The effect of drying methods on bioactive properties in three varieties of prickly pear (Oppuntia ficus indica)

Background/Aims: The prickly pear (PP) cacti (Opuntia ficus indica) are commonly utilised as a source of nutraceuticals due to its substantial bioactive composition. However, preservation of bioactivity can present a challenge with considerable losses of these compounds, depending on the type of drying technique used. Therefore, the aim of this study was to determine the optimum drying method to preserve the bioactive content of the commercially grown Australian PP’s. Methods: Three PP varieties (White, Orange, Purple) were dried using four different Methods (freeze dryer, draft oven, microwave and dehydrator). Total Phenolic (Folin-Cioceultau; Gallic acid equivalent, GAE); Flavonoid (AlCl3; Catechin equivalent, CE) and Betalain (Betaxanthin and Bethanin equivalent, BBE) content along with antioxidant characteristics (Trolox equivalent, TE), free radical scavenging activity (DPPH), reducing capacity (CUPRAC) and antioxidant capacity (FRAP) were determined spectrophotometrically. Kendall’s tau test was used to determine the best drying method in comparison to freeze drying. Results: Microwave drying produced the maximum levels for mean ± SEM total phenolic content in White (145.0 ± 15.5 μgGAE), Purple (129 ± 17.8 μgGAE) and Orange (138.7 ± 25.9 μgGAE) variety. In addition, in White and Purple variety, flavonoid (74.1 ± 8 μgCE and 66.2 ± 9.2 μgCE), CUPRAC (3261 ± 172.9 μMTE and 2743 ± 272.8 μMTE) and FRAP (1458.5 ± 32.3 μMTE and 1328 ± 146.3 μMTE) were also the highest. Total betalains, were highest in White PP (3.1 ± 0.5 mgBBE/100 g) following microwave drying, whereas Orange PP maximum was achieved using oven drying (3.2 ± 0.6 mgBEE/100 g) and Purple PP using dehydrator (2.9 ± 0.4 mgBEE /100 g); all p < 0.05. Conclusions: The method that preserved the highest amounts and activity of bioactives, during the drying process, in comparison to freeze-drying, was the microwave drying.