engleski

Accelerated Drying of Mushrooms, Brussels Sprouts and Cauliflower by Means of Power Ultrasound and its Impact on Food Quality

Drying is the most common way of preserving and extending the shelf life of food products such as fruit and vegetables. Many pretreatments have been used in an attempt to shorten the drying time of vegetables. Unfortunately the overall drying process is often accompanied by a reduction in nutritional and deterioration in techno-functional properties. The aim of this work was to use ultrasound as a pretreatment method prior drying of mushrooms (lat. Agaricus biosporus), Brussel sprouts (lat. Brassica oleracea var. gemmifera) and cauliflower (lat. Brassica oleracea var. botrytis) in order to achieve reduction in drying time and thereby reduce nutritional and techno-functional deterioration properties. Pretreatment with 20 kHz probe and 40 kHz bath for 3 and 10 min have been compared with blanched (80&ordm ; C / 3min) and untreated samples. Drying procedures were conducted at a temperature of 60&ordm ; C ; RH = 35, 3 % and air velocity (v = 0, 3 m/s) for sonicated, blanched and untreated samples. Also, freeze dried samples were compared. The pH, conductivity and temperature changes upon sonication and blanched pre-treatment were measured. The effect of ultrasound and blanching pre-treatments on weight and moisture loss/gain, upon drying and rehydration were also investigated. The pH decreased after ultrasound pre-treatments with probe and bath with the largest change observed using a 20 kHz probe for 10 min for all samples, as compared with blanching pre-treatment. Conductivity increased for all pre-treatments suggesting the loss of electrolyte. The highest increase was observed for blanching pre-treatment for all samples. The temperature rose during ultrasonic pretreatments by 1&ordm ; C using a bath and by 25 &ordm ; C using a probe. Weight loss during drying was highest after freeze-drying for all samples, followed by bath 3 min pre-treatment for mushrooms, and probe 3 min pre-treatment for Brussel sprouts and cauliflower. The drying time after ultrasound treatment was shortened for all samples, as compared to untreated. It was most reduced using a bath for 3 min for mushrooms, but for Brussel sprouts and cauliflower using a probe for 3 min. Rehydration properties (weight gain, %) were investigated, and it was found to be the best for freeze dried samples. The rehydration properties for ultrasound treated samples were higher than for untreated samples. For mushrooms, a bath for 3 min gave the best rehydration properties as compared to blanched and untreated. For Brussel sprouts and cauliflower the ultrasound treatment with a probe for 3 min was better than untreated.

ultrasound; vegetable; drying; conductivity; rehydration

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