Optimization of liquid-fermentation technology for black garlic

Abstract: In this study, fresh garlic was fermented into black garlic in high temperature and high humidity conditions. Five influencing factors (temperature, time, material selection, material-to-liquid ratio, and crushing granularity) were studied during fermentation process. Combining the measurement of soluble sugar content, total phenolic content, and superoxide dismutase (SOD)activity with sensory evaluation, we determined that it was mainly the Maillard reaction during the fermentation process. We selected 70, 80, and 85℃ for constant-temperature fermented garlic puree. On the basis of the effect of temperature on the black garlic fermentation we determined the time range of the subsection temperature-changing fermentation. Using a colorimeter, we dynamically detected the change of chromatic (L value) during the black garlic fermentation process, and we detected the content of soluble sugar, total phenolic content, and SOD activity. We found that the formation of garlic melanin was related to temperature and time. Garlic in high-temperature pre-fermentation conditions may form a large quantity of melanin. On the basis of constant temperature fermentation, the garlic puree was fermented with the subsection temperature-changing fermentation. The combinations of the selected temperature were: 65-80, 80-70, 85-65, 85-70℃. The pre-fermentation time was 5-6 d, and the post- fermentation time was 11-13d. Combined sensory evaluation with detection of the content of soluble sugar, total phenolic content, and SOD activity, we determined the temperature and time combinations of the subsection temperature-changing fermentation. On the basis of the subsection temperature-changing fermentation, material selection, material-to-liquid ratio, and crushing granularity had been systematically studied to determine the optimum technology parameters of the liquid black garlic fermentation. Data were expressed in terms of means and standard deviations and were analyzed by Duncan-type multiple comparison method using SAS 17.0 software, using P<0.05 as the significance threshold. Results showed that the temperature impacts on the fermentation of black garlic and the best process conditions were as follows: using subsection temperature-changing fermentation, temperature combinations selected for 85-70℃, the pre-fermentation time was 5-6 d, post-fermentation time was 11-13d. We used purple garlic as the raw material, a material-to-liquid ratio of 2:1, and a crushing granularity of 4mm. The resulting product was a uniform black brown, suitably sour and sweet, exhibited almost no acid smell, and compared with the unfermented garlic, the total phenolic content increased 5 times, SOD activity increased 15 times, and soluble sugar content decreased about 30%. Currently garlic consumption is mainly known for its raw materials and primary processing products, and its value is not high, so the study on the liquid fermentation technology of black garlic opens up a new field for the development and utilization of a garlic advanced-processing industry.