Absorptiometric measurement of tomatine in tomatoes

Abstract

Tomatine is a steroidal glycoalkaloid in the tomato plant (Lycopersicon escudentum) and other Lycopersicon and Solanum species. A simple and rapid method for the absorptiometric measurement of tomatine in tomato plants was developed. It was compared with measured values from the other methods such as HPLC, GC, and bioassay. Tomatine was extracted with 50% methanol/2% acetic acid and washed with hexane. The aqueous phase was hydrolysed with 1.5 N hydrochloric acid, and the resulting tomatidine (aglycon of tomatine) was extracted with chloroform. The extraction was then measured by generating a blue complex with bromothymol blue (sodium salt) at 620 nm. The results obtained by this method were congruous with those of the others. The calibration graph was linear in the range 0-5 mg/100 ml. Recoveries of spiked tomatine ranged from 96 to 101% for different amounts spiked. The tomatine content was 16.5 mg/100 g fresh weight in the mature green fruit, 4.4 mg/100 g fresh weight in the turning fruit, and 0.3 mg/100 g fresh weight in the mature fruit, ultimately. These results showed that the tomatine content in green tomatoes decreased during ripening. The tomatine in red tomatoes was localized to locular tissue and epidermis. The tomatine in the leaves and the flowers was much higher than the fruits. Wild type tomatoes contained larger amounts of tomatine than cultivated types.