Effects of pressure toasting, expander treatment and pelleting on in vitroand 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 b rans were studied. The treatments included pressure toasting (132 degrees C , 3 min), expander treatment (115 degrees C, 8 s) and pelleting (80 degrees C, 10 s). Toasting was the most effective treatment in altering rumen prot ein degradability, as it decreased rumen protein degradability, mainly by r educing its fractional degradation rate (k(d)). Expander treatment and pell eting both increased the washable protein fraction (W), whereas pelleting a lso increased k(d) resulting in a decreased amount of rumen undegraded inta ke protein (UIP). Toasting slightly decreased both total protein digestibil ity (TDP) and intestinal digestibility of rumen undegraded protein (DUP). E xpander treatment had no significant effect on TDP or DUP, whereas pelletin g generally increased TDP and DUP. The observed in situ effects of both exp ander 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 fo r in situ incubations, compared to incubations with broken samples in the c urrent 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 cas es, also DUS. Combinations of toasting, expander treatment and pelleting so metimes resulted in interactions, but the order of application of the treat ments hardly affected their effects on protein and starch degradability. Re sults of this study, as well as other published studies, show that the effe cts on starch and protein degradability are very much dependent on the cond itions applied during processing. A concept was proposed, describing the ef fects of heat, moisture level, shear and pressure during steam treatment on in situ starch degradability. (C) 1999 Elsevier Science B.V. All rights re served.