Food-borne illnesses continues to have an adverse affect on the health of the society as a whole, therefore, studying safe, cheap and effective methods of decontamination of foods have become imperative. Current study assessed the effectiveness of heat and low-pressure plasma treatment for the decontamination of dried, semi-dried and raw foods. These methods will help to produce foods that are free of microorganisms and free of any harmful residues. Heat, currently being assessed, is a conventional method that is easily reproducible, in the resource poor settings of a Bangladesh whereas low-pressure plasma is an eco friendly method whose application in the food industry has not yet been explored.
Growth reductions were observed in all samples subjected to heat treatments, with raw foods exhibiting elevated log reduction numbers. This can be attributed to the low water activity of spices and herbs, these conditions do not favor the growth of vegetative bacteria but do support the growth of spore forming bacteria, which may not be affected by heat treatments (Eliasson et al., 2015). Among semi-dried and dried foods, powdered spices demonstrated lower log reductions. All raw foods demonstrated similar log reductions.
Previous studies, by Lurie et al. (1998), have suggested that heat is more effective in eliminating the growth of fungus, which is supported by the current study, where average fungal reduction were significantly higher for raw foods and slightly higher in dried and semi dried foods, when compared to that of bacterial reduction. Heat was successful in completely halting the growth of microorganisms in 3 dried and semi-dried food samples and 4 raw samples demonstrated a halt in bacterial growth. Interestingly, in the case of log reduction of fungal counts in raw foods demonstrated many samples with absolute growth reductions.
Previous studies by Border and Rice-Spearman (1999) were able to observe complete halt in growth after 30 seconds when directly heating bacterial cultures.
Benefits of heat include increased storage life, yet there are factors to consider, such as heat tolerance limit and the temperature and time required to to decontaminate while
avoiding damage (Paul and Chen, 2000; Piyasena et al., 2003). Although studies have suggested the possible loss of quality as a result of heat treatments, it still follows the ideal treatment guidelines, as it leaves no residue (Matser et al., 2004; Selcuka et al., 2008). Heat has long been used to decontaminate milk, with sufficient historic data proving its role reducing the incidence of food-borne and water-borne illnesses associated with raw milk from a previous 25% to 1% currently (Claeys et al., 2013). Aside from loss of nutrients some other reported disadvantages may include decrease in seed germination (Selcuka et al., 2008).
Plasma treatments act by breaking down the whole cell, inactivating them or making them unculturable (Cappellas et al., 2000; Selcuka et al., 2011). This can be seen in the images produced by the scanning electron microscopy from the validation study (Fig. 4 and Fig. 5) demonstrating the breakdown of Staphylococcus spp. and Bacillus spp. after treatment.
The treatments have expressed a log reduction of bacterial growth between 2.37 and 5.75 and a fungal log reduction of 2.15 to 5.91. The log reductions were almost 6.00, hence plasma was able to nearly eliminate the growth of microorganisms. It has even shown complete elimination of microbes and fungus after treatments of 20 to 40 minutes in some samples.
Previous studies by Nishioka et al. (2014) showed a 97% decrease in fungal growth in seeds, while Selcuka et al. (2011) saw a 3 log reduction in fungal growth. These results were similar to our findings. It is to be noticed that most previous studies have not focused on the growth reductions of bacteria, after treatment. The current study will provide vital information on the effects of low-pressure plasma on bacterial and fungal growth in foods.
The purpose of examining the effects of low-pressure plasma treatment on foods was to begin studies into its implementation in the food industry. Various reviews have contemplated its effectiveness but none have quantified them, which was an objective of the current study. This study has observed higher log reductions in low-pressure plasma in comparison to heat. Plasma treatments are applied in a gas form which spreads uniformly and
inactivate organisms (Selcuka et al., 2011). The bacterial log reduction after plasma treatment was 4.87 more than that of heat for chilli powder and 5.76 more for ginger powder.
Differences of this nature were observed in all results. Low-pressure plasma treatments have not been associated with any of the side effects that heat possesses such as poor quality of food after the treatment, lengthy processing time and reduction in seed germination (Selcuka et al., 2008; Matser et al., 2004; Nishioka et al., 2014). In the current study, significant results of heat reduction were observed after 1 or 2- hours of treatment, where as low-pressure plasma began to show its effects after 10 to 20 minutes of treatment, therefore use of the latter would sufficiently reduce treatment time during production. Studies by Nishioka et al. (2014) and Selcuka et al. (2011) have shown, that low-pressure had no effects on the quality of sample being tested, and as mentioned before, it is also cost effective.
Air quality of the sampling area was also assessed and enormous bacterial and fungal counts were observed and reported in the previous chapter. To maintain decontamination, steps must be taken to stop future contamination from the environment after treatment. This can be achieved with the help of the government authorities such as Bangladesh Food Safety Authority (BFSA), Ministry of Food and Ministry of Health and Family Welfare. Along with taking steps in education and restructuring, authorities must also carry out frequent inspections of vendors, markets and production companies maintain the food quality (Adams and Moss, Food Microbiology). Inspection points should include personnel, environment, product and equipment. In order to maintain decontamination, actions need to be taken by a combined group of individuals from different ministries and testing institutions. In the past government actions have failed because of the lack of unity between the departments (Siddiqui, 2014). They need to work together to create a system which will work on both open markets and food companies. There are already rules in place to ensure food safety by the Ministry of Health and Family Welfare, Bangladesh Standards and Testing Institution
(BSTI) (Ministry of Information) and Ministry of Commerce (Islam and Hoque, 2013; Islam et al., 2015). Strict enforcement of the punishments mentioned in these laws are required.
The interest in safe, healthy and non-toxic methods of decontamination of foods has increased in recent times. This has contributed to increased research in other decontamination methods. Heat treatments were effective against bacterial and fungal growth, therefore there use in the agricultural and food industry will positively impact the health of the society.
Additionally, heat can be accessed at any point, and it will be inexpensive to carry out this treatment. Still, alternative effects with minimal use of chemicals, radiation and minimal effect on nutritional quality must be researched for the advancement of the food industry. Use of low-pressure plasma treatments in the food industry, will produce foods free of microorganism, with no harsh residues or compromised quality and nutritional value.
Therefore, its implementation in the food industry in the decontamination of dried foods would lead to the enhanced quality of foods.