Re-fermentation of decaffeinated Robusta bean using the mucilage analog of purple sweet potato (Ipomea batatas L.) to enhance coffee flavour

Abstract

Abstract Despite increasing consumer interest in decaffeinated coffee, its sensory acceptance remains limited due to flavor deterioration during the decaffeination process. Strategies to restore flavor precursors in decaffeinated coffee remain poorly explored, particularly through controlled re-fermentation using alternative mucilage substrates. This study aimed to determine the optimal timing and duration of re-fermentation for superior sensory quality and to analyse the impact of re-fermentation time and duration on chemical characteristics, including caffeine content, chlorogenic acid content, pH, total acidity, and total dissolved solids. The decaffeination process was conducted utilizing the Swiss Water Process method, followed by re-fermentation utilizing mucilage analog of purple sweet potato with fermentation durations of 0, 2, 3, and 4 days. The results showed an increase in the cupping test score from 74 (control) to a highest final score of 79.24 during a 4-day re-fermentation period. The results of chemical characteristic analysis show that re-fermentation significantly affects several quality parameters (p <0.05) compared to the decaffeinated control sample. The processed coffee shows chemical characteristics of 1.15% caffeine vs. 0.99% (control), total dissolved solids of 625 ppm vs. 434 ppm (control), pH of 5.04 vs. 4.67 (control), and not significant difference in chlorogenic acid and total acid parameters. The study concludes that re-fermentation using purple sweet potato mucilage analog effectively enhances the sensory profile of decaffeinated coffee. This method offers a low-cost approach for improving coffee quality using local materials.

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