The rates of food-borne illnesses continue to rise, having an impact on the society, economy and the health management in Dhaka, Bangladesh. Due to this rise, there has been increased interest in developing decontamination methods which are economic, safe, and
“green”. For this reason, the degree of contaminants present in raw, dried and semi-dried foods were examined in the current studies and subsequently two methods of decontamination were also examined, heat and low pressure plasma treatment, with the aim of establishing the latter as an alternative to current methods available in the decontamination of dried foods.
Bacterial and fungal analysis of 46 dried and semi-dried foods, collected from Dhaka Bangladesh, were carried out in Kindai University, Japan. Significant counts of bacteria and fungus were observed in dried (nuts, spices and herbs) and semi-dried foods reflecting poorly on the food quality of Dhaka, Bangladesh. Twenty-six samples were spices and herbs, with the majority showing initial microbial and fungal counts of 104. The bacterial and fungal counts of nuts and whole foods were scattered between 102 to 106. Semi-dried foods had initial counts of 104 to 106 for both bacteria and fungus. Among the total forty-six samples, the bacterial and fungal counts remained mainly within the range of 104 (23 and 25, respectively). Fifteen percent of the samples expressed results higher than the limits for bacterial counts in foods, set by various authorities, where as, eighty-one percent of the samples were higher than the fugal limits set.
Consumption of fruits and vegetables have increased in the recent times as a result of a rising interest of maintaining a healthy lifestyle. Advocates of healthy lifestyles have also promoted the consumption of fish in many occasions. Bacterial and fungal analysis of raw fruits, vegetables and fish also revealed significantly high counts. Of the fifty-one raw samples majority of the samples had an initial microbial count of 105. The 16 samples of
fruits showed initial bacterial counts ranging from 103 to 105, as seen in Table 6. The bacterial load of vegetables and seafood ranged from 104 to 106. The initial fungal counts for most samples were around 104. The fungal loads of fruits were between 103 to 104, whereas vegetables were within 104 to 105 and seafood within 103 to 106. All samples demonstrated resistance to oxacillin. This is particularly alarming as many of these foods are consumed raw.
These foods are staples in every diet, particularly sea fish, which is a popular item in the Bangladeshi community.
Air-borne pathogens were also tested to monitor the environment of the sampling area.
Large amounts of bacteria and fungus was found in the super market and vegetable and fish open markets. The bacterial and fungal counts of air-borne bacteria in the open vegetable market (0.79 cfu/L) were more than double that of the supermarkets (0.24 cfu/L), while in fish market it was 0.55 cfu/l. Average falling microorganisms for fish market was 252 cfu/pate/30 min (bacteria) and 52 cfu/plate/30 min (fungus); for vegetable market it was 165 cfu/plate/30 minute (Bacteria) and 30 cfu/plate/30 minute (fungi); and for supermarket 18.33 cfu/plate/30 minute (bacteria) and 4.33 cfu/plate/30 minute (fungi). The bacteria present in the air can contaminate the foods, contributing to the incidence of food-borne illnesses.
Proper precautionary measure, by the government authorities, are required to control environmental contamination of foods, and protect foods from re-contamination after suitable treatment. These pathogens, in both food and air, are affecting the health of the society and acting as the burden on the economy. Knowledge of the level of contaminants present will assist in maintaining and predicting the incidence of food-borne diseases.
As the incidences of food-borne illness rises, interest in decontamination method also rises. One method tested in the current study is the traditional method of heat. It is safe, economic and easily available. Significant log reductions in dried and semi-dreid foods were
observed, (average bacterial log reduction of 2.41, and average fungal log reduction of 3.27) after 2 hours of heat treatments in bacterial and fungal counts of samples.
