Assessment of maturity of Loire Valley wine grapes by mid-infrared spectroscopy

Aim: The objective of the present study was to assess the ripening of grapes collected at different stages of maturation between the “véraison” and harvest periods from mid-infrared spectroscopy (MIRS) analysis. Methods and results: Grape berries of Cabernet Franc collected in two locations of the Loire Valley region (Touraine and Anjou), from 28 vine plots and during two vintages (2005 and 2006) were analysed. With principal component analysis (PCA) of spectral data of grape musts, different levels of ripening were described during the three to four weeks before harvest. A separation according to origin (Touraine or Anjou) was also observed and confirmed by the results of partial least squares (PLS) discriminant analysis (88 % of correct classification). Similar evolutions and geographical discriminations were obtained for specific physicochemical parameters. By PLS regression, good predictions of titratable acidity and sugar concentration from berry spectral data were obtained, with root mean square error of prediction (RMSEP) of 0.53 g/L for titratable acidity (expressed in H2SO4) and 8 g/L for sugar concentration. Moreover, when the data from only one of the regions were considered, the predictions of titratable acidity and sugar concentration were improved and those of real acidity (pH) and maturity index were then satisfactory. The RMSEP values for samples from Touraine and Anjou were reduced, respectively, to 0.05 and 0.02 units for pH, 0.4 and 0.12 g/L for titratable acidity (expressed in H2SO4), 6.6 and 3.2 g/L for sugar concentration, and 5 and 2.2 units for maturity index. Conclusion: Spectroscopic and classic chemical analyses of grape berries yielded highly similar results. The evolution of berries from “véraison” to harvest can be characterized according to both time course and region. The samples showed similar PCA results for chemical and IR spectra parameters. PLS regression between chemical and spectral data showed that Fourier transform IR is a good method to predict acidity and sugar concentration throughout ripening. And the results for these parameters, as well as for pH, maturity index and anthocyanin concentration, are improved if the regressions are calculated from sample sets restricted to a single growing region. Consequently, a calibration model is required for each grape geographical origin. Significance and impact of the study: The potential of MIRS was demonstrated for the quantification of the main indicators of maturity during berry ripening. Furthermore, these spectra can be used to estimate grape maturity in particular in reference to a spectral database established over several years of study. The association infrared spectroscopy, chemometric methods and database will help to monitor ripening and to determine the optimum harvest date

Strategies for improving freeze-drying resistance of bacteria: Modulating membrane properties during fermentation

Communication orale sur invitationStrategies for improving freeze-drying resistance of bacteria: Modulating membrane properties during fermentation. 52. Annual Meeting of the Society for Cryobiolog

Cyclopropanation of unsaturated fatty acids and membrane rigidification improve the freeze-drying resistance of Lactococcus lactis subsp lactis TOMSC161

This work aimed at characterizing the biochemical and biophysical properties of the membrane of Lactococcus lactis TOMSC161 cells during fermentation at different temperatures, in relation to their freeze-drying and storage resistance. Cells were cultivated at two different temperatures (22 and 30 A degrees C) and were harvested at different growth phases (from the middle exponential phase to the late stationary phase). Bacterial membranes were characterized by determining the fatty acid composition, the lipid phase transition, and the membrane fluidity. Cultivability and acidification activity losses of L. lactis were quantified after freezing, drying, and 3 months of storage. The direct measurement of membrane fluidity by fluorescence anisotropy was linked to lipid composition, and it was established that the cyclopropanation of unsaturated fatty acids with concomitant membrane rigidification during growth led to an increase in the freeze-drying and storage resistance of L. lactis. As expected, cultivating cells at a lower fermentation temperature than the optimum growth temperature induced a homeoviscous adaptation that was demonstrated by a lowered lipid phase transition temperature but that was not related to any improvement in freeze-drying resistance. L. lactis TOMSC161 was therefore able to develop a combined biochemical and biophysical response at the membrane level during fermentation. The ratio of cyclic fatty acids to unsaturated fatty acids (CFA/UFA) appeared to be the most relevant parameter associated with membrane rigidification and cell resistance to freeze-drying and storage. This study increased our knowledge about the physiological mechanisms that explain the resistance of lactic acid bacteria (LAB) to freeze-drying and storage stresses and demonstrated the relevance of complementary methods of membrane characterization

