Effects of Thermal Pretreatments on the Physicochemical, Techno-Functional, Spectroscopic, and Microstructural Properties of Broccoli and Cauliflower By-Product Flours

Broccoli (Brassica oleracea var. italica Plenck) and cauliflower (Brassica oleracea var. botrytis L.) are widely produced in the Ecuadorian Andes, and their conversion into flours is a potential route to stabilize surplus or non-marketable produce. This study evaluated the effect of three thermal pretreatments, boiling (5 min), steaming (5 min), and microwave heating (600 W, 30 s), applied before convective drying (65 °C, 8 h), on the physicochemical, techno-functional, spectroscopic, and microstructural properties of broccoli and cauliflower flours, using untreated samples as controls. Drying reduced water activity to 0.305–0.501 in all flours. Steamed broccoli flour showed the highest water absorption index (5.63), whereas microwave pretreatment yielded the highest water solubility index in both broccoli (67.59%) and cauliflower (50.75%) flours. FTIR and Raman spectroscopy showed that thermal pretreatments largely preserved the characteristic chemical fingerprints of both vegetables, with treatment effects expressed mainly as changes in relative band contributions rather than the appearance of new spectral features. FTIR indicated the greatest relative changes in boiled cauliflower, consistent with carbohydrate leaching, whereas Raman coupled with OPLS-DA revealed treatment-dependent discrimination, mainly associated with carotenoid-related regions in broccoli and structural carbohydrate-related regions in cauliflower. SEM revealed vegetable-dependent changes in particle morphology: steaming produced loosely packed, porous agglomerates in broccoli and smaller particles in cauliflower, boiling yielded a denser particle surface in cauliflower, and microwave heating produced compact agglomerates in both vegetables. These results indicate that the pretreatments mainly modified the physical structure of the flours and that their effects depend on the vegetable matrix.