Changes of Physiochemical and Enzymatic Activities of doenjang Prepared with Different Amount of Rice koji during 30 Days of Fermentation

Yongwoo Jo,Mina K Kim,Woo-Suk Bang

doi:10.3390/foods10020372

Yongwoo Jo, Mina K Kim + Show 1 more

Open Access

https://doi.org/10.3390/foods10020372

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Journal: Foods	Publication Date: Feb 9, 2021
Citations: 7	License type: CC BY 4.0

Affiliation: Jeonbuk National University, Yeungnam University

Abstract

Koji is an intermediate fermentation agent, made by inoculating known microorganisms in grains, such as rice, beans, and barley, to hydrolyze starch or protein. The quality of koji can influence the final quality of doenjang. This study aimed to investigate changes in the physiochemical and enzymatic activities of doenjang prepared with different amounts of rice koji during a 30-day fermentation period. Three doenjang samples were prepared with varying levels of rice koji: K1 (11% reduced), K2 (control), K3 (11% increased). Physiochemical characteristics including pH, TA, acid value, moisture content, color, sugar and reducing sugar content, and enzymatic activities including α- and β-Amylase, acidic and neutral protease activities. Samples were taken every 5 days for 30 days of fermentation period. The doenjang with a high content of rice koji had higher levels of total sugars, reducing sugars, alcohol, and protein enzyme activity than the doenjang samples with a lower content of rice koji (p < 0.05). However, no differences in the physiochemical and enzymatic activities were found between the doenjang made with a lower amount of koji and the control doenjang during fermentation (p > 0.05).

Highlights

Doenjang is a traditional soybean fermented food ingredient in Korea
FermentatTiohn epesriuodgsa(draycso)ntent, which affects the sweetness of doenjang, is dependent on the amylase activity produced by the microorganisms involved in fermentation, as well as the protease activity that hydrolyzes the soy protein during fermentation [21,26,27]
The sugar content, which affects the sweetness of doenjang, is dependent on the amylase activity produced by the microorganisms involved in fermentation, as well as the protease activity that hydrolyzes the soy protein during fermentation [21,26,27]

Summary

Introduction

Adding doenjang can provide brothy and umami tastes to Korean cuisine due to the presence of amino acids, saccharides (mono-, di-, oligo-, and poly-), and other flavor compounds produced by the fermentation process. Companies have developed a method to mass produce commercially-available doenjang utilizing koji, an intermediate fermentation agent cultured by inoculating Aspergillus oryzae in starchy materials such as rice, soybean, barley, and wheat [6]. Manufacturing commercial doenjang using koji can allow controlling the fermentation process as fermentation agent by direct injection of known bacteria or fungi, primarily Aspergillus oryzae; making standardization and efficient production possible. The limitation of commercial doenjang is its lack of flavor and low umami taste that is attributed to amino acid degradation of the compounds produced by various microbial communities [4,5,7]

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