HKP-30/50/200 산업용 초미분(나노) 저온분쇄기

3. Analysis of the particulate formation using SEM (Scanning Electron Microscope)

Particle refining trend can be compared for mushrooms by comparing the particle shape and average particle size by using SEM

In particular,it was identified that licorice,a typical fibrous material,tends to fully form sphericity of the ultra-fine particles.

Microstructure of the food power used in food industry is in the range of 1~100㎛ as shown in Fig.1 and the cell wall,200~500㎛. If the raw material of oriental medicine,medical industry,and food industry is nano-pulverized in the particle size of 3㎛,the surface area increases and fine colloid solid powder can be made with high solubility. The physical characteristics of dispersion medium and dispersed phase in disperse system vary depending on the properties (e.g. electrical properties) of the particle surface and the interaction between particles.

Colloid is divided into hydrophilic colloid that is well dissolved in liquid and hydrophobic colloid that is not dissolved well. When protein is nano-pulverized under 3㎛ using recent ultra fine pulverizer,hydrophobic portion inside the protein is exposed so hydrophilic tendencies of the nano particle surface can increase. Thus pulverized protein can substitute fat which causes serious health problems in food industry. Also,fat is hydrophobic in water,but when pulverized protein is added,the oil attaches to the protein surface becoming hydrophilic. In actual cake,if the particle size of starch becomes under 30㎛,it can be present in hydrophilic colloid powder phase as shown in Table 1. If grain and herbal ingredients are nano-purverized under 10㎛,their colloid powders will easily melt in cold water. The cell wall of fruits,vegetables and grains consists of microfibril material cellulose amd matrix material such as hemicelluloses,pectin and glycoprotein,and enclusting material lignin (Fig. 2). And those components are strongly connected with covalent bond,hydrogen bond,ionic bond,hydrophobic bond,etc. so protect plant cell from external attack. Most of the cell wall constituents are not digested in the body and affect physiological functions as dietary fiber. The dietary fiber is divided into water-soluble dietary fiber and water-insoluble dietary fiber depending on the solubility. As passing through digestive tract,water insoluble dietary fiber increases volume of the stool by absorbing large amount of water and reduces the intestinal transit time and does physiological function of inhibiting the hydrolysis of starch and delaying absorption of glucose. Water soluble dietary fiber,in contrast,forms 3D gels,which delay the transit of food in the intestines and interfere with the absorption of glucose. In particular,they are known to play a role to decrease the amount of cholesterol present in the blood. Thus,if the content of soluble fiber can be increased by solubilizing insoluble cell walls,this can diversify physiological characteristics of the dietary fiber,as well as dissolute active components in herbal ingredients. In grains whose seeds are edible,the outside is surrounded by chaff (shell) and the inside consists of skin,albumen and gemmule (Fig. 3). The skin consisting seedcase and seed coat protects albumen and gemmule and contains large amount of crude fiber,ash and crude fat. Especially the cell membrane is made of fiber that is hard to dissolve with weak acids or bases. Although this part contains large amount of protein,fat,vitamin B1 and minerals,it is made up with hard and course tissue and most of it is usually removed in the secondary milling process. Since the gemmule at the bottom of grain kernel is the reproductive organ forming new plants as roots or leaves,it contains large amount of lipids,proteins,minerals and other nutrient;however,they are removed in the milling process. The endosperm is edible part accounting for the most of grain and rich in proteins. The skin and gemmule are rich in dietary fiber and biologically active substances. Particle size of rice starch is 2~12㎛,wheat and barley are 25㎛,buckwheat is 12.5㎛,potatoes is 45㎛,and sweet potato is15㎛. Generally,if starch particles are ultra fine pulverized in 1~30㎛ size,they can be used to make a superior water soluble gel food. As a generalized process in the current industry,the unique components of grains,fruits and medicinal plants are extracted with hot water. However,the ultra fine pulverizing technique that can turn fibers such as hemi-cellulose into dietary fibers using high shearing force and nano-size pulverize making these fiber soluble will become a generalized technology in the future food industry.

In recent power technology,there is a growing demand on ultra fine powder in order to produce high density and high concentrated products. In particular,demand for particle size control of ultra fine powder is increasing. In general industries,the products having cut size of 100㎛ - 2㎛ which represents the tendency of ultra fine powder are required. The pulverizer producing such ultra fine powder is called ultra fine pulverizer.

For ultra fine pulverization of dried powder,Impact mill with built-in or externally attached classifying device or fluid energy mil called Jet mill is used. Also,colloid mill or ultra-high pressure fluid pulverizer is used for wet ultra fine pulverization.

In recent powder processing technology of dietary fiber food and herbal ingredients processing industry,the powder are required with the particle size under 90%<10㎛ and average particle size under 3㎛. As shown in table 2,however,it is very hard to process fiber ingredients into products with an average particle size distribution of less than 10㎛ with regular pulverizer. Thus,they are processed mostly through pulverization->extraction->vacuum drying->powdering. For the reduction of these processes and ultra fine pulverization of fiber material,Korea Energy Technology has invented a new type of pulverizer that can pulverize with a high shear force. The newly developed ultra fine pulverizer reduces process of particle classifier by substituting the separate particle classifier that conventional pulverizer requires to produce the end-products with regular particle size range with the device inside the pulverizer. Table 2 compares the characteristics of pulverizer series with built in particle classifier in the fluid energy pulverizer with conventional food pulverizer. The ultra fine pulverizer developed by Korea Energy Technology reduces heat that occurs during pulverization to under 30℃ and nano-pulverizes the materials high in fiber up to 1~10㎛ range. The following is the pulverization and classification process of the low-heat nano-pulverizer. Input material is supplied to the pulverizer through the input unit by the door. In here,input material is evenly distributed,guided to the axial center by acceleration of the impeller,accelerated to the 1st acceleration track (H) and then 2nd acceleration track (I) using the thrust by the primary acceleration wing,and coarsely pulverized first with shock,shear and compression at the same time,and finally pulverized using the third track,which also creates boundary layer for particle classification. Thus,size reduction effect was designed to pulverize by impact action on the tracks and to low-heat pulverize by cooling action of the tracks at the same time. The material discharged through the outlet is separated from air in the downstream recovery device (always passes filter and collected in the collecting device). Outlet port has spatial figuration that can separate coarse powder from ultra fine powder using centrifugal force and drag force and it prevents the discharge of the non-classified material. Figure 5 shows the closed circuit low-heat ultra fine pulverizing system. In order to realize powder creation and automated process,the close circuit system is configured in the order of material storage->auto supplier->1st,2nd separator->dust collector,and it was designed to control the calculation of data and production based on MMI (man machine interface).

1) Particle size analysis of material

Particle size distribution of pulverized material was analyzed using Particle Size Analyzer (Malvern Ins. Ltd,Mastersiser-2000,U. K) which applies Mie’s light scattering theory. The particle size of each material was measured by using average data values obtained from repeated dry dispersions three times. Analysis results of each material are shown in Table 3. Mushrooms showed a distribution of the average particle size of 7 ~ 10㎛;liquorish and mugwort,which are classified as fiber,showed 6~24㎛. Also,red ginseng and rice showed average particle size of 7~10㎛.