Effect of storage on the vitamin B1 content of microwave- and conventionally treated milk

The effect of cold storage on the retention of vitamin B-1 in microwave-treated milk was evaluated. Results were compared with those obtained for milk stored under the same conditions, but heated previously with a conventional system (tubular heat exchanger). The conventional heating system was set up exactly in the same manner as the microwave one, except for the fact that the heating section was replaced by a coil of stainless steel tubing immersed in a temperature-controlled water bath. Heat treatment of milk at 80 degrees C for 15 s and 90 degrees C for 18 s did not produce losses of vitamin B1. On the contrary, after 2-3 d of cold storage at 4.5 +/- 0.5 degrees C, vitamin B1 content of microwave- and conventionally treated milk decreased by about 4%, resulting in 16-18% loss after 15-16 d. Under the assayed storage conditions, there were not found significantly differences between losses observed in milk heated with the microwave unit or with the tubular heat exchanger.