Abstract
A large proportion of fresh foods, particularly vegetables and fruits, are served intact on the table. Accordingly, such foods are in danger of being polluted by foreign matters which are far from edible, such as microbes present in the soil during cultivation, dust, earth, fertilizers, pesticides, bactericides, fungicides, and so on.
The authors attempted to utilize the supersonic washing procedure, which had been already used as washing machine and instrument to eliminate those pollutants.
As the preliminary study, experiments were done to investigate the effects of irradiation of supersonic waves on the destruction of vitamine, such as B1 and C, which are existing in the tissues, and as the result, it was reported that very little effect was produced by supersonic irradiation on those vitamins.
The subsequent study reported herein deals with the effects of the irradiation of supersonic waves (frequency: 20 kilocycles) on the removal of Cu2+ of copper-containing pesticides contaminated to several kinds of vegetables and fruits. The results are as follows.
It was ascertained that marketed fresh parsleys, strawberries, lettuces, and grapes contained 10, 1.8, 3.8, 3.5γ of Cu2+ per gram, respectively. On the other hand, if the Bordeaux mixture had been employed for them, it were found that these vegetables contained 3200, 66, 1080 and 340γ of Cu2+ per gram, respectively.
By manual washing, about 30% of copper were eliminated after one minute washing, and even after the 15 minutes treatment, this value was risen only to about 40%. On the contrary, by the supersonic washing, it was found that 60% of the ion were washed off in a minute and over 90% in ten minutes.
In conclusion, it has been verified that the irradiation of supersonic waves on vegetables and fruits is extremely effective for the elimination of the residual Cu2+.
There remains the danger, however, that the improper processing conditions may lead to the destruction of vegetable tissue cells, marring the external appearance of plant and debasing their value as food. In the ranges of this experimental conditions it was also confirmed that the effect produced by supersonic washing procedure for the first one minute, cannot be heightened even if the processing time is extended to 10 or 15 minutes, for the quantity of copper ions eliminated by this method is not in proportion to the duration of irradiation. The danger involved in prolonged treatment with supersonic wave is that tissue cells may be disintegrated by excessively long processing.
