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 method of purifying a galactooligosaccharides (GOS) composition with a purity ≥95% in which an overall percentage of the digestible sugars lactose, glucose and galactose is ≤5%, comprising providing a GOS mixture of a lower purity and subjecting the GOS mixture to at least 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. The method of claim 1 , wherein said method comprises a fermentation step with S. thermophilus followed by a fermentation step with S. cerevisiae.
3. The method of claim 1 , wherein said method comprises a fermentation step with S. thermophilus followed by a fermentation step with S. cerevisiae when a starting GOS mixture has a glucose ≤5% by HPLC area percent.
4. The method of claim 2 , wherein the fermentation step with S. thermophilus is preceded by a fermentation step with S. cerevisiae comprises when the starting GOS mixture has a glucose content >5% by HPLC area percent.
5. The method of claim 4 , wherein the fermentations with S. cerevisiae are conducted at pH 6.5±0.5 at a temperature of 35±5° C. for at least 12 hours using 15-40 g of dehydrated S. cerevisiae per kg of dry weight of starting GOS.
6. The method of claim 5 wherein the fermentation with S. thermophilus is 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. thermophiles per kg of dry weight of starting GOS.
7. The method prepared of claim 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. The method of claim 1 , wherein said fermentation steps are preceded by pasteurization undertaken at 75±5° C. for at least 5 minutes.