Killing bacteria with superheated steam by keara


									Killing bacteria
with superheated steam

For feed- and food manufac-                                  heat sensitive products because                           Nofima Ingrediens has carried out a
turers, drying in superheated                                elevated product temperature can                          series of experiments where mois­
                                                             cause damage to proteins. Nofima                          tened protein powder was dried in
steam (SHS) can offer several
                                                             recently demonstrated that protein                        SHS (300ºC) and hot air (300 ºC).
advantages as compared to                                    quality is maintained at short dry­                       To the powder was added a spore
hot air drying. Energy savings,                              ing times and can now document                            suspension of Clostridium sporo-
eliminated risk of dust explo-                               a very good effect on hygiene.                            genes, a harmless bacterium with
                                                             The drying method has therefore                           heat resistance similar to the food
sions, reduced fat oxidation
                                                             attained new actuality within the                         poisoning bacterium Clostridium
and improved odour control                                   feed and food industry.                                   perfringens. The common enteric
are examples. SHS also has the                               It is well known that the potential                       bacterium Escherichia coli was used
potential to kill microorganisms                             of heat to kill bacteria increases at                     as a surrogate for Salmonella. SHS
more efficiently than other dry-                             high moisture levels. In order to                         killed more than 99 % of the heat
                                                             obtain efficient heat kill in a dry­                      resistant spores in less than 0.5
ing gases and is therefore very                                                                                        minutes, while hot air at the same
                                                             ing process, the product should be
interesting in relation to food                              exposed to a high temperature                             temperature had negligible effect.
safety.                                                      while the water content is still high.                    The less resistant bacterium E.coli
                                                             In hot air drying the temperature in                      was rapidly killed in both drying
SHS is water vapour heated to a                              moist product will not exceed 60­70                       gases.
temperature above saturation tem­                            ºC, while in SHS it will attain the                       For further information, please
perature. When used as a drying                              saturation temperature of the dry­                        contact Halvor Nygaard,
gas, water will evaporate from the                           ing gas, i.e. 100 ºC at the pressure            ,
product and mix with the super­                              of 1 atmosphere. Hence, the killing                       dir. tel. (+47) 55 50 12 33
heated steam. Until now, the drying                          potential of SHS is bigger than air at
method has found limited use for                             the same temperature.

                           Survival of C.sporogenes     (ATCC 19404)                                             Survival of E.coli (ATCC 25922)
                           in hot air (300 C) and SHS (300 C) drying                                        in hot air (300 C) and SHS (300 C) drying

                100                                                                              100

                                                                       Hot air                                                                               Hot air
                 10                                                                               10
 Survival (%)

                                                                                  Survival (%)

                  1                                                                                1

                 0,1                                                                              0,1

                0,01                                                                             0,01
                       0           5         10         15        20                                    0          5          10          15            20

                                  Exposure time (minutes)                                                         Exposure time (minutes)

Survival of Clostridium sporogenes (spores) and Escherichia coli during drying in hot air and superheated steam (SHS).

                                                                         / Tel. +47 55 50 12 00

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