Moisture induced solid phase degradation of l-ascorbic acid part 2, separation and characterization of the major degradation products

Evaluation and application of a paper-based device for the determination of reactive phosphate in soil solution

The evaluation and validation of a new low-cost microfluidic paper-based analytical device (μPAD) for the determination of reactive phosphate in soil solution is described. This device allows up to 15 replicate measurements of reactive phosphate on one credit card-sized device and requires only a desktop or hand scanner for signal detection and quantification. The proposed method showed a linear response between 0.1 and 1.0 mg L and between 1.0 and 10.0 mg L P with a limit of detection of 0.05 mg L P. When applied to the analysis of soil solution, there was excellent agreement between results obtained using the μPAD and those obtained by a reference spectrophotometric method, as indicated by the following regression equation: [P] = (0.997 ± 0.005)[P] - (0.020 ± 0.008) ( = 0.997; = 110). It was found that the ambient temperature storage stability of the μPAD could be extended to 15 d by incorporating a removable polymeric interleaving sheet between the adjacent paper layers of the device. The observed sensitivity of the μPADs to sunlight, which was manifested by photoreduction of the chromogenic molybdate reagent used in the assay, was overcome by preparing the μPADs with an ultraviolet-filtering laminating material. The proposed method is rapid, with a reaction time of only 10 min, is easy to perform, and is suitable for application in the field.

Ascorbic acid: a review of its chemistry and reactivity in relation to a wine environment

Extensive reviews of research are available on the use of ascorbic acid, and its consequent degradation pathways, in physiological conditions or food matrices. However, very little information can be found for wine-related systems. This review highlights the relevant chemistry and reactivity of ascorbic acid with a focus on its behavior and potential behavior in a wine environment. The review describes the use of ascorbic acid as a complementary antioxidant preservative to sulfur dioxide along with the metal-catalyzed and radical-dependent manner by which it achieves this role. The relevant degradation products of ascorbic acid in aerobic and anaerobic conditions are presented as well as the interaction of these degradation products with sulfur dioxide and other wine-relevant sulfur compounds. Limitations in existing knowledge, especially regarding the crossover between the antioxidant and pro-oxidant roles of ascorbic acid, are identified.

Identification of a sotolon pathway in dry white wines

Sotolon (3-hydroxy-4,5-dimethyl-2(5H)-furanone) is a chiral furanone, an aroma compound known to be responsible for premature-aging flavor in dry white wines. Sotolon generally results from mild oxygenation during bottle aging, and until now, its formation pathways had not been elucidated. The ability of the main precursors described in the literature under very different experimental conditions to produce sotolon was tested. In model wine solution maintained at 40 degrees C for 6 months, sotolon was produced by the oxidative degradation of ascorbic acid. By use of GC-MS, 2-ketobutyric acid, produced by the oxidative degradation of the ascorbic acid in the model wine solution, was identified as a potent precursor of sotolon in this pathway. Ascorbic acid is an exogenous compound, added before bottling, but 2-ketobutyric acid was found even in white wines that had not been supplemented. Consequently, this sotolon formation pathway is also valid in white wines with no added ascorbic acid. In addition, we showed that Saccharomyces cerevisiae strains were capable of producing variable concentrations of this ketone during alcoholic fermentation. In model wine solution, certain yeast strains released large quantities of 2-ketobutyric acid, similar to those found in oxidized dry white wines. In view of these results, the role of yeast strains in this premature-aging phenomenon of dry white wines is discussed. Finally, these investigations revealed that one chemical mechanism responsible for the low concentrations of sotolon found in prematurely aged white wines made from various grape varieties was an aldol condensation between 2-ketobutyric acid and acetaldehyde.

Influence of simultaneous variations in temperature and relative humidity on chemical stability of two vitamin C forms and implications for shelf life models

Vitamin C powder ingredients are popular food fortificants and are among the most commonly added nutrients. While information on degradation kinetics and shelf life of vitamin C exists, current models are limited in their applicability to systems where relative humidity (RH) and temperature are varied simultaneously, and where phase transformations occur. This study monitored stability of two forms of vitamin C (sodium ascorbate and ascorbic acid) under various RH and temperature conditions. Vitamin C was measured colorimetrically, and stability data were used to improve understanding of vitamin C shelf life when deliquescence occurs during storage. RH and temperature both significantly impacted vitamin stability, though RH had a larger effect. Vitamin dissolution preceded extensive degradation and was found to be a good predictor of vitamin C loss. This research highlights the importance of considering phase transformations when constructing shelf life models and maintaining vitamin C in the solid state for enhanced stability.

Development and validation of a liquid chromatographic method for the determination of ascorbic acid, dehydroascorbic acid and acetaminophen in pharmaceuticals

A reversed-phase ion pair liquid chromatographic method (RP-LC) for the determination of dehydroascorbic acid (DHA) and ascorbic acid (AA) and also acetaminophen, which is combined in pharmaceuticals, is proposed and validated. AA and acetaminophen were analyzed directly, while DHA was determined after pre-column derivatization with 4,5-dimethyl-1,2-phenylenediamine (DMPD). The derivatization reaction was carried out under mild conditions (10min at ambient temperature) in the dark in sodium acetate buffer (80mM; pH 3.7) solution containing EDTA as metal scavenger. The chromatographic separations were performed on a Phenomenex Synergi 4u hydro-RP (150mmx4.6mm) under isocratic elution conditions, using cetyltrimethylammonium bromide (CTAB) as ion-pairing reagent in the mobile phase. Linear responses were observed for each compound. The intra-day precision (R.S.D.) was < or =1.40% and there was no significant difference between intra- and inter-day data. Recovery studies showed good results for all compounds (99.7-101.8%) with R.S.D. ranging from 0.56 to 1.82%. The limits of quantitation were about 40, 50 and 140pmol for acetaminophen, AA and DHA, respectively. The DHA impurity values found in dosage forms were < or =0.2% of AA.