3.4. Chemical characteristics of FOGs
3.4.1. Content of free fatty acids
In the standardized AOCS method, the content of free fatty acids
is expressed by assuming the molecular mass of oleic acid. This
assumption is not unreasonable; the mixture of free and esterified
fatty acids present in the FOGs was highly heterogeneous and oleic
acid predominated most commonly (Table 3). The content of free
fatty acids in FOGs extracted from 13 of the 14 samples of waste
varied widely (Table 2). The FOG with the lowest content of free
fatty acid (5.2%, as oleic acid) [Table 2] was from a firm that
produced fresh chickens only, while that with the highest content
(70.3%) was from a firm that prepared deep fried birds. These findings
suggest that much of the FFAs was generated by hydrolysis of
esterified lipids during cooking at elevated temperature. In addition