24 Questions
What is the underlying principle of the HORAC assay?
Evaluation of the protecting ability against the formation of hydroxyl radicals
What is the role of fluorescein in the HORAC assay?
To incubate with the sample to be analyzed
What is the purpose of the Fenton mixture in the HORAC assay?
To generate hydroxyl radicals
What is the unit of expression for the results of the CUPRAC assay?
Milligrams of Trolox per liter of extract
What is the mechanism of action of antioxidants in the DPPH assay?
Reduction of DPPH to its molecular form
What is the wavelength at which the absorbance is measured in the CUPRAC assay?
450 nm
What is the type of compound that the CUPRAC assay is typically used to measure?
All of the above
What is the purpose of the gallic acid solutions in the HORAC assay?
To build the standard curve
What is the wavelength at which the decrease of UV absorption is followed to evaluate the antioxidant concentration effect?
517 nm
Which method is based on the reduction of potassium ferricyanide by antioxidants, resulting in a blue-colored complex?
PFRAP (Potassium ferricyanide reducing power) method
What is the purpose of using Trolox as a standard antioxidant?
To standardize the antioxidant concentration effect
In the Fluorometry method, what is the excitation wavelength used to obtain the emission spectra?
310 nm
What is the wavelength range in which the fluorescence is measured in the Fluorometry method?
320-800 nm
What is the color of the complex formed in the PFRAP method?
Blue
Which antioxidants are typically used in the fluorometric method for the determination of antioxidant concentration in biodiesel?
BHA and TBHQ
What is the primary application of the Fluorometry method in the context of antioxidant determination?
Phenolic compound determination in oils
What is the primary function of antioxidants in the biological system?
To delay or inhibit the oxidation processes
Which of the following is NOT a consequence of excessive reactive oxygen species?
Immune system enhancement
What is the purpose of the fluorescent probe in the ORAC assay?
To detect antioxidant scavenging activity
What is the benefit of using the ORAC assay in the industry?
It allows for the measurement of antioxidant activity in both hydrophilic and hydrophobic compounds
What is the role of 2,2'-azobis-(2-amidino-propane) dihydrochloride in the ORAC assay?
It is a source of peroxyl radicals that model reactions of antioxidants with lipids
What is the advantage of using the ORAC assay compared to other antioxidant capacity analysis methods?
It provides a controllable source of peroxyl radicals that model reactions of antioxidants with lipids
What is the significance of the ORAC assay in the study of antioxidant compounds?
It is used to study the antioxidant capacity of a wide range of compounds and food samples
What is the outcome of the reaction between the fluorescent probe and the peroxyl radical in the ORAC assay?
A decrease in fluorescence intensity
Study Notes
Antioxidant Capacity Determination
- Antioxidant concentration can be evaluated by following the decrease of UV absorption at 517 nm, with Trolox used as a standard antioxidant.
PFRAP (Potassium Ferricyanide Reducing Power) Method
- An absorbance increase correlates to the reducing ability of antioxidants/antioxidant extracts.
- Antioxidants react with potassium ferricyanide, forming potassium ferrocyanide, which reacts with ferric trichloride, yielding a blue-colored complex with a maximum absorbance at 700 nm.
Fluorometry
- Fluorescence spectroscopy has been applied to determine phenolic compounds in oils.
- A method based on fluorescence is proposed to quantify BHA and TBHQ antioxidant concentration in biodiesel produced from sunflower and soybean oils.
- Biodiesel samples without BHA and TBHQ show a fluorescence band at around 420 nm, attributed to tocopherols inherent to the vegetable oils.
- The addition of BHA and/or TBHQ is responsible for the occurrence of a fluorescence band around 330 nm.
HORAC (Hydroxyl Radical Antioxidant Capacity) Assay
- Measures the antioxidant capacity of biological fluids, bio cells, and extracts under Fenton-like reactions.
- Use a Co(II) complex to evaluate the protecting ability against hydroxyl radical formation.
- Fluorescein is incubated with the sample, then the Fenton mixture is added, and fluorescence readings are taken every minute.
- Gallic acid solutions are used for building the standard curve.
CUPRAC (Cupric Reducing Antioxidant Power) Assay
- Measures polyphenol and flavonoid number and plasma serum antioxidant capacity.
- Standard antioxidants or extracts are mixed with CuSO4 and neocuproine, and the absorbance is measured at 450 nm after 30 minutes.
- Results are expressed in milligrams of Trolox per liter of extract.
DPPH Method (Standard 2,2-Diphenyl-1-Picrylhydrazyl)
- Measures the antioxidant activity of tissue extracts by acting as free radical scavengers or hydrogen donors.
- DPPH reacts with a hydrogen donor of an antioxidant, reducing the DPPH radical, causing a color change from purple to yellow.
ORAC (Oxygen Radical Absorption Capacity) Assay
- Measures the antioxidant scavenging activity against the peroxyl radical.
- Uses 2,2'-azobis-(2-amidino-propane) dihydrochloride as a controlled source of peroxyl radicals.
- Fluorescein is used as a fluorescent probe, and the reaction with the peroxyl radical causes a loss of fluorescence.
- Determines the quantity of antioxidant decomposition amount.
- Provides a controllable source of peroxyl radicals that model reactions of antioxidants with lipids in food and physiological systems.
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