The effect of osmotic dehydration and various methods of drying pumpkin on quality and color of final product

pumpkin is a cultivar of a squash plant, most commonly of Cucurbita pepo, that is round, with smooth, slightly ribbed skin, and most often deep yellow to orange in color. The thick shell contains the seeds and pulp. It is native to North America. Pumpkins are widely grown for commercial use and are used both for food and recreation. Pumpkins with high nutritional value has many applications in food and medical industries. The color of pumpkins derives from orange carotenoid pigments, including beta-kryptoxanthin, alpha and beta carotene, all of which are pro vitamin A compounds converted to vitamin A in the body. Pumpkins are very versatile in their uses for cooking. Most parts of the pumpkin are edible, including the fleshy shell, the seeds, the leaves, and even the flowers. Pumpkin purée is sometimes prepared and frozen for later use. The dried pumpkin can be stored for a long period of time due to low activities of microorganisms and enzymes resulting from lower water activities in the final dehydrated products compared to fresh once. This leads to high shelf life which contributes to food security. Pre-drying treatments like dipping in salt and sugar solutions could also be used to improve quality. Pre-drying treatments could be used to preserve color and flavor, minimize nutrient loss, stop decomposition enzyme action and ensure more even drying and to extend storage the shelf life of pumpkin. Similarly, the osmotic dehydration is carried out to improve food quality by inactivating enzymes, reducing microorganisms and preserve the natural color when pumpkin after osmotic dehydration is subjected to drying. In osmotic dehydration, by immersion in a high pressure solution, the water flows out of the cell membranes of the product, then flows into the intercellular spaces and finally reaches the solution. The purpose of this research was to evaluate the effects of pre-drying treatments and methods of drying on some chemical qualities of pumpkin fruit and produce dried pieces of pumpkin for direct consumption or addition to other products for enrichment. The required pumpkin fruits in this study was prepared from Mashhad in fall season. The fruits were completely healthy due to their apparent, texture and microbial properties. The fruits were washed, peeled and cut into uniform cubes of 1 cm. The fiber and seed were scraped off. then, soluble solids, color parameters (L* a* b*), pH, acidity, wet matter, reducing sugar of fresh pumpkin were measured. In this study, there were 2 osmotic solutions, salt solution (3, 6 and 9 percent) and sugar solution (40, 50 and 60 percent). pumpkin slices were weighed and then dipped in the salt and sugar solutions for 45 minutes for osmotic dehydration separately. Finally, the slices were drained well and spread for drying using three drying conditions. they dried in lab drier with hot air, in sun and shade. Drying slices was continued until the moisture content of the samples reached 15%. Rehydration, firmness and color parameters of dried pumpkin slices were measured. The statistical model used was factorial experiment based on a completely randomized design. The experiments were performed in 3 replications and data analysis and comparison of means were done in Duncan test using Mini Tab software. Two kinds of salt and sugar osmotic solutions were used to increase the drying speed of the pumpkin samples. Among salt solutions, 9% solution of salt resulted in the production of better color in pumpkin samples, but the texture of the samples was stiffer. among different concentrations of sugar solutions, 40% solution created more suitable color and texture in
dried samples than other solutions. The texture stiffness of the pumpkin slices that were pre-processed with sugar solutions were higher than those pre-treated with salt solution, but they were better in color. Since the dried samples pumpkin are exposed to heat during use, the stiffness of the tissue is eliminated. Among the different methods of drying the pieces of pumpkin, drying in the shade due to the lack of electric energy had economic justification. Also drying in the shade, had the least adverse effect on sample pigment destruction. The concentration of sugar solution in pretreating of pumpkin samples for drying, for creating desirable color and texture, was determined 40%. Drying of pumpkin in shade, because of remaining the color and economic reasons, was approved.