Functioning of Saccharomyces cerevisiae in honey coffee (Coffea canephora) and their effect on metabolites, volatiles and flavor profiles.

Post-harvesting and microbial activity of coffee play a critical role in the metabolites and the sensory quality of the brew. The pulped natural/honey coffee process is an improvised semi-dry technique consisting of prolonged fermentation of depulped coffee beans excluding washing steps. The starter culture application in coffee industry plays an important role to enhance the cup quality. This work focuses on the fermentation of pulped natural/honey Robusta coffee with a starter culture (Saccharomyces cerevisiae MTCC 173) and the identification of fermentation patterns through 1H NMR, microbial ecology, volatomics and organoleptics of brew. Fermentation was accelerated by yeast populace (10 cfu log/mL) for 192 h. Principal compound analysis performed on 1H NMR led to the investigation of metabolites such as sugars, alkaloids, alcohols, organic acids and amino acids. Detection of some sugars and organic acids represented that the starter cultures imparted few metabolic changes during the process. A major activity of sugars in fermentation with 83.3 % variance in PC 1 and 16.7 % in PC 2 was observed. The chemical characteristics such as carbohydrates (41.88 ± 0.77 mg/g), polyphenols (34.16 ± 0.79 mg/g), proteins (58.54 ± 0.66 mg/g), caffeine (26.54 ± 0.06 mg/g), and CGA (21.83 ± 0.04 mg/g) were also evaluated. The heatmap-based visualization of GC-MS accorded characterization of additional 5 compounds in treated (T) coffee contributing to sweet, fruity and caramelly odor notes compared to untreated (UT). The sensory outlines 72.5 in T and 70.5 in UT scores. Preparation of honey coffee with Saccharomyces cerevisiae is the first report, which modulated the flavor and quality of coffee.

Pulped natural/honey robusta coffee fermentation metabolites, physico-chemical and sensory profiles.

The pulped natural/honey coffee (HC) of Coffea canephora (Robusta) is an innovative modified semi-dry technique. Studies have focused on HC and washed coffee (WC) fermentation, microbial metabolites, quality of green and roasted, using 1H NMR, GC-MS, and sensory investigation. Pipecolate and 3-hydroxy-3-methyglutarate have been identified for the first time. Principal Component Analysis (PCA) variability of the roasted beans, with PC 1 depicting 87.4 % and 12.6 % PC 2 respectively highlights the impact of major sugars and secondary metabolites acquired through HC. The HC fermentation (192 h) influenced carbohydrates, organic acids, and secondary metabolites besides flavor precursors compared to WC (72 h). Although HC and WC beans share similar physical qualities, enhanced volatile compounds, enriched concentration, organoleptics with pleasant, sweet, tea rose and chocolaty flavors attributes were embodied in HC than WC. The pulped natural post-harvest technique in robusta is a value addition with quality that can fetch a better premium.