Abstract
One of the urgent problems in the dairy industry is to reduce power input in the process of dispersing milk fat while ensuring a high degree of homogenization. This problem can be solved through the development and implementation of a virtually unexplored jet-slot milk homogenizer. The principle of its action implies the preliminary separation of cream from whole milk and its feed into the high-velocity flow of skim milk. The homogenization process occurs by creating a sufficient difference in velocities of the disperse and dispersing phases of the milk emulsion, which is mathematically described by Weber's criterion. Experimental studies of the effect of fat content in cream, cream feed rate, and width of the annular slot on dispersion indices during processing in the designed homogenizer have been carried out. The mathematical dependence which relates these parameters was found. It was proved that to obtain a milk emulsion with a dispersion level of 0.8 μm, the width of the annular slot should be 0.1–0.5 mm, fat content in cream 40–50 %, and the feed rate less than 40 m/s. The results of the evaluation of dispersion quality show a 7 % decrease in the average diameter of the fat globules compared to the most common values obtainable in the valve homogenizer. A refined critical value of the Weber criterion for dispersion of the fat phase of milk was determined (29 units) which indicates an increase in the intensity of the homogenization process in comparison with the jet milk homogenizer with a separate cream feed. The derived critical value of the criterion is necessary to create a theory of the process of dispersing milk fat and develop more efficient designs of milk homogenizers
Highlights
Milk homogenization improves the taste of dairy products and extends their shelf life, so it belongs to standard operations used in the dairy industry
Power input into the process is 6‒8 kWh per ton of homogenized milk [1, 3] when ensuring a high degree of dispersion with the use of valve homogenizers
Scheme of jet-slot milk homogenizer with the separate feed of cream: tion or experimental establishment of the 1 – pipe of skim milk feed; 2 – confuser; 3 – annular slot; 4 – container with relative velocity of dispersing and disperse phases [3, 5]. Given such a wide range of fluctuation of Wek values, refinement of this value enough for the destruction of the milk fat globules is an important task in the study of the mechanisms of dispersion cream; 5 – diffuser; 6 – pipe of finished product removal; υc is cream feed rate; υsk is the rate of feed of skim milk; dc is the diameter of the confuser at the point of greatest chamber narrowing; h is the width of the annular slot; u is sliding velocity of fat globules relative to milk plasma; Fsk is the fat content in skim milk; Fc is the fat content in cream; Fst is the fat content in the finished product of the disperse phase of the milk emulsion
Summary
Milk homogenization improves the taste of dairy products and extends their shelf life, so it belongs to standard operations used in the dairy industry. The purpose of homogenization is a dispersion (reduction) of the average diameter of fat globules (ADFG) of milk from 3‒4 μm in nonprocessed milk to 0.75‒0.85 μm in a finished product. Study and development of power-efficient designs of milk homogenizers are characterized by the difficulty of observing the fat globule destruction processes. This is because of their microscopic size (less than 1 μm), high milk velocities (up to 100 m/s in valve homogenizers), and low transparency of the milk emulsion. The study of the process of milk fat dispersion in order to design power-efficient jet homogenizers is promising for the present-day food industry
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