Application of alginate and chitosan edible films incorporating natural antimicrobial agents
- Pathum Thani, Thailand : Asian Institute of Technology, 2004
- 183 p. : ill.
- Dissertation ; no. AE-04-06 .
- Asian Institute of Technology. Dissertation ; no. AE-04-06 .
A dissertation submitted in partial fulllment ofthe requirements for the degree of Doctor of Engineering, School of Environment, Resources and Development
Thesis (Ph.D.) - Asian Institute of Technology, 2004
Food quality and safety demands are becoming more and more intensive and specic with more information available to the buyers. Consumer awareness for safe, high quality, long shelf life, fresher, minimally processed and ready to eat foods has increased in recent times. The use of edible lms or coatings is one of the most effective methods in maintaining the quality and extending shelf life of processed foods. They can also function as a carrier of ingredients, such as antioxidants and antimicrobial agents. Alginate and chitosan are polysaccharides, abundantly available as natural materials. Coating meat products with alginate and chitosan has been shown to protect moisture loss, retard microbial growth and reduce lipid oxidation. In addition, it is known that some spice oils have antimicrobial and antioxidative activity. There is a limited research about employing these natural agents from plants to produce active edible lms or coatings for foods preservation. This study was carried out to utilize the beneficial potency of natural substances (Spice oils) by incorporating into alginate and chitosan lms to obtain active edible lms and coatings. Initially, garlic, citronella and onion oils were tested for antimicrobial and antioxidative activities to select the most potent one. Antimicrobial lms were then studied by incorporating antimicrobial agents such as garlic oi] (selected oil), potassium sorbate and nisin. The latter two are well known chemical and (bacteriocin) antimicrobial agents respectively. Five food pathogenic bacteria such as Escherichia coli, Salmonella wphimurium, Staphylococcus azrreus, Lister-11 monocytogenes and Bacillus cererrs were used to test antimicrobial activity of edible lms. Meatball was used as a model product to examine the efcacy of active edible coatings for quality preservation. When tested against the above mentioned bacteria, it was found that garlic oil had better antimicrobial activity than citronella and onion oils. Its antioxidant activity measured using 1,1-diphenyl-2picrylhydrazyl (DPPII) and deoxyribonucleic acid (DNA) cleavage protection methods was also found to be better than the other oils. The addition of glycerol at 40% (w/w of lm materials) as a plasticizer modied the mechanical, physical and microstructural properties of alginate and chitosan lms. In the alginate lms, glycerol reduced tensile strength from 73.36 to 66.11 MPa, while in chitosan lms it reduced tensile strength from 49.63 to 6.53 MPa. The elongation at break for alginate lm increased slightly from 2.65 to 4.05% by addition of glycerol. The elongation at break for chitosan lms was from 6.21 to 30.96%. In addition, glycerol caused an increase in water vapor permeability (WVP) value from 16.13 to 20.32 g.mm/m2.day.kPa in alginate lms and from 23.09 to 26.72 g.mmxm3.day.kPa in chitosan lms. Glycerol addition reduced the microstructure cavities in alginate lms, while in chitosan lm it modied its compact structure in multilayers as observed by 3 Scanning Electron Microscopy (S EM). As chitosan and alginate have complementary prOperties in terms of charge, composite and bilayer lms were made. Composite lms made of varying ratios between alginate and chitosan did not result in lms with desirable characteristics. In bilayer lms, it was found that laminating chitosan onto alginate lm could not replace the role of Ca ion as crosslinking agent in term of mechanical prOperties. Bilayer lms made from alginate