Physiochemical changes and nutritional content of black garlic during fermentation

Abstract

This study was conducted to understand the reactions involved in black garlic fermentation, and thereby to determine its maturity stage. Black garlic was produced from fresh garlic after fermentation at 70–75 °C and 80–90% relative humidity up to 12 days in this study. The enzymatic hydrolysis of fructans and oligosaccharides, and endophytic bacterial action were likely to be the dominant processes at the initial stage, and followed by non-enzymatic browning Maillard reaction. Fructose was initially detected at the highest concentration and started to decrease after 10 days together with the exponential increase of 5-hydroxymethylfurfural (5-HMF) content. The predominant acids were citric and succinic acids, whereas potassium was the most abundant minerals. The loss of pungent smell could be attributed to the degradation of sulfur containing compounds. The pH of fresh garlic was 6.61, and gradually decreased to <4.0 after 10 days. Fresh garlic lost about 22% of mass after aged in a high humidity environment. There was significant difference in the bioactivities of fresh and black garlic, but no difference among black garlic fermented for >8 days. Garlic fermentation involved multiple reactions including enzymatic hydrolysis, endophytic bacterial action, and non-enzymatic browning reaction to achieve maturity after 8 days.