Production of RNA derivatives by Kluyveromyces fragilis grown on whey Producción de derivados de RNA mediante Kluyveromyces fragilis inoculada en suero de queso

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Abstract
Aerobic fermentation of cheese whey by Kluyveromyces fragilis has been proposed as a means of reducing its pollution potential and of producing ribonucleotide derivatives. 5'-Ribonucleotides, such as 5'-GMP and 5'-IMP are high added-value products that are used as flavour enhancers in foods. 5'-Ribonucleotide derivatives, nucleosides, nucleoside analogues and free bases are known to have anti-tumour, anti-viral and probiotic effects. In this study, K. fragilis was grown in a medium containing dehydrated whey under aeration. After different times of fermentation (24, 48, 72 h) aliquots of cells were autolysed either by incubation at three different fixed temperatures (48, 50, 53 °C) for 48 h or by incubation through a temperature gradient (45-65 °C, increasing by 5 °C every 5 h). Autolysed cells were centrifuged and the supernatant was analysed by high perfor mance liquid chromatograpy. High concentrations of free bases (0.74%) and 3'-nucleotides (0.64%) on the basis of biomass (d.w.) were obtained by a specified autolysis condition (50 °C, pH 7.5, 48 h), but less than 0.1% of 5'-nucleotides were obtained. Autolytic enzymes were able to break the yeast cells and hydrolyse the molecules of RNA into compounds that have therapeutic effects (free bases), but were not able to transform them into 5'-GMP and 5'-IMP.