Bilayer Bifidobacterium animalis/xylooligosaccharides film enables long-term maintenance of probiotics activity and prolongs strawberry shelf life

Abstract

To address the low survival of fragile probiotics such as Bifidobacterium animalis (B. animalis) and the safety concerns of chemical antimicrobials in fruit preservation, we developed a bilayer synbiotic film for one-way release of probiotic metabolites. The film contains an inner sodium alginate (SA) matrix co-encapsulating B. animalis and xylo-oligosaccharides to sustain metabolic activity, and an outer gelatin (GE) layer that acts as a physical barrier against external stressors. Compared with monolayer films, the bilayer system (SA/GE–B/X) reduced oxygen permeability by 39.66 % and water vapour permeability by 12 %. It reduced visible light transmittance and completely blocked UVA, with increased maximum degradation temperature. Probiotic viability in SA/GE–B/X reached 9.68 log CFU g⁻¹ after drying and remained at 7.36 log CFU g⁻¹ after 30 days at 25 ℃, markedly higher than SA–B/X (4.82 log CFU g⁻¹). The SA/GE–B/X film extended strawberry shelf life to 14 days at 4 ℃, compared with 6 days for controls. It reduced weight loss at 25 ℃ (29.68 % vs. 35.12 % for the monolayer) and suppressed mould growth (3.55 vs. 5.71 log CFU g⁻¹). Under simulated digestion, the GE layer reacted with gastric fluid to form a protective gel, increasing probiotic survival 1.69-fold relative to SA–B/X. This synbiotic bilayer combines physical preservation, microbial regulation, and gut-health promotion, and offers a practical route for applying anaerobic probiotics in open packaging and eco-friendly, microbe-driven preservation.