A new rapid testing method of tomato vitamin C.

A new rapid method of quantifying tomato vitamin C using filter paper soaked in DCP, which is based on capillarity analysis (Kuroki, 1982), was studied. Filter paper (Toyo No. 526 4x8Omm) was dipped into 0.05-0.20% DCP in 95% ethanol solution and dried in an oven heater (30 deg. C) for one night to make DCP filter paper strips (DCPFS). The DCPFS was dipped into ascorbic acid standard solutions (5-50mg%, in 5% metaphosphoric acid) and the ratio of bleached (reduced) to total length was measured to make a calibration formula (Fig. 2).

Tomato fruits of 8 varieties were sampled at different growth stages and homogenized with a rotary type juicer. The lower clear part was collected in small glass bottle and tested with the DCPFS (see Fig. 1). The same samples were analyzed by the Fluorescence method (Kirk and Ting, 1975) to compare with the DCPFS method. The value of vitamin C concentration by the DCPFS method was slightly higher than by the Fluorescence method (Fig. 3) but there was a very high positive correlation between the two methods (r=0.962***).

These results indicate that the DCPFS method is a highly effective and simplified method to evaluate the vitamin C content of tomato fruits. It is possible to preserve the DCPFS for about one month in silicagel under room temperature.

Fig. 1 Modified DCPFS method for testing tomato vitamin C content

Fig. 2 Calibration curve of DCPFS method for estimating vitamin C content

Fig. 3 Correlation between DCPFS method and FLS method for testing vitamin C content