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Influence of grinding methodology, particle size, and on the assay of phenolic phytochemicals from five different wheat cultivars

Phenolic compounds are common dietary phytochemicals that are ubiquitously distributed in plant foods, including vegetables and grains. The significance of grinding methodology and particle size on the assay of phenolic phytochemicals from five different wheat cultivars was evaluated. Significant differences in the particle size distribution were observed when the same wheat sample was ground on different laboratory grinders. Different particle size fractions were collected by manually sieving ground wheat samples; assay of phenolic acids and antioxidant capacity of the various fractions showed major variations in both phenolic acids (PA) content and antioxidant capacity. Similar variations in particle size distribution, PA content, and antioxidant capacity were observed when the five cultivars of wheat samples were ground on two separate grinders. Three base hydrolysis procedures were also evaluated: pressurized liquid extraction (PLE), microwave assisted extraction (MAE), and ultrasonic assisted extraction (UAE). PLE provided the maximum extraction of PA. The yields of PA were ~15% lower by MAE and ~25% lower by UAE, compared to PLE. These results clearly indicate that sample preparation plays an important role in the accurate assay of phenolic phytochemicals from wheat. Funding: USDA/ARS and NIFA.