Germination induced metabolic changes to improve taste and flavor characteristics of off-grade Robusta coffee beans

Abstract

• Germination of off-grade Robusta coffee beans improved cupping scores from 43 to 80.5. • Germination removed compounds contributing to undesirable earthy and woody flavors. • Caffeine and chlorogenic acid decreased, mitigating bitterness and astringency. • Germination is a promising technique to enhance flavor quality of off-grade Robusta coffee. Most Robusta coffee ( Coffea canephora ) produced in South Sulawesi, Indonesia, is classified as off-grade owing to primary and secondary defects that affect flavor quality, as assessed by taints-fault parameters in cupping tests. This study investigated the potential of germination metabolism, activated through hot water treatment, to enhance the flavor quality of defective Robusta coffee beans. This study examined the effects of varying temperatures (50, 70, and 90 °C) and treatment durations (two and four hours) on germination and the subsequent changes in key chemical components, which include caffeine, chlorogenic acid, reducing sugars, proteins, amino acids, and flavor compounds. The results demonstrated a significant improvement in cupping score, from 43 to 80.5, under the optimal treatment of 90 °C for 4 h. The germination process can effectively remove certain compounds that contribute to undesirable earthy and woody flavor characteristics, such as 2-ethyl-6-methyl-pyrazine, 3-ethyl-2,5-dimethyl-pyrazine, guaiacol, and phytol. The germination process caused caffeine and chlorogenic acid contents to decrease from 1.33 % to 0.64–0.97 %, and from 6.8 % to 3.5–6.4 % respectively. These reductions in caffeine and chlorogenic acid mitigated off-flavors by decreasing bitterness and astringency. The effect of germination treatment on reducing sugars was temperature dependent where treatment at 50 °C tended to increase reducing sugars from 0.29 % to 0.35–0.37 % while treatments at 70 °C and 90 °C tended to decrease it to 0.15–0.26 %. These findings highlight the potential of germination as a transformative technique for improving flavor quality in off-grade Robusta coffee, offering a practical solution for coffee processors and roasteries to address off-flavor issues, elevate consumer acceptance, and expand market opportunities.

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