EFFECT OF EXTRUSION ON LIPID OXIDATION IN A FLAXSEED-BASED PRODUCT

Introduction Extrusion is a technology widely used in feed processing that consists of combining high temperatures and high pressures to the feed material. The main objective when used in a final feed is to improve digestibility, but it can also be used in raw materials such as rice bran (Riaz, 2000), corn or flaxseed products with the purpose of stabilizing them. Nevertheless, some investigators have reported how the extrusion temperature affects the lipid oxidation of the extrudate during the subsequent storage, regarding peroxides and n-hexanal formation (Rao and Artz, 1989; Gutkoski and Atia El-Dash, 1998; Kordi et al., 2015). In flaxseed based products the oxidation risk is particularly high due to the high linolenic acid content. Thus, the aim of the study was to evaluate how the extrusion process affects the lipid oxidation susceptibility of an extruded flaxseed-based product throughout its storage and how it can be protected. Materials and methods The study was conducted with a flaxseed/wheat blend with 15% total fat content. An accelerated study forcing oxidation was conducted to evaluate the oxidative stability of the non-extruded product, the extruded product and the extruded product with 200 ppm of an ethoxyquin and propyl gallate-based antioxidant applied. The extrusion was conducted with an Insta-Pro International extruder, model 2000R, using standard parameters. The accelerated test was conducted in plastic containers completely filled with each sample to avoid the existence of an air chamber, and protected from light in an oven at 50ºC. Primary oxidation products (Peroxide values) and secondary oxidation by-products (Volatiles and sensory evaluation) analyses were conducted with only one measurement, in order to evaluate the oxidative status at different points of the study, and as a result, the evolution of these parameters with time. Results During the 45 days of the accelerated study at 50ºC, sensory evaluation results correlated very well with peroxides value (PV) and with 1-penten-3-ol results at all evaluated points (Table 1). In an oxidation process many volatiles are formed as secondary oxidation products, but 1-penten-3-ol is the most indicative in flaxseed-based products, based in our experience. The non-extruded product did not present any sign of oxidation at any point of the study, whereas the extruded product without antioxidant started to present results indicative of oxidation at day 28. However, when the extruded product was treated with a proper dose of an antioxidant, oxidation did not occur throughout the evaluated time.