STABILITY OF FREEZE-DRIED LACTOBACILLUS DELBRUECKII SUBSP. BULGARICUS IN THE PRESENCE OF GALACTO-OLIGOSACCHARIDES AND LACTULOSE AS DETERMINED BY NEAR INFRARED SPECTROSCOPY

MAURICIO SANTOS; ESTEBAN GERBINO; CUAUHTÉMOC ARAUJO-ANDRADE; ELIZABETH TYMCZYSZYN; ANDREA GOMEZ-ZAVAGLIA

FOOD RESEARCH INTERNATIONAL

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2014 vol. 59 p. 53 - 60

0963-9969

The ability of two types of galacto-oligosaccharides (GOS) and lactulose to protect Lactobacillus delbrueckii subsp. bulgaricus upon freeze-drying was evaluated on the bases of their capacity to form glassy structures, using Near Infrared Spectroscopy (NIRS). After freeze-drying in the presence of cryoprotectants, microorganisms were stored at 4 oC at different relative humidities (RH) (from 11 to 80 %) up to 21 days. The loss of viability was determined by plate count and referred to viability before freeze-drying. For each storage condition, vitreous transition temperatures (Tg) were determined by differential scanning calorimetry (DSC). In parallel, near infrared (NIR) spectra registered in the 900-1700 nm region provided information regarding viability and RHs that could be correlated with the results obtained from plate counts and DSC. The comparison of NIR spectra of freeze-dried samples stored at the same RH but differing in the time of storage allowed the identification of spectral features related with viability. The spectral differences observed on samples stored in the same conditions (same time of storage and same cryoprotectant), but differing in RHs, were related with the amorphous and rubbery states. Based on the spectral information, a multivariate based classification model (PLS-DA) was defined to determine whether samples are in a rubbery or an amorphous state. The accuracy of the defined model supports the use of NIRS to classify the correct storage of unknown freeze-dried samples in a short time-consuming procedure. As the only information required is that contained in the NIR spectra, this model may result in a useful method at an industrial level, where the save of time is much appreciated.