Blends de óleo de fígado de bacalhau e óleo de linhaça: perfil de ômega-3, propriedades físicoquímicas e estabilidade termo-oxidativa

Abstract

Cod liver oil (CLO) and linseed oil (LO) are considered functional foods for containing high quantities of omega-3. While CLO contains long chain polyunsaturated fatty acids, as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), LO is considered as one of the biggests α-linolenic omega-3 (ALA) sources, which can be converted in EPA and DHA in the human organism. Beyond the fatty acids mentioned, CLO is also rich in D vitamin, being therefore indicated for the treatment of diseases such as rickets and osteoporosis. In this present study, blends containing CLO and LO were prepared in two different proportions of the two oils, with the aim of getting new compound oils with oxidative stability and omega-3 profile improved. The profile of fatty acids in the oils and blends were evaluated by Gas Chromatography Coupled to the Mass Spectrometer (GC-ME), and according to the chromatograms, CLO showed 22,59% of omega-3, 15,46% of EPA, 3,10% of DHA, 4,03% of ALA, whilst LO showed 51,70% of omega-3 ALA. The omega-3 content in the blends varied from 26,11 to 46,53% with EPA varying from 2,55 to 10,17%, and DHA from 1,28 to 3,10%. The ALA percentage varied from 13,28% to 42,86%, and the blend with highest omega-3 content was BLE4 (20%CLO80%LO). Considering possible mistakes on the GC-ME technique, the fatty acid profile of CLO, LO and blends, was also evaluated by Hydrogen Nuclear Magnetic Resonance (NMR 1H), a perfectly adequate technique for omega-3 quantification in oils and fats. In this technique CLO showed 23,02% molar of omega-3, which 10,12% molar corresponds to the EPA, 12,90% to the DHA, with non-measurable traces of ALA. For LO was observed 52,2% molar of ALA. EPA and DHA was not detected, since these fatty acids are not found in vegetable oils. The ômega-3 profile in the blends varied from 27,46 to 46,45% molar, BLE4 showed highest ômega-3 content among the other blends, in agreement with GC-ME data. In the evaluation of oxidative stability, Rancimat method, in 68 ºC, CLO showed 12,32 ± 0,24 h of induction period and LO, even though containing higher ômega-3 percentage (26,46 ± 0,07 h). The blends showed more stability than CLO, being BLE4 the most stable (23,12 ± 12 h), not having significant difference with the result obtained for BLE3 (21,80 ± 0,05 h) in (p<0,05). The study of thermic profile of CLO and LO were also evaluated by Term gravimetric Analysis (TG) and according to TG/TGA curves, the oils displayed similar thermic profile with onset temperature of 303,20 ºC and 305,16 ºC, respectively, for the first step of mass loss. The prediction of shelf life for the oils and blends, evaluated in 10 days of stocking in Schaal test conditions, employing 12 infrared spectroscopy (IR), indicated that during the stocking period there was an expressive increased in peroxides quantities, denoting the start of oxidative degradation process. In CLO, although it has also been evidenced a decrease in the signal of the peroxides, was observed an isomeration process, showing that also occurred degradation in the oil. Isomeration processes was observed in the blends, through observation of indicative bands of Trans bounds, though were not observed oxidative secondary products in the samples. These data suggests that CLO, LO and blends must be stocked in temperatures below 60 ºC during the stocking process, in order that functional properties be preserved.