Effects of seed moisture and micronizing temperature on lentil flour properties and the stabilities of colour and unsaturated lipids of beef-lentil systems
This study investigated the effect of seed moisture level of lentil and surface temperature of micronization (infrared heat treatment) on the physico-chemical and functional properties of resulting flours and how these flours affected colour and unsaturated lipid oxidation when incorporated into ground beef products. Flour from raw seed (non-tempered and non-micronized) was used as the control. Whole seeds of small green lentil (Lens culinaris L., var. Eston) without tempering (8% moisture) and tempered to 16% or 23% moisture was infrared heat treated (micronized) to 115, 130, 150 or 165 °C surface temperature. The decreased protein solubility (2-60%) and lipoxygenase (70-100%), peroxidase (32-100%) and trypsin inhibitory (up to 54%) activities of resulting flours indicated changes in the protein fraction due to heat-moisture treatment. Starch gelatinization was observed at the 23% moisture level and changes in pasting properties, and water and oil absorption capacities varied with treatment. The heat-moisture combinations modified properties of starch and protein to different degrees and, consequently, lentil flour functionalities. Incorporation of lentil flour as a binder in low fat (<10%) beef burgers at 6% (w/w) showed that flours from micronized lentil seeds enhanced retention of redness and suppression of lipid oxidation as indicated by Hunter a* values and thiobarbituric acid reactive substances values, respectively, in a retail display setting. Investigation of total phenolics in aqueous salt extracts of lentil flours showed a decrease in content with increased micronization temperature. The antioxidant assays showed no changes in the ferric ion reducing power or reduction of hydroxyl radical scavenging and superoxide radical scavenging activities with heat-moisture treatment. Reduction of lipoxygenase and peroxidase activities was evident in lentil flour aqueous salt extracts, and the enzyme activities were localized to seed cotyledons. The myoglobin-liposome model study showed that a flour extract from the 16% moisture and 150 °C treatment resulted in a slower rate of oxymyoglobin oxidation initiation than other treatments which had different levels of lipoxygenase and peroxidase activities. Unsaturated lipids accelerated oxymyoglobin degradation irrespective of the presence of lentil extract. The extended fresh red colour retention of ground beef due to addition of flours from micronized seed compared to that from non-micronized seed may be related to suppression of pro-oxidant activities and the activity of potential antioxidants. The putative antioxidative compounds in lentil that are available for meat components may include compounds other than lentil seed phenolics
