3.1.4. Extraction temperature
Temperature is the most important factor in the extraction of heat sensitive compounds. Along with the increase of temperature, the solvent diffusion rate and the mass transfer intensification result in the dissolution of components. The concentration of extracted oligosaccharides increased from 5.90±0.23 to 7.55 ± 0.32 g/100 g FW when extraction temperature increased from 20 to 50 C as reflected in Fig. 1D. Jiang et al.[32], optimizing the parameters of the ultrasound assisted extraction of oligosaccharides from longan fruit pericarp, found the optimal temperature to be 65 C. However, it should be noted that increasing the temperature beyond certain values might promote possible concurrent decomposition of oligosaccharides which were already mobilized at lower temperatures or even the degradation of oligosaccharides that were still present in the plant matrix. It was reported that significant hydrolysis of FOS took place at TP60 C [33]. Additionally, high temperatures may encourage solvent loss through vaporization and increase the cost of the extraction process. Therefore, extraction temperatures of 25, 40 and 55 C were chosen as the lower, middle and upper levels, respectively, to be applied in RSM optimization.