Effects of ageing and salt concentrations on metabolite profiles and their correlation with consumer acceptance in Korean traditional doenjang (fermented soybean paste)

Abstract

The effects of brine concentration (8%, 12%, 16% and 20%) and ageing (0 and 12 months) of Korean traditional doenjang (fermented soybean paste) on metabolite profiles and their relationship with consumer acceptance were investigated. Using ultra-performance liquid chromatography-quadrupole-time-of-flight mass spectrometry and gas chromatography–mass spectrometry, we identified 26 and 31 metabolites, respectively. After 12 months of ageing, the relative amounts of metabolites increased owing to the degradation of soy protein into peptides and amino acids. Functional metabolites, such as isoflavones and gamma-aminobutyric acid, were higher in the lower salt-containing and longer-aged samples. Generally, lowering the salt content of doenjang results in the production of more functional metabolites. In contrast, the consumer acceptance of low-salt-containing samples made with 8% brine showed significantly lower acceptance ratings than the regular doenjang samples due to over-fermentation, which generated high lactic acid and no sugar in the sample. The partial least significant regression analysis between metabolites and consumer acceptance ratings suggested that amino acids – alanine, valine, isoleucine, proline, serine, threonine, hydroxyproline, glutamic acid and phenylalanine – were key metabolites that highly correlated with consumer acceptance of doenjang. These metabolites can be adopted as indicators of highly acceptable doenjang products.