Effects of pressure toasting, expander treatment and pelleting on in vitro and in situ parameters of protein and starch in a mixture of broken peas, lupins and faba beans

The effects of several technological treatments on the rumen degradability and intestinal digestibility of a mixture of broken peas, lupins and faba beans were studied. The treatments included pressure toasting (132°C, 3 min), expander treatment (115°C, 8 s) and pelleting (80°C, 10 s). Toasting was the most effective treatment in altering rumen protein degradability, as it decreased rumen protein degradability, mainly by reducing its fractional degradation rate ( k d). Expander treatment and pelleting both increased the washable protein fraction ( W), whereas pelleting also increased k d resulting in a decreased amount of rumen undegraded intake protein (UIP). Toasting slightly decreased both total protein digestibility (TDP) and intestinal digestibility of rumen undegraded protein (DUP). Expander treatment had no significant effect on TDP or DUP, whereas pelleting generally increased TDP and DUP. The observed in situ effects of both expander treatment and pelleting could be explained by particle size reduction during processing. Toasting hardly affected rumen undegraded starch (UIS), which contrasts with previous studies in which ground samples were used for in situ incubations, compared to incubations with broken samples in the current study. Total starch digestibility (TDS) and intestinal digestibility of rumen undegraded starch (DUS) were not affected by toasting or expander treatment. However, pelleting significantly increased TDS and, in some cases, also DUS. Combinations of toasting, expander treatment and pelleting sometimes resulted in interactions, but the order of application of the treatments hardly affected their effects on protein and starch degradability. Results of this study, as well as other published studies, show that the effects on starch and protein degradability are very much dependent on the conditions applied during processing. A concept was proposed, describing the effects of heat, moisture level, shear and pressure during steam treatment on in situ starch degradability.