Heat and aldehyde treatments have been widely used to protect proteins from degradation in the rumen, and conditions that lead to an undegradable, but still digestible, product (bypass protein; BP) have been determined. The problem with these treatments is that the conditions that are used are quite severe, and damage to amino acids, particularly lysine, occurs. Excessive treatment can also yield an indigestible product. Recently, an alternative method involving the heating of soybean meal under milder conditions (150°C, 1 h) in the presence of glucose, fructose, xylose or lactose (non-enzymatic browning) was shown to yield a product high in UDP, but in which the lysine was predicted to remain available to the host animal [1-3].

In the present experiments, casein was used as a homogeneous model substrate to investigate how wide a range of conditions can be used for effective treatment of proteins with sugars. Although casein is atypical in that it is one of the most rapidly degraded proteins available, the results point to a versatility in the sugar treatment process that will enable different sugars to be used according to the type of process available. Preliminary experiments with soybean meal suggested that an effective way of optimising this effect may be to encapsulate the protein supplement with a sugar-protein mix.