Dry-roasting and pasteurisation of nuts using infrared heating
- How does it work?
- What can it be used for?
- What can it not be used for?
- Related Facilities
- Further Information
|Key words||Roasting, hot air roasting, infrared, pasteurization, Salmonella, almond, nut|
How does it work?
|Primary objective||To reduce processing time during dry-roasting and to meet pasteurisation requirements.|
|Working principle|| The processing efficiency and the microbial safety during dry-roasting of nuts can be improved using infrared (IR) heating. IR can be installed in front of a traditional hot air roasting equipment to accelerate the initial heating period, thus reducing processing time; the roasting can then be continued with hot air. This could provide up to 62% time reduction depending on which roasting temperature used (2). Also, this method meets a 4-log reduction of microorganisms at roasting temperatures of 130, 140 and 150˚C, when tested on medium roasted almonds (1, 2). Due to high energy transfer rates by IR heating, the pasteurisation temperatures are rapidly reached and the product is only exposed to high temperatures for a short time. In addition, no significant difference is observed in sensory quality of medium roasted nuts when IR is used in combination with hot air processing (2).|
|Additional effects||Reduced processing costs and energy usage due to the time reduction. The through put of the equipment could also be increased as the processing time is shorter.|
|Important process parameters|| Control of IR intensity due to the risk of overheating owing to the rapid heating rates (4).
Temperature control: in general, too high temperatures are not favoured by the industry because it might reduce the quality of the roasted product. IR absorption influences the heating efficiency.
|Important product parameters||The water activity (aw) of the product, since a reduction in aw increases the heat resistance of microbial cells (2,4).|
What can it be used for?
|Products|| This method has been evaluated for almonds but should be applicable for roasting of other nuts as well.
Could possibly be used for roasting of other products as well e.g. coffee beans; however this needs to be tested.
|Operations||Dry-roasting and pasteurisation.|
|Solutions for short comings||The technology can complement traditional roasting processes to shorten the processing time. The method could also be used for pasteurisation.|
What can it NOT be used for?
|Other limitations||Dry-roasting with only IR (not in combination with hot air processing) will result in a lower reduction of microorganisms (2).|
|Risks or hazards|| Observe safety regulations when using IR ovens.
Peanut dry roasting could lead to the increase in its allergenicity. Overheating of products containing reducing sugars and asparagine can lead to formation of Maillard reaction products such as acrylamide which is a carcinogenic compound.
|Maturity|| Appropriate processing parameters for roasting of other nuts need to be tested.
Possible equipment already exists, only processing parameters need to be defined. An industrial-scale infrared pasteurisation method has been developed by G. Bingal et al. for raw almonds (1).
|Modularity /Implementation||IR heaters can be installed in front of a regular roasting process in the existing production line.|
|Consumer aspects||Consumers will probably accept this non-chemical technology to increase the safety of the almond consumption. In California 2008 an outbreak of salmonellosis was associated with raw almonds and therefore the nuts must be treated to achieve pasteurisation needs.|
|Legal aspects||Please check local legislation.|
|Environmental aspects||This combined roasting method is an energy saving process.|
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|References|| 1. Bingol, G., et al. (2011) Infrared pasteurization of raw almonds Journal of food Engineering 104, 387–393.
2. Yang, J., Bingol, G., Pan, Z., Brandel, M. T., McHugh, T. H., Wang, H. (2010) Infrared heating for dry-roasting and pasteurization of almonds. Journal of Food Engineering, 101, 273-280.
3. Uysal, N., Sumunu, G., Sahin, S. (2009) Optimization of microwave-infrared roasting of hazelnut. Journal of Food Engineering, 90, 255-261.
4. Staack, N. (2008) Potential of infrared heating as a method for decontaminating food powder, Doctorial thesis (Dr.-Ing.), Berlin University of Technology
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