Effect of microwave pretreatment and adding strategies of Hongqu lees on the physicochemical properties and microbial communities of fermented large yellow croaker sauce

Abstract

The Aromatic Lees Large Yellow Croaker is a traditional solid-state fermented product from the southeastern coast of China. The liquid fermentation method for making fermented large yellow croaker sauce (LYCS) is a new attempt to obtain a unique fermented flavor more efficiently based on the traditional fermentation method. Hongqu lees impart unique flavors to fermentation, and different amounts of Hongqu lees added lead to fermentation systems with different initial physicochemical and microbiological properties. Microwave pretreatment before fermentation (MWP) was introduced as a key innovation technique aimed at reducing undesirable microorganisms in the fermentation raw material and enhancing the release of flavors in the fermentation. This study investigated the effects of MWP and different levels of Hongqu lees addition on the physicochemical characteristics and microbial composition of LYCS. MWP increased the total acid (TA), total nitrogen (TN), and trichloroacetic acid (TCA) - soluble peptides contents. Histamine content was significantly reduced by increasing the Hongqu lees addition to L2 (1:0.2 ratio of fish pulp to Hongqu lees). In terms of taste profile, MWP effectively reduces bitterness but also leads to a loss of umami. The main volatiles detected in LYCS were esters and alcohols. Without MWP, LYCS emitted unpleasant volatile odors in the L1 and L2 experimental conditions (1:0.1 and 1:0.2), and MWP effectively reduced these undesirable effects. The dominant bacteria identified in LYCS were Lactobacillus. MWP eliminated Lactococcus, which was derived from large yellow croaker and had a negative effect on LYCS. Moreover, an increase in Hongqu lees additions led to a reduction in the relative abundance of Clostridium. The comprehensive results showed that MWP improved the quality of LYCS, and the optimal addition of Hongqu lees was observed at the L2 level (1:0.2) following MWP. These findings provide a theoretical basis for the development of LYCS as a novel product.