HUSSAIN TANVEER ROLL # 28 WAHEED IKRAM ROLL # 33 BSc(Hons) Food Science and Technology 8 th Semester (Regular)

 Introduction  History  Why VHT system was developed  Principle of VHT  Three effective methods of VHT system  Features of differential pressure treatment system  Comparison

 Pre storage treatment of fruits and vegetables  Those treatments given to the commodity, after harvesting to reduce post harvest losses, enhance storage life and quality  Other examples of pre storage treatments are Cleaning Packing Washing Curing Sorting Pre cooling Grading Chemical treatment Waxing Vapor heat treatment

Adopted as a quarantine measure in 1929 when Mediterranean fruit fly invaded into the state of Florida VHT emerged in Japanese plant quarantine in 1969 Revived as non hazardous tool of disinfection VHT has been carried out for many years without any problem for many years Most outstanding innovation in VHT was development of differential pressure treatment

 Treatment system of this type uses differential pressure to induce efficient circulation of vapor heat through all spaces in-between fruits so that every each individual fruit is always evenly and uniformly exposed to vapor heat atmosphere  At present all the fruits being imported to Japan on the condition of VHT, are processed with differential pressure type treatment system

 VHT has been carried out successfully without any problem for many years  An accident arose in 2002, when live larvae of oriental fruit fly were detected on the treated papaya shipments from the Philippines  Investigation for the cause reveled that the owner of the facilities had neglected manufacturers maintenance  It is considered that improper maintenance seriously downgraded the performances of facilities to give rise to cold spots in the treated fruits and led to survival of fruit fly

 To Control the infections of fruit flies in fruits  Like mango, papaya, mangosteen, lychee, guava, etc.  Treatment consists of stacking the fruits in boxes in a room which is heated and humidified by injection of steam  Temperature and exposure time may be adjusted depending upon the stage at which the fly is to be killed i.e. egg, larvae, pupae, adult

 The most difficult stage to control by VHT is larval stage as the insect goes further into the fruit and away from the surface, thus requiring high temperatures for short time  Generally treatment of citrus, papaya, mango and pineapple may be given at 43◦C in saturated air for 8hrs followed by maintaining the temperature for further 6hrs

DIFFERENTIAL PRESSURE METHOD Panel Type facilities Container type facilities BLOW IN METHOD HORIZONTAL AIR STREAM METHOD

PANEL TYPE FACILITIES In the interior of treating chamber, plastic food containers with perforated bottom are stacked onto a pallet up to several layers Forming a chimney shaped processing space CONTAINER TYPE FACILITIES Plastic containers of similar standards are stacked onto a pallet up to several layers Forming a chimney shaped processing unit

PANEL TYPE FACILITIES Chimney is covered with a bell shaped hook having an axial fan on top By running axial fan the chimney turns into diff. pressure unit Panel type system consists of plural number of diff. pressure units accommodated in panelized treatment chamber CONTAINER TYPE FACILITIES Plural number of this unit are set in one containerized treatment chamber By operating plural fans, temperature and humidity controlled air envelops all the fruits in each unit, in one treatment chamber

PANEL TYPE FACILITIES Provided with temperature and humidity conditioned air by forced circulation 1 unit load of fruits involves 24 containers About 530kg of average sized mango can be treated per unit CONTAINER TYPE FACILITIES All the interior of one containerized chamber turns into diff. pressure unit 1 unit load of fruits involves 36 containers About 460kg average sized mango can be treated per unit

 Used until the late 1960s  Fruit loaded wooden boxes are stacked onto a pallet up to several layers  Wooden box is designed to allow for aeration through openings at the bottom and spaces between side crosspieces  Two holes for handling the box on opposite side frames serves for aeration as well

 Temperature and humidity conditioned vapor heat is continuously blown into the fruit loaded boxes by fans from the ceiling and the side wall positions  Course of air stream is not restrained  Most of the blown air flows through the less air resistant space outside of wooden boxes  Relatively small portion flows into the air resistant interior of the wooden boxes  Short exposure treatment differ in the run up of fruit temperature arises, depends upon the laid position of treated fruits

 Improved version of blow-in type treatment method  In which the original defect has been alleviated to a considerable extent  It features multi layered treating shelves which are interspaced liked the rearing shelves of silkworm used in sericulture  All the fruits laid in one layer in the shelf are designed for exposure to horizontal air streams

 Air passes mostly on the upper surface of laid fruits and also partly on the lower surface through openings, underneath the fruit layer  Fruit contact with vapor heat is better than that of blow-in type treatment and gets closer to that of differential method treatment  Because the course of air stream is not fully restrained, the basic problem remains that more air flows over top surface of treated fruits  Flow is much less in the air resistant space like contact points between fruits and lower side of fruit layer

 First feature is forced circulation of air by differential pressure  Second feature of this system lies in container for holding fruits for the treatment  Third feature is possibility of quick run up treatment  Forth feature is scarce irregularity in run up of fruit temperature  Fifth feature is quick post treatment cooling  Container for treatment can also serve as container for transport