Process for the production of ultrapure galacto-oligosaccharides

Abstract

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 .