Composition and Nutritional Value of Acid Oils and Fatty Acid Distillates Used in Animal Feeding

Abstract

Acid oils (AO) and fatty acid distillates (FAD) are oil refining by-products rich in free fatty acids. The objective of this study is their characterization and the identification of their sources of variability so that they can be standardized to improve their use as feed ingredients. Samples (n=92) were collected from the Spanish market and the MIU value (sum of moisture, insoluble impurities, and unsaponifiable matter), lipid classes, fatty acid composition, and tocol content were analyzed. Their composition was highly variable even between batches from the same producer. As FAD originated from a distillation step, they showed higher free fatty acid amounts (82.5 vs 57.0 g/100 g, median values), whereas AO maintained higher proportions of moisture, polymers, tri-, di-, and monoacylglycerols. Overall, the MIU value was higher in AO (2.60-18.50 g/100 g in AO vs 0.63-10.44 g/100 g in FAD), with most of the contents of insoluble impurities being higher than those in the guidelines. Tocol and fatty acid composition were influenced by the crude oil's botanical origin. The calculated dietary energy values were, in general, higher for AO and decreased when a MIU correction factor was applied. The analytical control and standardization of these by-products is of the outmost importance to revalorize them as feed ingredients.

Keywords: MIU value; acid oils; animal feed; energy; fat by-products; fatty acid distillates; nutritional value; pig; poultry.

Figure 1

Principal component analysis on the compositional parameters (32 variables, mean centered and scaled to unit variance) of acid oils from chemical refining (AO, n = 79). (a) Score plot colored according the botanical origin (see Table 1 for abbreviations); (b) loading plot (abbreviations: M, moisture; I, insoluble impurities; U, unsaponifiable matter; MIU, sum of M, I, and U; FFA-AC, free fatty acids determined by titration (acidity); POL, polymeric compounds; TAG, triacylglycerols DAG, diacylglycerols; MAG, monoacylglycerols; FFA-SE, free fatty acids determined by size exclusion chromatography; T + T3, sum of α-, β-, γ-, and δ-tocopherols and α-, β-, γ-, and δ-tocotrienols) and U/S ratio, ratio of unsaturated to saturated fatty acids calculated as explained in Table 3.

Figure 2

Principal component analysis on the compositional parameters (27 variables mean centered and scaled to unit variance, POL, TAG, DAG, MAG, and FFA-SE were excluded) of fatty acid distillates from physical refining (FAD, n = 13). (a) Score plot colored according the botanical origin (see Table 1 for abbreviations); (b) loading plot (see Figure 1 for abbreviations).

Figure 3

Boxplots for moisture (M), insoluble impurities (I), unsaponifiable matter (U), and the sum of them (MIU) according to botanical groups for (a) acid oils from chemical refining (n = 79) and (b) fatty acid distillates from physical refining (n = 13) (see Table 1 for botanical group abbreviations). Within each type of refining and variable, botanical groups bearing different letters (a–c) are significantly different according to Kruskal-Wallis test and post-hoc comparisons (p ≤ 0.05).

Figure 4

Saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), and unsaturated/saturated ratio (U/S ratio) boxplots according to botanical groups for (a) acid oils from chemical refining (n = 79). and (b) fatty acid distillates from physical refining (n = 13) (see Table 1 for botanical group abbreviations). Within each type of refining and variable, botanical groups bearing different letters (a–e) are significantly different according to Kruskal–Wallis test and post-hoc comparisons (p ≤ 0.05).

Figure 5

Triacylglycerols (TAG), diacylglycerols (DAG), monoacylglycerols (MAG), and free fatty acids (FFA-SE) boxplots according to botanical groups for (a) acid oils from chemical refining (n = 79) and (b) fatty acid distillates from physical refining (n = 8, lauric FAD group was excluded) (see Table 1 for botanical group abbreviations). Within each type of refining and variable, botanical groups bearing different letters (a–c) are significantly different according to Kruskal–Wallis test and post-hoc comparisons (p ≤ 0.05).

Figure 6

Tocopherols (T), tocotrienols (T3), and Vitamin E content according to botanical groups for (a) acid oils from chemical refining (n = 79) and (b) fatty acid distillates from physical refining (n = 13) (see Table 1 for botanical group abbreviations). Within each type of refining and variable, botanical groups bearing different letters (a–c) are significantly different according to Kruskal–Wallis test and post-hoc comparisons (p ≤ 0.05).

Figure 7

Apparent metabolizable energy (AME) calculated for adult broilers according to Wiseman’s equation [28] and by applying the MIU (g/100 g) correction to it [32] of (a) acid oils from chemical refining (n = 79) and (b) fatty acid distillates from physical refining (n = 13). See Table 1 for botanical group abbreviations. Within each type of refining and variable, botanical groups bearing different letters (a–d) are significantly different according to Kruskal–Wallis test and post-hoc comparisons (p ≤ 0.05).