Among the vegetables tested, after heat treatment three samples showed bacterial log reductions of 3.00 and higher, whereas one sample was below 1.00. Four samples of the fruits demonstrated bacterial log reductions of more than 3.5, whereas Berry showed the lowest log reduction of 0.76. Sufficient bacterial log reductions were observed among the sea foods, with most samples demonstrating a log reduction of 3.00 and higher. Heat was more efficient in reducing fungal growth with log reductions not venturing below the 1.00 and various samples showing log reductions more than 5.00. Five vegetables had fungal log reductions of 5.00 and higher. On contrast fruits had slightly lower reductions mostly ranging from 4.00 to 4.36. Similarly, log reductions for sea foods ranged from 4.04 and 5.34. This further established the use of heat in eliminating the growth of pathogens. Aided by the the low cost and ease of availability, this method can be carried out in any setting. Yet, heat treatments have also been linked with some adverse effects, therefore alternative methods with similar or greater rates of decontamination need to be studied.
Although heat was effective, it does have the ability to effect food quality and nutritional values. For this reason, current study also assessed the effect of low-pressure plasma treatment on seven dried sample, to test the application of this novel approach in the food industry. Many consumers are advocating the use of green methods of decontamination.
Low-pressure plasma treatment would be very effective as it exerts no affect on the foods, and a lack of vacuum equipment makes it cost effective. Log reductions observed were higher than that of heat, with an average log reduction of 4.43 and 3.80 for bacteria and fungus, respectively. In case of bacterial growth reductions chili (5.75), turmeric (5.18) and coriander powder (5.40) exhibited the best results, whereas, cumin (2.37) showed the lowest rate of reduction. In fungal growth highest reduction rate was observed in ginger (5.91) and
lowest in cumin (2.15). No bacterial growth was observed in poppy seeds after 20 min and in pine nuts after 40 min. To the best of our knowledge, its application in seeds have been observed, but its application on foods have not been explored. Current study observed low-pressure plasma treatment as more effective than heat and void of all side-effects of heat and previous methods of decontamination.
In order to maintain food safety proper education must be given to all vendors of Dhaka, to ensure they are aware of microorganisms and their role in spoilage, hygiene, handling and storage, cleaning, standards and limits. Setting up mechanisms to protect food from environmental contaminants in open markets will also ensure quality is upheld for a longer period of time. Methods such as ceilings, covering produce with protective films and maintain the quality of water used for cleaning. These should be coupled with frequent government inspections of the production and shopping facilities, personnel, environment, both raw and finished products, and equipment and tools of production and distribution.
Finally, strict enforcements of rules of food safety is required with emphasis of punishment for those who violate them.
Bacterial and fungal contamination are numerous in Bangladesh; hence methods of decontamination are important to the food industry. Heat and low-pressure plasma machine would both be effective in the elimination of pathogens and produce healthy foods, which are safe and economical, but low-pressure plasma treatment can be applied as an alternative to heat in dried foods for enhanced quality of foods. Application of this method will greatly enhance the food quality and benefit the food industry.
I would like to thank Department of Agriculture, Kindai University for accepting me into the Doctor course and allowing me to use their laboratories for carrying out my research.
I would also like to thank Department of Microbiology, Stamford University Bangladesh for allowing me to use the laboratory and for their continued support.
I would specially like to thank my supervisor, Prof. Sakagami, for his guidance and continued support during my course. Without him and his counsel I would not be able to complete the research. I would also like to thank him for his patience and support with the editing of papers for submitting into journals.
I would like to thank Prof. Hatcho and Prof. Hosoya for their helping on referee reading of my doctoral manuscript.
I would also like to thank Dr. Mori for helping me throughout my course and providing me with extra guidance. I really appreciate her assistance during my studies and publications.
I would like to thank for Dr. Nishioka and Dr. Shimizu for their supports on the technical fields of Low-pressure plasma treatment and Scanning electron microscopic study.
I would like to thank for many students in the laboratory of environmental chemistry.
I would also like to thank my Parents, without whom it would not have been possible for me to reach where I have. They have supported and encouraged me to try my hardest and be the best that I could, without them I would be nothing. I would also like to thank my husband, who has supported me and given me the strength to carry on with the course even when I was so far away from my family.
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