Spore inactivation and quality of paprika powder heated by near-infrared radiation (original) (raw)
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Journal of Food Engineering, 2008
A process to decontaminate paprika powder using variable near-infrared (IR) radiation was tested using a closed sample holder allowing water to be retained in the powder. The reduction in the concentration of Bacillus cereus spores and changes in water activity (a w ) and colour were measured during IR heating. High heat flux was applied initially to heat the powder rapidly to the desired temperature, followed by low heat flux to maintain the temperature for a given time. The water activity (a w ) value of the powder could be maintained within the bulk of the closed sample, but the surface a w value decreased during heating. Due to carotenoid sensitivity to temperature, surface and overall colour values declined, though remaining acceptable values of medium red and red, respectively. For powder with an a w value of 0.88 heated to 95-100°C, the load of B. cereus spores was reduced by 4.5 log 10 CFU/g within 6 min; the final spore concentration remained approximately 2 log 10 CFU/g due to tailing. Reducing pH to 4.0 from 4.5 did not significantly affect the reduction of the B. cereus spore concentration.
Effect of infrared heating on quality and microbial decontamination in paprika powder
Journal of Food Engineering, 2008
Infrared radiation (IR) was explored as a technique for decontaminating paprika powder. The effect of water activity (a w) and IR heat flux on paprika temperature and water loss were measured during near-or medium-IR heating. Paprika was evaluated in terms of colour, a w , natural flora, and inoculated Bacillus cereus spores. Surface temperatures were considerably higher than temperatures inside the powder, especially at low a w ; greater differences were observed with medium-than with near-IR. Surface darkening was observed, though the overall colour was not considerably affected. IR effectively removed water from paprika, especially at a w 0.5 and 0.8, resulting in unsatisfactory spore reduction. However, at a w 0.8, the load of the natural flora was reduced (P < 0.05). In a w 0.96 powder, areas with high remaining a w displayed a reduction >6 log 10 CFU/g for B. cereus (P < 0.05). In addition, no microbial counts of the natural background flora were observed in the paprika.
Frontiers in microbiology, 2015
There is currently a need in developing new decontamination technologies for spices due to limitations of existing technologies, mainly regarding their effects on spices' sensory quality. In the search of new decontamination solutions, it is of interest to compare different technologies, to provide the industry with knowledge for taking decisions concerning appropriate decontamination technologies for spices. The present study compares infrared (IR) and microwave decontamination of naturally contaminated paprika powder after adjustment of water activity to 0.88. IR respectively microwave heating was applied to quickly heat up paprika powder to 98°C, after which the paprika sample was transferred to a conventional oven set at 98°C to keep the temperature constant during a holding time up to 20 min. In the present experimental set-up microwave treatment at 98°C for 20 min resulted in a reduction of 4.8 log units of the total number of mesophilic bacteria, while the IR treatment sh...
A new high temperature short time process for microbial decontamination of seeds and food powders
Powder Technology, 2005
The process for heat treatment of seeds and food powders patented and developed by our laboratory is based on very short heat stresses (from 0.1 up to 30 s) at very high temperatures (in the range of 200 to 600 -C) followed by an instantaneous cooling due to a cold gas (À 80 -C). The decontamination of dried powders is difficult, and the difficulty correlates with the presence of a specific microflora adapted to low water content. Using this new thermal process, experiments with Bacillus subtilis spores and Saccharomyces cerevisiae cells dried on glass beads were carried out. Destruction levels obtained are in the range of 5 to 8 log according to initial water activity level. Our results showed that heat resistance of spores and vegetative cells was strongly improved for initial a w values in the range of 0.3 to 0.5. Our work also evaluated the effects of microbial distribution and powder granulometry on decontamination efficiency. The impact of heat treatment on product organoleptic qualities, notably color, has been also measured. D
Journal of Food Protection, 2005
The thermal treatment of Saccharomyces cerevisiae cells, which were homogeneously incorporated into dried wheat flour particles, was performed for various particle radii (0.8 to 1.6, 1.6 to 2.8, 2.8 to 3.2, and 5 mm) and for an initial water activity of 0.20. A new high-temperature short-time process developed by our laboratory for powder decontamination was used at 150, 200, and 250°C for 5 to 30 s, and significant destruction of up to a 6.7-log reduction, depending on treatment conditions and granule size, was achieved. This study confirms the strong influence of granulometry on the microbial destruction of homogeneously contaminated powdered products. Moreover, a thermal model was developed that takes into account the thermal properties of each component, the variations during heat treatment, and the energy required for phase change. This model provides a tool for predicting yeast destruction.
