Abstract
| - The study evaluated a recently developed bioassay for determiningdigestible reactive lysine whenapplied to skim milk powder and field peas, which had been exposed tovarying degrees of heattreatment. Semi-synthetic corn starch-based diets containing therespective material as the solesource of protein were formulated and fed to growing rats. Chromicoxide was included as anindigestible marker. Digesta were sampled from the terminal ileumpost-mortem, and diet anddigesta were analyzed for amino acid content (including reactivelysine, which was determinedfollowing guanidination). True ileal reactive lysine and totallysine digestibilities were calculated.For the heated skim milk powder, both total and reactive lysinedigestibility decreased from 97%and 100% (unheated) to 44% and 85%, respectively (121 °C for 10min). A similar trend was observedfor the heated peas where total and reactive lysine digestibilitydecreased from 83% and 88%(unheated) to 43% and 67%, respectively, in the maximally heatedpeas. In all cases, total lysinedigestibility significantly underestimated reactive lysinedigestibility. In contrast, digestible totallysine (conventional method) overestimated digestible reactive lysinefor all the skim milk powdersamples and some of the pea samples. This overestimation wasalmost double for the maximallyheated skim milk powder where digestible total lysine was 11.2 gkg-1 and digestible reactivelysinewas 5.7 g kg-1. Keywords: Lysine; digestibility; availability; processing;heat
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