N,N-dimethylpiperidinium (mepiquat) Part 2. Formation in roasted coffee and barley during thermal processing

Abstract

Previous work in model systems has demonstrated that mepiquat can be formed under typical roasting conditions from the amino acid lysine via the Maillard reaction and trigonelline, the latter alkaloid serving as a methyl donor. This study shows for the first time that mepiquat is formed in low mg kg^–1 amounts during the coffee roasting process and consequently can be detected in roast and ground as well as soluble coffee up to levels of 1.4 mg kg^–1. Darker roast coffees contain relatively higher amounts of mepiquat versus light roasted beans, with an excellent correlation of mepiquat formation to roast colour (r² = 0.99) in robusta beans. A survey of 20 of the major green coffee origins (robusta and arabica coffees) showed the absence of mepiquat (<0.005 mg kg^–1). Preliminary studies indicate that mepiquat is not formed during processing (thermal treatment) in most of the cereal-based foods such as pizza and ready-to-eat cereals, but was detected in barley after roasting (0.64 mg kg^–1). Mepiquat can therefore be considered a process-induced compound formed from natural constituents during the roasting process. Even considering a high intake of seven cups per day of soluble coffee containing 1.4 mg kg^–1 mepiquat in the coffee powder (the highest amount measured in this study), the resulting intake would exhaust less than 0.2% of the ADI of mepiquat.

Keywords:

• Maillard reaction
• N,N-dimethylpiperidinium
• mepiquat
• roasting
• coffee
• cereals
• barley
• thermal treatment
• lysine
• trigonelline

Acknowledgements

The authors thank Mr David Baxter, NQCC, for arranging the sampling and shipment of green coffees. Thanks also to Dr Anthony Huggett for critically reading the manuscript.