Preparation, characterization, and antibacterial properties of a soybean protein isolate/gelatin composite film containing rosemary-modified bentonite and application of fresh lemon slices

To address the rapid deterioration of fruit slices, soy protein isolate (SPI) and gelatin (GEL) composite films were optimized for food packaging using rosemary-modified bentonite (RB) as an active ingredient and glycerol as a plasticizer to enhance flexibility. Composite films with RB demonstrated superior ultraviolet-visible (UV-Vis) light barrier properties, increased opacity, and enhanced mechanical performance, achieving a tensile strength of 2.27 MPa. Barrier properties were significantly improved, with reduced water vapor transmission rate (1.85 x 10-3 g & sdot;m- 2 & sdot;s- 1) and oxygen permeability (6.69 x 10-3 g & sdot;m- 2 & sdot;s- 1), alongside elevated hydrophobicity, antibacterial activity, and antioxidant capacity (DPPH scavenging activity: 54.74 %; ABTS scavenging activity: 53.89 %). In preservation trials with fresh lemon slices, RB/SPI/GEL-2 films reduced weight loss to 37.89 %, maintained firmness at 0.99 N, stabilized pH at 3.14, and extended freshness lifetime by delaying mold formation. These results confirm that RB/SPI/GEL films effectively preserve freshness and minimize nutritional loss in lemon slices, demonstrating their feasibility for fruit preservation applications.