Quality of paprika powder during heating by infrared radiation
Special Symposium - Innovations in Food Technology (LMC Congress)
Innovations in Food Technology - Poster Session (LMC/Food - P1)
Keywords: Infrared radiation; Water activity; Paprika powder; Colour; Bacillus cereus spores
Herbs and spices are a large group concerning powdered foods. Despite their contribution to taste, colour and odour in foods, they are also known to be a large source of food spoilage, due to their high microbial contamination caused by poor sanitary conditions during growing, harvest and processing. One of the most frequently found spore-forming bacteria concerning spices is Bacillus cereus. It is important to decontaminate food powders efficiently, especially when the powder will be added to a product with high water content. However, the decontamination of dried powders is difficult, and the difficulty correlates with the presence of a spore-forming microflora adapted to low water content as well as the high thermal resistance of microorganisms in dry systems.
In this work, infrared radiation (IR) was explored as a technique for decontamination of paprika powder. Infrared is a part of the electromagnetic optical spectrum (wavelength 0.76-1000 µm), that causes heating on surfaces. The advantage of IR is the fast heating, as energy is transferred by radiation from the heater to the food by no heating of air between heater and food.
Paprika powder having water activities (aw) of 0.5, 0.8 or 0.96 was exposed to infrared heat treatments with constant heat flux (near-IR at 11 and 25 kW/m2, medium-IR at 5 and 11 kW/m2). The effect of IR on paprika was evaluated in terms of temperature distribution, colour, water activity, and reduction of bacterial spores. Temperature was measured in four different locations (on surface, and in depths of 1, 3 and 8mm) throughout a 10 mm powder bed. Thermal inactivation in paprika powder was studied for the natural background flora and for inoculated spores of Bacillus cereus.
The temperature distribution in paprika powder during the infrared treatment is affected by the water activity, the infrared heat flux and the wavelength. Higher the heat flux higher the surface temperature and higher the temperature difference between the surface and the inside of the powder. Water activity of 0.96 showed lower surface temperature and longer heating time, but a more uniform temperature distribution. Due to the higher surface temperatures, changes of colour and water activity were observed on the surface. However, the overall colour and water activity were not significant affected.
Decontamination of Bacillus cereus was not very effective for infrared heating at high heat fluxes and lower water activities (aw of 0.5 and 0.8), due to surface overheating and increased microbial thermal resistance. At aw of 0.96, total reduction of Bacillus cereus spores was observed in the inside of the powder (detection limit at 1 log10 CFU/g) , but the overall sample showed only a reduction of 1.5-2 log10 CFU/g, due to high viable counts on the surface. For the natural background flora, at aw 0.80 reduction of up to 2 log10 CFU/g was observed, while no remaining viable counts were observed for the whole sample at aw of 0.96.Wetting of powder is therefore necessary to achieve significant microbial reduction.
Presented Wednesday 19, 13:30 to 15:00, in session Innovations in Food Technology - Poster Session (LMC/Food - P1).
