Effect of blanching on the quality of Brussels sprouts (Brassica oleracea L. gemmifera DC) after frozen storage

Three blanching conditions previous to freezing and frozen storage of Brussels sprouts were compared in terms of their combined effects on texture, surface colour, total chlorophyll, radical scavenging activity (RSA), ascorbic acid and total flavonoids content. The blanching alternatives were: immersion in water (50 °C; 5 min) followed by blanching in water (100 °C; 3 min) (PB); microwave heating (700 W, 5 min) followed by blanching in water (100 °C; 2 min) (MW); and direct blanching in water (100 °C; 4 min) (DB). Fresh controls and treated samples were frozen then stored at −18 °C for 8 months. Texture of sprouts was significantly affected by blanching although all treatments had a similar effect. Freezing and frozen storage caused an additional loss of firmness, but the magnitude was lower than that induced by blanching. With respect to surface colour, the PB method gave the highest −a∗ values as well as a better Chroma retention than the controls. All treatments increased RSA, ascorbic acid and total flavonoids contents. The only significant differences between treatments was the slightly higher value for −a∗ and Chroma for the PB method and an increase in final RSA levels for the MW pre-treatment.