Valorization of Agricultural Byproducts into Sustainable and Active Food Packaging Systems

Abstract

Globally, plastic production is mounting to new heights every year, along with its waste accumulation in the environment. Predominantly, food packaging consumes colossal amounts of synthetic plastics over any other packaging materials due to their undeniable advantages. However, the non-biodegradable nature, insufficient recycling rates, and migration of additives necessitate a sustainable alternative. Biopolymers (i.e., biodegradable polymers) stand out as a viable alternative; they are from renewable sources and are biodegradable in the end. In that regard, biodegradable packaging materials developed using agricultural byproducts could be a novel strategy to overcome the environmental and economic concerns in the processing industries. This thesis demonstrates a feasible route to divert underutilized agricultural byproducts into sustainable materials for food packaging applications. This thesis investigates the potential of three different starches from byproducts (jackfruit seeds, jamun seeds, and litchi seeds) and xyloglucan from tamarind kernels in film forming to obtain strong mechanical, water-resistant, and antimicrobial/antioxidant properties. To achieve this goal, three strategies have been explored, namely starch recovery, starch-xyloglucan complexing, and active nanoparticle incorporation. In the first part of this thesis, jackfruit seed starch (JSS) and tamarind kernel xyloglucan (XG) were extracted from their sources. The JSS films displayed weaker mechanical and water vapor barrier properties than XG films. The blending of XG with JSS improves the material strength attributed to intermolecular interactions. Furthermore, JSS/XG nanocomposite films were synthesized by incorporating zinc oxide nanoparticles (ZNPs). The ZNPs-incorporated films demonstrated increased surface hydrophobicity and water resistance. Loaded ZNPs effectively transferred stress to the interface and enhanced the tensile strength (20.65 MPa), elongation at break (38%), and elastic modulus (0.39 GPa). The nanocomposite films showed strong growth inhibition activity against Staphylococcus aureus and Escherichia coli. Additionally, the JSS/XG/ZNPs coated tomato fruits resulted in delayed weight loss (up to 40%) compared to uncoated fruits at the end of storage. In the second part, bio-nanocomposite films using jamun seed starch (JaSS), tamarind kernel xyloglucan (XG), and chitosan nanoparticles (ChNPs) were developed. The blending of JaSS and XG promotes a dense polymer network with enhanced packaging attributes in the composite films. The addition of 3% w/w ChNPs significantly enhanced the tensile strength (20.42 MPa), elastic modulus (0.8 GPa), and surface hydrophobicity (89°), along with reduced water vapor permeability (4.32 × 10-9 g m-1s-1Pa-1) of the JaSS/XG films. The films exhibited strong antimicrobial activity against Bacillus cereus and Escherichia coli. More interestingly, a JaSS/XG/ChNPs coating applied on sapota fruits retarded the weight loss and color change up to 12 days of storage. In the third part, starch from litchi seeds (LSS) was extracted, and composite films were developed with xyloglucan (XG) and lignin nanoparticles (LNPs). The XG addition strengthened the weak polymer networks of LSS and improved the rheological, molecular, morphological, mechanical, and barrier properties. The lignin nanoparticles loading into the LSS-XG network further increased the tensile strength (14.83 MPa), elastic modulus (0.41 GPa), and surface hydrophobicity (80.07°) and reduced the water vapor permeability (5.63 × 10-7 g m-1s-1Pa-1). The phenolic hydroxyls of LNPs imparted strong UV-shielding and free radical scavenging activities to the composite films. These attributes aided in preserving the quality of coated banana fruits with minimal weight loss and color change. The last part presents the discussion of the resultant properties among the prepared bio-nanocomposites. LSS films exhibited the highest strength, stiffness, and water vapor permeability. JaSS films showed the highest flexibility and least water solubility. JSS films demonstrated the highest surface hydrophobicity and water vapor barrier. The complexing of starch and xyloglucan synergistically enhanced the intrinsic properties of starch films. The inorganic ZNPs enhanced maximum strength, stiffness, and antimicrobial activity, whereas the organic ChNPs and LNPs effectively enhanced the water-resistant attributes of the composite films. Overall, this research highlights the potential transformation of underutilized abundant byproducts into sustainable active bio-nanocomposites for food packaging applications. The prepared active bio-nanocomposites exhibited a promising potential in retarding the quality deterioration of highly perishable fruits that extends the shelf life and mitigates the economic and nutritional losses.