抄録
In the VRS determination by STROHECKER's method difficulties were experienced due to foaming in the distillation and due to tediousness in removing protein coagulum adhered to distillation flask. Data in Table 3 clearly indicate that volatile reducing substance (VRS) can be determined on an extract as well which is freed from protein by magnesium sulfate. So, the above trouble can be easily removed by employing this extract.
Since it has been found that both neutral and basic volatile reducing substances were increased at incipient spoilage (Fig. 2), the steam distillation of the extract is to be carried out in alkaline reaction (about pH 9.3). This improvement in the method gives rise to a more pronounced increase in VRS at incipient spoilage. Data illustrated in Fig. 3 demonstrate that VRS is, among several chemical indices, the most sensitive one for bacterial spoilage of the mackerel flesh.
The present method in which six-minute distillation followed by 5-minute boiling with potassium permanganate is employed, enables us to run six determinations with a single apparatus within one hour.
