Abstract
Deterioration of food quality during packaging, distribution, and storage of perishables (e.g., fish, meat, milk, vegetables) is a global concern. Worldwide, consumers are demanding safe foods that are minimally processed and retain quality and health properties. This necessitates the development of novel, biodegradable, and functional packaging materials. The challenge is that using plastic-based polymers and synthetic preservatives is not suitable for developing effective food packaging due to their harmful health effects and unfriendly nature in the environment. Therefore, there is growing interest in using biodegradable functional biomaterials, such as chitosan (CH), in active and intelligent packaging technologies to extend and monitor food quality to ensure consumers' health and safety. Hence, the main objective of the current study was to utilise bioactive chitosan to fabricate biodegradable active and intelligent/multifunctional packaging materials for sustainable applications in the food industry.
In light of the development of desirable food packaging materials, chitosan films were fabricated in the first and second experimental studies using the solvent casting method by adding polyvinyl alcohol (PVA)/glycerol, green synthesis chitooligosaccharide (COS), and gallic acid. The physical, mechanical, barrier (e.g., moisture, water vapour permeability (WVP), and opacity), structural, and thermal properties of fabricated chitosan films were investigated. The use of bio-composite in CH films exhibited a synergistic effect, resulting in a film with a homogenous/smooth surface and excellent mechanical and thermal properties obtained. Additionally, incorporating COS and gallic acid reduced the moisture content, WVP, and transparency. Moreover, the chitosan hydrogel films exhibited good colour and strong UV-barrier properties.
In the third study, the focus shifted to the antioxidant and antimicrobial effects of the films. Additionally, the biodegradation patterns of active chitosan films were examined. The active chitosan films, which contained PVA/glycerol, COS and gallic acid, demonstrated strong DPPH (93.88 ± 1.32% - 99.48 ± 0.24%) and ABTS (97.84 ± 0.97% - 98.06 ± 0.91%) radicals scavenging capacity. They also demonstrated a robust ability to convert ferrous (Fe+2) iron (217.36 - 230.93 mM Fe2+/g sample). Additionally, the fabricated films showed inhibitory rates against Escherichia coli, Listeria innocua, and Saccharomyces cerevisiae in the ranges of 42.66% - 59.49%, 52.32% - 79.29%, and 53.88% - 79.55%, respectively. Moreover, the fabricated active chitosan films were biodegradable in the soil, confirming to ecofriendly nature. The biodegradation of active chitosan films in soil showed that adding PVA/glycerol, COS, and gallic acid took a comparatively longer time (70-105 days) compared to 63 days for neat chitosan film.
In the fourth study, New Zealand blackcurrant extract anthocyanins were incorporated with the active chitosan film to make it intelligent. The blackcurrant extract anthocyanins in active chitosan films exhibited pH sensitivity and observable colour changes from red to yellow at pH 1 to 14. The colour-changing properties of active chitosan films at different pH indicate their suitability to detect food quality and their potential in the applications of the food industry. Furthermore, the inclusion of blackcurrant extract anthocyanins in active chitosan films significantly (p<0.05) improved the mechanical, barrier, structural, and thermal properties of films. The addition of anthocyanins to active chitosan films improved their antimicrobial action against Escherichia coli (49.78 ± 6.94% - 65.15 ± 8.67%), Listeria innocua (61.11 ± 3.79% - 79.13 ± 2.87%), and Saccharomyces cerevisiae (53.88 ± 6.54% - 82.29 ± 3.14%), as well as their antioxidant properties. This included the ability to scavenge DPPH (99.85% - 99.96%) and ABTS (98.81% - 99.95%) radicals and exhibit FRAP activity (323.72 - 323.94 equivalent mM Fe2+/g sample). Additionally, all the chitosan films were found to decompose in soil within 28 days.
In the fifth study, the cytotoxicity of prepared active and intelligent films was investigated using HaCaT and Caco-2 cells. The results showed that more than 90% cell viability was observed for HaCaT cells exposed to the active chitosan films, while viability ranged from 77 - 83% for cells exposed to the intelligent chitosan films, respectively. Similarly, Caco-2 cells demonstrated greater than 72% - 78% cell viability on active chitosan films and 71% - 75% cell viability on intelligent chitosan films. These findings indicated that the fabricated active and intelligent films were safe for human use as food packaging materials. Therefore, in the sixth study, the extension of food quality and detection of food freshness biomarkers were assessed using the fabricated active and intelligent films. The results demonstrated the ability of the developed active and intelligent chitosan films to prolong the shelf life of the tested foods by controlling the growth of microbes in tomatoes and weight loss in green grapes, as compared to the non-packaging group. Furthermore, the total volatile basic nitrogen (TVBN) value in film-packed pearl fish fillets in the presence of active and intelligent chitosan films was found to be lower than in non-packaging fish, suggesting that the produced films had the capacity to control fish spoilage during storage. Additionally, the use of intelligent films and their capacity to change colour in response to rising levels of TVBN from lamb and salmon meat or acidity in milk demonstrate that the fabricated films had the potential to be used to track food freshness biomarkers.
The findings of this PhD project indicate that adding PVA/glycerol, COS, gallic acid, and anthocyanins from blackcurrants to chitosan films improved their mechanical barrier, structural, thermal, functional, and pH sensitivity. This made the chitosan films multifunctional, suitable for extending food shelf life, and detecting food quality. The results obtained could be of great interest to the active and intelligent food packaging industry as they can help reduce global food loss and ensure consumer safety and environmental sustainability.