[Paper Review] Developing ZnO Nanoparticle embedded Antimicrobial Starch Biofilm for Food Packaging

Prakash Kumar, Sanjeev Gautam|arXiv (Cornell University)|Sep 11, 2019

Nanocomposite Films for Food Packaging1 references7 citations

TL;DR

This study develops antimicrobial starch-based biofilms embedded with ZnO nanoparticles synthesized via sol-gel and green (neem extract) methods, enhancing food packaging safety and biodegradability. The green-synthesized ZnO in film F2 showed superior antimicrobial activity (14 mm inhibition zone against E. coli) and better preservation of grape freshness over 7 days compared to chemically synthesized counterparts.

ABSTRACT

Starch based bio-films act as biodegradable packaging material for coating and wrapping food products, which is alternate to the synthetic polymer. Nanoparticles (NPs) are also alternative to antibiotics to target pathogens. Through interaction of nanoparticles with food packaging material the overall quality of the packaged food also get enhanced. In this research work, ZnO NP embedded corn starch films were developed. First, ZnO NP were synthesized by two approaches (a) Sol-gel approach and (b) Green synthesis approach; and then ZnO NP embedded corn-starch bio-films were developed. In sol-gel technique ZnO NP were synthesized at different pH ranging from 8 to 11, with an average crystallite size of 28 to 53 nm. In green synthesis technique ZnO NP were synthesized by using Azadirachta indica (Neem) at different concentration of 2\% and 3\% with an average crystallite size of 36 nm and 32 nm, respectively. Characterization of synthesized ZnO NPs were done with XRD, UV-DRS, UV-VIS, FTIR and FE-SEM. The functional properties of the ZnO embedded starch film were enhanced with addition of 5\% citric acid solution(w/w) as cross-linker and 0.90 g glycerol(w/w) as plasticizer. Film-F1 embedded with chemically synthesized ZnO NP, Film-F2 embedded with biochemcially synthesized ZnO NP and Film-F3 without being embedded by any NPs. Characterization of synthesized films were done with SEM and XRD. Film solution of F2 showed higher antimicrobial effectiveness than F1; against E.coli and S.aureus bacterial strains with an inhibition zone of 14 mm and 6 mm. 7days biodegradability analysis of the films were also done. Along with this, their current application and future perspectives in the food sector are also explored

Motivation & Objective

• To develop biodegradable, antimicrobial starch-based biofilms as sustainable alternatives to synthetic polymer packaging.
• To compare the efficacy of chemically synthesized ZnO nanoparticles (sol-gel method) versus biologically synthesized ZnO nanoparticles (using Azadirachta indica) in starch films.
• To evaluate functional, mechanical, and antimicrobial properties of ZnO-embedded starch films for food packaging applications.
• To assess biodegradability and shelf-life extension potential using real food models (e.g., grapes).

Proposed method

• ZnO nanoparticles were synthesized via the sol-gel method at pH 8–11, with crystallite sizes ranging from 28 to 53 nm.
• ZnO nanoparticles were also synthesized using Azadirachta indica (neem) extract at 2% and 3% concentrations, yielding crystallite sizes of 36.34 nm and 32.68 nm, respectively.
• Corn starch films were fabricated with 5% citric acid (cross-linker) and 0.90 g glycerol (plasticizer) to enhance functional properties.
• Three film types were produced: F1 (chemically synthesized ZnO at pH 10), F2 (neem-synthesized ZnO at pH 10), and F3 (control, no NPs).
• Characterization included XRD, UV-DRS, FTIR, FE-SEM, and EDX to confirm ZnO formation and film structure.
• Functional properties (WVP, solubility, tensile strength, opacity, swelling, moisture content) and antimicrobial activity (zone of inhibition) were evaluated.
• Biodegradability was tested over 7 days, and qualitative freshness assessment was performed on grape-wrapped films.

Experimental results

Research questions

• RQ1 How does the synthesis method (sol-gel vs. green) affect the size, morphology, and crystallinity of ZnO nanoparticles in starch films?
• RQ2 What is the impact of ZnO nanoparticle incorporation on the mechanical and barrier properties of starch-based biofilms?
• RQ3 How do ZnO-embedded films compare in antimicrobial efficacy against E. coli and S. aureus?
• RQ4 To what extent do ZnO-embedded films extend the shelf life of perishable foods like grapes?
• RQ5 How does the biodegradability of ZnO-embedded starch films compare to control films over 7 days?

Key findings

• The green-synthesized ZnO nanoparticles using 3% neem extract produced a crystallite size of 32.68 nm, with a Zn:O atomic ratio of 1.22:1, indicating high purity.
• Film F2, embedded with neem-synthesized ZnO NPs, exhibited the highest antimicrobial activity, with a 14 mm inhibition zone against E. coli and 6 mm against S. aureus.
• Tensile strength was highest in F1 (12.50 ± 0.18 MPa), followed by F2 (11.34 ± 0.27 MPa), and lowest in F3 (10.22 ± 0.11 MPa), indicating improved mechanical strength with chemically synthesized NPs.
• Water vapor permeability (WVP) increased from F1 (2.42 × 10⁻¹² g⁻¹s⁻¹Pa⁻¹) to F2 (2.85 × 10⁻¹²) to F3 (3.16 × 10⁻¹²), suggesting higher moisture permeability in films without NPs.
• Biodegradation percentage increased over 7 days, with F1 showing the highest biodegradation rate, followed by F2 and F3, indicating enhanced biodegradability with ZnO NP content.
• In a qualitative freshness test, grapes wrapped in F2 film retained the highest freshness and received the highest overall acceptance on a 9-point hedonic scale, outperforming F1 and non-wrapped controls.