Fifty healthy volunteers were randomly allocated in the probiotic arm. To eliminate residual traces of gluten and similar proteins from the faecal material, both groups underwent a gluten-free diet (GFD) from day-1 to day-10. After 10 days, gluten administration started. The increasing administration plan was as follows: 50 mg/day for 4 days; 1 g/day for subsequent 4 days; 3 g/day for subsequent 4 days; and 10 g/day (in this case, reintroducing an equivalent amount of wheat-based bread - 4 slices) for subsequent 20 days. At this stage (10 + 4 + 4 + 4 + 10 days = total of 32 days), the administration of the probiotic preparation was interrupted, with a period of 10 days of wash-out.

Twenty healthy volunteers were randomly allocated in the placebo.To eliminate residual traces of gluten and similar proteins from the faecal material, both groups underwent a gluten-free diet (GFD) from day-1 to day-10. After 10 days, gluten administration started. The increasing administration plan was as follows: 50 mg/day for 4 days; 1 g/day for subsequent 4 days; 3 g/day for subsequent 4 days; and 10 g/day (in this case, reintroducing an equivalent amount of wheat-based bread - 4 slices) for subsequent 20 days. At this stage (10 + 4 + 4 + 4 + 10 days = total of 32 days), the administration of placebo preparation was interrupted, with a period of 10 days of wash-out.

Probiotic preparation including multi-species strains of Lactobacillus and Bacillus. The probiotic was administered at baseline and interrupted after 32 days. At the same time the other arm received placebo. Gluten was provided after 10 days of gluten free diet in increasing amounts

The collection of faecal samples will be at baseline (T0); 10 days of GFD (T1); 4 days of 50 mg/day gluten intake (T2); 4 days of 1 g/day gluten intake (T3); 4 days of 3 g/day gluten intake (T4); 20 days of 10 g/day gluten intake (T5), of which 10 last days were the wash-out (T6).The gluten degrading efficiency of the probiotic will be assessed in all above mentioned time points with competitive Elisa using the R5 antibody for hydrolysed gluten (gliadin epitopes). The concentration of gliadin (ppm) will be then converted to gluten according to the multiplication factor (2) reported by the manufacturer.

Fecal samples DNA from baseline, intervention period and wash out will be sequenced targeting the V4 region of 16s rRNA gene to evaluate the alterations of the gut microbiome and possible modulation in the PR arm due to the probiotic mixture administrated

Fecal samples at the beginning of intervention (T1), end of intervention (T5) and wash-out (T6) will be evaluated for their organic volatile compounds by GC-MS. Volatile compounds and short chain fatty acids composition will be compared between the intervention groups PL vs PR. 4-methyl-2pentanol (final concentration 1 mg L-1) will be used as an internal standard in all analyses, to quantify the identified compounds by interpolation of the relative areas versus internal standard area.

Fecal samples at the beginning of intervention (T1), end of intervention (T5) and wash-out (T6) will be evaluated for SCFA by GC-MS. SCFA compounds and short chain fatty acids composition will be compared between the intervention groups PL vs PR. A stock solution containing the mixture of SCFA standards (acetic acid, butyric acid, propionic acid, isobutyric acid and valeric acid) will be dissolved in ultrapure water to obtain a calibration curve ranging from 1 μg mL-1 to 250 μg mL-1.The calibration curve will be constructed by plotting the normalized peak area versus concentration of individual SCFA. The relative peak of SCFA in faecal sample will be integrated and the concentration of SCFA will be calculated by the calibration curve equation