Feeding system effect on Amiata donkey's milk flavours

Ten animals were assigned to two groups consisting of 5 each one, homogenous for days of lactation (90-146 days). One group received a basic forage diet with access to pasture (FO) while the other group was stabled and fed with forage and concentrate (CO) according to NRC requirements for lactating donkeys. The trial lasted 60 days. Every 15 days the donkeys were milked. On each sample of milk, three times replicated, the quali-quantitative aromatic profile was investigated by SPME-GC/MS and the results, expressed as percentages of the relative peak areas, were submitted to ANCOVA using the following model: yij = μ + ai +b*xij + eij; where ai = effect of diet, xij = days of lactation. The most representative compounds of the aromatic profile of the feeds were hydrocarbons and aldehydes. In the milk, 42 volatile compounds were identified and quantified. The most abundant desorbed volatiles were acids which showed significant differences (P=0.005) between FO (80.07%) and CO (60.51%) groups, followed by ketones (FO 4.38%; CO 10.44%, P=0.156), hydrocarbons (FO 3.21%; CO 10.19%, P=0.111), aldehydes (FO 1.96%; CO 2.94%, P=0.354), esters (FO 1.32%; CO 1.91%, P=0.499) and alcohols (FO 0.22%; CO 0.21%, P=0.904). In both groups, caprylic acid (FO 34.01%; CO 24.98%, P=0.008) and caprynic acid (FO 40.56%; CO 30.64%, P=0.009) were the most representative compounds. The m-cymene, identified only in the milk of FO group (0.17%), could represent a tracing compound of the feeding system. Data obtained should be supported by further studies based on the sensorial analysis to assess the olfactory threshold of some volatile compounds