Folates in lettuce: a pilot study

BACKGROUND: Leafy vegetables are good sources of folates and food shops nowadays offer an increasing number of lettuce varieties. OBJECTIVE: To obtain data on the folate content and forms in common lettuce varieties and spinach sold in the Nordic countries, and to investigate effects of different storage conditions and preparations in the consumer's home or at lunchtime restaurants. DESIGN: Folate was analysed in eight different lettuce varieties and spinach using a validated high-performance liquid chromatographic method and the detected forms of folates were confirmed by a mass spectrometric detector [liquid chromatography–mass spectrometry (LC-MS)] following heat extraction, deconjugation with rat serum and purification by solid-phase extraction. RESULTS: Folate content, expressed in folic acid equivalents, in the lettuce samples varied six-fold, from 30 to 198 µg 100 g(−1) on a fresh weight basis. The folate content was decreased by 14% after storage at 4°C for 8 days and by 2–40% after storage at 22°C for 2–4 h, depending on whether samples were stored as whole leaves, or small torn or cut pieces. LC-MS confirmed the identity of the folate forms: H(4)folate, 5-CH(3)-H(4)folate, 5-HCO-H(4)folate and 10-HCO-H(4)folate. CONCLUSION: The considerable variation in folate content between varieties of lettuce in this pilot study, with one variety reaching the level found in spinach, indicates the potential to increase folate intake considerably by choosing folate-rich varieties of lettuce and storing at low temperatures.