Effect of rice koji levels on the physicochemical and sensory aroma profiles of doenjang

BACKGROUND: Doenjang, a traditional Korean fermented soybean paste, is often made with rice koji, which provides enzymes and fermentable sugars. However, little is known about how different amounts of rice koji influence fermentation and sensory traits. The present study examined the effects of rice koji levels on the physicochemical, enzymatic and sensory properties of doenjang using descriptive analysis. RESULTS: Samples with a higher amount of rice koji showed increased soluble solids, alcohol content and α-amylase activity, indicating a starch-centered fermentation pathway. These samples also exhibited stronger fruity and fermented aromas, such as banana peel and alcohol notes. By contrast, samples with lower rice koji levels displayed higher pH, moisture content and protease activity, suggesting protein-based fermentation. These samples developed more complex, traditional flavors, including meju, musty and yeasty aromas. Color values (a*, b*) also increased under low-koji conditions, likely as a result of enhanced browning reactions related to amino acid degradation. Overall, the rice koji level significantly influenced both the metabolic balance between carbohydrate and protein fermentation and the resulting sensory characteristics. CONCLUSION: Rice koji amount critically influences the biochemical and sensory traits of doenjang. High levels promote carbohydrate metabolism and fruity flavors, whereas low levels favor protein breakdown and stronger traditional aromas. These findings help guide fermentation strategies for quality improvement in traditional doenjang.