Food Science and Quality Management, 2013
Spores of Bacillus cereus, like other bacterial spores, are heat and radiation resistance causing problem in food processing because of the high temperature or irradiation dose needed to inactivate them. In this work, combination treatments of heat and irradiation were tested for their potential to reduce heat-resistance of B. cereus spores in raw milk, carrot juice and water. D T and Z-values were used to characterize heat resistance of these spores, whereas D 10-values were used to characterize radiation resistance. The results obtained indicated that D 85-values ranged from 24.9 to 35.2 min, D 90-values ranged from 7.6 to 11.6 min and D 95-values ranged from 2.4 to 4.7 min. The Z-values of B. cereus spores in the used media ranged from 9.81 to 11.24 o C. The D 10values ranged from 1.9 to 2.6 kGy. Pre-irradiation treatment at 4 kGy followed by heating reduced D 90-values 2.8 to 3.4 times. The obtained findings indicated the effectiveness of irradiation at 4 kGy followed by heating in a same process to ensure safety of raw milk or carrot juice contaminated with Bacillus cereus.
Water activity affects heat resistance of microorganisms in food powders
International Journal of Food Microbiology, 2005
To study the factors and mechanisms involved in microorganisms' death or resistance to temperature in low-water-activity environments, a previous work dealt with the viability of dried microorganisms immobilized in thin-layer on glass beads. This work is intended to check the efficiency of a rapid heating -cooling treatment to destroy microorganisms that were dried after mixing with wheat flour or skim milk. The thermoresistance of the yeast Saccharomyces cerevisiae and the bacterium Lactobacillus plantarum were studied. Heat stress was applied at two temperatures (150 or 200 jC) for treatments of one of four durations (5, 10, 20, or 30 s) and at seven levels of initial water activity (a w ) in the range 0.10 to 0.70. This new treatment achieved a microbial destruction of eight log reductions. A specific initial water activity was defined for each strain at which it was most resistant to heat treatments. On wheat flour, this initial a w value was in the range 0.30 -0.50, with maximal viability value at a w = 0.35 for L. plantarum, whatever the temperature studied, and 0.40 for S. cerevisiae. For skim milk, a variation in microbial viability was observed, with optimal resistance in the range 0.30 -0.50 for S. cerevisiae and 0.20 -0.50 for L. plantarum, with minimal destruction at a w = 0.30 whatever the heating temperature is. D
Thermal Inactivation of Microorganisms
Critical Reviews in Food Science and Nutrition, 2014
This paper serves as an overview of various aspects of thermal processing. Heat processing of foods has a long history and is still one of the most important preservation methods. To guarantee microbiological safety and stability, large safety margins are often applied in traditional heat processes. Because of the need for more fresh like foods, there is a need for milder preservation methods without compromising on safety and stability. The review deals with heat resistance data and mathematical models that describe heat inactivation. The effects of food composition are not yet fully clear and more knowledge of the cell physiology of the target microorganism could be of help in predicting the effects of food constituents. Finally, special attention has been paid to biological time temperature indicators to enable proper process calculations.
Thermal inactivation of Bacillus cereus spores in infant formula under shear conditions
Dairy Science & Technology, 2013
During production of spray-dried infant formulas, spores of Bacillus cereus have to be inactivated in order to assure product safety. The heating step which aims at the inactivation of bacterial spores can be conducted either before concentration of the product or afterwards. However, spores tend to show increased heat resistance in concentrated products. The aim of this study was therefore to determine the inactivation kinetic parameters for the inactivation of B. cereus spores in concentrated infant formula as well as in non-concentrated infant food. Spores of B. cereus IP5832 were suspended in reconstituted infant formula (10 and 50% total solids) and heat-treated at temperatures from 90 to 110°C under shearing at g & ¼ 500 s À1. Additionally, experiments at 95°C were performed in tubes without shearing in phosphate buffer and nonconcentrated infant formula. In tubes, the inactivation curves exhibited tailing. When applying heat and shear stress, linear inactivation curves were observed in both the concentrated and the non-concentrated infant formula. The kinetic parameters E a and k ref (ϑ ref =100°C) based on the employed Arrhenius model were 201 kJ.mol −1 and 0.011 s −1 and 201 kJ.mol −1 and 0.021 s −1 for the concentrated and the nonconcentrated medium, respectively. The D values in the concentrated product at the examined temperatures were twofold higher. The heat sensitivity (z value) of the spores was not altered by concentrating the medium. The data from this study can be used to design or evaluate heating processes for concentrated products aiming at the inactivation of B. cereus spores.