1,720,991 research outputs found
Continuous fluorescence-based quantitative antioxidant assay using vegetable oil as an oxidizable substrate
No full textSeveral spectrophotometric assays, such as 1,1-diphenyl-2-picrylhydrazyl (DPPH) and oxygen radical absorbance capacity (ORAC), are commonly used to assess antioxidant activity. However, these methods often lack real-world relevance as they do not inhibit autoxidation in actual food substrates. Although direct measurement of oxygen consumption or peroxide formation during inhibited autoxidation offers certain advantages, it is labor intensive and requires specialized equipment. In this study, we introduce a small-volume inhibited autoxidation approach that utilizes a standard microplate reader and a food-derived oxidizable substrate, specifically stripped sunflower oil (SSO), and styrene-conjugated BODIPY (STY-BODIPY) chromophores that oxidizes with the substrate, enabling straightforward monitoring of the reaction progress without interfering with it. The rate of initiation (Ri) was controlled by using azobis(isobutyronitrile) (AIBN) at 30 °C (Ri = 8.6 ± 0.5 × 10−10 M s−1) to accurately determine the rate constant of antioxidant reaction with peroxyl radicals (kinh). The method was standardized using the synthetic α-tocopherol analogue 2,2,5,7,8-pentamethyl-6-chromanol (PMC) as a reference antioxidant and was successfully applied to evaluate its synergistic interactions with γ-terpinene, quercetin, and caffeic acid. The rate constant for the reaction of peroxyl radicals with STY-BODIPY was determined, kST = 890 ± 52 M−1 s−1. Induction time (τ) of PMC increased in a concentration-dependent manner by the synergistic interactions of PMC/γ-terpinene, PMC/quercetin, and PMC/caffeic acid. The kinh value for PMC in SSO at 30 °C remained constant at 1.5 × 106 M−1 s−1. The validity of this approach was further confirmed using isothermal calorimetry, demonstrating its potential as a reliable and accessible tool for antioxidant testing in food systems
Hydrogen and Atom Transfer Activity of Saffron Extracts by Square Wave Voltammetry
No full textSaffron is an edible spice with highly appreciated sensory and antioxidant properties. One of the most representative redox species found in saffron extracts is crocin, whose content is used to evaluate the quality and value of the resulting spice. In this study, a voltammetry method based on the direct detection of crocin at a bare glassy carbon electrode is presented. The principle of the method is based on the monitoring of the anodic wave exhibited by crocin (0.1–1.0 mM) after its mixing with the azo radical initiator AAPH (20 mM) in ethanol:acetonitrile (1 : 1) solution. The decay rate of the anodic peak (E=+434 mV vs. Ag/Ag+), as a result of the consumption of crocin by AAPH, was used as index of the hydrogen transfer capacity and, thus, of its antioxidant activity. With a decay rate of k=0.02 h−1, crocin exhibits only a weak antioxidant activity in comparison with tocopherols (k=0.13 h−1), but still sufficient to protect against the oxidation of safranal, a further redox species found in saffron extracts and mainly responsible for its flavor. The proposed approach was finally applied to discriminate saffron extract samples from different geographical origins. The proposed approach is suitable to characterize the quality of saffron extracts and estimate its antioxidant properties
Effects of ascorbic acid and light on reactions in fresh-cut apples by microcalorimetry
No full textDuring the manufacturing of fresh-cut apples, a number of biochemical events, overall exothermic, con-tribute to increasing the reaction rate of the fruit and the browning of its wounded surface. This workapplied isothermal microcalorimetry to compare the overall effect of such complex events before andafter treatments with ascorbic acid solutions, pulsed lights or UV-C lights. Briefly, apple samples werecut into cylinders and dipped in solutions containing ascorbic acid (0–2.5%) or exposed to high energydoses of light (from 6 to 175 kJ/m2). In general, the heat-flow signal recorded by microcalorimetry wasinversely proportional to the intensity of the applied treatment. In case of treatments with ascorbicacid, the heat-flow signal was empirically deconvoluted in three distinctive signals, respectively, (I) anexponential decay, (II) a gaussian central curve and (III) a final logistical function. The first and the thirdfunctions were constant regardless of the concentration of ascorbic acid used. Only the second Gaussianfunction was correlated with the concentration of ascorbic acid and the area was used to evaluate theefficacy of the process. Overall, this work contributes to the understanding of the heat produced by fruitafter wounding and, from a practical standpoint, can help compare the effects of different treatments onfresh cut fruits
Dietary Fibers Effects on Physical, Thermal, and Sensory Properties of Low-Fat Ice Cream
No full textThis study investigated the effect of incorporating dietary fibers, inulin, acacia, oat, and apple, in a low-fat vanilla ice cream. A significant increase in the ice cream mixture viscosity was observed with the addition of dietary fibers. Significant differences (p<0.05) were observed in the crystallization temperature when apple and oat fibers were used. Additionally, low-fat dietary fiber ice creams displayed statistically lower (p<0.05) glass transition and melting temperatures than full-fat ones, with the most pronounced reductions observed for samples enriched with acacia and apple fibers. Dietary fibers affected (p<0.05) the sensory profile of low-fat ice cream. However, inulin and acacia fibers samples showed a sensory profile comparable to the full-fat ice cream for nearly all attributes. These findings suggest that utilizing inulin and acacia fibers in low-fat ice cream yields characteristics of full-fat, underscoring the potential for crafting high-quality, reduced-fat ice cream products
Lactic acid fermentation enriches the profile of biogenic fatty acid derivatives of avocado fruit (Persea americana Mill.)
No full textThis study investigated the capability of selected autochthonous lactic acid bacteria to enrich the portfolio of bioactive compounds of avocado fruit (Persea americana Mill.), with the perspective of producing dietary supplements or pharmaceutical preparations. Fermented avocado puree resulted in high levels of total free amino acids. Fermentation also led to a marked increase of antioxidant activity, with the highest levels found in water and hexane soluble extracts. Bio-converted phenolic compounds and fatty acids derivatives resulting by the bacterial metabolism were likely responsible for the increased antioxidant activity. Fermentation caused the fortification of avocado puree with some hydroxy fatty acids, which deserved marked attention due to their health-promoting activities. Oleic and linoleic acids were highly metabolized by Lactobacillus plantarum AVEF17, leading to high levels of mono, di-, and tri-hydroxy-octadecenoic acids
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Antioxidant efficiency and oxidizability of mayonnaise by oximetry and isothermal calorimetry
Full text link: This study aimed to introduce a new method based on isothermal calorimetry (IC) for measuring the autoxidation rate in mayonnaise samples. Mayonnaise samples were prepared by homogenizing an aqueous phase, consisting of vinegar and egg yolk, with various oil phases, including sunflower, corn, extra virgin olive, grape seed, and apple seed oils at 60 °C. The rate of free radical formation (Ri) was controlled by adding AIBN (Ri = 4.4±0.1×10-9 M/s). The autoxidation rate determined by IC was highly correlated with the one measured using the oxygen uptake method (R2 = 0.99). The IC method accurately indicated the antioxidant capacity and rates of both inhibited and uninhibited periods, together with the oxidizability of mayonnaise samples. The mayonnaise made with extra virgin olive oil exhibited the lowest oxidizability, while sunflower oil showed maximum antioxidant efficiency. A significant advantage of the IC method was its ability to simultaneously measure up to 24 samples with minimal effort
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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