In vitro gastrointestinal resistance of Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12 in soy and/or milk-based synbiotic apple ice creams

• Synbiotic ice creams developed with milk, soy, and whey protein isolate/inulin.
• Viability, in vitro GI resistance, and morphological changes were assessed.
• Counts were above 7.5 log CFU/g both by culture-dependent methods and PMA-qPCR.
• Survival rates were above 50% in all the ice creams after the in vitro assay.
• Scanning electron microscopy confirmed the intensification of the in vitro stress.

The viability and resistance to simulated gastrointestinal (GI) conditions of Lactobacillus acidophilus La-5 and Bifidobacterium animalis Bb-12 in synbiotic ice creams, in which milk was replaced by soy extract and/or whey protein isolate (WPI) with inulin, were investigated. The ice creams were showed to be satisfactory vehicles for La-5 and Bb-12 (populations around 7.5 log CFU/g), even after the whole storage period (84 days/− 18 °C). In all formulations, the propidium monoazide qPCR (PMA-qPCR) analysis demonstrated that probiotics could resist the in vitro GI assay, with significant survival levels, achieving survival rates exceeding 50%. Additionally, scanning electron microscopy images evidenced cells with morphological differences, suggesting physiological changes in response to the induced stress during the in vitro assay. Although all formulations provided resistance to the probiotic strains under GI stress, the variation found in probiotic survival suggests that GI tolerance is indeed affected by the choice of the food matrix.