Hot air drying is conventionally applied for the production of dried fruit; however, hardening and browning of the fruit pulp surface often occurs during processing. We demonstrated that microwave irradiation of Japanese pear pulp or grape, followed by hot air drying, produced high quality semi-dried fruit. Dried Japanese pear produced using this method showed uniform softness and a vivid yellow-orange color. In the case of dried grape products, microwave irradiation pretreatment improved the retention of both skin color (yellow-green and red) and original flavor (such as muscat and foxy). In addition, microwave pretreatment shortened the subsequent hot air drying period by approximately 30% for Japanese pear and 60% for grape. This method could be applied to other fruits such as apple, pear and peach. Dissemination of the method has resulted in commercialization of some dried fruit and confectionary products. However, a system capable of mass production, resulting in reduced production costs, is needed to promote the practical use of this method.
The quality control of frying oil and the management of cooking processes are critical to the taste of fried foods, and to the safety and economic efficiency of the commercial production of fried foods. The authors conducted research to assess the degradation of frying oil by studying its electrical properties and observed peculiar behavior of the dielectric constant believed to be caused by water present in the frying oil. An analysis of the dielectric constant suggested that water remains in high-temperature frying oil for a relatively long period of time. It is generally thought that water promptly reaches its boiling point of 100°C when added to high-temperature frying oil and is immediately discharged from the oil and into the atmosphere as steam. Verification that water indeed remains in frying oil at elevated temperature for long periods of time would indicate that there is a mechanism that hinders the discharge of water from high-temperature oil. Accordingly, in this paper we reproduce the conditions in which water remains in the frying oil and consider the factors causing this retention. We also discuss methods for extending the life of frying oils by controlling and managing the degradation of oil caused by hydrolysis when used frying oil is stored.
Soymilk specific for tofu is not used in drinks because of its bean-like flavor. Conversely, soymilk destined for drinks is not used for tofu production because it forms a soft curd. The difference in these soymilks is due to the milling temperature; room temperature is used for tofu, while high temperatures are used to inhibit the activity of oxidative enzymes in soymilk for drinks. The composition of these soymilks was discussed from the viewpoint of the previously described formation mechanism of soymilk and tofu, new data about the components, and recent soymilk composition data for drinks. The results showed that the composition of oil bodies was the same for both tofu and drinks, but the protein fraction for drinks contained a greater level of small particles compared to that for tofu. Thus, precise temperature regulation is important for soymilk processing.
In this paper, the effects of oil bodies, coagulant, pH and enzyme treatment on the aggregation behavior of soymilk were reviewed from the viewpoint of a colloidal dispersion system. The applicability of Einstein's and Krieger-Dougherty's theories of viscosity was examined using soymilk samples. The oil bodies in the soymilk behaved as suspended substances, and it was possible to predict the relative viscosity from the volume fraction of the oil bodies. The coagulation of soymilk with magnesium chloride was also investigated, and the validity of the novel viscous model with the effect of cross-linkage was discussed. The viscosity during coagulation could be predicted by the model, based on particle size as a property of the dispersion system. From the results of the effect of pH on the stability of soymilk using the centrifugal method, the state of soymilk components changed in three steps as a function of decreasing pH. The aggregation of high-fat soymilk digested by papain required heat pretreatment. It was suggested that oleosin, which stabilized the oil body emulsion, was digested by papain and the aggregation was promoted by heat pretreatment.