Ziya Günata

Wine flavor enhancement through the use of exogenous fungal glycosidases

Abstract The use of a pectinase enzyme preparation in winemaking containing relevant glycosidase activities for the hydrolysis of glycosidically bound aroma compounds allowed to increase the levels of volatiles, monoterpenes, C 13 -norisoprenoids, and benzene derivatives. The highest increase was for the wine obtained from the juice enriched by glycosides through the contact of juice with skin parts of grape berry. Enzyme treatment enhanced the attributes, honey, lime, and smoky. The enzyme-treated wines were highly significantly different from the control wines and preferred to control wines.

Odor-active compounds in cooked rice cultivars from Camargue (France) analyzed by GC-O and GC-MS.

Volatile compounds of cooked rice from scented (Aychade, Fidji) and nonscented (Ruille) cultivars grown in the Camargue area in France were compared to that of a marketed Asian scented one (Thai) by gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS). GC-O analyses of the organic extracts resulted in the perception of 40 odorous compounds. Only two compounds, oct-1-en-3-one and 2-acetyl-1-pyrroline, were almost always perceived. Hierarchical cluster analysis showed that most of the difference between rice odors was linked to quantitative differences with only 11 compounds being specific to some of the rice. Sixty compounds were identified and quantified by GC-MS, including a few new odor-active components. Principal component analysis enabled us to differentiate scented cultivars from a nonscented one, and scented rice cultivars from Camargue from a Thai sample. Calculated odor-active values evidenced that the Thai sample odor differed from that of scented Camargue cultivars because of the degradation of lipids and of cinnamic acid compounds.

Purification and partial characterization of β-glucosidase from grape

Abstract β-Glucosidase was isolated from mature grapes (cv Muscat of Alexandria) and partially purified. The procedure used chromatography on Ultrogel AcA 44 and DEAE-Sepharose CL-6B. Two distinct peaks with β-glucosidase activity were reported. Except for their M r (98 000 for β-glucosidase 1, 50 000 for β-glucosidase 2) no differences occurred in other biochemical characteristics. For both, the optimum pH of activity was 5.0, the optimum pH for stability between 6 and 8, and the optimum temperature 45°. Their heat stabilities were also quite similar. The K m and V max values differ according the substrates. Affinity was maximal for p -nitrophenyl-β- d -glucoside. For natural substrates, the two enzymes had a high affinity for geranyl-β- d -glucoside. Glucose and gluconolactone were competitive inhibitors with K i of 170 and 0.215 mM respectively. Ca 2+ and Cu 2+ ions and p -chloromercuribenzoate also inhibited the enzymes.

Quantification of 2-acetyl-1-pyrroline in rice by stable isotope dilution assay through headspace solid-phase microextraction coupled to gas chromatography–tandem mass spectrometry

A new and convenient synthesis of 2-acetyl-1-pyrroline (2AP), a potent flavor compound in rice, and its ring-deuterated analog, 2-acetyl-1-d(2)-pyrroline (2AP-d(2)), was reported. A stable isotope dilution assay (SIDA), involving headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-positive chemical ionization-ion trap-tandem mass spectrometry (GC-PCI-IT-MS-MS), was developed for 2AP quantification. A divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber was used for HS-SPME procedure and parameters affecting analytes recovery, such as extraction time and temperature, pH and salt, were studied. The repeatability of the method (n=10) expressed as relative standard deviation (RSD) was 11.6%. A good linearity was observed from 5.9 to 779 ng of 2AP (r(2)=0.9989). Limits of detection (LOD) and quantification (LOQ) for 2AP were 0.1 and 0.4 ng g(-1) of rice, respectively. The recovery of spiked 2AP from rice matrix was almost complete. The developed method was applied to the quantification of 2AP in aerial parts and grains of scented and non-scented rice cultivars.

