In general, raw materials used in food processing are comprised of complex tissues. The chemical composition (e.g. moisture, protein content, lipid content) of each type of tissue varies depending on the tissue’s biological function. These differences in chemical composition determine the mechanical properties of each material and affect their temperature dependence. Hence, by understanding the temperature dependence of the mechanical properties of the tissues found in the raw food material, and then devising the optimal temperature and method for processing, materials which cannot be prepared by conventional methods may be mechanically processed with comparative ease. The authors examined new food processing technologies which facilitate the mechanical processing of food materials by controlling their temperature, and which can adjust the mechanical properties (e.g. fracture stress, elastic modulus, Poisson’s ratio, brittle temperature) of various tissues in the food material, in order to create the best state for processing. In this paper, a mechanical processing method which actively takes advantage of the changes in the mechanical properties of the food material according to the tissue’s temperature dependence is introduced.
When oil-droplet size in an O/W emulsion is reduced to a certain point, the oxidation reaction itself becomes a rate-limiting step because of the necessity for a sufficient supply of oxygen through the oil-water interface. Therefore, it would be generally predicted that the lipid oxidation rate does not depend on further reduction in oil-droplet size. However, we propose two models, both of which predict that lipid oxidation is suppressed or retarded by reducing the oil-droplet size. In one, surfactants covering the oil-water interface anchor their hydrophobic moiety into the oil droplet to dilute the lipid to be oxidized. Decrease in the lipid concentration would bring about deceleration of lipid oxidation. In the other model, no influence of oxidized lipid in an oil droplet on lipid oxidation in other oil droplets is assumed. Under this condition, lipid oxidation is more retarded for smaller oil droplets. These two effects would synergistically operate to retard lipid oxidation with reduction of oil-droplet size in an O/W emulsion. Also with microencapsulated lipids the surface-oil content would affect lipid oxidation behavior. The effect of oil-droplet size on this parameter was examined by two- and three-dimensional models based on the percolation theory. Both predicted that surface-oil content would be lower for smaller oil droplets. It was also shown that the distribution of ratios of size of oil droplets to microcapsules had only limited influence. Therefore, stochastic models showed the possibility that lipid oxidation is suppressed or retarded by reducing the oil-droplet size in both O/W emulsions and microencapsulated lipid systems.
Drying process is very important preservative method for foods and usually brings about some degradation of the final products. For this reason, some handlings such as pretreatments (physical, thermal, chemical etc.) are generally required to preserve the product quality either during drying or storage. One of the most important exporting stuff of Turkey is dried fruits and vegetables and the most acceptable dried grape (raisin), apricot, fig, tomato, hazelnuts over the world are produced in Turkey. In this article, some traditional and commercial applications to decrease quality losses during drying and storage of fruits and vegetables in Turkey and some constraints about these applications were explained and discussed. In addition to these applications, some results of recent researches performed in Turkey to keep the quality of dried fruits and vegetables and decrease the activity of molds and yeasts were explained.
The encapsulation of flavors is the important process in food industry. The encapsulation of flavors with spray drying and the flavor release from spray-dried powder were reviewed. The hydrophobic flavor was in the form of emulsion before spray drying. Therefore, the researches were mainly related to the forming of emulsion which wall material containing emulsifier properties are required. On the other hands, the hydrophilic flavor was mainly related to the antioxidant and coloring flavor powder. The hygroscopicity of powder and their stickyness during the spray dryer were important points to improve which the remaining of hydrophilic flavors were less concerned. The morphologies, and flavor release behavior are important physical properties of the flavor encapsulated powder. Especially, the correlation equations for the flavor release are summarized in the relation with Avrami or Weibull equation. The glass transition temperature is important to estimate the collapse of the powder and the permeation of the powder matrix to flavor compounds. The flavor release (mass transfer of flavor) rate is affected by temperature difference (T-Tg). In this review, recent researches are summarized in the flavor encapsulation in spray drying, especially for tropical flavor encapsulation.
Water activity (aw) was measured for various two component aqueous solutions at various inter-solute interactions and the observed aw was compared with the theoretical prediction by Ross equation assuming no inter-solute interactions. For solutions with neutral components including electrolytes, sugars, and neutral amino acid, solute-solute interaction was weak so that no substantial deviation was observed for observed aw from that predicted by Ross equation. When acid and base were involved, the deviation between the two was large because of the neutralization. For a solution containing macromolecule, bovine serum albumin (BSA) and sucrose mixture showed a strong cooperative effect between solutes to reduce aw much smaller than the theoretical expectation. In a case with an amino-carbonyl reaction between glycine and ribose kept at 60℃, a drastic increase in optical absorbance at 327 nm was observed with time and aw increased accordingly because of the water liberation at the initial stage of the Schiff-base formation and the following complex Maillard reaction process to reduce the number of solute molecules in the system.
Effects of ratio of first and second cooking periods before and after freeze on physical characteristics in green soybeans were determined to study effects of gelatinization level before freezing, in the condition that total cooking period was set at 210 seconds. The green soybeans gelatinized to 55-83% by first cooking exhibited higher firmness and higher crispness index (CI) after both they were thawed and fully gelatinized by second cooking, compared with other gelatinization degree at first cooking. The firmness and CI of green beans frozen with gelatinization level less than 41% were relatively high after thawing but decreased severely after second cooking. The green beans gelatinized over 92% by first cooking had considerably low CI after thawing. SEM imaging confirmed that cell structure of green soybeans gelatinized to 55-83% by first cooking was more intact even after they were thawed and fully then gelatinized than that of soybeans cooked with other condition.
Since emulsification for the production of O/W emulsions is a process associated with a gain in interfacial energy, its energy efficiency was defined as the ratio between the interfacial energy acquired and the energy consumed during emulsification. The energy efficiency thus defined could then be comprehensively correlated with the energy consumed by three different emulsification processes, - rotor-stator homogenization, high-pressure homogenization, and membrane emulsification. This correlation suggests that membrane emulsification resembles a high-pressure process from the viewpoint of energy consumption.