In the present work, a simple and high-throughput analytical procedure based on ultrasound-assisted extraction with diluted acid was proposed for the determination of Ca, Mg, K, P, S, Fe, Cu and Mn in guarana samples using inductively coupled plasma optical emission spectrometry. Two multivariate approaches were employed for optimization of the extraction procedure: mixture and Doehlert designs. The best experimental conditions were established by application of a multi-response function (overall desirability). An extractor medium composed of diluted nitric acid was selected for analytes extraction. Optimized conditions for ultrasound-assisted extraction followed the temperature of 60 °C, sonication time of 10 min and power of 100% applied to the ultrasonic bath. After the analytical validation step, the proposed procedure was successfully employed for determination of essential elements in thirty-three guarana samples from the state of Bahia, Brazil. Mass fractions higher than 0.42% (m m -1 ) were found for potassium in all analyzed samples. For the other macro-elements, the mass fraction ranged from 514 mg kg -1 (magnesium) to 0.19% m m -1 (calcium). The mass fraction of micro-elements ranged from 5.1 to 91.3 mg kg -1 for cooper and iron, respectively.

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Bioconversion by Hermetia illucens larvae is a novel technology for organic waste treatment and valorization. However, since the possible uses of products from this process are in agriculture and livestock, the bioconversion must guarantee the mineral quality of both the Hermetia illucens larvae frass and larval biomass. Therefore, this study aimed to assess the mineral content changes for both the larval biomass and larvae frass of Hermetia illucens after the manure bioconversion to determine their suitability as animal feed and organic fertilizer, respectively. Hermetia illucens larvae were put into a plastic box containing fresh cattle manure, and the control treatment with the same conditions without larvae was established. After the first pre-pupae were detected, frass and larvae were collected, and their mineral content was analyzed. At the end of the experiment, the larvae showed increases in some micro and macronutrients, especially calcium and manganese, increasing up to 2.6 and 22.6 times the initial concentration, respectively. The toxic elements concentration was increased in larval biomass, but these levels met the international legislation for animal feed. As a result, the mineral content in larval biomass revealed that Hermetia illucens could be potentially used as animal feed, which could be comparable with fish meal, and is probably better than soybean meal. However, the larvae frass could only be used as organic fertilizer in a Canadian context, with further treatment for decreasing the chromium content being necessary.