Determinação do perfil de ácidos graxos em Brachiaria spp. por eletroforese capilar

Abstract

Forages are the major components of ruminant diets, being a source of energy and nutrientsfor milk and meat production. Among the fatty acids found in forages, two (C18:2 n-6 and C18:3 n-3) have received particular attentiondue to theirroles as precursors for the synthesis of conjugated linoleic acid (CLA), a class of health enhancing compounds predominantly found in dairy products. The objective of this study was to develop an alternative method for quantification of C18:2 and C18:3 in forages through the capillary electrophoresis (CE) technique, using Brachiaria ruziziensesas the reference forage. The analytical procedure involved CE with indirect detection zone in the UV at 224 nm, capillary external coating of Teflon and analysis time around 10 minutes. Arotational central composite design (star design) with triplicate at the central point was used to optimize the composition of the electrolyte systemin order to separate the C16:0/C18:2 pair. The following electrolyte composition was obtained: 15.0 mmol L-1 NaH2PO4/Na2HPO4 buffer (pH~6,8), 8.0 mmol L-1 Brij 35, 4.0 mmol L-1 SDBS, 1.5% v/v n-octanol and 43,5% v/v ACN.Additionally, three methods of lipid extraction were tested: 1. Hara & Radin, 2. Micro Folch and 3. Bligh &Dyer; the best results were achieved by using the method of Hara and Radin.After optimizing the electrolyte systemand choosing thelipid extraction method, two calibration curves were made usingdifferentconcentrations of selected fatty acids and C13:0 as the internal standard. After checking for no occurrence of lack of fit of the models, a response factor (RF) was calculated and applied in the quantification ofselected fatty acids in the forage sample. The optimized CZE method was then compared to gas chromatography (the AOCS official method for fatty acid analysis) through the paired t-test. There was no difference between methods withina 95% confidence interval ( p= 0,12 ).Our results indicate that the optimized CE method proposed herein can be used to quantify the most abundant fatty acids in forage samples. Thisalternative methodhassomeadvantages over the traditional GC method: less timeconsuming, no derivatizationstepor specific separation columns required, and lower analytical cost.