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Nanocomposites improve tomato and peach shelf lifeA food packaging material consisting of bacterial cellulose impregnated with silver nanoparticles has proved successful in doubling the shelf life of fresh tomatoes.
Silver nanoparticles, known for their antimicrobial properties, were incorporated into bacterial cellulose prepared using Gluconacetobacter xylinus bacteria to produce semicrystalline cellulose nanofibre from a standard glucose media. The antimicrobial activity of bacterial cellulose was first tested on bacteria and fungi isolated from rotten tomatoes and later on mixed microbial culture. Composites (bacterial cellulose impregnated with silver nanoparticles) with <2% (w/w) silver showed 99% antimicrobial activity which was sustained for up to 72 hours against spoiled food derived mixed culture. Composites were found to have better antimicrobial activity than colloid with the equivalent amount of silver.
Tomatoes wrapped in the bacterial composite remained fresh and showed no symptoms of decay after 30 days at room temperature, compared with 15 days for tomatoes packed in polyethylene.
Apart from antimicrobial activity, the composite creates favourable conditions for gas and moisture exchange and also acts as an ethylene blocker preventing excess ripening.
In a separate study, a biodegradable nanocomposite film incorporated with microbial synthesized silver nanoparticles improved the shelf life of 'Shan-i-Punjab' peaches, a low chill cultivar which matures in mid-summer in north west India and has a short shelf life. The film - a blend of chitosan and rice starch with good mechanical and tensile strength, and oxygen and water vapour barrier properties - showed antimicrobial activity against Gram-negative (E. coli) and Gram-positive (Staphylococcus aureus) human pathogens in in vitro tests.
After 12 days’ storage at 4°C, physiological weight loss was 4.75% in peaches wrapped in the chitosan rice starch composite film with silver nanoparticles, compared with 15.44% in control peaches (no wrapping). Microbial counts on fruit surfaces were also lower in the wrapped fruits compared with control fruits.
This is reported to be the first work on the evaluation of biodegradable rice starch/chitosan nanoparticle-incorporated film for enhancing the shelf life of peaches.
Publication date: 4/12/2018