Bioaccessibility of polyphenols and antioxidant capacity of fresh or minimally processed modern or traditional lettuce (Lactuca sativa L.) varieties

Modern city lifestyle is characterized by an increased demand for fresh or minimally processed foods. Lettuce (Lactuca sativa L.), mainly iceberg lettuce, is the main vegetable used during the manufacture of fresh-cut salads. The current study evaluated the phenolic content and antioxidant activity of ten fresh and minimally processed lettuce varieties. The phenolic content of selected lettuce samples varied significantly among varieties. Although a higher phenolic content was observed in modern lettuce varieties, when compared to the traditional ones (except for the landrace Frances 219/855), the antioxidant capacity of modern and traditional lettuce varieties was similar. Minimal processing followed by storage for a 7-day period led to an increased phenolic content in varieties Rutilai RZ, Abago RZ, Maravilla LS044, Frances 219/855, Negre borratger 386/935, and D'hivern LS008, supporting the hypothesis that wounding can induce the accumulation of phenolic compounds in lettuce leaves. For example, the total phenolic content of Frances 219/855 after processing and storage increased from 8.3 to 11.3 mg/100 g (p < 0.05). Accumulation of phenolic compounds after minimal processing was not observed in all the studied samples, suggesting that this effect could be matrix-dependant. The amount of bioaccessible polyphenols was higher after minimal processing and storage. Indeed, the amount of bioaccessible polyphenols after a simulated gastrointestinal digestion of fresh or minimally processed Pelikan lettuce was calculated as 32.6 or 43.3 mg/100 g respectively (p < 0.05), suggesting that the increased amount of polyphenols caused by processing and storage can also lead to a higher amount of bioaccessible phenolic compounds.