Effect of Fermentation Temperature on the Main Flavor Substances in Low-Salt Shrimp Paste

In order to study the effect of fermentation temperature on the flavor substances in low-salt shrimp paste, the natural fermentation of shrimp paste was carried out at 10, 15, 20 or 25 ℃. The contents of free amino acids, free fatty acids and volatile compounds in shrimp paste were determined by high performance liquid chromatography (HPLC), gas chromatography (GC) and gas chromatography-ion mobility spectrometry (GC-IMS), respectively. The results showed that 17 free amino acids and 26 free fatty acids were detected in each shrimp paste sample. The content of flavor amino acids was highest in shrimp paste fermented at 10 ℃, and the content of free fatty acids was highest in shrimp paste fermented at 20 ℃. A total of 69 volatile compounds were identified in all samples, including 19 alcohols, 13 aldehydes, 13 ketones, 12 esters, 2 alkenes, 2 ethers, 1 acid and 7 other compounds. The relative contents of alcohols and ketones were higher in shrimp paste fermented at 10 ℃ and 15 ℃. The relative contents of ammonia were higher in shrimp paste fermented at 20 or 25 ℃. Principal component analysis (PCA) showed that volatile compounds were significantly distinguishable in low-salt shrimp pastes fermented at different temperatures. A total of six differential volatile compounds (variable importance in projection (VIP) >1, P < 0.05) were identified by orthogonal partial least squares-discriminant analysis (OPLS-DA), namely 3-methyl-1-butanol (monomer and dimer), ethyl acetate dimer, ethyl acrylate, 2-methylbutanal dimer and ammonia. Cluster heatmap analysis showed that the flavor of low-salt shrimp paste fermented at 10 and 15 ℃ was similar, and the flavor of low-salt shrimp paste fermented at 20 and 25 ℃ was similar. The results of this study may provide a theoretical basis for promoting the thermostatic fermentation of commercialized low-salt shrimp paste.