Effects of pH and temperature of extraction medium on effective diffusion coefficient of anthocynanin pigments of black carrot (Daucus carota var. L.) Original Research Article

Restrictions imposed on artificial food colorants have resulted in extensive research on natural pigments in recent years. Among the natural colorants, anthocyanin pigments are responsible for red, purple and blue colors of many plants and black carrot (Daucus carota var. L.) has just been known as a potential source of anthocyanin due to its higher stability because of its acylation compared to the ones obtained from other sources. For a commercial production process, it is important to shorten the extraction time. Therefore, effective diffusion coefficient (Đ-value) and effects of different parameters on image-value should be known during extraction. The objectives of this study were to determine the image-value of anthocyanin pigments of black carrot and to determine the effects of temperature and pH on image-value. Black carrot samples, 1 cm in thickness, were fixed to a thin wire and dipped into 600 mL McIlvaine buffer solution at different temperatures (20, 37.5 and 50 °C) and pHs (2, 3 and 4). Extracted pigment concentration versus time was determined using the pH-differential method. Unsteady state equation for an infinite slab with a convection boundary was then used to determine the image-values. The image-values changed from 0.18 × 10−10 (pH = 4, T = 25 °C) to 7.37 × 10−10 (pH = 2, T = 50 °C) showing a synergistic effect of low pH and high temperature on image-values. In addition, these effects were also investigated by using dried carrot samples, and it was concluded that the structural changes play an important role, and ordinary diffusion models were not suitable to determine the change in image-values of anthocyanin pigments in dried samples. Optimization of an industrial scale production is important to speed up the process. These results may be used for the further optimization studies to design a commercial production.