Sterilization of instruments in solar ovens.

AIMS: The sterilization of instruments in rural health clinics in less developed countries is an increasing problem as chemical methods can no longer be recommended and fuel wood is becoming increasingly scarce. It seems obvious, therefore, to utilize solar energy for sterilization purposes. METHODS AND RESULTS: A solar oven was designed and manufactured using local materials and simple tools. It was tested by physical, chemical and microbiological methods and, after successful testing, installed in a rural clinic. The oven was able to generate temperatures above 180 degrees C. On days with direct sunlight the oven fulfilled the international recommendations for hot air sterilization. The chemical indicators, Browne's tubes type 3 and 5, also changed colour. It was difficult to reach the right value for the sterilization effect during months with a low sun position. A moveable oven, or two ovens, must be installed to solve this problem. CONCLUSIONS: The solar oven has proven to be a realistic method for the sterilization of instruments. SIGNIFICANCE AND IMPACT OF THE STUDY: The solar oven is easy to make and use. It saves fuel and can be used in most tropical areas.

Decontamination of drinking water by direct heating in solar panels.

A device was developed for direct heating of water by solar radiation in a flow-through system of copper pipes. An adjustable thermostat valve prevents water below the chosen temperature from being withdrawn. The results show that it is possible to eliminate coliform and thermotolerant coliform bacteria from naturally contaminated river water by heating to temperatures of 65 degrees C or above. Artificial additions of Salmonella typhimurium, Streptococcus faecalis and Escherichia coli to contaminated river water were also inactivated after heating to 65 degrees C and above. The total viable count could be reduced by a factor of 1000. The heat-resistant bacteria isolated from the Mlalakuva River (Tanzania) were spore-forming bacteria which exhibited greater heat resistance than commonly used test bacteria originating from countries with colder climates. To provide a good safety margin it is recommended that an outlet water temperature of 75 degrees C be used. At that temperature the daily production was about 501 of decontaminated water per m2 of solar panel, an amount that could be doubled by using a heat exchanger to recycle the heat.

Microbiological screening method for indication of irradiation of spices and herbs: a BCR collaborative study.

A BCR1 collaborative study was conducted with a microbiological screening method based on the combined use of the direct epifluorescent filter technique (DEFT) and the conventional aerobic plate count method (APC) for detection of irradiation of spices and herbs. Collaborative samples of whole allspice, whole and powdered black peppers, whole white pepper, paprika powder, cut basil, cut marjoram, and crushed cardamom irradiated with doses of 0, 5, and 10 kGy were analyzed by 8 laboratories. The total number of the collaborative samples, with arbitrarily labeled codes, was 192. The percentage of acceptable results was 95.5%. The identification of irradiated from nonirradiated spices and herbs was analyzed statistically by using explorative techniques. The average values of the differences between DEFT and APC in samples irradiated with doses of 5 and 10 kGy were 5.1 and 6.1 logarithmic units, respectively. The differences between DEFT and APC generally increased to at least 3.5 logarithmic units, whereas the difference in the case of unirradiated spices was insignificant. However, conclusive evidence of irradiation relies on the knowledge that the sample was not fumigated or heat treated. The reproducibility relative standard deviations for the differences were 12.3, 19.9, and 20.7% with the doses of 10 and 5 kGy and for unirradiated samples, respectively, indicating acceptable variabilities among laboratories.