Assessing the potential of coffee fermentation by-products through color metrics in ohmic heating-based processing

Abstract

A cutting-edge method for processing coffee has recently been developed that employs ohmic heating-based fermentation combined with a semi-carbonic maceration technique. This innovative process involves fermenting whole coffee cherries without removing their skin and pulp. In addition to altering the properties of coffee beans, this method may facilitate the extraction of bioactive compounds, such as anthocyanins, from the fruit skin into the surrounding liquid medium. This study marks the initial investigation into how processing conditions impact the colorimetric properties of the resulting by-product solution, with a particular focus on its potential as a source of anthocyanins. Fermentations were conducted at 31 °C and 35 °C over a period of 36 h, with data collected every 4 h. Color parameters (L*, a*, and b* values) and pH were measured to calculate the color difference (ΔE), chroma variation (ΔC), and hue angle. The results revealed noticeable color changes beginning at 16 h, characterized by a decrease in the L* value, increases in ΔC and ΔE, and a hue angle shift from dark green to red. Simultaneously, the pH of the solution decreased, suggesting enhanced anthocyanin stability under acidic conditions. These findings provide evidence of anthocyanin extraction during fermentation and support further exploration of the characterization and extraction of bioactive compounds in fermentation by-products.