Elsevier

Food Hydrocolloids

Volume 60, October 2016, Pages 476-485
Food Hydrocolloids

Preparation of antimicrobial agar/banana powder blend films reinforced with silver nanoparticles

https://doi.org/10.1016/j.foodhyd.2016.04.017Get rights and content

Highlights

  • Preparation of binary blend films of agar and banana powder (A/B).

  • A/B composite films reinforced with silver nanoparticles (A/B/AgNPs).

  • Banana powder content influenced the A/B film properties.

  • A/B/AgNPs composite film exhibited distinctive antimicrobial activity.

Abstract

Binary blend films of agar and banana powder (A/B) and A/B composite films reinforced with silver nanoparticles (A/B/AgNPs) were prepared using a solution casting method and their properties were characterized. The SEM micrographs and FT-IR results confirmed the formation of physical interactions between polymer matrices and nanofillers. Apparent surface color and transmittance of the composite film were greatly influenced not only by the mixing of banana powder with agar but also by the incorporation of AgNPs. The UV light absorption, water vapor barrier properties, and antioxidant activity of A/B blend films increased with the increase in the concentration of the banana powder, while the mechanical properties decreased. The A/B/AgNPs composite film exhibited distinctive antimicrobial activity against food-borne pathogenic bacteria, Escherichia coli and Listeria monocytogenes with stronger antibacterial activity against Gram-negative bacteria than Gram-positive bacteria. The binary blend of A/B films are expected to be used for the edible film or coating of foods and their nanocomposite films with antimicrobial activity have a potential to be used as food packaging material for maintaining the safety and extending the shelf life of packaged food.

Introduction

Recently, biopolymers from various natural resources such as starch, cellulose, agar, alginate, carrageenan, gelatin, soy protein, whey protein, and wheat gluten have been used as eco-friendly packaging materials for the substitute of non-biodegradable petroleum-based plastic based packaging materials (Shankar et al., 2015a, Shankar et al., 2015b, Giménez et al., 2013). As one of such biopolymers, agar has been widely used for the preparation of biodegradable packaging films due to its good film forming property with abundance, renewability, and biocompatibility (Wang & Rhim, 2015). Agar is a hydrophilic polysaccharide extracted from the Gelidiaceae and Gracilariaceae families of seaweeds and mainly composed of alternating repeating units of d-galactose and 3, 6-anhydro-β-galactopyranose (Gehrke, 1993, Tako et al., 1999). High compatibility with other biopolymers of agar with good film-forming properties made it as a good candidate for blending with other biopolymers to enhance the properties of the blended films (El-Hefian et al., 2012, Varshney, 2007, Wang and Rhim, 2015). Various materials, such as protein (Wang & Rhim, 2015), nano-clay (Kanmani & Rhim, 2014a), nanocellulose (Shankar & Rhim, 2016), grapefruit seed extract (Kanmani & Rhim, 2014b), lignin (Shankar et al., 2015b), and metallic nanoparticles (Shankar & Rhim, 2015) have been blended with agar to improve the mechanical, water resistance, and functional properties of the films. However, to the best of our knowledge, the report on banana powder as a reinforcing agent in agar biopolymer is not available in the literature so far.

Banana, Musa sapientum Linn. is a tropical fruit which contains a high amount of polysaccharide (starch 61–76% dry basis), proteins, and fat (Waliszewski, Aparicio, Bello, & Monroy, 2003). In addition, at the green stage, banana is a major source of macro-elements and it contains health-beneficial ingredients such as resistant starch and dietary fibers that have the potential to increase the hydrophobicity of polymers (Anyasi et al., 2013, Pelissari et al., 2013). Moreover, the polyphenolic compounds included in banana are expected to enhance the functional properties, to secure the food safety, and to extend the shelf-life of food (Pereira and Maraschin, 2015, Sothornvit and Pitak, 2007, Waliszewski et al., 2003). Banana peel extract has been used for the synthesis of silver nanoparticles for the test of their antimicrobial and free radical scavenging activities (Kokila, Ramesh, & Geetha, 2005).

