Package icing method results in inexpensive facilities expenses for precooling, and thus is an economically excellent precooling method. We examined vegetables that are suitable to this method and the retaining period of ice in polystirene foam containers with various external temperatures.
Regarding the polystirene foam container developed for package icing for the transportation of broccoli, we measured the temperature change in the box when package icing is applied without putting vegetables under the conditions similar to those of the market distribution. The calculation of the heat transmission based on the measurement results revealed a certain tendency in the relation between the external temperature and the remaining hours of the ice.
We placed polystirene foam containers containing Japanese radiches in the thermostatic chambers at the temperatures of 5,15 and 25ﾟC and investigated the relation between the quantity of ice, the temperature declines of the Japanese radishes and the
air in the boxes, the thermal capacity of Japanese radishes and the thermal insulation of the polystirene foam. The analysis of the results shows that the calculated values and the measured values roughly agree each other.
We put eggplants, spinach, cucumbers and Chinese cabbages into polystirene foam containers, set some ice on and below the vegetables and analyzed the relation between the external temperature and the positions of the ice and the freshness of vegetables. The results reveal the fact that the temperature of the vegetables changes according to the position of the ice and that the cooling rate of the vegetables differs according to the position of the ice and according to the external temperature.
While focusing on hydrocooling, we also examined air cooling, vacuum cooling and no-cooling for the freshness of Japanese radishes, broccoli and spinach.
Japanese radish had the least weight loss. Thus, hydrocooling was the most suitable for it. Broccoli stored with hydrocooling had little weight loss but great change of color. Broccoli stored with vacuum cooling had great weight loss and little change of color. As for spinach, it showed the best performance with little weight loss in hydrocooling. Less