Modélisation du pH, de l'extrait sec et de la minéralisation du caillé pendant l'égouttage d'un fromage à pâte molle

International audienceThe influence of the temperature at the rennet addition (31.2, 32.0 and 32.8 °C) and of the starter type on the soft cheese drainage process was studied. Off-line measurements of pH, calcium and phosphorous concentrations, as well as dry matter of the curd were performed in parallel with on-line measurements of the weight and pH of the whey. Only the starter type was found to have a significant influence on the curd and whey pH, on the calcium concentration in the curd and on the calcium/dry matter ratio. Correlations were established between weight of the whey and dry matter of the curd, as well as between pH of the whey and physico-chemical measurements in the curd. Linear regressions gave satisfactory results only when performed separately for each type of starter. Artificial neural networks allowed the building of common models for both starters and predicting curd pH, calcium concentration and the calcium/dry matter ratio using the pH of the whey at one hour after moulding.Au cours de l'égouttage en moule de fromages à pâte molle, des mesures de pH, de concentrations en calcium et phosphore ainsi que de l'extrait sec du caillé ont été effectuées parallèlement aux mesures en ligne de la masse et du pH du sérum. Les effets de la température d'emprésurage (31,2 ; 32,0 et 32,8 °C) et de la nature des levains ont été évalués sur l'évolution de ces grandeurs. Seule la nature des levains présente un effet significatif sur les évolutions du pH du caillé et du sérum, sur la concentration en calcium du caillé et sur le rapport Ca ++ /extrait sec. Des corrélations sont établies entre la masse de sérum égoutté et l'extrait sec du caillé ainsi qu'entre le pH du sérum et les grandeurs physico-chimiques mesurées dans le caillé. Dans ces relations, les régressions linéaires multiples n'apportent des résultats corrects que lorsqu'elles sont établies séparément, en fonction du levain utilisé. La mise en oeuvre de réseaux de neurones artificiels permet d'établir un modèle unique pour l'ensemble des variables recherchées

Developpement de methodes de mesure en ligne de la concentration en ethanol dans les procedes de fermentation

SIGLEINIST T 77388 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Classification of red wines analysed by middle infrared spectroscopy of dry extract according to their geographical origin

Mid-infrared transmission spectroscopy and classical analyses have been used to classify 165 wines of the same variety (Gamay), from three geographical origins (Gaillac, Beaujolais and Touraine). For spectroscopic analyses; the wines were dried on polyethylene membrane and infrared spectra were recorded by transmission between 800 cm-1 and 1800 cm-1. Classical analyses included pH, total acidity, total phenol, colour, sugars and major acids. The three groups of wines were classified by applying factorial discriminant analyses with cross validation. 97 p. cent of wines were correctly classified, based on the infrared data, versus 67 p. cent based on the classical analyses

Ripening conditions: an asset to control Listeria monocytogenes in cheeses

International audienc

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

Logiciel PreMatuBay (Prédiction de la Maturation des baies de raisin par réseau Bayésien dynamique)

PreMatuBay, un outil innovant pour prédire la maturité des baies de raisin. L’évolution de la composition des baies de raisin au cours de la maturation est un facteur déterminant pour le choix de la date de récolte et des itinéraires technologiques. Un réseau bayésien dynamique couplé à un système expert flou intégrant des données d’expertise et météorologiques (température, ensoleillement, hygrométrie, pluviométrie) a permis de modéliser l’évolution de trois paramètres représentatifs de la maturité des baies (acidité totale, concentrations en sucre et en anthocyanes). Ce réseau a été validé sur trois millésimes. Un logiciel a été développé pour sa mise en oeuvre auprès des professionnels. Il gère l’acquisition des données météorologiques et calcule les valeurs des variables de maturation à un horizon de 7 à 10 jours sur la base des prévisions météorologiques. Il peut être consulté par les viticulteurs pour suivre et anticiper la maturation des baies sur leurs parcelles à l’aide d’une interface web conviviale. La qualité des estimations pourra être améliorée en intégrant d’autres millésimes. Il est également envisagé d’adapter le modèle à la détermination d’autres variables de maturation, à d’autres cépages et dans d’autres régions viticoles

L’emballage une contrainte ou une innovation pour les fromages : exemple d’un fromage AOP à pâte persillée ?

