Bioactive Compound Profile and Nutrition Values of Kava (Piper methysticum) Cultivated in Fiji

Piper methysticum G. Forst. (kava) is an important horticultural shrub of the Pacific, used as an ingredient of the intoxicating kava beverage, dietary supplement, and medicine around the globe. This study presents the first systematic evaluation of the phytochemical composition and nutrition values of roots and rhizomes of kava cultivated on three key kava-growing areas of Fiji (Rotuma, Kadavu, and Vanua Levu) by quantifying their kavalactone and flavokavain content, as well as measuring their calorific value, protein concentration and ash contents. Dried roots and rhizomes of the studied cultivars exhibited relatively high kavalactone concentrations (8.9–13.8 and 3.9–8.9 wt.%, respectively); favorable lactone profiles, with kavain as the major lactone component (2.1–4.6 and 1.1–2.6 wt.%, respectively); and low flavokavain contents (below 0.25 wt.%). The protein and ash contents of roots were measured to be 2.7–5.0 wt.% and 3.2–6.2 wt.%, respectively, and calorific values of roots were measured as 17.1–19.4 MJ·kg−1—values that are systematically higher than those found for rhizomes (1.6–3.2 wt.%, 2.3–4.6 wt.%, and 16.5–17.7 MJ·kg−1, respectively). A positive relationship between the calorific value and total kavalactone content was observed. A novel, unclassified kava cultivar (named Matanitabua) was discovered in Vanua Levu and identified as a noble kava cultivar.