Improvement of ‘Injera’ Shelf Life Through the Use of Silver(Ag) and Zinc Oxide (Zno) Nanoparticles

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Addis Ababa University


About two-third of Ethiopian diet consists of Injera, a thin, fermented traditional baked bread, made from the most popular grain of teff(Eragrostis tef (Zucc) Trotter). Even though it is a nutritious food, the shelf life of injera does not usually exceed 3 days due to mould spoilage. This research was conducted with the aim to evaluate the effect of biosynthesized silver Nano particles (AgNPs) and Zinc oxide nanoparticles (ZnONPs) in improving injera shelf life. AgNPs and ZnONPs are synthesized from Eucalyptus globulus and Calpurnia aurea (Ait.) Benth leaf extracts, respectively. Formation of nanoparticle was confirmed by color change and by characterization techniques (UV-vis spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Antimicrobial test on Aspergillus, Pencillinium, and Rhizopus spp. was conducted using disc diffusion method. Then both nano particles were dip-coated on plastic zipper bags at different percentages after disinfection with 70% alcohol and dried in an oven at 600c and used for injera storage. The shelf life was determined as one day before mold growth appearance. Moisture content and pH was determined by oven and pH meter, respectively. Internal temperature of the package during storage was measured by infrared spectroscopy whereas pour plate method was used for mold and yeast count. Finally, migration level was determined by Microwave Plasma - Atomic Emission Spectroscopy (MP-AES). The results from Uvi-vis spectroscopy shows that characteristic peaks observed at 420 and 300 to 400 nm for AgNPs and ZnONPs, respectively. The XRD data also shows that both synthesized nano particles were below 100nm. The SEM image shows that AgNPs was mostly irregular whereas ZnONPs was mostly rod shaped. The result has shown that both of them have significant antimicrobial effect against the studied fungus. ZnONPs has induced greater inhibition zone than AgNPs, which is caused by difference in crystallite sizes (ZnONPs = 64.25nm, AgNPs = 84.07nm).The shelf life of the stored injera samples were increased significantly based on their concentrations. For both Ag and ZnONPs , the optimum concentration was 50% in which injera shelf life increased for 10 days to 15 days, respectively. Both NPs have no significant effect on moisture, pH and internal temperature of the package during storage. The Cfu/g of molds and yeast decreased as the percentage of these nanoparticles coated on plastic bags increased. At 50% concentration the migration was 1.34 and 375mg/Kg for both Ag and ZnONPs, respectively. The migration of both Ag and ZnONPs was relatively high, which was increased with concentration and time of storage. Because, it needs further study and improvements to use these nano particles for injera storage. Thus, it would be advisable if these nano particles will be incorporated as ingredients of plastics to decrease this migration problem.



Injera, Nano Particles, Moulds and Yeasts, Shelf Life, Dip Coating, Storage