In Vitro Bioactivity of Australian Finger Lime Cultivars as an Initial Evaluation of Their Nutraceutical Potential

There is increasing interest in Australian finger lime (Citrus australasica) due to its nutritional and bioactive potential. In this study, polar extracts from five finger lime cultivars were investigated for their potential bioactivity using a range of assays: antioxidant capacity (total phenolic content (TPC), ferric reducing antioxidant power (FRAP), and cupric reducing antioxidant capacity (CUPRAC)), total monomeric anthocyanin content (TMAC), anti-diabetic activity (α-glucosidase and α-amylase inhibition), anti-Alzheimer activity (acetylcholinesterase inhibition), Skin-whitening activity skin-brightening activity (tyrosinase inhibition), and anti-inflammatory activity (COX-2 inhibition). Commercial Tahitian lime was used as a “control” (comparison). The TPC ranged from 328 to 779 mg GAE/100 g dry weight (DW) in the pulp (compared to 1043 mg GAE/100 g for Tahitian lime) and from 755 to 1048 mg GAE/100 g in the peel (1704 mg GAE/100 g for Tahitian lime). A similar range of variation was seen for FRAP, ranging from 114 to 436 mg TE/100 g DW in the pulp (422 mg TE/100 g for Tahitian lime) and 259 to 495 mg TE/100 g DW in the peel (491 mg TE/100 g for Tahitian lime). Similarly, the TFC was generally lower in finger lime pulp (100–392 mg QE/100 g DW) compared to Tahitian lime (312 mg QE/100 g). The polar extracts did not show any significant inhibition of α-glucosidase, α-amylase, tyrosinase, or COX-2. One finger lime variety showed moderate (>50%) inhibition of acetylcholinesterase (AChE) at the highest concentration screened (~1500 mg/L), as did Tahitian lime. Additionally, in silico docking against acetylcholinesterase suggested that some of the polyphenols present, including catechin, quercetin-3-glucoside, and cyanidin-3-glucoside, could potentially dock to AChE and inhibit it. This is the first time the species has been investigated for many of these bioactive properties, and also the first time in silico docking has been performed to explore which potential compounds from this species could provide its bioactivity. Although little bioactivity was generally found across the applied bioassays, these findings nevertheless provide important basic data for future research and any claims about the potential health benefits of Australian finger lime.