Black garlic: Effects of the processing on the kinetics of browning and moisture transfer and on antioxidant properties

This work aimed to investigate the effects of temperature and relative humidity on the moisture transfer kinetics and browning during black garlic processing. The final product quality was also evaluated based on the total phenolic compounds (TPC) content and antioxidant activity (AA). Garlic bulbs were stored in a temperature and humidity controlled room in NaCl and KCl saturated solutions at 65, 72.5, and 80 degrees C for several days. The diffusion equation that considered external resistance was able to represent the mass transfer kinetics well. The browning kinetics was modeled according to a zero-order reaction. Black garlic of a suitable color (L* approximately equal to 10) was obtained in short time periods of 5 days at 80 degrees C, 8 days at 72.5 degrees C and 15 days at 65 degrees C with the water content nearly 42% (NaCl) and 45.5% (KCl), also permitted some formation of TCP compounds and an increasing in AA. Practical applications Despite a number of works concerning the production of black garlic, literature remains somewhat empirical and, because of this, there is a lack of mathematical models describing this process. Black garlic processing is in general carried out under a controlled high-temperature and relative humidity for a long time period. This is, therefore, an energy intensive process. However, as demonstrated in this study, if the operation variables are properly chosen, it is possible to reduce the processing time and, thus, the energy expenditure. Therefore, the present results are useful for the process design and manufacturing of black garlic.