Free amino acid production during tomato fruit ripening: a focus on L-glutamate

AUGUSTO SORREQUIETA, GISELA FERRARO, SILVANA B. BOGGIO AND ESTELA M. VALLE

AMINO ACIDS

Springer

Año: 2010 vol. 38 p. 1523 - 1532

0939-4451

Abstract In tomato, free amino acids increase dramaticallyduring fruit ripening and their abundance changeddifferentially. More evident is L-glutamate which gives thecharacteristic ‘‘umami’’ flavor. Glutamate is the principalfree amino acid of ripe fruits of cultivated varieties. In thispaper, we examined the capacity of tomato fruits to processendogenous as well as exogenous polypeptides during theripening transition, in order to analyze their contributionto the free amino acid pool. In addition, the activity ofsome enzymes involved in glutamate metabolism such asc-glutamyl transpeptidase (c-GTase), glutamate dehydrogenase(GDH), a-ketoglutarate-dependent c-aminobutyratetransaminase (GABA-T), alanine and aspartate aminotransferaseswas evaluated. Results showed that peptidaseswere very active in ripening fruits, and they were able torelease free amino acids from endogenous proteins andglutamate from exogenously added glutamate-containingpeptides. In addition, red fruit contained enough c-GTaseactivity to sustain glutamate liberation from endogenoussubstrates such as glutathione. From all the glutamatemetabolizing enzymes, GDH and GABA-T showed thehigher increase in activities when the ripening processstarts. In summary, tomato fruits increase free amino acidcontent during ripening, most probably due to the raise ofdifferent peptidase activities. However, glutamate level ofripe fruit seems to be mostly related to GDH and GABA-Tactivities that could contribute to increase L-glutamate levelduring the ripening transition