Jean-Michel Le Quéré

Infrared glass fibers for in-situ sensing, chemical and biochemical reactions

Infrared optical fibres based on chalcogenide glasses have been designed for evanescent wave spectroscopy. The sensitivity of the optical sensor is improved in tapering the sensing zone by chemical etching and the working optical domain of the system has been tested on a chloroform sample. This original remote sensor, based on the analysis of infrared signatures, has been applied to follow the fermentation process in cider fabrication as well as to detect and monitor a bacterial biofilm.

Polyphenol Profiling of a Red-Fleshed Apple Cultivar and Evaluation of the Color Extractability and Stability in the Juice

Red-fleshed apples can be used for the production of innovative products such as rosé juices and ciders. Phenolic compounds including procyanidins (i.e., condensed tannins) and anthocyanins were quantified in the fruits and juices of a red-fleshed apple cultivar by chromatography coupled to UV-visible and mass spectrometry. Juice color was characterized by colorimetry. The influence of oxygen, pH, sulfites, ascorbic acid, and copper on the color stability of the juice was studied in an experimental design. Fruits were rich in polyphenols (0.5 g/100 g FW), with anthocyanins and procyanidins accounting for 9 and 73% of total polyphenols, respectively. Extractability of anthocyanins in the juice was 26%. Juice storage under air atmosphere at 35 °C resulted in significant browning with the anthocyanin level decreasing up to 86% after 14 days. In contrast, color was stable for storage under argon atmosphere. Sulfites, ascorbic acid, and copper have only a slightly influence on color stability in those conditions.

HPLC-DAD-MS Profiling of Polyphenols Responsible for the Yellow-Orange Color in Apple Juices of Different French Cider Apple Varieties.

The pigments responsible for the yellow-orange coloration of apple juices have remained largely unknown up to now. Four French cider apple juices were produced in conditions similar to those used in the cider-making industry. The oxidized juices, characterized using the CIE L a b parameters, displayed various colors depending on the apple variety and native phenolic composition. HPLC-DAD-MS revealed contrasting pigment profiles related to oxidized tanning and nontanning molecules. The latter were divided into two groups according to their polarity and their visible spectra. With regard to phenolic classes, flavanol monomers and hydroxycinnamic acids played an essential role in the formation of oxidation products. Interestingly, dihydrochalcones appeared to include precursors of some yellow compounds. Indeed, the yellow pigment phloretin xyloglucoside oxidation product (PXGOPj), derived from phloretin xyloglucoside, was clearly identified in apple juices as a xyloglucose analogue of the yellow pigment phloridzin oxidation product (POPj), previously characterized in a model solution by Le Guernevé et al. (Tetrahedron Lett. 2004, 45 (35), 6673-6677).

Haze in Apple-Based Beverages: Detailed Polyphenol, Polysaccharide, Protein, and Mineral Compositions

Producers of apple-based beverages are confronted with colloidal instability. Haze is caused by interactions between molecules that lead to the formation of aggregates. Haze composition in three apple-based beverages, namely, French sparkling cider, apple juice, and pommeau, was studied. Phenolic compounds, proteins, polysaccharides, and minerals were analyzed using global and detailed analytical methods. The results explained <75% (w/w) of haze dry mass. Polyphenols, represented mainly by procyanidins, were the main compounds identified and accounted for 10-31% of haze. However, oxidized phenolic compounds were probably underestimated and may represent a high proportion of haze. Proteins were present in all of the samples in proportions of <6% of haze except in two apple juice hazes, where they were the main constituents (18 and 24%). Polysaccharides accounted for 0-30% of haze. Potassium and calcium were the main minerals.