Preparation and characterization of lactic acid bacteria composite fresh-keeping material and its application in passion fruit preservation

Abstract Objectives To enhance the postharvest preservation quality of passion fruit, a bio-physically synergistic composite preservation material (LABM-SA) was developed in this study by combining lactic acid bacteria metabolites (LABM), cell-free supernatant (CFS), and sodium alginate (SA). This material was designed to inhibit spoilage microorganisms, reduce water loss, maintain fruit nutritional components, and extend shelf life. Materials and Methods Passion fruits were treated with coating solutions containing 2.0% SA blended with CFS at different volume fractions (10%, 20%, and 30%). The material structure was characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), ultraviolet-visible (UV-vis) spectroscopy, and anti-desiccation tests. Key preservation indices were measured during 15 d of storage at 25 °C. These indices included the weight loss rate, hardness, colour, shrinkage index, soluble solid content (SSC), titratable acidity (TA), ascorbic acid (vitamin C) content, and water distribution. Results Characterization results revealed that exopolysaccharides from LABM and SA were cross-linked through hydrogen bonding and van der Waals forces, forming a stable three-dimensional network structure. Preservation tests demonstrated that the 10% LABM-SA treatment achieved optimal performance. The weight loss rate was significantly reduced by 23.0%. The shrinkage index decreased by 33%. The onset of hardness decline was delayed by 3 d. Peel browning and colour deterioration were effectively suppressed. The final SSC content increased by 0.95 g/100 mL. The TA retention rate reached 75.35%, while the vitamin C retention rate attained 78.35%. Water distribution also significantly improved. Under refrigeration at 4 °C, the composite coating was shown to regulate ice crystal formation, mitigate chilling injury, and enable long-term storage, performing better than the other treatments. Conclusions The LABM-SA composite material effectively maintained the appearance, texture, and core nutritional qualities (sugars, acids, and vitamin C) of passion fruit through the synergistic action of biological activity and physical barrier properties. This study provides an innovative solution for the green preservation of high-moisture fruits and vegetables.