Screening of microbial isolates for extracellular fructosyltransferase production

Fructooligosaccharides are gaining importance by leaps and bounce every day due to their low caloric value and accompanying health benefits for the consumer. Hence, newer potential sources for the fructosyltransferase (Ftase) enzyme are thoroughly scrutinized. The present work was carried out for preliminary and secondary screening of the microbial isolates for determination of the Ftase producing potential. Three classes of microorganisms’ viz. molds, yeasts and bacterial isolates were qualitatively screened. The preliminary screening revealed molds as the most potent group exhibiting greater zone of hydrolysis in the range of 0.30 ± 0.10 to 2.58 ± 0.10 cm. The secondary screening of 20 selected mold isolates was performed in liquid batch culture. Four isolates identified as Aspergillus niger, Aspergillus flavus, Aspergillus stallus and Aspergillus versicolor exhibited higher fructosyltransferase : invertase ratio which is most critical for the synthesis of fructooligosaccharides due to higher transferase activity and low hydrolytic activity. A. niger exhibited highest Ftase activity, 36.88 ± 0.23 IU/mg. A. flavus produced 21.45 ± 0.33 IU/mg of Ftase. A. stallus produced 18.09 ± 0.14 IU/ mg and A. versicolor was found to produce 23.78 ± 0.12 IU/mg of Ftase without any cultural medium optimization. Key words: Prelimnary screening, secondary screening, fructosyltransferase, fructooligosaccharides.