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

MAURICIO SANTOS, ELIZABETH TYMCZYSZYN, ESTEBAN GERBINO, NATALIA SOSA, CUAUHTEMOC ARAUJO-ANDRADE, CAROLINA SCHEBOR, ANDREA GÓMEZ ZAVAGLIA

Pornichet

Congreso; New Frontiers in Anhydrobiosis; 2013

INRA

The important role of lactic acid bacteria as starters in the elaboration of dairy products highlights the need of both appropriate preservation and reliable evaluation. Freeze-drying is one of the most common procedures for starter preservation. However, the decrease of water activity is responsible for a dramatic reduction in viability. To avoid this, the use of protective agents is mandatory. Polyhydroxylated compounds, such as sucrose and trehalose, have been used consistently as protectants. The formation of glasses in the dried state, in which biochemical reactions are considerably retarded, has been proposed to explain their protective capacity. The goal of this work was to investigate the efficiency of galacto-oligosaccharides (GOS), known as prebiotics, to protect Lactobacillus delbrueckii subsp. bulgaricus during freeze-drying. Lactobacillus delbrueckii subsp. bulgaricus CIDCA 333 was freeze-dried in the presence of GOS of different composition. Samples were stored at relative humidities (RH) ranging 11-80% and survival of microorganisms at 32, 20 and 4ºC was investigated by plate counting during 45 days. At 32ºC, a drastic viability loss was observed. At 20ºC, survival was dependent on the water content (the lower the RH the higher the survival). At 4ºC, no decay in viability was observed. The correlation between molecular mobility (determined by 1HNMR) and loss of viability explained the efficiency of GOS as protective agents. The preservation of microorganisms was improved at low molecular mobility and this condition was obtained at low water contents and low storage temperatures. In parallel assays, a combined approach of near infrared spectroscopy (NIR) and multivariate analysis was used to assess bacterial viability and amorphous-rubbery transitions of the freeze-dried samples stored at different RHs. Based on the spectral information, a multivariate based classification model (PLS-DA) was defined to determine the physical state of samples directly from the NIR spectra. As the physical state of starters is related with their shelf-life, this model provided support for the use of NIR spectroscopy to quickly assess the proper storage of starters.