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Gerbino E.,Center for Research and Development in Food Cryotechnology | Mobili P.,Center for Research and Development in Food Cryotechnology | Tymczyszyn E.E.,Center for Research and Development in Food Cryotechnology | Araujo-Andrade C.,Autonomous University of Zacatecas | Gomez-Zavaglia A.,Center for Research and Development in Food Cryotechnology
Journal of Applied Microbiology | Year: 2012

Aims: To set-up an experimental and analytical methodology to evaluate the feasibility of developing simple, accurate and quantitative models based on Raman spectroscopy and multivariate analysis for the quantification of metal ions adsorbed to the bacterial surface of Lactobacillus kefir. Methods and Results: One millilitre cultures from two strains of Lact. kefir in the stationary phase were harvested and washed twice with ultra pure water. The bacterial pellets were resuspended into 1ml solutions of Pb +2, Cd +2 or Ni +2 ranging from 0 to 0·9mmoll -1. The suspensions were further incubated for 1h at 30°C at pH 5·5. After centrifugation, the pellets were kept to register the Raman spectra and the supernatants were used for the analytical determination of Pb +2, Cd +2 and Ni +2. Micro-organisms nontreated with metal ions were used as controls. Principal component analysis (PCA) was performed over the preprocessed Raman spectra to evaluate whether the clusters obtained could be correlated with the concentration of metal ions attached to the bacterial biomass. After that, partial least squares (PLS) models were calibrated with the aim of quantifying the metal ions adsorbed to the bacterial surface. According to the analytical determinations, the maximum binding capacity of all the metals (q max) attained values that are comparable with those observed for other lactic acid bacteria (ca. 0·200mmolg -1). The spectral analysis revealed that the main functional groups involved in the bacteria/metal interaction are carboxylates, phosphates and polysaccharides. In PCA, the first two principal components explain more than 72% variance of the spectral data set contained in the data structure, allowing a clear discrimination among samples of different concentrations. Based on this information and using as reference the results obtained by analytical methods, PLS prediction models were successfully defined for the quantification of Pb +2, Cd +2 and Ni +2 attached to the bacterial surface. Conclusions: The calibration and validation of methods based on multivariate analysis allowed the definition of models for the quantification of Pb +2, Cd +2 and Ni +2 attached to bacterial surfaces. The high percentages of explained variances in PCA gave a strong support to calibrate the prediction models, depicting very good correlations with the reference method (correlations ~0·90 in all cases). Significance and Impact of the study: Lactobacillus kefir CIDCA 8348 and JCM 5818 bind Pb +2, Cd +2 and Ni +2 in an efficient way. This fact gives support for their potential use as sequestrants of traces of these metals in products addressed to human and animal consume. The prediction models developed would be useful for the determination of the investigated metal ions in unknown samples giving at the same time, structural information about this interaction. This is certainly the most important contribution of this work. © 2012 The Authors. Journal of Applied Microbiology © 2012 The Society for Applied Microbiology.


Santos M.I.,Center for Research and Development in Food Cryotechnology | Araujo-Andrade C.,Autonomous University of Zacatecas | Tymczyszyn E.E.,Center for Research and Development in Food Cryotechnology | Gomez-Zavaglia A.,Center for Research and Development in Food Cryotechnology
Food Research International | Year: 2014

Galacto-oligosaccharides (GOS) and lactulose are well-recognized prebiotics widely used in functional food and pharmaceutical products, but there is still a lack of knowledge regarding their physical-chemical properties. In this study, a physical-chemical approach on two GOS of different composition (GOS Cup Oligo H-70® and GOS Biotempo) and lactulose was assessed. Mid infrared and Raman spectra of the freeze-dried sugars allowed their structural characterization in the amorphous state, lactulose, showing the main spectral differences.Freeze-dried sugars were then equilibrated at 4. °C at relative humidity (RH) ranging from 11% to 80%. Near-infrared reflectance spectra were registered in each condition in the 900- to 1700-nm region. A principal component analysis (PCA) was performed on the three sugars equilibrated at different RH. In all the three sugars, the groups observed explained more than 95% of the variance and were related with the RH of the samples. According to the loading plots of PC1, the main differences related with RH were observed in the 1380- to 1500-nm region.As the amorphous states are very sensitive to changes in temperature and moisture content, and the moisture content is related with the parameter T-Tg (T: storage temperature; Tg: vitreous transition temperature), an effort was made to determine this parameter directly from the NIR spectra. To this aim, a partial least square model (PLS) was defined. Tg values obtained by differential scanning calorimetry (DSC) were used to calculate the T-Tg values of reference. The model was validated with an independent set of data. The mean of predicted values fitted nicely T-Tg obtained from DSC (correlation=0.966; R2=0.934), thus supporting the use of the PLS model to investigate unknown samples.The stability of amorphous sugars in foods and pharmaceuticals is of practical and economical importance because it affects different quality attributes of foods, including texture, aroma retention and shelf life. Therefore, predicting T-Tg, a parameter that is independent on the sugar investigated, directly from their NIR spectra is of utmost importance to determine the shelf life of food and food-related products and up to our knowledge has never been determined hereto. © 2014 Elsevier Ltd.

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