The membrane emulsification method combined with preliminary emulsification enables us to prepare O/W or W/O type emulsions with narrow particle size distribution at high production rate without high mechanical stress. The method also prepares stable food emulsions with unique properties such as ultra-high concentration, multi-phase, solid fat particle in water without agglomeration and so on. This paper introduced an interesting feature of the membrane emulsification method combined with preliminary emulsification. Highly concentrated emulsions were prepared from the low concentration pre-emulsified emulsions by the membrane phase inversion method. The maximum concentration obtained was ca. 90% for O/W emulsion, and ca. 85% for W/O emulsion. The W/O/W emulsions of very small particle (mean diameter, Dp≅2.5μm) with narrow particle size distribution (coefficient of variation, α≅0.1) could be obtained using a PTFE membrane (mean pore size = 1.0 μm) . The permeating flux of pre-emulsified W/O/W emulsion through the membrane was ca. 4-10m3/m2/h at 0.3 MPa. The encapsulation efficiency was not affected by the particle size of W/O emulsions. Increasing passage times through membrane decreased effectively the particle diameter of emulsion. Solid fat (melting point: Tm≅313 K) in water (O/W) emulsions prepared by the method were liquid state, and mean particle diameter (Dp≅2.0 μm) was almost unchanged during standing for several days at room temperature. This indicated that no appreciable aggregation of fat particles in O/W emulsions was observed.
For the construction of functional predictive models describing thermal death behaviors of foodborne spoilage and pathogenic microorganisms in foods, abundant thermal death data should be collected. We have been carrying out the build-up of thermal death database by taking two approaches. One is Thermokill Database R, which is a collection of data taken from research papers published in academic journals so far. The first version of this database, TKDB9100, was just completed and consisted of 3, 436 records containing approximately 7, 200 D values and 1, 450 Z values, which were published from 1991 to 2000. Based upon information from TKDB9100, we are further constructing a data library containing a variety of data distribution and interrelationships among many parameters and conditions. Another database is Thermokill Database E, which is a database obtained by experiments performed under defined conditions. Some of the examples of such information from these two databases are demonstrated. Finally, we describe the prospect of use of those in thermal processing of foods.
High temperature short time processing (sterilization and pasteurization) by continuous flow system, which consists of heat exchangers and a holding tube, offers shelf stable foods of high quality. Since the lethal effect for food is calculated based on the temperature histories, the engineering knowledge such as flow behavior and heat transfer is indispensable. To ensure microbial safety, thermal schedule to sterilize all parts of the food under the worst condition must be established. The continuous flowing sterilization of liquid food such as beverage has already been widely used as useful producing method. However, the lethal effect might be underestimated because the understanding of their flowing characteristics is insufficient. There are many difficulties with sterilization of the food containing particles. The evaluation of flow velocity distribution of the particles and the boundary heat transfer coefficients between the particle and fluid are especially important to calculate the lethal effect.
In order to clarify the rheological characteristics of the coagulated egg processed by ohmic heating, heating rate of liquid egg containing 0-2% salt was investigated under conditions of applied voltages ranged from 19 to 73 V and constant frequency of 60 Hz, and then the rheological behavior of coagulated egg was studied with stress relaxation tests in which the material was compressed to a constant strain. The average heating rate of liquid egg was directly proportional to the square of applied voltage, and it increased linearly with increasing salt content. The stress relaxation of coagulated egg consisted of three steps that could be expressed with a five-element Maxwell model. Analysis of the stress-relaxation of coagulated egg showed that the viscosity decreased, while the elasticity increased with increasing salt content in the range of 0-0.5%. However, there was no apparent effect of applied voltage on the viscoelasticity of coagulated egg.
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