5.3. Determination of total free amino acids
When extracting the free amino acid in the samples, 5 g of solid samples for non-fermented and fermented pork jerky were respectively cut up. Then the solid samples and 5 mL of liquid samples for remaining fermented medium and the medium before fermentation were placed into beakers with adding 50 mL distilled water and 5 g acticarbon. After heated and boiled for 5 min, hot water was used to wash the acticarbon. The filtrate was respectively detected for the free amino acid contents of the samples, including non-fermented pork jerky, fermented pork jerky, remaining fermented medium, and the medium before fermentation using the colorimetric method of ninhydrin (Wu, Li, & Ma, 2006). Accordingly, ninhydrin was added to the samples under acidic conditions and the absorbance of the solution was ascertained at 570 nm.