Development of a simplified lipid model of bacterial membrane to investigate specific interactions with oligosaccharides

Development of a simplified lipid model of bacterial membrane to investigate specific interactions with oligosaccharides. 56. Annual Meeting of the Society for Cryobiolog

New insights in reactive extraction mechanisms of organic acids: An experimental approach for 3-hydroxypropionic acid extraction with tri-n-octylamine

A detailed study of 3-hydroxypropionic acid (3-HP) reactive extraction with tri-n-octylamine (TOA) is proposed for the first time. It aims at uncovering some solvent-solutes interactions and providing global mechanisms to better understand and design the reactive liquid-liquid extraction of 3-HP in a biotechnological process. Eleven solvents of similar molecular sizes and several chemical types (alcohols, esters and alkanes) were investigated to understand their role on the extraction ability. Alcohols were found to be the best solvents thanks to their H-bond donor characteristic and water loading that allowed good solvation of the acid-amine complexes. Further investigations were then undertaken, for n-decanol and oleyl alcohol as solvents, varying acid (0.0028-0.56 mol/L corresponding to 0.25-50 g/L) and amine (02,3 corresponding to 0-100% v/v) concentrations. At 0.011 mol/L (1 g/L) of 3-HP, maximum extraction yields of 77% for n-decanol and 51% for oleyl alcohol were found for 0.46 mol/L TOA (20% v/v). The initial TOA purity proved to have a major impact on the extraction yield at low initial acid concentration (<0.1 mol/L = 10 g/L). Impurities from the TOA manufacturing process were identified as n-octylamine and di-n-octylamine and quantified in the aqueous phase after extraction. Their major effect on the extraction yield has been assessed (up to 86% decrease)

Strong effect of Penicillium roqueforti populations on volatile and metabolic compounds responsible for aromas, flavor and texture in blue cheeses

International audienceStudies of food microorganism domestication can provide important insight into adaptation mechanisms and lead to commercial applications. Penicillium roqueforti is a fungus with four genetically differentiated populations, two of which were independently domesticated for blue cheese-making, with the other two populations thriving in other environments. Most blue cheeses are made with strains from a single P. roqueforti population, whereas Roquefort cheeses are inoculated with strains from a second population. We made blue cheeses in accordance with the production specifications for Roquefort-type cheeses, inoculating each cheese with a single P. roqueforti strain, using a total of three strains from each of the four populations. We investigated differences between the cheeses made with the strains from the four P. roqueforti populations, in terms of the induced flora, the proportion of blue color, water activity and the identity and abundance of aqueous and organic metabolites as proxies for proteolysis and lipolysis as well as volatile compounds responsible for flavor and aroma. We found that the population-of-origin of the P. roqueforti strains used for inoculation had a minor impact on bacterial diversity and no effect on the abundance of the main microorganism. The cheeses produced with P. roqueforti strains from cheese populations had a higher percentage of blue area and a higher abundance of the volatile compounds typical of blue cheeses, such as methyl ketones and secondary alcohols. In particular, the Roquefort strains produced higher amounts of these aromatic compounds, partly due to more efficient proteolysis and lipolysis. The Roquefort strains also led to cheeses with a lower water availability, an important feature for preventing spoilage in blue cheeses, which is subject to controls for the sale of Roquefort cheese. The typical appearance and flavors of blue cheeses thus result from human selection on P. roqueforti, leading to the acquisition of specific features by the two cheese populations. These findings have important implications for our understanding of adaptation and domestication, and for cheese improvement