Bioactivities of crude caffeine: Antioxidant activity, cyclooxygenase-2 inhibition, and enhanced glucose uptake

► Crude caffeine is an intermediate by-product produced during the decaffeination process. ► We discovered that crude caffeine possessed unexpected bioactive properties. ► Crude caffeine had antioxidant activities, inhibited COX-2, and increased glucose uptakes. ► Pure caffeine, accounting for ∼90% of the crude caffeine mass, had negligible such bioactivities. ► Crude caffeine may serve as a novel functional ingredient in the food industry.