Evaluation of The Relative Humidity Of Bacterial Samples Embedded in a Gos Matrix by Means of NIR Spectroscopy And Chemometrics

M.I. SANTOS, C. ARAUJO-ANDRADE, E.E. TYMCZYSZYN, E. L. ESPARZA-IBARRA, L. DELGADILLO-RUIZ AND A. GÓMEZ ZAVAGLIA

Oxford

Congreso; XV European Conference on Biological Molecular Spectroscopy. Oxford. 25-30/8/2013.; 2013

ECSBM

The development of functional foods containing probiotics and prebiotics is of great interest because of their significant health benefits [1]. To obtain concentrated viable probiotic starters, the preservation conditions are critical. During the preservation processes (i.e.: freeze-drying, vacuum drying, spray drying), the decrease of water activity produces damages on the cellular structures, decreasing the bacterial viability. To prevent these damages, sugars are usually incorporated as cryo or thermoprotectants. The protective effect of sugars has been ascribed to their ability to replace water molecules during dehydration, thus maintaining the biological structures in hydrated conditions. The role of galacto-oligosaccharides (GOS) as cryoprotectants has been reported recently [2]. Tymczyszyn et al. (2011) demonstrated that commercial GOS preparations are very good cryoprotectants of Lactobacillus delbrueckii subsp. bulgaricus, a species particularly sensitive to any preservation process. Near infrared (NIR) spectroscopy is a valuable method to analyze components of several agricultural products in a nondestructive way [3]. The NIR region is a wide region of the electromagnetic spectrum (wavelengths between 730-2300 nm) strongly influenced by the presence and state of the water molecules in the sample. Spectral features in the NIR region arise from combinations and overtones of the fundamental vibrations associated with C-H, O-H and N-H bonds. As a consequence, the diversity of spectral signatures composed of stretching and bending vibrations, provides a rich source of information that requires a reliable analysis. Strong NIR absorption water bands occur around 1400-1440 nm and 1900-1950 nm and have often been used for the analysis of water content in food [3]. In addition, the water status of plants can be determined with remote sensing applications using NIR reflectance. The aim of this work was to develop a method based on NIR reflectance spectroscopy and chemometrics to monitor the relative humidity (RH) of Lactobacillus delbrueckii subsp. bulgaricus embedded in different GOS matrices. The results obtained from the NIR spectra analysis, showed a good correlation between the relative humidity of the GOS matrices and spectral variations in the 1300?1500 nm region, ascribed to water absorption bands. These results may be relevant for the food industry, because the only registration of a NIR spectrum to evaluate the relative humidity would facilitate the experimental determination and also would save a lot of time, which is particularly valuable at an industrial level.