Nano Biofortification of Australian Purple Rice Using Electrochemical Behavior to Optimize Zinc Retention and Anthocyanin Bioavailability

Abstract

Zinc deficiency is a serious problem in cereal dependent populations and the use of purple rice is a potential carrier matrix for combined micronutrient delivery and polyphenol based functionality. This review aims to summarize available evidence on nano biofortification of rice via zinc (mainly ZnO and other nano zinc systems) and explore the potential of electrochemical methods to optimize the biofortification of zinc in Australian purple rice and anthocyanin bioavailability. Literature suggests that grain mineral can be significantly enriched by agronomic means, particularly via genotype selection, although this is severely constrained by the association of these minerals with the bran (localized mineral deposition in the grain), by polishing losses and by binding to phytate and by processing-induced re-distribution [1] to [6], [18] to [25]. Meanwhile, the anthocyanins of purple rice—mainly Cyanidin 3-O-glucoside and Peonidin-3-O-glucoside—are present in the outermost parts of the rice grain, and are unstable to degradation under heat treatment, neutral to alkaline digestion and upon storage for a long period [8] to [14], [40] to [50].

On one hand, nano zinc systems provide a mechanistic opportunity that can change the dissolution process, adhesion to the leaf surface, leaf cell wall, root uptake, xylem loading and sink allocation, but on the other hand, raise unanswered questions regarding particle transformation, zinc ion release, oxidative stress, and food safety [26] to [39]. The particular relevance of electrochemical methods here is due to the redox activity of anthocyanins and the related phenolics, and the ability to determine zinc in a sensitive manner using stripping methods. Thus, the combined electrochemical platform could be used for assessment of antioxidant potential and changes in zinc speciation, matrix interaction, and digestion – all at rapid speed for treatment screening and formulation optimization to [51] to [60]. The review suggests an integrated framework to link nano zinc treatment, grain micro distribution, polishing severity, digestion stage, cooking and electrochemical fingerprint in a multi objective optimization workflow. A similar scheme might speed up the process of establishing Australian purple rice as a functional grain with an even higher retention of zinc and a higher concentration of bioavailable anthocyanin metabolites.