OXIDATIVE STABILITY OF FLAXSEED LIPIDS DURING BAKING

This study examined the stability of whole and ground flaxseed, either alone or as an ingredient in a muffin mix, by measuring oxygen consumption and changes in alpha-linolenic acid under various conditions. When ground flaxseed was heated at 178 degrees C in a sealed tube, headspace oxygen deceased from 21 to 2% within 30 min, while that of whole flaxseed decreased only slightly up to 90 min at 178 degrees C. Under the same conditions, the oxygen consumption of lipids extracted from an equivalent amount of flaxseed was between the whole flaxseed and the ground flaxseed. After heating to 178 degrees C for 1.5 h, alpha-linolenic add decreased from 55.1 to 51.3% in ground flaxseed, and to 51.7% in lipid extracts, but it remained unchanged in the whole flaxseed. Ground flaxseed with large (<20 mesh) or small (>35 mesh) particle size absorbed more oxygen than samples with medium particle size when heated at 122 degrees C for 8 h. Long-term storage of whole or ground flaxseed or lipid extracts showed that all three preparations were stable at room temperature for 280 d with 12 h light/dark cycles, A muffin mix, containing 28.5 wt% flaxseed flour, consumed oxygen more rapidly than a control muffin without flaxseed flour at a baking temperature of 178 degrees C for 2 h, but the alpha-linolenic acid remained unchanged in both muffin mixes. Polymers derived from triglyceride oxidation and new trans isomers of alpha-linolenic acid were not detected under the present experimental conditions. Under typical baking conditions, there is minimal loss of alpha-linolenic acid from flaxseed, although the manner of incorporation of flaxseed in food products should be considered to minimize oxidation of alpha-linolenic acids.