Effects of pretreated garlic on bacterial composition and metabolite profiles during kimchi fermentation

This study investigated the effects of pretreated garlic on the fermentation characteristics of kimchi; four types of kimchi using pretreated garlic [raw (RGK), frozen (FGK), blanched (BGK), and blanched-frozen (BFGK)] were prepared; fermentation was carried out at 4 C-degrees for 6 weeks. The fermentation properties, microbial community composition, metabolic compounds, and volatile organic compounds (VOC) were investigated. The total viable bacterial count in blanched garlic was reduced significantly compared to those in raw and frozen garlic. Latilactobacillus spp. became the dominant species in all kimchi samples as the fermentation progressed. Of the 145 metabolites observed by gas chromatography and mass spectrometry, 51 volatile metabolites were observed. Glucose, fructose, sucrose, lactic acid, citric acid, and mannitol were present as major metabolites (variable importance in projection scores >1.0). Frozen garlic (FGK and BFGK) reduced the production of sulfuric VOC compounds, while raw garlic increased the production of these compounds, specifically that of allyl methyl sulfide, dimethyl disulfide, and dimethyl trisulfide. In conclusion, the condition of garlic added to kimchi affects the abundance of microorganisms during initial fermentation and the quality characteristics of kimchi during the fermentation period. These results help establish garlic pretreatment conditions for kimchi manufacturing.