ABSTRACT
This study was conducted to analyze the drying kinetics of carrot slices in electrohydrodynamic (EHD) dryer at different electrode distances. Higher drying rate was observed up to about 70% (w.b.) moisture content, which has been noted as first falling rate period. The time taken to dry the carrot slices to the safe moisture content of 2.5% (wb) was about 9, 8.5 and 6.8 h at a distance of 7, 5 and 3 cm respectively. Five empirical models, Page Model, Newton model, Henderson and Pabis model, logarithmic model and two term model, were tested for the best fit. The drying rate constant (k) increased in all the empirical models as the distance between the electrode decreased. For 7 cm electrode distance, the Page model fitted best whereas the Logarithmic model was found to be the best fit for 5 and 3 cm electrode distance. There is no significant difference found in shrinkage of dried carrot slices at different electrode distance. Rehydration ratio increased as the distance between electrodes decreased. Moisture diffusivity increased as the distance between the electrode decreased. No significant difference in colour, ß-carotene and sensory attributes were found between fresh and EHD dried carrot slices at 3 cm electrode distance. Specific energy consumption was significantly influenced by the electrode distance.
ABSTRACT
Growing fruit and vegetable processing industries generates a huge amount of by-products in the form of seed, skin, pomace, and rind containing a substantial quantity of bioactive compounds such as polysaccharides, polyphenols, carotenoids, and dietary fiber. These processing wastes are considered to be of negligible value compared to the processed fruit or vegetable due to lack of sustainable extraction technique. Conventional extraction has certain limitations in terms of time, energy, and solvent requirements. Ultrasound assisted extraction (UAE) can extract bioactive components in very less time, at low temperature, with lesser energy and solvent requirement. UAE as a non-thermal extraction technique is better equipped to retain the functionality of the bioactive compounds. However, the variables associated with UAE such as frequency, power, duty cycle, temperature, time, solvent type, liquid-solid ratio needs to be understood and optimized for each by-product. This article provides a review of mechanism, concept, factor affecting extraction of bioactive compounds with particular focus on fruit and vegetable by-products.
