Cooking Can Improve Vegetable Nutrition

Everyone knows that processed vegetables deliver poorer nutritional quality than fresh, raw veggiesexcept everyone is probably wrong. Research is showing that cooking can increase the nutrient availability, and a new study by Italian researchers accepted for publication in the Journal of Agricultural and Food Chemistry (Effects of Different Cooking Methods on Nutritional and Physicochemical Characteristics of Selected Vegetables, C. Miglio, E. Chiavaro, A. Visconti, V. Fogliano and N. Pellegrini, ASAP Article, 10.1021/jf072304b) adds credence to the theory that cooked vegetables might be nutritionally superior.

Ideally, vegetable nutrients should be preserved and physiologically available. Research shows naturally occurring phytochemical compounds in vegetables provide antioxidant properties, and diets that include significant amounts might create a decrease in degenerative processes that lead to disease. Additionally, optimal quality after processing can lead to greater acceptance and consumption of these beneficial phytochemicals. The objective of the study was to evaluate the effect of three common cooking techniquesboiling, steaming and fryingon phytochemical contents, total antioxidant capacities (TAC) and physicochemical parameters of carrots, zucchini (courgettes) and broccoli.

The study found water-cooking techniques better preserved the antioxidant compounds, particularly carotenoids, in all three of the vegetables and optimized ascorbic acid levels in carrots and zucchini. Steamed vegetables maintained a better texture than boiled ones; however, boiling vegetables limited their discoloration. Fried vegetables showed the least softening, but retained less antioxidant compounds. All cooked vegetables showed an overall increase in their Trolox equivalent antioxidant capacity (TEAC), total radical-trapping antioxidant parameter (TRAP), and ferric-reducing antioxidant power (FRAP) values. The researchers attributed this to matrix softening and increased extractability of compounds, which might be partially converted into more antioxidant compounds. In broccoli, steaming increased the level of glucosinolates, phytochemicals that research indicates can fight cancer, especially in their isothiocyanate hydrolysis form.

The researchers conclude these results suggest that for each vegetable a preferential cooking method could be selected to preserve or improve its nutritional and physicochemical qualities. This selection may help consumers on the choice of cooking practices to improve the nutritional quality of foods, as well as their acceptability.