the flouris thrownby centrifugal forcebetween two flat steeldiscsor platesthat
revolve on a central shaftat veryhighspeed. Small, round,hardenedsteelposts
are closelyspaced in two concentricringsbetween the two discs.The impactof
the flour againstthe revolvingdiscsand posts and againstthe housing of the
machinemeansthat all stages of insectsand mites,including eggs,that maybe
in the flour are killed.The treated flourpasses out througha spoutat the baseof
the machine.
Heat treatment
Heat treatmentis oftenusedin the sterilization of grainsand driedfruitto free
themof insects. Manyof the driedproduct infesterscan be killed if the products
are exposed to temperaturesof 55 and 60 ÎC, for 1 hourdepending on the insect
and stage. However,difficultiesin attainingthesetemperaturesin insulated
grainmasslimitthe use of this technique.
Freezing
Withcertain typesof infesters freezing for longperiodsof timecan also help kill
all stagesof insectdevelopment. Withcertaincommodities (verylow moisture)
holding the productatˇ18 ÎC or below for 14 dayswill kill eggs,larvae, and
adults. It is critical thatˇ18 ÎC be achievedand that the material be heldfor the
full 14 days.
Aeration and refrigeration
Aeration is the process of cooling the commodities with ambient air.
Refrigeration involvespassing ambient air through refrigerationsystem to
lowerits temperature,beforeit is blownthroughthe grain.The purpose is to
prevent moisture migration,retardthe development of insectinfestation and
prevent biological deterioration of the commodities.
Ionizingradiation
This provideschemicalresiduefree process to disinfestcommoditiesof live
insects. The sensitivityof the various live organismsto ionizingradiationis
varied. For example,insects are about a hundred times more resistant to
radiation than humans. The sensitivityof insects to gamma rays variesaccording
to the speciesand stageof development. The egg stageis more sensitive than
larvaeand adults. Thereis a dosagelimitationof 10 kGyof gammaradiation in
food.Thecommonuse of radiationis to preventsproutingof potatoesand
onions and the controlof microbial infections of spices and meat.
The disadvantagesof this methodare:
∑ economically,it is an expensivemethod;
∑ the difficultiesin transferringthe commodity to the radiationarea;
∑ proofthat no chemical changes occurred in the commodity afterradiation;
∑ the acceptanceof the radiatedcommodity by the consumer.
422 Handbookof hygiene controlin the foodindustry