Abstract
Strawberries have a very short post-harvest life mostly due to their relatively high water content, intense metabolic activity and susceptibility to microbial rot. Antimicrobial low-density polyethylene nanocomposite films containing ZnO nanoparticles at different mass fractions were prepared by melt mixing and followed by compression moulding using a hot press machine. Fresh strawberries were packed in nanocomposite films and stored at 4 °C. Their microbial stability, ascorbic acid content and titratable acidity were evaluated after 0, 4, 8, 12 and 16 days of storage. Microbial growth rate was significantly reduced up to 16 days as a result of the use of nanocomposite packaging material containing ZnO nanoparticles. By increasing the ZnO nanoparticle mass fraction to 5%, the antimicrobial activity of the film increased. All packages containing the ZnO nanoparticles kept the microbial load of fresh strawberries below the level that affects shelf life (5 log CFU/g) up to 16 days. The lowest degradation of ascorbic acid content (6.55 mg per 100 g), and loss of acidity (0.68%) were observed in packages containing 3% of ZnO nanoparticles with 10% polyethylene-grafted maleic anhydride.
Highlights
Strawberries are highly perishable mainly due to fungal decay
Film-grade Low-density polyethylene (LDPE) resin pellets (LF0200, melt flow index (MFI) 2 g per 10 min, density 0.92 g/mL, softening point 94 °C), polyethylene-grafted maleic anhydride (PE-g-MA) containing 1 % malic anhydride and antimicrobial agents including ZnO nanoparticle powder with an average particle diameter of about 10–30 nm were obtained from Pishgaman Nano Material, Tehran, Iran
The transmission electron microscopy (TEM) images of nanocomposite LDPE film with 3 % ZnO nanoparticles and PE-g-MA show that the nanoparticles are well dispersed in the polymer matrix, with aggregates ranging from 10 to 20 nm with an average size of 16 nm (Figs. 1c and d)
Summary
Strawberries are highly perishable mainly due to fungal decay. Their post-harvest shelf-life at low temperatures (0–4 °C) is approx. Among fresh fruits and vegetables, strawberries are especially interesting because they are fragile and sensitive to mould, which causes significant loss on the market [3]. Active packaging is a new generation of food packaging based on nanocomposites made by incorporating metal nanoparticles into polymer films [17]. It ensures microbial safety of food, and can extend the shelf life of products [18]. There is a better interaction between polymer matrix and filler in
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