A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Food Engineering and Bioprocess Technology

Thesis (M.Sc.) - Asian Institute of Technology, 2017

Postharvest loss due to microbial infestation has become one of the major threat worldwide due to its impact in economic loss and endanger human health. This research was conducted to investigate the synergistic effects of natural photosensitizer under the illumination of blue(465 nm) Light Emitting Diode (LED) as antimicrobial treatment on the surface of food samples. These natural compounds called a photosensitizer containing a photo-active molecule which may react to light in precise wavelength and by the presence of oxygen might fit the required energy to excite radical oxygen species lead to cell destruction. LED offers non-thermal process which may not damage the food quality, such as the physical characteristics in texture and maintain the nutritional component in food. The selected natural photosensitizer compounds which show significant effects as antimicrobial treatment, i.e. curcumin from turmeric, chlorophyllin, and anthocyanin from mangosteen extract was assessed to diminish the growth of Escherichia coli employing surface treatment method. Antimicrobial susceptibility test in vitro was examined on the surface of agar directly inside chamberusing141,52 mW.cm-2LED intensity. The result of the investigation was selecting curcumin from turmeric extract as the most effective photosensitizer compound. Curcumin activated by 465nm LED light able to reduce up to 7 log CFU/ml on the surface of Mueller-Hinton Agar and may retard 2.4 log CFU/gram of E coli on the surface of grapes. Scanning Electron Microscopy(SEM)image of the damaged cells shows its effects onto cell destruction by breaking the cell wall of the bacteria. Application of this treatment onto fruit surface on chemical and physical properties after storage was observed and resulting in no significant difference in Vitamin C content and DPPH inhibition.