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The effect of microwave and convection reheating on the vitamin B₁₂ content of roast beef produced in a cook/freeze foodservice system Gellman, Catherine Elizabeth


The purpose of this study was to determine the effect of microwave and convection reheating on the vitamin B₁₂ content of roast beef produced in a cook/freeze foodservice catering system. Two concentrations of vitamin B₁₂ in a phosphate buffer, as well as vitamin B₁₂ found in roast beef, were used throughout this study to detemine the effects of domestic and commercial microwave reheating and convection reheating on vitamin B₁₂. All the vitamin analysis was done using a radioisotope dilution (RID) assay (Bio-Rad Laboratories). In order to study the effects of microwave radiation without heat on vitamin B₁₂, two solutions containing 200 pg/mL and 1500 pg/mL (nominal) were exposed to microwave radiation for time periods of up to one hour in a 625 watt and a 1300 watt microwave oven. The temperature was maintained at 0°C by resting the vials in an ice bath. Retentions ranged from 86.57 ± 3.79 % to 110.29 ± 4.94 %. A fair amount of variability was present in the data, and as a result, the differences in retention were found to be non-significant. The differences between retentions in the two oven types as well as between the two concentrations of the vitamin were also found to be non-significant. Buffer samples were exposed to temperatures of 50°C - 70°C in a 625 watt microwave, a 1300 watt microwave and a convection oven set at 180°C, to detemine the effect of heat on vitamin B₁₂. The destruction of the vitamin was not significant. Retentions ranged from 82.45 ± 3.57 % to 103.3 ± 4.6 %. Non-significant differences were found between the oven types and the two concentrations of the vitamin. Precooked, frozen and thawed roast beef samples were reheated to 70°C in the 2 microwaves and for 30 minutes in the convection oven set at 180°C in order to simulate a hospital cook/freeze catering system. Analysis of the samples indicated that all of the original B₁₂ was present after the samples were reheated. When the meat and drip portions of the samples were analyzed separately, 2.9 - 9.2 % of the vitamin was found in the drip, however, this amount was not significant. The amount of vitamin B₁₂ present in the drip was found to be related to the amount of drip released from the sample. Samples reheated in the 625 watt microwave released significantly less (p< 0.05) drip than samples reheated in either the 1300 watt microwave or the convection oven. The results of these studies suggest that reheating does not appear to have a significant effect on vitamin B₁₂ retention.

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