ARS | Publication request: Assay dilution factors confound measures of total antioxidant capacity in polyphenol-rich juices

Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 27, 2011
Publication Date: February 1, 2012
Citation: Bolling, B., Chen, Y., Kamil, A.G., Chen, C. 2012. Assay dilution factors confound measures of total antioxidant capacity in polyphenol-rich juices. Journal of Food Science. 77(2):H69-75.

Interpretive Summary: The potential health benefits of dietary antioxidants are suggested by research studies showing an inverse association of intake with reduced risk of chronic diseases such as cancer, cardiovascular disease, cataract, Alzheimer disease, age-related macular degeneration, and rheumatoid arthritis. The antioxidant content of fruit and vegetables and related products, including juices, has been increasingly used to promote their putative health benefits to consumers. Several chemical assays of total antioxidant capacity (TAC) have been developed to more readily assess and rank overall antioxidant capacity of foods and beverages. However, the extent to which sample dilution factor (DF) affects Total Antioxidant Capacity (TAC) values is poorly understood. Thus, we examined the impact of DF on an array of TAC assays using pomegranate juice (PJ) and grape juice (GJ). We found that DF had a significant impact on the TAC values of the test juices. Thus, reporting TAC or TP using a single DF may introduce uncertainty about the confidence of TAC assay values, especially when comparing different juices.

Technical Abstract: The extent to which sample dilution factor (DF) affects Total Antioxidant Capacity (TAC) values is poorly understood. Thus, we examined the impact of DF on the ORAC, FRAP, DPPH, and Total Phenols (TP) assays using pomegranate juice (PJ), grape juice (GJ), selected flavonoids, ascorbic acid, and ellagic acid. For ORAC, GJ was comparable to PJ at DF 750, but at DF 2000, the ORAC value of GJ was 40% more than PJ. Increasing DF increased GJ and PJ DPPH, TP, and FRAP values 11 and 14 %, respectively. Increased test concentrations of quercetin and catechin resulted in 51 and 126% greater ORAC values, but decreased naringenin by 68%. Flavonoids, but not ellagic acid or ascorbic acid, may contribute to the dilution effect on the variation of final TAC values. Thus, reporting TAC or TP using a single DF may introduce uncertainty about the confidence of TAC assay values, especially when comparing different juices. These results underscore the importance of using compatible test standards for reporting TAC values.