Galacto-oligosaccharides as protective molecules in the preservation of Lactobacillus delbrueckii subsp. bulgaricus

E.E. TYMCZYSZYN; E. GERBINO; A. ILLANES; A. GÓMEZ-ZAVAGLIA

Kosice

Congreso; International Scientific Conference on Probiotics and Prebiotics - IPC2011. Kosice, Eslovaquia. 14-16/6/2011.; 2011

IPC

  Introduction Galacto-oligosaccharides (GOS) are produced by transgalactosylation of lactose, the reaction leading to a variable number of galactose units linked to a glucose unit. The composition of GOS can vary quite markedly in regard to their degree of polymerization (DP), being their prebiotic effect mainly associated with tri and tetrasaccharides. The important role of lactic acid bacteria and bifidobacteria as probiotics emphasizes the necessity of appropriate processes for their preservation. Among them, freeze-drying has been the most widely used method. However, during this process, the number of viable bacteria is dramatically reduced. Therefore, the use of cryoprotectants becomes mandatory, and sugars are the compounds the most consistently used in this function. Considering the polyhydroxylated nature of GOS, it is reasonable to assume that they may also act as cryoprotectants. The goal of this work is to determine the efficiency of GOS in the recovery of Lactobacillus delbrueckii subsp. bulgaricus, a particularly sensitive species to any preservation process, after freeze-drying. Methods Two types of commercially galacto-oligosaccharides were studied: GOS A and GOS B. The mixtures contained different percentages of GOS with different DP, lactose, galactose and glucose, as determined by HPLC. Cultures in the stationary phase were harvested by centrifugation and the pellets resuspended in solutions containing the different GOS preparations at 19 or 38% w/w. The suspensions were frozen at -80ºC for 24 hours. The samples obtained in each condition were stored at 5 ºC or at 25 ºC. The recovery after different times of storage was analyzed by plate counts. After rehydration growth kinetics carried out in milk, were followed by measuring the decrease of pH during incubation at 37ºC.   Results After freeze-drying in the absence of cryoprotectants, a decrease of 5 logarithms in the cell forming units with respect to the control was observed. GOS A and GOS B at 19 and 38%, were very efficient cryoprotectants in the recovery of L. bulgaricus. The presence of GOS reduced bacterial damage upon freeze-drying as revealed by the decrease in the lag times in growth kinetics carried out in milk, being GOS B at 38% the condition where the lowest level of damage was observed (lag time: 5.5 hours). The increase in the lag times could be correlated with the concentration of each component in the GOS mixture, following the pattern: DP4<DP3<DP2. The survival of microorganisms after long term preservation, indicated that cryoprotection mediated by GOS B 19% (storage temperature: 5 ºC) is the best condition for storage. Discussion GOS are widely known by their prebiotic properties. However, their role as protective molecules has not been reported nor properly explored up to now. In this work the protective capacity of GOS in the preservation of Lactobacillus bulgaricus was demonstrated. The novel role of GOS as protective molecules opens up several perspectives in regard to their applications. The supplementation of probiotics with GOS allows the production of self-protected synbiotic products, galacto-oligosaccharides exerting both a prebiotic and protecting effect.