Relationship between antioxidant capacity and total phenolic content of red,rosé and white wines

Phenolic compounds are one of the most important quality parameters of wines, since they contribute to wine organoleptic characteristics such as colour, astringency, and bitterness. Furthermore, several studies have pointed out that many show biological properties of interest, related to their antioxidant capacity. This antioxidant activity has been thoroughly studied and a wide variety of methods have been developed to evaluate it.     

Synthesis and antioxidant activity of selected 4-methylcoumarins

A series of selected 4-methylcoumarins (4-methyl-2H-1-benzopyran-2-ones) were synthesised and tested for radical-scavenging ability using the stable 1,1-diphenyl-2-picrylhydrazyl radical, and for reducing power ability with a test based on the reduction of ferric to ferrous cation. All studied compounds showed activity comparable to Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), an already known antioxidant, which is used as standard in most of the testing methods. Observations from the study were made with regard to structural features that regulated the behaviour of the compounds. The antioxidant activity of some 4-methylcoumarin representatives is presented here for the first time and extends our knowledge of the range of valuable biological activities and possible roles in therapy and for food preservation associated with this group of compounds.     

ABTS radical scavenging capacity in green and roasted coffee extracts

The impact of two parameters (temperature and duration) on the radical scavenging capacity of individual compounds, and total extracts found in coffee was investigated. Phenolic coffee extracts of light (200 °C), medium (225 °C) and dark (235 °C) roasted coffees in a range of 0–30 min were analyzed by an on-line RP-HLPC-ABTS^•+ decolourization assay. This study revealed a general decrease of radical scavenging capacity related to native phenolic compounds. Processing coffee beans leads to generation of up to 10 new radical scavengers. The roasting process influences not only color and taste in coffees, but also the radical scavenging capacity of coffee as well. Phenolic content in roasted coffee and green coffee is very different. Six compounds identified as caffeoylquinic acids and dicaffeoylquinic acids, endowed with radical scavenging capacity were found in green coffee, whereas depending on the roasting process, roasted coffees can present up to 16 different radical scavengers. The compounds formed during the roast are most likely chlorogenic acids derivatives, of which 4 could be clearly identified as two feruloylquinic acids and two caffeoylquinides. In longer roasting durations, these molecules are subjected to auto-degradation, thus total radical scavenging capacity in coffee decline along with roasting (duration and temperature).     

Thermal oxidation of vanillin affects its antioxidant and antimicrobial properties

Accelerated oxidation of vanillin was studied by isothermal and non-isothermal differential scanning calorimetry (DSC) in model solutions. Exothermic peaks of DSC thermograms, due to the oxidation of vanillin, were observed. Vanillin oxidation to vanillic acid was confirmed by the detection of vanillic acid in heated vanillin samples using GC–MS. The effect of temperature on vanillin oxidation was studied by conducting DSC experiments with pure vanillin at several different final temperatures and by subsequent determination of vanillin and vanillic acid by GC–MS.     

In vitro antioxidant properties and phenolic composition of Salvia halophila Hedge from Turkey

An endemic plant of Turkey Salvia halophila Hedge (Lamiaceae) was examined for its antioxidant activity and phenolic compositions. The aerial part of S. halophila was extracted with different solvents in an order of increasing polarity such as hexane, ethyl acetate, methanol, and 50% methanol using a Soxhlet apparatus. Water extract was also prepared from S. halophila by reflux. All solvent fractions were investigated for their total phenolic contents, flavonoids, flavonols, qualitative–quantitative compositions, iron(III) reductive activities, free radical scavenging activities and the effect upon linoleic acid peroxidation activities. The peroxidation level was also determined by the TBA method. The results of activity tests given as IC₅₀ values were estimated from non-linear algorithm and compared with standards via BHT, ascorbic acid, gallic acid. Polar fractions were found more active among the others in free radical activity system whereas non-polar fractions protected the peroxidation of linoleic acid. Rosmarinic acid was the most abundant component, in the extracts.