Title : Application of radiation processed oligo-chitosan as natural food preservative in subtropical region
In many cases, chitosan oligomers possess more bioactivity compared to chitosan itself. There are many methods for preparing these oligomers from which radiation processing is one of the best methods as it is fast, easily optimizable and works without any extra chemical requirement. However, there is no data based on subtropical region like Bangladesh where fresh fruits and vegetables are more prone to spoilage because of the weather conditions and suitable environment for microbial growth. In this research chitosan solution was irradiated by Co-60 gamma radiation in various radiation doses. Resulting oligo-chitosan are characterized and applied on different fresh fruits and vegetables to evaluate food preservation behavior of the oligomers. Our research study suggested that oligo-chitosan strongly performs as food preservatives. However, required oligo-chitosan concentration were different for different food varieties for best performances. 1500 ppm 40 kGy irradiated chitosan (2% w/v solution in 2% v/v acetic acid) treated ripe mangoes showed best self-life extension. Treated mangoes were well in condition for 9 days but untreated mangoes spoiled in 3 days at room temperature. On the other hand, 100 ppm irradiated chitosan treated green mango maintainedgood conditions for 65 days whereas untreated green mangoes rotted in 18 days at 4°C. Sliced mangoes showed edible quality for 4 months and 7 months at room temperature and 4°C respectively when submerged in 30 ppm irradiated chitosan solutions. Irradiated chitosan solution treated litchi showed considerably lower browning index and relative low leakage rate at room temperature and 4°C as well. Untreated litchi was damaged within 2 days in room temperature and 7 days at 4°C but 1500 ppm irradiated chitosan treated litchi were good in condition for 28 days at room temperature and 4 months at 4°C respectively. Canned untreated litchi damaged in 6 days at 4°C whereas 50 ppm irradiated chitosan treated canned litchi were eatable for 60 days. Local blackberry (Jaam) showed best result in 1000 ppm of irradiated chitosan solution. The treated blackberry fruits were good in condition for 5 days but untreated blackberries lost their edible quality in 18hrs at room temperature. Strawberrytreated with 500 ppm chitosan showed the best resultswith respect to fungal and bacteria resistance and enhanced preservation period. Treated strawberry maintained edible condition up to 3 days without plastic wrapping whereas untreated wasn’t edible after 2 days at room temperature. At 4°C, self-life of treated strawberry reached up to 15days whereas untreated strawberry unqualified after 4 days of preservation. Besides, irradiated chitosan treated (1500 ppm) bitter gourd and betel leaf showed better fungus resistance than untreated vegetables. In another research, 5000 ppm irradiated chitosan treated Telapia fish showed very promising results to maintain freshness up to two weeks at 4°C. In case of dry fish, 5000 ppm Irradiated chitosan treated sample showed the best fly repellant activity and maintained quality in both sunlight and shady conditions. All of these results suggested that gamma radiation treated chitosan can be a very promising and safe food preservative option for subtropical countries like Bangladesh.