Rheological characterization of cactus pear mucilage for application in nutraceutical food products
Mucilage could exert therapeutic, nutritional and functional advantages if applied as a functional ingredient in innovative nutraceutical food products. Mucilage has unique flow behaviour that should be fully understood in order to predict its behaviour during processing, packaging, preparation and consumption. Extraction and drying of mucilage from mature cladodes from four cultivars, harvested in winter (July 2014), involved a patented procedure of slicing, microwave cooking, macerating, centrifuging at 8000 rpm for 15 min, and freeze-drying at -60°C for 72 h. The viscosity of 5% reconstituted freeze-dried mucilage was determined using the line-spread test (cm) and a rotational RV Brookfield viscometer (cP) at 50 rpm after 60 s. Flow behaviour was determined by controlling the rate of spindle rotation (5, 10, 20, 50 and 100 rpm), time intervals (15, 30, 60, 90 and 120 s), temperature (5, 10, 20, 40, 60 and 80°C), pH ( >11, 9-10, 8-9, 7-8, 5-6, 4-5, 3-4 and 1-2), and ionic strength (NaCl, CaCl2, FeCl3 at 0.1, 1, 10, 100 and 1000 mM) of reconstituted mucilage. The four cultivars had viscosities between 26.0 and 29.8 cm (not significantly different) using the line-spread test and 150 and 328 cP using the viscometer. In the controlled-rate and time-interval tests, mucilage showed non-Newtonian, pseudoplastic tendencies but no rheopectic or thixotropic behaviour. Mucilage exhibited dynamic yield (0.38-0.74% torque), indicating the force needed for it to start moving. Viscosity increased at lower temperatures (200-418 cP) and decreased at higher temperatures (50-120 cP). In alkaline regions (pH >11-8), viscosities of native mucilage increased (360-2400 cP), and they decreased (60-600 cP) in acidic (pH 6-1) regions. Monovalent ions had little, divalent more, and trivalent the most influence on native mucilage viscosity. The properties of the innovative products, environmental conditions and handling could have adverse effects on the consistencies of mucilage-containing food products.
Du Toit, A., De Wit, M., Seroto, K.D., Fouché, H.J., Hugo, A. and Venter, S.L. (2019). Rheological characterization of cactus pear mucilage for application in nutraceutical food products. Acta Hortic. 1247, 63-72
Opuntia ficus-indica, Opuntia robusta, cladodes, viscosity, flow behaviour, non-Newtonian, pseudoplastic