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Kinetic Dehydration for Producing Shelf-stable Summer Onion and Ginger Products

M. M. Alam
Scientific Officer
Spices Research Center, BARI, Shibganj, Bogra.

Abstract/ Executive Summary:

The experiment was conducted in the department of Food Technology and Rural Industries, BAU, Mymensingh during the period from July to November 2008 to study the drying behavior of onion and ginger using mechanical drier and development of dehydrated onion and ginger products. Three different thickness (3, 5 & 7mm slice) and three different temperatures (52⁰C, 60⁰C and 68^oC) were used in this study for onion and ginger drying. The study revealed that 3mm thick slice required the least time to dry followed by 5mm thick slice while the highest drying time was for 7mm thick slice. It was also noticeable that for reaching to a specific moisture ratio, 68^oC temperature took the least time to dry, followed by 60^oC, while the highest was required at 52^oC. Onion and ginger powder were stored in alluminium foil packet at refrigerated temperature as well as room temperature. Both powders were acceptable in refrigerated temperature and caking was observed in onion powder at room temperature up to reporting

Keywords: GINGER, KINETIC DEHYDRATION, PRODUCTS, SHELF-STABLE, SUMMER ONION.

Location: Department of Food Technology and Rural Industries, BAU, MymensinghSpices and Research Center, BARI, Shibganj, Bogra.

Start Date: 00-07-2008

End Date: 00-11-2008

Program Area: Postharvest and Agro-processing

Commodity: Ginger, Onion

Objectives:

To study about drying of onion and ginger in a suitable environment to produce good quality stable dried products.
To improve the efficiency of drying system by the analysis of the drying process.

Methodology:

The experiments of a single layer drying of onion and ginger at different thickness and various air temperatures were conducted in laboratory type mechanical dryer (Fisher, Model 438 F) at the food technology laboratory, BAU, Mymensingh. The dryer mainly consisted of a blower, heating unit, drying chamber and sample container . It was adjusted with the thermostat to control the temperature in the drying chamber. Summer onion and ginger were collected from the Spices Research Centre farm of BARI, Shibgonj, Bogra. Samples were sliced to three different thickness (3, 5 and 7mm) by sterilized slicer. Three different slice thickness (3, 5 and 7mm) of onion and ginger were selected for this study. Usually spices are being dried with in the temperature range of 60 to 85⁰C. Sliced samples were placed on the tray in a thin layer in a mechanical drier. Samples were dried until the products were reached in equilibrium moisture content. Air flow and RH were maintained constant in the drier. Dehydrated onion and ginger product were grinded in a grinding machine. This powder were packed in HDPE, Al-foil and stored at room and refrigeration temperature for shelf life study.

Source of Information: Reaerch Report, 2009. Spices Research Center, BARI, Shibganj, Bogra.

Article Link (Online Journal):

Funding Source:

1. Government

Budget: 150,000/-

Total Budget (Tk.) : 150,000/-

Achievement/Findings:

No constant rate period was observed from the drying curves. From figures and equations, it was observed that thickness had profound influence on drying time. The drying time with specific moisture ratio is proportional with sample thickness and inversely proportional with drying rate constant. This implies that at specific moisture ratio, more amount of water is evaporated per unit area for a given time from the samples with higher thickness than that of lower thickness when it is exposed to same drying temperature. On the other hand, the drying time to a specific moisture ratio is inversely proportional with drying temperature and proportional with drying rate constant. It revealed that 3mm thick slice required the least time to dry, followed by 5mm thick slice, while the highest drying time was required to dry 7mm thick onion slice. It was also noticeable that 68^oC temperature was required for least time to dry, followed by 60^oC, while highest drying time was required at 52^oC to dry onion and ginger slice. At very high temperature, drying rate may initially increase, however, ultimately resultant case hardening will reduce drying rate and product quality will deteriorate due to cooking instead of drying. High temperature also may scorch the product and thus selection of optimum temperature for drying is of significance (Islam, 1980). It has been observed that at room temperature moisture content, colour, flavour and texture of onion powder were acceptable up to two month but all these quality attributes of the ginger powder are found acceptable up to reporting when packed in alluminium foil. But in case of refrigeration temperature all the quality attributes of onion and ginger powder are found acceptable up to reporting when packed in alluminium foil.

Knowledge Management: Journal, Report/Proceedings