Pecan shell by-products—phenolic compound contents and antimicrobial properties

Abstract

Pecans are a popular nut throughout the world. The USA produces several million kg/yr of pecan kernels and shells. Pecan kernels have high phenolic compound content and pecan shells have even higher phenolic concentrations than the kernels. High phenolic contents in biological materials have been linked to high antioxidant and antimicrobial activity. If pecan shells could be shown to have good antimicrobial potential, then it would demonstrate possible alternative uses for this by-product of pecan production. The total phenolics, flavonoids, and phenolic acid contents were determined for native pecans from Central Texas. Then, the in vitro antimicrobial activity of pecan shell water extracts was determined for four microbes (Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Streptococcus mutans) and general oral cavity bacteria. The total phenolic content of the shells was 60% higher and the total flavonoid content of the shells was five times higher than the kernels. The pecan shells contained gallic, vanillic and caffeic acid. Water extracts from pecan shells inhibited the growth of the bacteria studied, and inhibited the growth of oral cavity specimens. Overall, the pecan shell water extracts showed good potential for antimicrobial activity.