2.1. Raw Materials and KEFIR Grains

Kefir grains belonged to LETMi laboratory (Tunis, Tunisia) and consisted of a symbiotic consortium of lactic acid bacteria (Leuconostoc spp., Lactobacillus spp., and Lactococcus spp.) and yeasts (Saccharomyces spp. and Zygosaccharomyces spp.), as previously characterized [25]. Grains were routinely propagated in pasteurized cow’s milk at room temperature (ca. 25 °C). After filtration, grains were collected and used to inoculate the mixtures [26].

Whey permeates (WP) was supplied by a dairy industry (Béja, Tunisia) and used at different concentration ranging from 10% to 15% (w/v) (WP composition: proteins 3%, lactose 85%, and ash 7%). Oat flour (OF) was obtained from a local supermarket (Tunis, Tunisia) (14.8% proteins, carbohydrates 66.3%) and used at different concentrations ranging from 3% to 5% (w/v). Carob decoction (15 °Brix) was obtained by boiling carob pods (100 g carob pods/150 mL distilled water) for 30 min. After cooling, the decoction was filtered with Whatman paper and stored until uses.