Effects of ethanol pretreatment on the properties of yacon slices subjected to different drying methods

Abstract

Yacon is a tuberous root widely consumed due to its high content of fructooligosaccharides (FOS). However, its high moisture content (~89% w.b.) makes it highly perishable. Drying is an alternative that reduces moisture content, extending the product shelf life, although some degradation also occurs. Pre-drying treatments, such as ethanol immersion, can improve processing efficiency and contribute to obtaining a higher-quality product. Additionally, drying methods such as intermittent microwave drying can ensure shorter drying times and better preservation of nutritional value. Therefore, this study aimed to investigate the effect of different drying methods applied to yacon slices, as well as the effect of ethanol pretreatment. The work was divided into three parts: the first article presented a comprehensive literature review on drying methods and pretreatments applied to yacon, highlighting gaps and advancements in the literature. The second article investigated the impact of ethanol pretreatment on convective drying and the properties (color, shrinkage, FOS content, antioxidant activity, total phenolics, and microstructural analysis) of yacon slices. The third article addressed intermittent microwave drying of yacon slices, also using ethanol as a pretreatment. The effects of ethanol on drying and product properties were further investigated. In the convective drying trials, ethanol pretreatment reduced drying time by up to 28.00% and energy consumption by 22.72%, while preserving color and shrinkage parameters. Additionally, higher drying temperatures led to the degradation of bioactive compounds. The best treatment in this case was drying at 50°C without ethanol pretreatment, as it resulted in higher FOS retention (51.00%). In the intermittent microwave drying trials, ethanol pretreatment further reduced drying time by up to 34.62% and energy consumption by 32.41%, while preserving antioxidant capacity, total phenolic compounds, and FOS retention. The best treatment in this case was drying at 52°C with ethanol pretreatment. Furthermore, it is worth emphasizing that the combined use of ethanol pretreatment and intermittent microwave drying provided a more efficient and sustainable approach, aligning with the United Nations Sustainable Development Goals (SDGs).