Effect of Timing and Duration of Salt Treatment during Growth of a Fragrant Rice Variety on Yield and 2-Acetyl-1-pyrroline, Proline, and GABA Levels

In greenhouse experiments, Aychade, a fragrant rice variety, was grown under one level of salt solution (EC of 3800 ± 400 μS·cm(-1)) sufficient to induce salt stress in rice. Timing and duration of salt solution application varied according to the growth stages. 2-Acetyl-1-pyrroline (2AP), a characteristic flavor compound of fragrant rice as well as biogenetically related compounds, proline, and γ-aminobutyric acid (GABA) were quantified. Salt treatments induced 2AP synthesis in the leaves, but the increase was often higher in the vegetative phase. This increase was correlated with proline level but not with that of GABA. Interestingly the grains from all the salt treated plants contained significantly higher levels of 2AP (733-998 μg·kg(-1)) than those from the control (592 μg·kg(-1)). The highest 2AP synthesis occurred when the plants were subjected to salt treatment during whole vegetative or reproductive phases. However in the latter case crop yield decreased significantly.

Grapefruit juices impair the bioaccessibility of β-carotene from orange-fleshed sweet potato but not its intestinal uptake by Caco-2 cells.

Among various factors influencing β-carotene (Bc) bioavailability, information on interactions between carotenoids or other micronutrients such as flavonoids during a meal that contains different plant-derived foods is quite limited. Because orange-fleshed sweet potato (OFSP) is an important Bc-rich staple food, a source of vitamin A in developing countries, this study focused on the effect of citrus fruit juice carotenoids and flavonoids on Bc bioaccessibility from OFSP. In vitro digestion coupled with the Caco-2 cell culture model was used to evaluate the bioaccessibility and cellular uptake of Bc from OFSP in the presence of pink grapefruit (pGF) or white grapefruit (wGF) juices. The addition of grapefruit juices significantly decreased the bioaccessibility, by up to 30%, but not the cellular uptake of Bc from boiled OFSP. Lycopene, but more probably naringin, present in grapefruit juices was suspected to be responsible for the inhibitory effect of the citrus juices on Bc bioaccessibility. This inhibition was apparently due in part to competition for incorporation between Bc and naringin into mixed micelles during in vitro digestion. In contrast, Bc uptake from dietary micelles was not impaired by naringin.

Production of a recombinant carotenoid cleavage dioxygenase from grape and enzyme assay in water-miscible organic solvents

A recombinant carotenoid cleavage dioxygenase from Vitis vinifera L. was produced by Escherichia coli as a fusion with the glutathione-S-transferase (GST) protein under different bacterial growth conditions. The enzyme production was monitored by a GST assay. Addition of Triton X-100 prior to bacterial cell disruption doubled the release of soluble protein. A simple spectrophotometric enzyme assay was developed to measure carotenoid cleavage activity using lutein as substrate. Enzyme activity showed a 26-fold increase with the addition of 10% (v/v) acetone in the reaction mixture.

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.

Biotransformation of C13-norisoprenoids and monoterpenes by a cell suspension culture of cv. Gamay (Vitis vinifera)

A cell suspension culture of cv. Gamay was studied for its ability to metabolize two different C13-norisoprenoidic volatiles, β-ionone and dehydrovomifoliol, together with monoterpenes, geraniol and linalool, biogenetically common pathways sharing compounds. β-Ionone was totally metabolized leading to fourteen norisoprenoidic volatiles oxygenated mainly at carbons 3 or 4 of the cyclohexane ring or reduced at side chain. The biotransformation of dehydrovomifoliol was at a lesser extent, giving rise to oxygenated and reduced derivatives. The norisoprenoidic metabolites were present both under free and glycosylated forms. Geraniol and linalool were also metabolized, leading to several free and glycosylated compounds.

Analysis of neutral lipids from microalgae by HPLC-ELSD and APCI-MS/MS.

A method was developed to analyze neutral lipids through the use of three triglycerides, four free fatty acids, six di- and four mono-glycerides standards by high performance liquid chromatography (HPLC) normal phase coupled with either with evaporative light scattering detector (ELSD) or with mass spectrometry (MS) operating in atmospheric pressure chemical ionization (APCI) mode. The method was applied to the determination of the neutral lipid fraction from a Botryococcus braunii race A (B. braunii) culture. This method led us to identify neutral lipids synthesized by B. braunii in a single analysis within 45min through HPLC-APCI-MS/MS technique.