Currently, biomass contributes to ∼14 % of global energy needs. Therefore, many studies and policies have been developed in order to expand the participation of renewable energy in the global energy matrix. In this context, ethanol has received substantial interest. This work investigates ways to improve efficiency in ethanol production from sweet potatoes, considering the costs that make the process potentially implementable. The following aspects were investigated: (i) conversion efficiency according to the post‐harvest time; (ii) influence of the heating method (water bath (conventional) and microwave) as well as the corresponding processing costs. The conversion efficiency increased significantly during sweet potato ripening, where the highest value was achieved 25 days after harvest. This is a very important result since it has a strong impact on the final cost. Among the heating methods, the conventional one was slightly superior in terms of conversion efficiency (9 % higher at 25 days) and also had better results regarding cost analysis. Among four designed scenarios, the largest cost difference was 17.5 %. Instead of a definitive elimination of microwave heating, the results should be analyzed to identify where the microwave heating should be improved in order to make it more attractive in the future.

Sweet potato is an attractive feedstock for ethanol production due to its high starch content and favorable agronomic characteristics. This paper proposes a simple equation to estimate the total reducing sugars (including glucose from starch) in sweet potatoes based on their moisture content (low cost and simple measurement). It allows the calculation of the ethanol production potential of a given sweet potato mash. According to the equation, the ethanol potential increases non-linearly with increasing concentrations of sweet potato mash in the fermenting medium (w/v), reaching a constant value for high concentrations (22 % of ethanol to 10 kg: L of a sweet potato with a moisture content of 66 %). Additionally, the ethanol yield potential is very sensitive to the sweet potato moisture, increasing linearly when the moisture decreases. We emphasize that the relations proposed in this paper can be used by other researchers, who can apply them to their specific cases.

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When producing ethanol from sweet potatoes, the fermentation generates slurry with nutritional content but underutilized for human consumption. Therefore, the nutritional properties of the flours obtained from the fermentation slurry of orange‐fleshed sweet potato (rich in carotenoids) was investigated. Three drying methods were carried out to produce slurry flours: convective using a hot‐air (60°C), microwave, and lyophilization. For carotenoids determination, were applied a conventional method and the Raman spectroscopy, a modern and alternative technique. Regarding the drying methods, the microwave was the most promising since it produced flour presenting higher levels of carotenoids (β‐carotene 849.7 µg/g and lycopene 548.4 µg/g). Also, the microwave drying time was 15 min, being much faster than the other methods. In the centesimal analysis of macronutrients, the slurry flours presented high fiber content, around 55 g/100 g. Finally, biscuits containing parcels of the flours demonstrated potential acceptability, by sensory analysis evaluating aroma and appearance. Practical applications Since ethanol is a product of worldwide importance, and it is produced mainly from corn and sugar cane, the production from sweet potatoes as an alternative raw material has interested researchers from different countries. Knowing that the ethanol production from sweet potato generates a residual slurry, this study focuses on adding value to this slurry, producing a nutritious flour. The potential for industrial application is promising, assuming it is a residue of an industrial infrastructure already installed. For the industry, obtaining more than one product in the same process represents a financial advantage and resource optimization.

RESUMO -A produção de etanol no Rio Grande do Sul é inexpressiva diante do seu consumo, fato este que se deve, principalmente, à inaptidão do clima gaúcho para a produção de cana-de-açúcar. Diante desta realidade, há um mercado oportuno para matérias-primas alternativas. A batata-doce foi selecionada para o estudo devido ao seu elevado potencial de produtividade agroindustrial. Experimentos foram realizados em etapas. Primeiramente, avaliou-se o desempenho da hidrólise do amido, sob diferentes temperaturas, na etapa de liquefação, sendo constatado o melhor resultado na temperatura de 85 o C. Na segunda etapa, empregou-se o aquecimento prévio com micro-ondas, a temperatura de 85 o C serviu como referência. Mediante os resultados de hidrólise e fermentação, concluiu-se que a inclusão da etapa de aquecimento por micro-ondas é bastante promissora, já que o tempo de aquecimento é rápido (2,5 minutos) e a temperatura de liquefação pode ser reduzida.