Effects of cooking techniques on vegetable pigments: A meta-analytic approach to carotenoid and anthocyanin levels

•Natural pigments, such as carotenoids and anthocyanins, are sensitive to heat and light.•Different cooking techniques result in the degradation or increase of these compounds.•Carotenoids were most degraded by frying and most enriched by a stewing technique.•Anthocyanin levels were lowest with pressure steaming and highest with microwaving.•These findings can be used to improve the dietary intake recommendations of these compounds.

The aim of this study was to review studies that evaluated the effects of cooking techniques on carotenoids and anthocyanins in vegetables and to release a meta-analysis of the findings. A literature search was conducted to identify studies that evaluated the effects of cooking techniques on the levels of carotenoids and anthocyanins in vegetables. The database search found 404 results, and an additional 18 articles from 1992 to 2013 were selected that met the inclusion criteria. A meta-analysis with a random effect model was conducted using the weighted response ratios (R*) calculated for each experiment. Significant reductions of carotenoid levels after microwaving (R* = 0.79) and frying (R* = 0.59) and an increase after stewing (R* = 1.33) were reported; for anthocyanins, reduction was observed after moist-heat techniques such as pressure boiling (R* = 0.11) and pressure steaming (R* = 0.01), and steaming tended to reduce their concentration (R* = 0.34; p = 0.054). Increases of anthocyanin levels were observed in dry-heat cooking techniques such as microwaving (R* = 3.51) and baking (R* = 2.95). Cooking techniques influence the levels of natural pigments in vegetables, and depending on the technique, their levels may increase or decrease. Carotenoids were most degraded in frying and most increased during the stewing technique, while anthocyanins were most degraded in pressure steaming and most increased in the microwaving technique.