Date of Award

2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Dr. Isam Eldin Hashim

Second Advisor

Dr. Alaa AI-Bakir

Third Advisor

Dr. Adam Aboubacar

Abstract

Methyl bromide is a highly effective fumigant to control infestation of dates by insects such as saw-toothed grain beetle, Oryzaephilus surinamensis. The use of methyl bromide will be phased out by 2015 due its adverse effects on Ozone layer. Therefore, environmentally friendly and cost-effective alternatives for controlling insects in dates during storage are needed. Such a treatment should not degrade quality of dates.

The objective of this study was to investigate the effectiveness of conventional heating, freezing, and microwave heating as alternatives to methyl bromide fumigation and to determine the effect of these treatments on date’s quality. Date samples were heated using a conventional oven at 55, 60 and 65°C for 5, 15 and 30 minutes. They were frozen using a home freezer at -18, -25 and -30°C for 5, 15 and 30 minutes. They were heated in a home microwave oven for various times at different power settings. After these treatments, their texture, color, moisture, water activity, sugar composition and sensory properties were evaluated.

The heating treatment for 5 min was effective at all temperatures (55, 60 and 65°C) tested. The shortest effective heating treatment (55°C for 5 min) did not affect the texture and sensory quality of the dates. Moisture content, water activity and sugar composition were not affected by any of the heat treatments. The lightness of date samples were increased with heating time and temperature. Heat treatments also increased redness and yellowness. Even the mildest heat treatment affected the instrumental color properties significantly.

Freezing treatment for 5 min was not 100% effective at any of the freezing temperature used. Adult insects were eliminated; however, all larvae were not killed. Freezing treatment at -18°C was not effective for any time period tested. The highest effective temperature was -25 °C which needed at least 15 min to eliminate both adult insects and larvae. Freezing at -30°C for at least 15 minutes also resulted in 100% mortality. Freezing caused a lighter yellow color affecting sensory color perception. The b value of treated samples decreased which indicated a decrease in yellowness. Water activity was increased as a result of freezing treatment. Texture parameters and moisture were not significantly affected by freezing.

For the microwave treatment, as the power level was increased mortality was increased. However, none of the treatments applied resulted in complete disinfestation. Dates vacuum packed, sealed and immersed in hot water and heated by pulsed heating for a total time of 110 s provided 100% mortality.

It can be concluded from this study that conventional heating, freezing and microwave heating can be used for controlling insect infestation in dates. Heat treatment at 55°C was determined as the best treatment that effectively disinfests without causing a significant change in the quality of dates. However, long term storage studies should be performed to make sure that heating does not cause any adverse effects on quality which will become noticeable during long term storage.

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