RHEOLOGICAL CHARACTERIZATION OF COFFEE MUCILAGE

Rheological behavior of mucilage obtained from two varieties of coffee grown in Colombia (Caturra and Colombia) was studied as a function of ripe cherry content (RCC) and postharvest time (PHT). A Brookfield HB DV-III viscometer was used in concentric cylinder geometry over a she ar rate range of 4.8 to 120 s(-1). The power-law model was used to des cribe the shear stress versus shear rate data, and the consistency ind ex (K) and flow behavior index (n) were determined. The mucilage is a highly viscous and pseudoplastic (n < 0.3) fluid. The K increased and n decreased as the RCC and PHT increased. The mucilage of the Caturra variety was more viscous and shear thinning than that of the Colombia variety. Microstructural examination of the mucilage revealed that cer tain weak structures as phloem vessels found in the mucilage may be de stroyed upon application of shear stress and may contribute to the pse udoplastic nature of the mucilage. Diffusion of tannin from the pulp t o mucilage with delay in postharvest processing may be responsible for increased apparent viscosity with increased PHT.