Chlorogenic acid retention in white and purple eggplant after processing and cooking

The stability of vegetable antioxidants in response to processing and cooking treatments may be affected by the variety. However, the information available in the literature is very limited. In this work we determined the influence of the eggplant variety (white - cv 'Cloud Nine' and purple - cv 'Lucia') on pulp chlorogenic acid content (5-O-caffeoyl-quinic acid; CQA) and antioxidant capacity (AC) in response to common pre-processing (cutting, salting or blanching), processing (air-vacuum- solar- and freeze-drying, slow- and fast-freezing) and cooking methods (microwaving, baking, grilling, steaming, boiling or pressure cooking). Fresh purple 'Lucia' eggplants showed higher AC and CQA content (16%) than white 'Cloud Nine' fruit. Fruit pre-processing caused significant losses of AC, with the effect being higher in the purple cultivar. Hot air- and sun-drying almost depleted CQA in both cultivars. In contrast, white eggplants retained higher AC upon freezing and microwaving. Wet cooking methods (boiling and pressure cooking) markedly increased fruit AC indicating that these preparation procedures improved antioxidant extractability. The eggplant cultivar has a major influence in antioxidant retention during processing and cooking; the white variety 'Cloud Nine' proved in general, more suitable for processing in terms of antioxidant retention than the purple 'Lucia' genotype.