A Study on drying characteristics of grape and Kahramanmaraş

ABSTRACT Turkey has a high potential of fruit and vegetables production. Crops, mainly grape end red pepper are important export items as well as in national market However, problems encountered during drying of these foodstuffs, in particular to quality retention, have not been resolved yet. Therefore, drying which is the most essential process for obtaining a good product quality is chosen as the main focus of this research. Traditionaly, in Turkey grapes and peppers are dehydrated in open atmosphere by exposing them to the sun shine, and this process usually takes 7-8 days. During this time, the products may get contamined due to soil, sand particles and other matters exist in drying environment. In this study, our aim to improve the quality of grapes and peppers by using hot air and various pretreating solutions. Therefore, drying characteristics of both products are studied. For seedless grapes and red peppers, drying experiments were carried out in a drier obtained from API ( PASILAC Inc. We used potassium carbonate and alkali emulsion of ethyl oleate (AEEO) for pretreatment of grapes prior to drying. Grapes, then, are dried with air at different temperatures (50, 55, 60 and 70°C). We also dried grapes with air at 60 and 70°C without pretreatment with any solution in order to compare the drying time. It is observed that grapes pretreated with AEEO solution got dried faster than the grapes pretreated with potassium carbonate, and the ones dried naturally. Colour analysis of grapes showed that the best results are obtained in grapes which were pretreated with AEEO and dried with air at 60°C. In peppers drying experiments, red peppers grown in Kahramanmaraş region are used. In this experiments, solution of AEEO pretreatment was used, firstly. In order to determine the effect of the composition of pretreating solution, various solutions were prepared and used. Among these solutions, 2% AEEO + 5% K2CO3 solution has led to the fastest drying rate. Peppers pretreated with various solutions are dried with air at 50, 55, 60 and 70°C. A better quality is obtained at lower air temperatures but with longerdrying time. Peppers are also dried without pretreatment (i.e. naturally). Pretreated peppers got dried fester than the ones dried naturally. Peppers pretreated with 2% AEEO + 5% K2C03 solution are first dried with air 70°C for 4 hours (time to reach critical moisture content) and then with cooler air at 50°C in order to see the effect of gradual drying. In another experiment, same starting conditions are maintained but in the second step air at 55°C is utilized. Peppers are also sliced into 1 cm in length. These peppers are dried at 60°C: 1- naturally, 2- by pretreating with 2% AEEO + 5% K2CO3 solution. Colour analysis showed that red color is preserved better in peppers pretreated with AEEO solution than those dried naturally. In sliced peppers similar results are obtained. This study showed that AEEO solution helps to preserve and condition both the quality and appearance of the grapes and peppers. Wax layer on grapes and peppers are destructed by AEEO leading to diffusion of water towards the surface of the product easily. Consequently, the quality of the product and the performance of the drier are increased using AEEO. From the data obtained, drying curves of grapes and peppers are plotted using Page and Exponential equations. Coefficients of determination (r2) of these equations are also given, r2 of Page equation is higher than r2 of Exponential equation.