Experimental Study On The Caking Characteristics Of The Skim Milk Power

Skim milk powder is a very popular insant powder food which is good for heath. It is very easy for the product to become sticky and go caking under some conditions, which has harmful influence on its processing and storage and ruins the taste and the quality of the skim milk powder. However, the problem of the powder caking is not completely solved until now. Traditional theories, such as liquid brige caking mechanism and crystalloid brige mechanism, is unable to explain a caking characteristics of the amorphous powder that the powder cakes more easily on a higher temperature upon the dew point. The skim milk powder is a kind of food powder containing amorphous components and its caking behavior has to be explained with the caking mechanism based on the glass transition of the amorphous polymer powder.Many scientists from all over the world have paid great attentions on the glass transition phenomenons of food for its importance on controlling the food caking. Glass transition temperature has become a very important property and attracts great interests of food engineers. But almost all the domestic scientific articles in this field are related to summaries. Few quantitative experimental studies on the food powders caking could be found. Although some foreign scientists have studied the caking or the flowability of the food powder and the relationship with the glass transition, most work of them is focus on the mechanism explaination for the caking phenomenons. The quantitative experimental study on preventing caking or improving flowability is still seldom. Most of the equipment in the experiments is too complex to use. And the technique used for the study is so simplex that the data can not be used to represent the caking characteristics of the food powders comprehensively.In order to solve such problems, a blow-test equipment and a multifunctional ergometer are setted up in this paper. The caking trends of the lactose, which is the most important amorphous component in the skim milk powder, are analyzed theoritically and measured experimentally. The cross-polarizer microscope is used for judging whether the skim milk powder is crystal or amorphous and the morphological appearance of it. Based on the study of lactose caking, blow-test, rheometer, pin-stab and sheering method are established to get caking characteristics and caking dynamic data of the skim milk powder. The effects of temperature, relative humidity and time on caking of the skim milk powder are estimated. Gum xanthan and β -cyclodextri are introduced to control the caking of the skim milk powder by influencing the glass transiton of the lactose with different mechanisms. Theeffects of the additives are evaluated with above methods. Monte Carlo simulation program is designed for analyzing the glass transiton phenomenon and the effect mechanism of additives. The theoretical analysis and the experimental data verify further the caking mechanism based on the glass transition, and the mechanism can be used to analyze and solve the caking problem of the food powder. The experiment techniques in this paper can be widely applicated for the studies on the caking of other food powders. The data and the results are instructional for the processing and the storage of the skim milk powder and other amorphous food powders.