Bionanocomposite packaging materials with antibacterial function is believed to be one of the promising active packaging materials to extend the shelf-life of food, maintain the food safety, quality, and to improve the storage period by destroying or inhibiting the food pathogenic microorganisms (Kanmani and Rhim, 2014a, Shankar et al., 2014a). Silver nanoparticles (AgNPs) have been most widely used for the preparation of nanocomposite in the food packaging and biomedical applications due to their high surface area, unique optical, magnetic, electric, catalytic, thermal stability, and broad-spectrum of antimicrobial properties. Instead of hazardous chemical reagents, various biopolymers such as gelatin (Kanmani & Rhim, 2014a), glucose, starch (Cheviron et al., 2014, Vigneshwaran et al., 2006), and chitosan (Huang & Yang, 2004), as well as plant extracts (Shankar et al., 2014b, Shankar et al., 2014c) have been used for the synthesis of AgNPs. Therefore, in the present study, banana powder was used as a reducing and stabilizing agent for the preparation of AgNPs.

The objectives of the present study were to prepare agar/banana powder binary blend films (A/B) and agar/banana powder blend films with AgNPs (A/B/AgNPs) and to characterize their properties for their potential use as food packaging application. Banana powder was aimed to blend with agar to improve the water barrier and functional properties such as ultraviolet (UV) screening effect, antioxidant, and antimicrobial activity of the A/B binary blend film. Banana powder is rich in carbohydrate composed of starch as the main constituent with good film-forming property (Waliszewski et al., 2003). A small amount of protein, ash, and fat presented in banana powder played an important role in the optical, physicochemical properties when used as a main or a part of the raw material to form a film (Pelissari et al., 2013). In addition, banana powder contained some phytochemicals such as tannins and terpenoids (β-carotene) as phytochemicals (Anyasi et al., 2013). Tannins are one of a polyphenolic compound found in unripe fruit that can provide antioxidant activity and help in reducing metal ions to nanoparticles (Pereira & Maraschin, 2015).

Section snippets

Materials

Green banana (M. sapientum Linn.) at the age of 112–116 days after petal fall was obtained from the orchard of Kasetsart University, Khamphaengsaen Campus, Nakhonpathom, Thailand. Food grade agar was purchased from Yun Doo Co., Ltd. (Uijeongbu, Gyeonggi-do, Korea). Glycerol was procured from Daejung Chemicals & Metals Co., Ltd. (Siheung, Gyeonggi-do, Korea). 2, 2-Diphenyl-1-picrylhydrazyl (DPPH) was purchased from Sigma–Aldrich Chemical Co. (St. Louis, MO, USA). Tryptic soy broth (TSB) and

Optical properties of films

Apparently all the films formed were flexible and free-standing. Surface color and transmittance of the films were greatly influenced by blending with banana powder as shown in Table 1. The neat agar film (A4/B0) was clear and transparent with a high lightness value of 92.3. Addition of banana powder decreased Hunter L-value and increased Hunter a- and b-values, in which the lightness (Hunter L-value) decreased monotonously and the redness (a-value) increased quadratically with the increase in

Conclusion

Well compatible agar/banana powder blend films with and without AgNPs inclusion were prepared to improve the water sensitivity and functional properties such as antioxidant and antimicrobial activity of agar film. The blending of agar with banana powder with different mixing ratio and incorporation of AgNPs significantly influenced the film properties such as color, transmittance, mechanical, moisture content, solubility, water contact angle, water vapor permeability, thermal stability,

Acknowledgments

This research was supported by the Thailand Research Fund through the Royal Golden Jubilee Ph.D. Program (Grant No. PHD/0265/2552), and the Agriculture Research Center (ARC 710003) program of the Ministry of Agriculture, Food and Rural Affairs, Republic of Korea.

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