Free tocopherols as chemical markers for Arabica coffee adulteration with maize and coffee by-products

• Free tocopherols were explored as discriminants for roasted coffee adulteration.
• γ-tocopherol is the main descriptor for adulterations with both maize and coffee by-products.
• Tocopherol ratios enable to distinguish maize, husks and cleaned husks.
• The methodology proposed is simple to implement and highly robust.

Coffee adulteration with coffee by-products is increasing, due mostly to its chemical and sensorial similarity with ground roasted coffee. Based on the recognized effectiveness of tocopherols as markers for coffee adulteration with maize, we have further explored their ability to distinguish adulterations with coffee husks, the main residue of coffee dry processing. For the purpose, a ground roasted arabica coffee sample was adulterated with 5–50% (w/w) of roasted husks, cleaned roasted husks (without the inner parchment layer), and roasted maize. Extracted lipids were analysed by normal-phase HPLC, with florescence detection, and the tocopherol amounts analysed by mean tests, regression analysis, PCA, LDA and SIMCA. γ–tocopherol, detected in residual amounts in roasted coffee, was inversely proportional to coffee purity, being the compound that better contributed for adulteration detection, independently of the adulterant tested. Coffee richness in β–tocopherol, in opposition to all the adulterants tested, also contributes for this discrimination. Based on the tocopherol profiles, adulterations can be perceived at the lowest amounts tested (5%), but higher amounts are necessary for identification of the adulterant, namely ≥10% for maize and from 20% upwards for coffee by-products. For heavy adulterations is even possible to distinguish between husks and cleaned husks. This method is simple to implement in food analysis laboratories, with applicability for adulteration screening or to complement other instrumental methods.