THE LENTIL-MEAT SYSTEM: INVESTIGATING THE ANTIOXIDANT EFFECT OF LENTIL ON COLOUR AND LIPID OXIDATION OF RAW BEEF BURGERS
Li, He 1986-
Discoloration and lipid oxidation are the main deteriorative causes of raw meat products. The flour of lentil, when heat treated, was found to protect fresh meat colour and inhibit lipid oxidation when incorporated into raw meat products. In order to postulate a possible mechanism of this useful functionality of lentil flour, three studies were conducted. In the first study, the impact of infrared heating to 115 and 150 oC and water bath heating of 90 oC (30 min) of different seed components of two Canadian lentil cultivars were evaluated. Enzyme activities, soluble proteins and phenolics that promote and negate oxidation reactions were assayed. The second study was designed to investigate the effects of seed coat and cotyledon with or without heat treatment in relation to enzyme and antioxidant activities in the ground meat system. It was investigated the effects on colour parameters (L*, a* and b*) and myoglobin redox states (met-, oxy- and deoxy-) of the product surface and lipid oxidation (thiobarbituric acid reactive substances: TBARS) during the refrigerated storage of lentil-ground meat product for 7 days. In the third study, the usability of lentil as a binder was evaluated when ground beef burgers containing the same levels of lentil components were stored for 12 weeks under frozen (-20 oC) condition, in terms of the effect on colour, myoglobin redox states and lipid oxidation. In the first study, it was found that the lipoxygenase, peroxidase and glutathione reductase activities were mostly found in cotyledon rather than in seed coat. The seed coat exhibited higher superoxide dismutase activity than cotyledon. The heat treatments tested were able to deactivate lipoxygenase, peroxidase and glutathione reductase significantly (P<0.05), but not the superoxide dismutase (P>0.05). Heat treatments significantly (P<0.05) increased Fe2+ chelating activity for all samples. Soluble proteins in the seed coat (hull) showed higher antiradical (1,1-diphenyl-2-picryl-hydrazyl: DDPH and 2,2’-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid): ABTS) and antioxidant (ferric reducing antioxidant potential: FRAP, Fe2+ chelating) activities than those obtained from the cotyledon, and this corresponded with the higher amount of protein-bound phenolic compounds. The extracts (water and 70% (v/v) ethanol) of the seed coat contained a higher (P<0.05) level of total phenolics, condensed tannins and total flavonoids than cotyledon extracts. Water and 70% (v/v) ethanol extracts from the seed coat were able to reduce approximately 10 - 20% metmyoglobin to form oxymyoglobin, but the cotyledon extract could not. The addition of metmyoglobin was found to dramatically increase the rate of linoleic acid oxidation by 1000 fold. However, the addition of 70% (v/v) ethanol and water extracts of seed coat were able to significantly lower (P<0.05) such high oxidation rate initiated by metmyoglobin. The water extracts of cotyledon when used at higher levels were able to lower the oxidation rate, but were not as effective as the water extract of seed coat. In the second study, it was found that the heat-treated lentil flour (whole seed) delayed the lowering of a* value (redness) of beef burgers and reduced the lipid oxidation product generation (P<0.05) during the 7-day storage compared with the controls. However, the products with raw lentil flour (whole seed) accelerated the decrease in a* value. It was also observed that the flour of seed coat and cotyledon separated from heat-treated seeds were able to delay discoloration of beef burgers (P<0.05), however, raw cotyledon flour could not. Burgers with added seed coat flour either from raw or heat-treated seeds developed lower (P<0.05) level of TBARS than control burgers and those with cotyledon flour at the end of storage. Negative correlations between redness and metmyoglobin and between redness and TBARS were obtained. In the third study, no difference (P>0.05) was observed on the a* value of the burgers containing heat-treated flour and raw flour that were stored for 12 weeks under -20 oC while all samples showed higher a* values than the control. The burgers containing cotyledon flour of heat-treated seeds showed lower level (P<0.05) of metmyoglobin than the burgers with seed coat flour. Burgers containing all types of lentil flour had a lower (P<0.05) level of TBARS generated than the control group. Among these flour types, a lower level of lipid oxidation (P<0.05) occurred in the burgers containing heat-treated lentil flour than the ones containing raw flours. Within burgers with added raw seed flour, the addition of cotyledon one showed higher TBARS values than those containing seed coat one (P<0.05). Significant negative correlations were found between a* value and metmyoglobin and between a* and TBARS values. Overall, it was found that the antioxidant activity of the water soluble components of the lentil seed is the main factor that protects colour and retards lipid oxidation in raw meat products, via metmyoglobin reduction, Fe2+ chelating, free radicals scavenging and inhibition of unsaturated lipid oxidation catalyzed by metmyoglobin. The pro-oxidative activities of lentil components are mainly due to the oxidative enzymes and these enzymes are more sensitive to heat. The performance of lentil flour differs in meat products under refrigerated and frozen conditions. But heat-treated lentil flour can be considered more stable in providing colour protection and inhibiting lipid oxidation during storage.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentFood and Bioproduct Sciences
SupervisorShand, Phyllis; Wanasundara, Janitha
CommitteeTanaka, Takuji; Nickerson, Michael; Bandy, Brain; Juárez, Manuel
Copyright DateMarch 2017