Kakadu plum (Terminalia ferdinandiana Exell.): Provenance authentication to support first nations enterprises, regulators, and consumers

Abstract

Terminalia ferdinandiana Exell., commonly known as Kakadu plum, is a native fruit that holds cultural and economic significance for Australian Indigenous people. This wild-harvested fruit, owing to its remarkable nutritional and medicinal properties, has seen a rapid rise in demand from a farmgate value of just over $200,000 in 2012, $1.6 million in 2019 and is predicted to attain a farmgate value of up to $3.5 million Australian dollars by 2025. To secure the Kakadu plum industry from fraudulent activities, it is crucial to develop reliable methods to verify the origin of fruit products. This research aims to determine multi-elemental fingerprints of authentic Kakadu plum samples harvested in northern Australia and build a statistical model to authenticate their geographic origin. Kakadu plum fruit from 21 regions across the Kimberley region of Western Australia and Northern Territory (n = 443) were analysed for 30 mineral elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Br, Rb, Sr, Y, Zr, Cd, Sn, Sb, Nd, Hf, Pb, Bi, and U) using Itrax micro X-ray fluorescence. A Kakadu plum reference database was then created for storing the analytical data and providing access for statistical analyses. The elemental fingerprint of these reference samples were analysed by principal component analysis (PCA), and random forest (RF) was employed to develop a pattern recognition classification model that predicts the origin of each sample. PCA results showed that this technique is not suitable for geographic origin authentication, as there was a significant overlap in plum samples and there were no well-defined groups of Kakadu plum fruit for each location. Despite similarities in elemental fingerprints of plums between neighbouring geographic locations, the application of RF as a method for reliably classifying the geographical origin of samples is demonstrated. An overall accuracy of approximately 82% is achieved, and the model revealed that the soil-derived elements Rb, Cu, Cr, and Mn, are the most important origin markers for effectively differentiating Kakadu plums between the 21 locations. This is the first research focussed on using elemental fingerprinting to authenticate the geographic origins of Kakadu plum harvest sites and is a significant step towards supporting Aboriginal community-based enterprises to protect this cultural resource across Northern Australia and safeguard both producers and consumers against fraud.