Antibacterial PLA Composites Prepared with Bay Leaf (Laurus Nobilis L.) Extract

Summary

In this study, polylactic acid (PLA), a biodegradable polymer, was modified with antibacterial properties by extracting active compounds from bay leaves (Laurus nobilis L.) and preparing PLA composites. For antibacterial analysis, S. Enteritidis 13076 isolates were used as the bacterial strain. The antibacterial effect and percentage of bay leaf extract were determined and this ratio was applied to PLA composite films.

1. Introduction

Biodegradable polymers hold great importance in many areas of technological advancement. To meet increasing demand for sustainability and environmental cleanliness, research efforts aimed at developing food packaging materials that decompose completely in the environment are steadily increasing. Biopolymers, owing to their biodegradability, are suitable alternatives to be converted into environmentally friendly food packaging materials. Biopolymers are regarded as alternatives to oil-based plastics because they are biodegradable and renewable. Today, technological advancement has led to the development of synthetic biopolymers including polylactic acid (PLA), polycaprolactone (PCL), polyglycolic acid (PGA), polyvinyl alcohol (PVA) and polybutylene succinate (PBS). The advantages of synthetic biopolymers include the ability to develop many properties such as durability, flexibility, high gloss, transparency and tensile strength, as well as the potential to create a sustainable industry [1]. Poly(lactic acid) (PLA), one of the biodegradable polymers, is highly effective today. PLA is a biodegradable, biocompatible and non-toxic polyester that is transparent, has high modulus and strength, and is a good alternative to oil-derived polymers. PLA possesses many properties including good processing characteristics, adjustable degradation rates and pharmacokinetic and pharmacological efficacy [2]. The fact that PLA is environmentally friendly and possesses biocompatibility provides a wide range of applications in plastic applications, packaging-wrapping, textile applications, agricultural products, single-use products and the medical field [3]. In recent years, interest in and demand for agents obtained from natural sources has increased due to the emergence of many adverse effects of synthetic antibacterial agents on human health. Studies have shown that essential oils obtained from plants possess antimicrobial, antifungal and antioxidant properties [4]. Dried leaves and essential oil of bay (Laurus nobilis L.) are used in the food industry as flavoring and food preservative agents. Studies have determined that the main components are 1,8-cineole, linalol, trans-sabinen hydrate, α-terpinyl acetate, methyl eugenol, sabinene and eugenol [5].

2. Materials and Methods 2.1. Materials

The bay leaves (Laurus nobilis L.) used in this study were collected from the Black Sea Region. The PLA used in the experiment was Ingeo™ Biopolymer 2003D obtained from Natureworks. The PLA used in the experiments contained 96% poly(L-lactic acid) (PLLA) and 4% poly(D-lactic acid) (PDLA).

2.2. Methods

In this study, the antibacterial effect of bay leaf extract was performed according to Wang and Rham (2015). Plate Count Agar (PCA) was used as the culture medium. Following decimal dilutions, the drop plate method was applied for inoculation. Additionally, to determine the qualitative antibacterial effect, sterilized discs were saturated with bay leaf extract and the disc diffusion method was applied. After determining the antibacterial effect and percentage of bay leaf extract, this ratio was applied to PLA composite films. PLA composite films were prepared using the solvent casting method. PLA was mixed with chloroform and bay leaf extract at a ratio of 33% was added to the resulting solution and stirred using a magnetic stirrer for 1 day to achieve homogeneity. The resulting solution was poured into sterilized petri dishes and dried at room conditions for 7 days.

3. Results and Discussion

This section presents the results of antibacterial analysis of the composite film prepared with bay leaf extract and PLA. Figure 1 shows the antibacterial effect of bay leaf extract on S. Enteritidis ATCC 13076 as a result of the drop plate method applied. After the incubation period, no visible growth was observed around the surface where the bay leaf extract was in contact.

Figure 1. Antibacterial effect of bay leaf extract on S. Enteritidis ATCC 13076

To demonstrate the quantitative effect, the results of microbiological cultures for bay leaf extract and PLA composite film prepared with bay leaf extract are shown in Table 1 and Table 2.

Table 1. Microbiological culture results of bay leaf extract

Table 2. Microbiological analysis results of PLA film prepared with bay leaf extract

CFU: Colony forming unit

4. Conclusion

As a result of the studies conducted, it was observed that bay leaf extract has an antibacterial effect on S. Enteritidis 13076 strain. Based on microbiological cultures, as shown in Table 1, bay leaf extract demonstrated a significant antibacterial effect on S. Enteritidis ATCC 13076 strain. However, when inoculation was performed on PLA film prepared with bay leaf extract at the same ratio, no antibacterial effect on the aforementioned microorganism was detected (Table 2). The reason for this is considered to be that volatile oils with antibacterial properties, such as 1,8-cineole, which are among the main components of Laurus nobilis L., may have evaporated along with chloroform during the drying of PLA films. The results are of a nature that will guide our future studies on the preparation of natural antibacterial polymer composites.   Feza Geyikçi Ondokuz Mayıs University Faculty of Engineering Department of Chemical Engineering   Ayça Aydın Ondokuz Mayıs University Faculty of Engineering Department of Chemical Engineering       Belgin Sırıken Ondokuz Mayıs University Faculty of Veterinary Medicine    

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