Evaluating U.S. sheep breeds for milk production. IDF Bulletin No. 202:
218-220.
Braatz, D.R.. 1961. A method to improve the storage life of frozen concentrated milk. Ph.D.
Thesis, Univ. of Wisconsin-Madison.
Casper, J.L., W.L. Wendorff, and D.L. Thomas. 1998. Seasonal changes in protein composition
of whey from commercial manufacture of caprine and ovine specialty cheeses. J. Dairy Sci.
81: 3117-3122.
Casper, J.L., W.L. Wendorff, and D.L. Thomas. 1998. Functional properties of whey protein
concentrates from caprine and ovine specialty cheese wheys. J. Dairy Sci. 82: 265-271.
Desai, I.D., T.A. Nickerson, and W.G. Jennings. 1961. Studies of the stability of frozen milk. J.