Intra-laboratory validation of microplate methods for total phenolic content and antioxidant activity on polyphenolic extracts, and comparison with conventional spectrophotometric methods.
BACKGROUND
Total phenolic content (TPC) and antioxidant activity (AA) assays in microplates save resources and time, therefore they can be useful to overcome the fact that the conventional methods are time-consuming, labour intensive and use large amounts of reagents. An intra-laboratory validation of the Folin-Ciocalteu microplate method to measure TPC and the 2,2-diphenyl-1-picrylhydrazyl (DPPH) microplate method to measure AA was performed and compared with conventional spectrophotometric methods.


RESULTS
To compare the TPC methods, the confidence intervals of a linear regression were used. In the range of 10-70 mg L(-1) of gallic acid equivalents (GAE), both methods were equivalent. To compare the AA methodologies, the F-test and t-test were used in a range from 220 to 320 µmol L(-1) of Trolox equivalents. Both methods had homogeneous variances, and the means were not significantively different. The limits of detection and quantification for the TPC microplate method were 0.74 and 2.24 mg L(-1) GAE and for the DPPH 12.07 and 36.58 µmol L(-1) of Trolox equivalents. The relative standard deviation of the repeatability and reproducibility for both microplate methods were ≤ 6.1%. The accuracy ranged from 88% to 100%.


CONCLUSIONS
The microplate and the conventional methods are equals in a 95% confidence level.
Public University of Navarra, Food Technology Department, Campus Arrosadia s/n, Pamplona, 31006, Spain.
Gloria
G
Bobo-García
Gabriel
G
Davidov-Pardo
Cristina
C
Arroqui
Paloma
P
Vírseda
María R
MR
Marín-Arroyo
Montserrat
M
Navarro
D000975:Antioxidants / Q000032:analysis*; D001713:Biphenyl Compounds; D005504:Food Analysis / Q000379:methods*; D005638:Fruit / Q000737:chemistry; D056604:Grape Seed Extract / Q000737:chemistry; D057230:Limit of Detection; D027845:Malus / Q000737:chemistry; D008982:Molybdenum; D010636:Phenols / Q000032:analysis*; D010851:Picrates; D010936:Plant Extracts / Q000737:chemistry*; D059808:Polyphenols / Q000032:analysis*; D012680:Sensitivity and Specificity; D013662:Tea / Q000737:chemistry; D017973:Tungsten Compounds
D000975:Antioxidants; D001713:Biphenyl Compounds; C029556:Folin's phenol reagent; D056604:Grape Seed Extract; D010636:Phenols; D010851:Picrates; D010936:Plant Extracts; D059808:Polyphenols; D013662:Tea; D017973:Tungsten Compounds; D008982:Molybdenum; C004931:1,1-diphenyl-2-picrylhydrazyl
DPPH; Folin-Ciocalteu; apple extract; grape seed extract; green tea extract