Domestic cooking practices strongly affected the nutritional
quality of all 13 frozen vegetables. Four home cooking procedures
and three classes of phytochemicals were tested and revealed the
difficulty for establishing an order between the more and less
suitable procedures. This has two main reasons: i) folates, carotenoids
and vitamin C presented different levels of sensitivity and ii)
effects were strongly dependent on the vegetables. However, all
vegetables combined, on the fresh weight basis, boilingwas the less
suitable method, with a high loss of vitamin C (51%) and folates
(68%) and a slight loss of lutein (15%) and b-carotene (9%). On
the dry weight basis, boiling remained the less suitable for vitamin
C (44%) and folates (65%) but not for carotenoids. It led to a
better extractability of lutein (þ9%) and b-carotene (þ20%).
Depending on the vegetables and phytochemicals, steaming,
microwaving or pressure cooking could be the best method to
preserve the nutritional quality.
The absence of general results for all components and all vegetables
(except for boiling) highlights the difficulty in giving a
simple real recommendation for the cook to best preserve the
nutritional quality of frozen vegetables.