• Asian-Australasian Journal of Animal Sciences
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• v.20 no.2
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• pp.273-282
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• 2007

This study was carried out to compare the changes of nutrients, sensory and chemical properties of freeze-concentrated and evaporated milks during storage. For pasteurization, the freeze-concentrated milk containing 27% of total solid was treated with 150 rpm ozone for 5 min, and 99% of microflora was eliminated. Also, the activities of protease and lipase decreased 93.31% and 96.15%, respectively, and phosphatase showed negative activity. Total bacteria count was maintained below$2.0{\times}10^4$CFU/ml. During storage, TBA absorbance was lower in freeze-concentrated milk than that in the evaporated milk. The production of short-chain free fatty acids and free amino acids increased proportionally to the storage period in both samples. While the short-chain free fatty acid production was lower in the freeze-concentrated milk compared with that in the evaporated milk, the production of individual free amino acid was similar in both samples. In sensory evaluation, cooked flavor and color were much lower in the freeze-concentrated milk than that in the evaporated milk. Overall acceptability score was higher in the freeze-concentrated than the evaporated milk. Based on above results, ozone treatment for the freeze-concentrated milk pasteurization was positive at the elimination of microflora and enzyme inactivation. During storage, the freeze-concentrated sample minimized the change of color and TBA absorbance, the production of short-chain free fatty acid and vitamins than the evaporated milk. Therefore, the freeze-concentrated milk process in the present study resulted in the positive effect in minimizing nutrient loss and keeping quality of milk during storage.

• Food Science and Biotechnology
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• v.15 no.6
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• pp.844-850
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• 2006

This study was designed to compare various quality characteristics, such as nutrient composition and physicochemical and sensory properties of freeze-concentrated milk made by a newly developed continuous multi-stage process with those of evaporated milk. The freeze concentration process reduced the water content up to 73%. Most of the physicochemical properties of evaporated milk were different from raw milk; however the freeze-concentrated milk showed little difference from the raw milk. The thiobarbituric acid value and free fatty acid concentrations were significantly greater in the evaporated milk than in the freeze-concentrated milk. Several effects on sensory characteristics, such as off-taste, were significantly stronger in the evaporated milk. Overall, this study indicates that the newly developed freeze concentration technique results in improved physicochemical and sensory properties, and has little effect on most nutrient levels when compared with the evaporation process. Further research is necessary to further elucidate the chemical and sensory properties of freeze-concentrated milk.

• Food Science and Biotechnology
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• v.15 no.5
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• pp.756-762
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• 2006

Freeze concentration of milk was carried out through the controlled recrystallization of ice in a multi-stage freeze concentrator. Rheological characteristics of ice slurries were analyzed to determine efficient concentration levels for the freeze concentration process. It was determined that efficient concentration level was 17% of total solids in the first and 27% in the second stage. Physicochemical properties were compared between freeze concentrated and evaporated milk. Freeze concentrated milk was more similar in color appearance to control milk than was evaporated milk. pH significantly decreased in evaporated milk than in freeze concentrated milk. pH of freeze concentrated milk resulted in similar value to control. These results indicated the advantages of freeze concentration as a non-thermal milk processing technology in terms of physicochemical properties. Consequently, we investigated the influence of ice recrystallization on the rheological characteristics of ice slurries and physicochemical properties of freeze concentrated milk.

• Proceedings of the Korean Society for Food Science of Animal Resources Conference
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• 2005.05a
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• pp.297-302
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• 2005

Physicochemical properties were compared between freeze concentrated and vacuum evaporated milk through colour, brix, viscosity, freezing point and pH measurement. Brix and viscosity in each concentrated milk significantly increased due to solute concentration(p<0.05), and there was not much difference between freeze concentrated and evaporative one. Brix results were numerically modeled with the logarithmic regression: Y=-33.460+18.4513 ${\cdot}$ ln(X), $R^2=0.9798$ and this model was fairly fit to predict the solute concentration in the middle of freeze concentration process. Freezing point significantly decreased according to concentration increment(p<0.05) and there was not the significant difference between freeze concentrated and evaporated one. Whereas, in colour and pH value, there were some differences between freeze concentrated and evaporative milk. Vacuum evaporated milk expressed higher discoloration comparing to freeze concentrated one. In pH values, evaporated milk showed the significantly decreased results comparing to freeze concentrated sample, whereas the pH value of freeze concentrated sample expressed the similar value to the reference milk.

• Journal of Dairy Science and Biotechnology
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• v.14 no.2
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• pp.185-193
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• 1996

This study was to investigate principle of freeze concentration such as nucleation, crystal growth and procedure of freeze concentration, essential factor and application of freeze concentration. Especially, quality of milk was emphasized. For exemple, in sensory evaluation of freeze concentrated and reconstituted skim milk and whole milk, taste, color, mouth feel and texture were superior to control. Recently developed technique of freeze concentration for quality milk and dairy products may be expected for advanced quality of various milk and dairy products in near future.

• Korean Journal of Food Science and Technology
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• v.17 no.6
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• pp.500-505
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• 1985

A method to store concentrated milk in the liquid state at $-15^{\circ}C$ was developed, and quality changes during storage of milk were evaluated. Combined cryoprotectants (CCP) suitable for storing concentrated milk in the liquid state at $-15^{\circ}C$ were consisted of 17.74% sucrose, 8.87% glucose, 8.87% fructose, 2% glycerol, 0.25% sodium hexametaphosphate, 0.25% NaCl and 0.02% ascorbic acid. The amount of CCP to be added to concentrated milk to depress freezing point to $-15^{\circ}C$ was 38% by weight. Gelation due to protein denaturation was the most serious quality change during storage, which adversely affected appearance and utilization of the stored product. Gelation was observed after 3 weeks storage in the control, but it was not in milk with CCP throughout 18 weeks storage. Amount of protein precipitated increased in the control during storage, whereas there was no protein precipitated in milk with CCP. Surface color and peroxide value of the control and treatment did not change significantly during storage, and there were no marked differences between the control and treatment. These results indicated that quality of concentrated milk could be preserved, without gelation, by storing milk with CCP in the -liquid state at the frozen storage temperature. Besides, energy required for freezing preservation of milk could be significantly reduced by elimination of phase changes for freezing and thawing, and the stored product could be continuously processed for the final products without long waiting time for thawing.