Les fromages AOP sont des produits particuliers à emballer. Les caractéristiques de perméabilité aux gaz et à la vapeur d’eau des emballages influent sur la composition de la communauté microbienne et sur son métabolisme comme il est illustré pour deux fromages AOP. L’emballage de portion de Saint Nectaire sous film peu perméable à l’air et à la vapeur d’eau réduit les niveaux de levures et de bactéries d’affinage, altère l’aspect de la croute et modifie le profil aromatique. Il en est de même pour les fromages Bleu d’Auvergne conservés dans des cellules à teneurs contrôlées en O2 et CO2. Une atmosphère contenant 2,5% d’oxygène et 10% de C02 seraient la plus favorable pour obtenir des fromages ayant des caractéristiques microbiennes (diversité des bactéries d’affinage) et un profil de composés d’arôme proches de ceux conservés en pain entier. Cette méthodologie de caractérisation guidera le choix des emballages en fonction de leur perméabilité.Packaging PDO cheeses is very specific. The gas and water vapor permeability characteristics of the packaging influence the composition of the microbial community and its metabolism as illustrated for two PDO cheeses. The Saint Nectaire portion packaging under film very few permeable to air and water vapor reduces the yeast levels and ripening bacteria, affects the appearance of the rind and impacts the profile of aromatic compounds. It is the same for Bleu d'Auvergne cheese stored in ripening cells with controlled content of O2 and CO2. An atmosphere with 2.5% oxygen and 10% CO2 would be the most suitable to get microbial (diversity of ripening bacteria) and aromatic profiles characteristics, similar to those of the whole cheeses. This methodology of characterization will orient the choice of packaging depending on their permeability

Initial studies into the characterisation of ripening stages of Emmental cheeses by mid-infrared spectroscopy

Experimental Emmental cheeses were analysed to evaluate the potential of mid-infrared spectroscopy to follow the ripening process. Cheeses were sampled at seven different ripening stages and were analysed. The infrared spectra were obtained by placing the cheese slices directly over the attenuated total reflectance crystal. Analysis of variance showed significant (P $\leqslant$ 0.05) absorbance changes between spectral sets in the regions assigned to vibrations of alcohol, amide and hydrocarbon chains. Principal component analysis (PCA) made it possible to describe four groups including samples ripened during 21, 27 and 34 days (G1), 51 and 58 days (G2), 65 days (G3) and the samples at the end of the ripening (mould opening, about 85 days) (G4). Using general discriminant analysis of spectral data, it is not possible to correctly distinguish samples according to seven dates of sampling, but samples belonging to the four groups identified by PCA are predicted well by the regression model

Development and validation of a dynamic system for monitoring in vitro food digestion

The best model for studying food digestion remains the Human himself. An alternative to in vivo assays is to use in vitro digestion system. The complexity is to perform a device able to mimic accurately the fate of the food occurring in the human digestive tract. The objective of this work was to develop a simple and rather cheap dynamic digestion system enabling the study of the disintegration occurring in the gastro-intestinal tract of neonate and to validate it towards in vivo data. Digestion of an infant formula was studied both in vitro and in vivo using the piglet model. The formula was adapted to the energy and protein requirements of piglets. Six piglets were slaughtered 30, 90 and 210 min after the meal intake. Effluents from the different compartments of the gut were collected at these 3 time points. In parallel, the same infant formula was digested using the in vitro dynamic digestion system. The device consists in two compartments i.e. stomach and small intestine, and is computer-controlled. Milk proteolysis was followed by SDS-PAGE and ELISA both in vivo and in vitro. The validation was assessed by comparing the kinetics of residual immunoreactivity of β-lactoglobulin and caseins. Results showed a good accordance between the 2 systems of digestion. A level of in vitro/in vivo correlation was established with a correlation coefficient of 0.987. Casein content decreased rapidly during the first 30 minutes of gastric digestion. In contrast, β-lactoglobulin remained much longer intact in the stomach (120 min after ingestion). Intestinal digestion resulted in rapid and drastic hydrolysis, no more intact proteins were detected. This validation on infant formula, using the piglet model, has confirmed that this in vitro dynamic digestion system is reliable