Spectrophotometric Profiles of Off-Flavor Aldehydes by Using Their Reactions with 2-Thiobarbituric Acid

Certain fungi thrive in highly radioactive environments including the defunct Chernobyl nuclear reactor. Cryptococcus neoformans (C. neoformans), which uses L-3,4-dihydroxyphenylalanine (L-DOPA) to produce melanin, was used here to investigate how gamma radiation under aqueous aerobic conditions affects the properties of melanin, with the aim of gaining insight into its radioprotective role. Exposure of melanized fungal cell in aqueous suspensions to doses of γ-radiation capable of killing 50 to 80% of the cells did not lead to a detectable loss of melanin integrity according to EPR spectra of melanin radicals. Moreover, upon UV-visible (Xe-lamp) illumination of melanized cells, the increase in radical population was unchanged after γ-irradiation. Gamma-irradiation of frozen cell suspensions and storage of samples for several days at 77 K however, produced melanin modification noted by a reduced radical population and reduced photoresponse. More direct evidence for structural modification of melanin came from the detection of soluble products with absorbance maxima near 260 nm in supernatants collected after γ-irradiation of cells and cell-free melanin. These products, which include thiobarbituric acid (TBA)-reactive aldehydes, were also generated by Fenton reagent treatment of cells and cell-free melanin. In an assay of melanin integrity based on the metal (Bi+3) binding capacity of cells, no detectable loss in binding was detected after γ-irradiation. Our results show that melanin in C. neoformans cells is susceptible to some damage by hydroxyl radical formed in lethal radioactive aqueous environments and serves a protective role in melanized fungi that involves sacrificial breakdown.

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“…6 ). The chromophore with a λ max = 450 nm has been reported for TBA adducts of saturated and unsaturated aldehydes [36] – [39] .…”

Section: Resultsmentioning

confidence: 95%

“…Malondialdehyde (MDA) is among the expected soluble products from γ-irradiation of cells along with other TBA-reactive substances arising from damage to biomolecules [26] , [35] , [36] . No report of such products coming from melanin, however, could be found.…”

Section: Resultsmentioning

confidence: 99%

Protection of Melanized Cryptococcus neoformans from Lethal Dose Gamma Irradiation Involves Changes in Melanin's Chemical Structure and Paramagnetism

et al. 2011

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“…In preliminary experiments, addition of TBA reagent to cooked meat samples containing raisins resulted in development of a yellow rather than a pink chromagen. Other investigators have also reported the development of a yellow interfering chromagen when TBA reagent was added to samples containing sugars or aldehydes (Jardine and others 2002; Almandos and others 1986; Sun and others 2001; Guzman‐Chozas and others 1997). Havens and others (1996) measured the absorbance of the yellow chromagen at 450 nm as a measure of lipid oxidation in freeze‐dried ground beef patties.…”

Section: Discussionmentioning

confidence: 99%

Evaluation of Antioxidant Effects of Raisin Paste in Cooked Ground Beef, Pork, and Chicken

Vasavada

Cornforth

2006

Journal of Food Science

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The objective of this study was to evaluate the possible antioxidant activity of raisin paste added to raw ground beef, pork, or chicken before cooking to 163 °C. Samples were held at 2 °C for up to 14 d. TBA values were measured using a distillation method, to avoid yellow color interference found in “wet” TBA methods. Sample meat flavor intensity, rancid flavor intensity, and raisin flavor intensity were evaluated by a trained panel (n = 6). Addition of raisin paste lowered (p < 0.05) TBA values and decreased panel scores for rancid flavor scores of all meat samples in a concentration‐dependent manner. Highest antioxidant effects were obtained with a minimum of 1.5%, 2.0%, or 2.0% raisin paste in cooked ground beef, pork, or chicken, respectively. There was a high correlation (0.93, 0.94, 0.94) between TBA values and sensory rancid flavor scores in beef, pork, and chicken samples respectively. Addition of a reducing sugar (glucose) was nearly as effective as raisins for maintenance of low TBA values and rancid flavor scores, probably due to antioxidant effects of Maillard browning products. There was no detectable raisin flavor in cooked ground beef samples with added raisins. However, all meats with added glucose had a higher raisin flavor intensity score than controls, indicating that panelists associated sweetness with raisin flavor. Maillard browning (sample darkening) was evident after cooking of ground chicken with either raisins or glucose.

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“…The extinction coefficient of 4‐nitrophenol at 405 nm was determined to 12920 cm −1 ·M −1 under the reaction buffer conditions (Figure S12). DDVP hydrolysis was monitored by measuring the absorbance at 490 nm after the addition of TBA (final concentration, 2 mM) and acetic acid (final concentration, 30% [vol/vol]), and heating for 1 hr at 100°C (GuzmanChozas, Vicario, & GuillenSans, 1997). A minimum of three replicates were performed for each kinetic assay.…”

Section: Methodsmentioning

confidence: 99%

Molecular binding scaffolds increase local substrate concentration enhancing the enzymatic hydrolysis of VX nerve agent

Lang

Hong

Baker

et al. 2020

Biotech & Bioengineering

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Kinetic enhancement of organophosphate hydrolysis is a long‐standing challenge in catalysis. For prophylactic treatment against organophosphate exposure, enzymatic hydrolysis needs to occur at high rates in the presence of low substrate concentrations and enzymatic activity should persist over days and weeks. Here, the conjugation of small DNA scaffolds was used to introduce substrate binding sites with micromolar affinity to VX, paraoxon, and methyl‐parathion in close proximity to the enzyme phosphotriesterase (PTE). The result was a decrease in KM and increase in the rate at low substrate concentrations. An optimized system for paraoxon hydrolysis decreased KM by 11‐fold, with a corresponding increase in second‐order rate constant. The initial rates of VX and methyl‐parathion hydrolysis were also increased by 3.1‐ and 6.7‐fold, respectively. The designed scaffolds not only increased the local substrate concentration, but they also resulted in increased stability and PTE‐DNA particle size tuning between 25 and ~150 nm. The scaffold engineering approach taken here is focused on altering the local chemical and physical microenvironment around the enzyme and is therefore compatible with active site engineering via combinatorial and computational approaches.

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Spectrophotometric Profiles of Off-Flavor Aldehydes by Using Their Reactions with 2-Thiobarbituric Acid

Cited by 17 publications

References 20 publications

Protection of Melanized Cryptococcus neoformans from Lethal Dose Gamma Irradiation Involves Changes in Melanin's Chemical Structure and Paramagnetism

Protection of Melanized Cryptococcus neoformans from Lethal Dose Gamma Irradiation Involves Changes in Melanin's Chemical Structure and Paramagnetism

Evaluation of Antioxidant Effects of Raisin Paste in Cooked Ground Beef, Pork, and Chicken

Molecular binding scaffolds increase local substrate concentration enhancing the enzymatic hydrolysis of VX nerve agent

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