An analysis of the changes on intermediate products during the thermal processing of black garlic

•Garlic fructan degraded into fructose and glucose during thermal processing.•The reason black garlic becomes sweet is primarily the result of increased fructose content.•The colour of black garlic becomes dark primarily due to the Maillard reaction.•The Maillard reaction in black garlic occurs through Heyns pathway as important as Amadori pathway. The thermal processing of black garlic was simulated. Fresh garlic was incubated at 55°C with 80% humidity and sampled every 5 or 10days. The changes in relevant products were as follows: the fructan content was decreased by 84.79%, and the fructose content was increased by 508.11%. The contents of Maillard reaction intermediate products were first increased and then decreased. The colour of garlic gradually became dark and the pH decreased from 6.13 to 4.00. By analyzing these changes, the mechanism of black garlic formation and the changes on the Maillard reaction were revealed. The sweetness of black garlic resulted mainly from the fructose that was produced, and the black colour was largely due to the Maillard reaction between fructose/glucose and amino acids. An understanding of this process is useful to explain the formation mechanism of black garlic and could lead to better control of the quality of black garlic.