STUDIES ON EFFECT OF SLICE THICKNESS AND TEMPERATURE ON DRYING KINETICS OF KOTHIMBDA (Cucumis callosus) AND ITS STORAGE
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Date
2014-07
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jau,junagadh
Abstract
Cucumis callosus (Rottl.) Cogn (Cucurbitaceae) is very common throughout the India and commonly known as “Kothimbda” in Gujarat. It is one of minor vegetables of family cucurbltaceae which comprises of 120 genera and 825 species. Kothimbda is rich source of vitamin C (29.81mg/100gm) to human beings. The post-harvest loss of Kothimbda varies from 30 to 40 per cent due to its perishable nature. The farmers producing Kothimbda of our country are still using the traditional drying techniques for drying of Kothimbda and so far very little scientific research work has been undertaken on standardization of dehydration technology especially for Kothimbda. Appropriate size of slices and drying temperatures are good for drying and improve the appearance, colour and quality of dehydrated product. Conventional air-drying is the most frequently used dehydration operation in food. The drying kinetic is greatly affected by air conditions (air temperature, air humidity and air velocity) and material properties. The Kothimbda slice was dried in Industrial tray dryer with three levels of drying temperature (50, 60 and 70 °C) and three levels of thickness (3mm, 5mm and 7 mm). The air velocity was kept constant at 1.5 m/sec throughout the experiment. Besides mechanical drying the slices of 3, 5 and 7 mm thickness were dried in solar cabinet dryer also. The observations on reduction in weight were taken regularly with increase in time and were evaluated in terms of drying characteristics. During 50 and 60 °C drying treatment the drying rate (g/g DM-h) for 5 mm thickness slice sample was found maximum followed by 3 and 7 mm. While for 70 °C and solar drying treatment the drying rate (g/g DM-h) of 3 mm slice sample was observed maximum followed by 5 and 7 mm. Three drying models i.e. Page, Henderson and Pabis and Logarithmic were tested for their validity. The values of coefficient of determination (R2) for all the three models under all the treatments were found to be above 0.9, suggesting good fit of the observations. Though, the value of R2 under the Logarithmic Model was more followed by page and Henderson and Pabis, indicating the Logarithmic model more reliable for prediction and found best fitted. For all the drying treatments taken the value of drying constants a, k and c
Abstract
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under Logarithmic Model was varying from 0.00018 to 0.00233, 1.17 to 1.66 and -0.05244 to 0.01749 respectively The temperature and slice thickness affected significantly on the ascorbic acid content during drying of Kothimbda slice. The maximum ascorbic acid content was found in the powder prepared from slices of 7 mm thickness and dried at 50 °C/60 °C temperature followed by powder prepared from slices of 5 mm thickness and dried at 50 °C/60 °C temperature. While, the lowest in the Solar dried samples of 5 mm thickness slices. The dried Kothimbda slice obtained from the different treatments was converted in to powder of 16 mesh and stored at room temperature for 90 days in Glass bottles, Polyethylene pouches of 300 μ thickness and Aluminum coated P.P. bags. During storage observations in terms of ascorbic acid were recorded at 15 days interval. The ascorbic acid content of the stored dried Kothimbda powder was decreasing with the increase in storage period under room temperature storage. The maximum percent loss in ascorbic acid content was found in 3 mm slice followed by 7 mm. The loss in ascorbic acid during storage was minimum in the powder made from the solar dried samples followed by 70, 60 and 50 °C. The loss in ascorbic acid during storage was minimum in the powder packed in Glass bottle followed by HDPE bag and Aluminum Coated P.P. bag. Considering the analysis of observation of both drying and storage study, it was concluded that, to get good quality of Kothimbda powder and effective drying of Kothimbda slice, the Kothimbda slice of 5 mm thickness should be dried at 60 °C air temperature with air velocity of 1.5 m/sec. Moreover, to minimize the loss in ascorbic acid content of Kothimbda powder (16 mesh) during storage for 90 days at room temperature, it should be packed in Glass bottle.
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food engineering