Heat stability of the fermented milk

The fermented milk was heated at various temperatures for 30 min. Following immediate icing, the Ig production stimulating activity wasassayed. HB4 C5 cells were cultured at 1x105 cells/ml for 6 h in ITES-ERDF medium supplemented with heat-treated fermented milk. As indicated in Fig. 2, the Ig production stimulating activity of the fermented milk was relatively heat-stable. Distinctively, the activity was facilitated 2.5-fold by thermal treatment at 65°C.

On the other hand, the fermented milk was treated with 50 ^g/ml of trypsin for 30 min, and the digestion was terminated by the addition of 250 ^g/ml of soybean trypsin inhibitor. Then, the activity was assayed by using of HB4C5 cells. As indicated in Fig. 3, the Ig production stimulating activity against HB4C5 cells was completely lost by trypsin digestion. These results suggest that the active substance in the fermented milk is heat stable protein.

Figure 2. Heat stability of the fermented milk.

Figure 3. Effect of trypin digestion of the fermented milk on its activity.
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