Combined effects of irradiation and the use of natural antioxidants on the shelf-life stability of overwrapped minced beef.

Five batches of aerobically packaged minced beef from Friesian cattle were irradiated at 0, 1, 2, 3 or 4 kGy using a (60)Co irradiation source. The five batches were as follows: non-supplemented (C), dietary α-tocopheryl acetate supplemented (S), α-tocopheryl acetate supplemented with water soluble rosemary extract added after mincing (Rw), α-tocopheryl acetate supplemented with oil soluble rosemary extract added after mincing (Ro) and α-tocopheryl acetate supplemented with water and oil soluble rosemary extracts added after mincing (R). Incorporation of antioxidants resulted in better retention of colour. Irradiation at 4 kGy increased Hunter 'a' values up to day 4 with α-tocopheryl acetate supplementation and up to day 6 when rosemary extracts were added. Irradiation at 4 kGy increased Hunter 'b' values on days 4, 6 and 8 in the control samples. Antioxidants decreased metmyoglobin values on day 0 and day 2 for non-irradiated (0 kGy) samples and for the entire display period for irradiated samples. Antioxidants increased the oxymyoglobin values up to day 4 for the 1, 2 and 3 kGy beef samples and over the entire display period for the 4 kGy samples. TBARS values for each treatment group increased with increasing irradiation dose. α-Tocopheryl acetate supplemented samples had lower TBARS values than control samples at all irradiation doses. The levels of α-tocopherol in samples on day 0 decreased with increasing irradiation dose for the (C) and (S) samples. However, levels of α-tocopherol in samples on day 0 increased with increasing irradiation dose for Ro, Rw and R samples. All antioxidant treatments were effective at inhibiting lipid peroxidation even at the highest irradiation dose applied. Irradiation caused a significant reduction in the polyunsaturated fatty acid (PUFA) content, mainly in C18:2 after storage at 40°C under fluorescent light for 8 days.

Luminometric and differential scanning calorimetry (DSC) studies on heat- and radiation inactivation of Bacillus subtilis luxAB spores.

A bioluminescent derivative of Bacillus subtilis containing a plasmid encoding a luxAB fusion under control of a vegetative promoter and gives bioluminescence upon addition of an exogenous long-chain aldehyde has been used as test organism. Its spore populations have been produced and their heat- and radiation survival curves established. Heat-sensitization effect of pre-irradiation of spores was proven not only by colony counting but also with differential scanning calorimetry. Under a linearly programmed temperature increase, the heat destruction of spores surviving 2.5 kGy gamma irradiation resulted in at a few centigrade lower temperature than that of untreated spores. Heat denaturation endotherms in the DSC-thermogram of irradiated spores were shifted to lower temperatures as well. Comparative turbidimetric, luminometric and phase-contrast microscopic studies of untreated, heat-treated and irradiated spore populations showed that the kinetics of germination and the light emission during germination of radiation-inactivated spores were the same as those of untreated spores, revealing that the pre-formed luciferase enzyme packaged into the spores during sporulation remained intact after an irradiation dose causing 90% decrease in number of colony forming spores. Therefore, in contrast to heat-treated spores, the initial bioluminescence reading upon germination of irradiated spores does not reflect the viable count of their population.

Addition of synthetic and natural antioxidants to α-tocopheryl acetate supplemented beef patties: effects of antioxidants and packaging on lipid oxidation.

Friesian steers (n=5), aged 26-27 months, were fed a diet containing 2000 (supplemented) IU α-tocopheryl acetate/head/day for approximately 50 days prior to slaughter. Muscularis semimembranosus muscles from supplemented cattle were held in frozen storage (-20°C×12 weeks) following which they were minced and divided into five batches. The batches contained: (1) control, containing only vitamin E supplemented beef (C); (2) vitamin E supplemented beef with 4% soya oil (S); (3) vitamin E supplemented beef mixed with 0.2% Duralox NMC dissolved in 4% soya oil (R1); (4) vitamin E supplemented beef mixed with 0.25% Herbalox type 25 (containing 25 natural antioxidant extracts of rosemary) dissolved in 4% soya oil (R2); and (5) vitamin E supplemented beef mixed with a 1:1 mixture of 0.01% (w/w) BHA and 0.01% (w/w) BHT dissolved in 4% soya oil (B). The meat was then aerobically packaged (A) or packaged under the following modified atmospheres (MAP); 30:70 (M(1)); 70:30 (M(2)) or 80:20 (M(3)) (O(2):CO(2)). Oxidative stability (TBARS) and Hunter 'a' values (redness) were determined in all beef patties over 8 days of refrigerated (4°C) storage. Under MAP or aerobic packaging conditions, elevated oxygen levels brought about increased (P<0.05) TBARS numbers during refrigerated storage. However, the addition of rosemary extracts or BHA/BHT significantly (P<0.05) improved the oxidative stability of dietary α-tocopheryl acetate supplemented beef. Rosemary extracts were as effective in reducing TBARS as the combination of synthetic antioxidants, BHA/BHT.

Effects of dietary vitamin e supplementation and packaging on the quality of minced beef.

Friesian cattle, aged 26-27 months, were fed a diet supplemented with 2000IU α-tocopheryl acetate/kg feed/day and another group was fed a basal diet (20IU/kg feed/day) for approximately 50 days prior to slaughter. Following frozen storage (-20°C for 8 weeks) semimembranosus muscles from basal and α-tocopheryl acetate supplemented cattle were minced and vacuum packaged, aerobically packaged or packaged under modified atmospheres (MAP) (30% O(2): 70% CO(2); 70% O(2): 30% CO(2); 80% O(2): 20% CO(2)). Samples were held under refrigerated (4°C) display (fluorescent lighting, 616 lux) for eight days. Vacuum-packaged samples were held under similar conditions but in complete darkness and allowed to bloom for a minimum of 4hr prior to taking colour readings. TBARS values and Hunter a values in minced beef were measured every two days. α-Tocopherol concentrations were significantly (p<0·05) higher in minced meat samples from the supplemented group than in the basal group. Significant (p<0·05) reductions in α-tocopherol concentrations in supplemented meat samples were observed with increased concentrations of oxygen in different packaging systems after eight days of refrigerated storage. TBARS values were reduced over the whole retail display period for all packaging systems when α-tocopheryl acetate supplemented beef was used. TBARS values increased as oxygen levels increased in MAP. Hunter a values showed that vitamin E supplementation in combination with vacuum packaging and MAP improved the colour stability of meat during the first 4 days of storage, however, the failure of MAP to extend meat colour for longer periods of time was probably the result of prior storage at -20°C for 8 weeks.