Values shown as mean ± SD of the replicates. ND: Not determined.
Table 4 shows kinematic viscosity, density, and trace metals contents of the tested samples. Density and viscosities were measured at a temperature in with all samples were liquid (40°C), except for bacuri fat, completely melted after 55°C. Viscosity is a measure of resistance to flow of a liquid. It is also related to spreadability and sensorial perception of the fat. Bacuri fat had the lowest kinematic viscosity (28.28 mm2/s). Since viscosity is directly proportional to the chain length of FA in the triglycerides (Hoekman, Broch, Robbins, Ceniceros, & Natarajan, 2012), the high short chain length FA contents of bacuri fat (70.17% of FA ≤ C16) explains the low viscosity values of this sample. Pracaxi oil (32.53% of FA ≥ C20) exhibited the highest viscosity (48.85 mm2/s), which is in agreement with the value reported by Pereira Lima et al (2017).
The density of vegetable oils and fats has been reported to be directly proportional to the degree of unsaturation and inversely proportional to the chain length of the FA in its composition (Hoekman et al., 2012). Values obtained for the samples ranged from 904.17 g/cm3 to 894.13 g/cm3. Notably, the range of densities was small, in agreement with results reported by Ceriani et al (2008) for pure fatty compounds and other oils.
Metals cause deterioration of the product’s quality and can be encountered throughout the processing of edible fats and oils (O’Brien, 2009). Notable among these metals are iron, calcium, and magnesium. Contents of these three trace metals in all of the samples, except for bacuri fat, were low, comparable to olive oil (Benincasa, Lewis, Perri, Sindona, & Tagarelli, 2007). Brazil nut oil and patawa oil samples presented phosphorus contents lower than 1 mg/kg, while the other fats and oils presented levels between 20 and 32 mg/kg. Since a phosphorus content lower than 5 mg/kg is one of the requirements for physical refining (O’Brien, 2009), all of the samples, except for Brazil nut and patawa oils, would demand industrial degumming processes, such as water degumming, in order to control phosphorus contents (Dijkstra & Segers, 2007).
Table 4Trace metals contents, kinematic viscosity, and density of the fats and oils