Antioxidants measures

Quantification of antioxidant action usually relies on the reducing ability of antioxidants, measured either by electron transfer, reaction [16.15], or by hydrogen atom transfer reactions, reaction [16.16] ... 

For many decades, the standard technique for measuring carotenoids has been high-pressure liquid chromatography (HPLC). This time consuming and expensive chemical method works well for the measurement of carotenoids in serum, but it is difficult to perform in human tissue since it requires biopsies of relatively large tissue volumes. Additionally, serum antioxidant measurements are more indicative of short-term dietary intakes of antioxidants rather than steady-state accumulations in body tissues exposed to external oxidative stress factors such as smoking and UV-light exposure. 

Sun T and Powers JR. 2007. Antioxidants and antioxidant activities of vegetables. In Shahidi F, Ho C-T, editors. Antioxidant Measurement and Applications. Washington, DC American Chemical Society, pp. 160-183. 

At best, then, consumption of green tea beverage or capsules containing the concentrated catechins as a cytoprotective and antioxidant measure is logical and supported by much data. At worst, this is a pleasant custom which appears to do no harm in the vast majority of cases. 

There are few direct comparisons of total phenol values and antioxidant measurements, although some do exist (e.g., Baderschneider... 

Synthetic antioxidants BHT and TBHQ did not affect the color development in TBA analysis. With the analysis of extracted TL to lipid classes of nonpolar lipid (NL) and polar lipid (PL) fractions, the antioxidants did not interfere with the PL analysis. With NL analysis, the peak for TBHQ overlapped with that of sterol and BHT overlapped with triacylglycerols. Peaks for BHA and free fatty acids (FFA) were almost inseparable. However, because the levels of antioxidants measured in the fish TL are very low, the effect of BHA in the determination of FFA in fish samples is expected to be negligible. 

Szalkowski, C. R. and J. B. Garber. 1962. Antioxidant measurement, determination of 2,6-di-rerr-butyl-4-hydroxytoluene (BEIT) Application to edible fats and oils. J. Agric. Food Chem. 10(6) 490-495. 

Plasticity Retention Index. The oxidation behavior of natural mbber may affect both the processing characteristics and final vulcanizate performance, and the plasticity retention index (PRI) test can be used to give an indication of both. Natural antioxidants present in natural mbber give some protection and a measure of the efficacy of protection is given by PRI. PRI% = P q j Pq x 100, where Pq is the initial Wallace plasticity and P q is the... 

Finally, candidate lubricants containing the antioxidants are tested in fleets of automobiles for thousands of miles. The engines are dismantled and examined for wear and coatings of varnish and other deposits. The lubricant is evaluated for sludge, viscosity, acidity, etc. Since evaluation in automobiles is expensive and time-consuming it is reserved for only the most promising candidates. Oxygen uptake tests are also used to measure oxidative stabiUty (28). 

The activity of antioxidants in food [ 1 ] emulsions and in some biological systems [2] is depends on a multitude of factors including the localisation of the antioxidant in the different phases of the system. The aim of this study is determining antioxidant distributions in model food emulsions. For the purpose, we measured electrochemically the rate constant of hexadecylbenzenediazonium tetrafluorborate (16-ArN,BF ) with the antioxidant, and applied the pseudophase kinetic model to interpret the results. 

Table 10.8 Comparison oE antioxidants in polyethylene in both the absence and presence of copper powder and carbon black (data based on ICI literature). Induction time assessed from oxygen uptake measurements using a Barcroft manometer...

Table 2 Melt Stabilizing Efficiency of Antioxidants in PP (processed in an internal mixer at 190°C). Melt flow index (MFI) Measured at 230 C and 2.16 Kg...

In a typical example (33) a fresh feed of 8% polybutadiene rubber in styrene is added with antioxidant, mineral oil, and recycled monomer to the first reactor at 145 lbs./hr. The reactor is a 100-gallon kettle at approximately 50% tillage with the anchor rotating at 65 rpm. The contents are held at 124°C and about 18% conversion. Cooling is effected via the sensible heat of the feed stream and heat transfer to the reactor jacket. In this reactor the rubber phase particles are formed, their average size determined and much of their morphology established. Particle size is controlled to a large measure by the anchor rpm. 

---