Effect of demucilagination and soaking in water with organic acids on the microbial, chemical, and sensory characteristics of coffee (Coffea arabica)

Abstract

There are divided opinions regarding sensory quality of mechanically demucilaginated (MD) coffee versus coffee that has undergone conventional fermentation (biological demucilagination). Fermenting and washing (wet process) requires high amounts of water that has contaminating effects upon its completion. Studies indicate that MD with soaking in organic acids could develop similar sensory quality to wet processed coffee. Organic acids are bioactive compounds that are naturally produced during conventional fermentation, which is why coffee has unique characteristics in the final cup profile. This study was conducted to assess the effects of soaking with organic acids (citric, ascorbic, and acetic) on the microbial, chemical, and sensory attributes of MD coffee. A Completely Randomized Design (CRD) was used, with a factorial arrangement (2×4+2) for a total of 10 treatments. The treatments were two soaking times (24 and 48 hours) and four soaking solutions (citric, ascorbic, acetic acid and water) in coffee with mechanical demucilagination, one treatment with mechanical demucilagination and one with fermentation and washing, both without soaking or acids. Microbiological counts of fungi, yeasts, and lactic acid bacteria (LAB) were carried out before and after soaking. Sensory characteristics were evaluated through cupping and chemical content and properties were studied by liquid chromatography and spectrophotometry. Microbial population demonstrated normal succession throughout the experiment with LAB been the most prevalent family during MD and fermentation. Soaking coffee in acid solutions maintained overall cupping scores with different attributes being detected by panelists. Phenolic compounds, caffeine and chlorogenic acids increased in soaked samples (acetic acid) but were similar to the control (fermentation). Flavonoid content ranged from 22 to 35 mg EC/g and was higher in samples soaked in acids compared to the controls. Green coffee extracts in general showed antioxidant activities greater than 80.9% comparable to other studies. Soaking time did not improve the quality characteristics of the coffee, but the type of acid used was able to modify the content and proportion of various families of chlorogenic acids in green coffee and total polyphenols, while maintaining sensory properties in comparison to fermented coffee.