The influence of blanching pretreatments on the quality of dehydrated broccoli stems

Different blanching treatments were applied to sliced broccoli stems prior to dehydration in order to improve product quality. The pretreatments used were a conventional blanching in water at 100 degrees C, and a stepwise bla nching using different temperatures for the first step (50, 55, 60, 65 and 70 degrees C). Five rehydration temperatures were used (25, 40, 55, 65 and 80 degrees C). Rehydration rate, chlorophyll content and texture of the reh ydrated product were evaluated. Rehydration was modeled based on Fick's dif fusion equation. A good agreement between the model and the experimental da ta was obtained when D-eff and W-e values were identified for each temperat ure (average percent variation 99.3). Samples stepwise blanched at 60 degre es C showed, on average, the lowest W-e and E-a values. Stepwise blanching at 60 and 65 degrees C and rehydration at 25, 40 and 55 degrees C were the combinations that gave the firmest product. Stepwise blanching at 50 degree s C and rehydration between 25 and 65 degrees C was the combination that pr eserved the highest chlorophyll content. From these results, it seems diffi cult to obtain firm samples with high chlorophyll content without any chemi cal additive.