Application of CFS-Loaded CMC/GEL Spray Coating for the Small Fruit Blueberries Preservation

Blueberries are highly susceptible to decay due to mechanical damage such as bruising or impact. Traditional postharvest preservation methods such as brush and dip coating generate solvent waste, incur high labor costs, and may also leave visible brush marks. Moreover, due to their "one-by-one" coating process, which lowers the processing efficiency, these traditional methods are not suitable for small fruits such as blueberries. To solve this problem, a functional spray was developed in this work using gelatin (GEL) and sodium carboxymethyl cellulose (CMC) as the matrix, and a cell-free supernatant (CFS), produced by the centrifugation of lactic acid bacteria fermentation broth, was used as the active ingredient. Microstructural (SEM), intermolecular interaction (FTIR), and crystal structure (XRD) analyses of a CFS/CMC/GEL composite film demonstrated that the components of the functional spray had good compatibility. Moreover, this film had a greater water vapor permeability (WVP), reduced transmittance, and enhanced light-blocking properties compared with a CMC/GEL film. The 100% CFS/CMC/GEL functional spray exhibited improved antimicrobial performance against Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and yeast. Finally, a blueberry preservation experiment indicated that the blueberries sprayed with 100% CFS/CMC/GEL exhibited a lower decay rate, reduced weight loss, and lower malondialdehyde (MDA) level compared with the control group, whereas total soluble solids (TSS) and titratable acidity (TA) levels were higher. Notably, the firmness of the blueberries did not significantly change. These spray coating preservation tests demonstrate that the CFS/CMC/GEL composite coating effectively extends the shelf life of small fruits such as blueberries.