The effect of processing treatments on the rumen microbial digestion in vitro of skimmilk powder protein

Abstract

The microbial degradation of the protein of skimmilk powders manufactured and treated in different ways (high-, medium-, and low-heat spray, instant, roller, formaldehyde-treated spray) and milk powder products (skimmilk powder-wheat flour granules, skimmilk powder-barley flour pellets) was determined in anaerobic, rumen simulating conditions in vitro. The tests showed that milk protein was decomposed rapidly and extensively in rumen fluid buffer. The heat treatment had a slight N solubility-reducing effect. Formaldehyde treatment decreased the degradation of the protein at the beginning of the incubation, but this effect became smaller as incubation proceeded. After 48 h the N solubility of the treated skimmilk powder was about the same as that of untreated spray powder. The variation in the in vitro N solubility of formaldehyde-treated skimmilk powder was greater than with the other powders and products. The skimmilk powder-wheat flour granules were hard products which remained indigestible for several hours. At the end of the microbial digestion test the addition of skimmilk powder increased the N solubility of wheat flour protein. On the basis of the results obtained from the digestion test on a pelleted skimmilk powder-barley flour product it can be assumed also that the addition of skimmilk powder caused an increase in the N solubility of barley flour protein.