Impact of fermentation on nitrogenous compounds of cocoa beans (Theobroma cacao L.) from various origins.

Tangential filtration technique was used to separate and quantify three different fractions of nitrogenous compounds depending on their molecular size, during cocoa fermentation. On every phenotype and origin analyzed, protein profile of non-fermented samples was similar. During fermentation course, proteins get degraded with a concomitant increase in amino acids content. Peptides between 3 and 10 kDa were observed at low levels. A strong correlation between amino acids and ammonia nitrogen, a fermentation marker was found. Attention was drawn on each fraction, and enabled to point out other phenomenon occurring during fermentation. The migration of some nitrogenous compounds towards the bean shell during fermentation was demonstrated. Acetone treatment of cocoa powder prior to SDS-PAGE led to losses of nitrogenous compounds. This result gives clues on the tanning phenomenon carried out by polyphenols on nitrogenous compounds, phenomenon which increases during fermentation.

Near infrared spectroscopy as a new tool to determine cocoa fermentation levels through ammonia nitrogen quantification.

Fermentation is a key step in obtaining fine cocoa through the formation of potent aroma precursors. The fermentation level of cocoa beans is traditionally assessed by measuring the amount of ammonia nitrogen (NH3) using the time-consuming Conway technique. Near infrared spectroscopy (NIRS), a rapid and efficient tool, was used to analyze NH3 levels in several hundred cocoa samples at different fermentation levels from six geographical origins. Fermentation levels were expressed as the number of fermentation days and sum of temperatures. The correlation between Conway results and NIRS spectra enabled the development of a reliable and accurate NIRS calibration to determine NH3 content. We confirm that NH3 is produced during fermentation and its amount depends on the fermentation time, sum of temperatures and geographical origin. NIRS could be used by chocolate manufacturers as a routine method to sort cocoa samples according to their level of fermentation.

A study by spectroelectrochemical FTIR and density functional theory calculations of the reversible complexing ability of an electroactive tetrathiafulvalene crown.

We report on the study of the electrochemically targeted complexation/expulsion of a metal cation (Ba2+) by a crown ether tetra(thiomethyl)tetrathiafulvalene derivative (crown-TTM-TTF). Real time, in situ FTIR spectroelectrochemistry was used to obtain spectroscopic evidence of this electrochemically triggered phenomenon. Density functional theory calculations allowed the spectral information collected to be assigned. Both experimental and theoretical results clearly show that neutral crown-TTM-TTF complexes well Ba2+. Complexation is evidenced by a significant downshift of the frequency corresponding to the asymmetric stretching of the C-O-C ether groups. Concerning the cation crown-TTM-TTF, the spectroscopic signal of the complex form was difficult to identify, first because of the rather low value of the complexation constant and second because the vibration modes involving the oxygen atoms (which are the most affected by the complexation) were found by calculation to occur in the lower spectral region (<1000 cm(-1)), which is not accessible in our experimental conditions. In the case of the dication crown-TTM-TTF, it is now clear that the complex form does not exist, which means that the electrochemical formation of the dication necessarily involves the expulsion of the barium ion.

Changes in acidity and in proton transport at the tonoplast of grape berries during development.

As in many fruits, the induction of grape berry (Vitis vinifera L.) ripening results in intense breakdown of malic acid. Using membrane fractions, we tested the hypothesis that changes in acidity resulted from malate vacuolar decompartmentation. The hydrolytic activities of the two primary vacuolar pumps inorganic pyrophosphatase (V-PPase; EC 3.6.1.1) and vacuolar ATPase (V-ATPase; EC 3.6.1.3) increased throughout development with an acceleration during ripening, as confirmed by Western blotting and analysis of transcript expression. The ratio of V-PPase activity to V-ATPase activity was always in favour of V-PPase and reached its maximum value at véraison. The rate of anion transport strongly increased during ripening. Before ripening, tonoplast passive permeability was low, but rose during ripening. Our data indicate that tonoplast leakage dramatically increased during ripening. This leakage is probably the prime cause of malate decompartmentation, amplified by the incapacity of oxidative phosphorylation to face increased energy demand.

A spectroelectrochemical study of the reduction of a Schiff base cryptand.

The electrochemical reduction of a bicyclic hexaimino Schiff base cryptand 1 (N[(CH2)2N-CH-meta-C6H4-CH=N(CH2)2]3N) and that of one of its strands 2 ((CH3)2CH-N=CH-meta-C6H4-CH=N-CH(CH3)2) has been studied by visible and near infrared in-situ spectroelectrochemical techniques. These results are in good agreement with those obtained using alkali metals, but in this case the effect of the formation of ion pairs is minimized through the use of tetrabutylammonium cations. It is confirmed that 1- and 1= have the same visible and near IR spectrum. The spectrum of the products of the electrochemical reduction of 2 is similar to those of 1- or 1=.