PROCESS FOR THE PRODUCTION OF ULTRAPURE GALACTO-OLIGOSACCHARIDES
The present invention describes a process for preparing ultrapure (≧95%) galacto-oligosaccharides (GOS), starting from GOS at lower purities by using sequential microbiological purifications involving Saccharomyces cerevisiae and Streptococcus thermophilus.
1 . A process for preparing GOS mixtures with a purity 95% in which the overall percentage of the digestible sugars lactose, glucose and galactose is ≦5%, starting from GOS mixtures of a lower purity, said process comprising one fermentation step with Streptococcus thermophilus and at least one fermentation step with Saccharomyces cerevisiae , where said purity is calculated by any analytical method able to distinguish and quantify GOS and said digestible sugars.
2 . A process according to claim 1 wherein said fermentation step with S. thermophilus is followed by a fermentation step with S. cerevisiae.
3 . A process according to claim 2 comprising, when a starting GOS mixture has a glucose content the HPLC area percent of which is ≦5%, a fermentation step with S. thermophilus followed by a fermentation step with S. cerevisiae.
4 . A process according to claim 2 wherein, when the starting GOS mixture has a glucose content the HPLC area percent of which is >5%, the fermentation step with S. thermophilus is preceded by a fermentation step with S. cerevisiae.
5 . A process according to any one of claims 1 - 4 wherein the fermentations with S. cerevisiae are conducted at pH 6.5±0.5 at a temperature of 35±° C. for at least 12 hours using 40-15 g of dehydrated S. cerevisiae per kg of dry weight of starting GOS.
6 . A process according to any one of claims 1 - 5 wherein the fermentation with S. thermophilus is preferably conducted at a temperature of 40±5° C. maintaining the pH at 6.0-6.5 by adding a base, for at least 15 hours and using 1-0.4 g of dehydrated S. thermophilus per kg of dry weight of starting GOS.
7 . A process according to any one of claims 1 - 6 wherein after the fermentation steps the mixture is subjected to further processing by means of ceramic ultrafiltration, nanofiltration, decolorization with carbon and ion-exchange resin deionization.
8 . GOS mixtures with a purity ≧95% wherein galacto-disaccharides other than lactose are present in quantities ≧1% and the overall percentage of the digestible sugars lactose, glucose and galactose is ≦5%.
9 . Pharmaceutical or food compositions comprising the GOS mixtures according to claim 8 .