Abstract
Methylene chloride decaffeination processes for ground and whole guaraná seed cores were evaluated. Ground seeds were contacted with solvent in shaking flasks in a controlled temperature water bath. The experimental design included three solid/liquid ratios [1:4, 1:6, 1:8 (w/w)] and two temperatures (25 and 30°C). Caffeine was also extracted from 100 g batches of whole seed cores in a solid/liquid packed bed extractor with a solid/liquid ratio of 1:50 (w/w); this was used with three solvent flow rates (436, 522, and 667 ml/min) at two temperatures (21 and 30°C). For optimal extraction of caffeine from the ground seeds a solid/liquid ratio of 1:6 was adequate at 30°C (- 90% extraction after 23 h) but not at 25°C. However, with a solid/liquid ratio of 1:8 the temperature effect was not significant (p < 0.05), both temperatures yielded a 93% extraction after 23 h. Caffeine was extracted from unground seed cores at a lower rate because of decreased contact surface area and a greater radial mass transfer distance. At 21°C, there was no significant difference (p > 0.05) between extraction rates with solvent flows of 522 and 667 ml/min. This indicated that caffeine diffusivity was limiting mass transfer and boundary layer effects had become negligible. Caffeine extraction at 30°C continued to increase with solvent flow because of a higher diffusivity. Diffusivity values calculated from the mass transfer model were 0.29 x 10-6 cm2/s at 21°C and 0.95 x 10-6 cm2/s at 30°C. For industrial applications, design of a solid/liquid packed bed extractor with high solvent flow and temperature capability would probably be economically justified.
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