Quality Attributes of Some Vegetables and Fruits Preserved by Sun and Oven Drying Methods
Nareman S. Eshak
Drying is one of the most appropriate techniques for producing of shelf stable food products. However, drying can result in significant loss of available bioactive compounds. This study investigated the effect two methods of drying (sun and oven) on the quality characteristics of vegetables (onions and garlic) and fruits (dates and figs). The vegetables and fruits of both types were dried by the two methods. In comparative to the fresh sample, the dried samples showed a highly significant (P˂ 0.01) difference was observed in moisture between fresh and dried vegetables and fruits. The oven dried samples had the lowest moisture. In contrast, protein, ash, crude fat, fiber and carbohydrates of fresh samples exhibit the least among the three samples in each type of vegetables and fruits. Also, the results showed a highly significant (P<0.01) difference between fresh, sun and oven dried date in potassium and slightly significant (P<0.05) in fig but no significant difference in garlic and date regarding potassium. Sodium content recorded highly significant difference (P<0.01) between the three crops (onion, date and fig) except garlic. Also, iron content the highest value revolved significant only in the oven drying. There was generally significant (P<0.01) difference between the three types in each vegetables and fruit in phosphorous. Physical evaluation showed significant differences among sun and oven drying in all samples except in onion. In this study observed the oven dried vegetables and fruits were rated lowest by the panelists in all the sensory attributes and overall acceptability. However, there was significantly difference (P<0.05 and P<0.01) between the sun and oven drying from the fresh vegetables and fruits in all the sensory attributes. Sun and oven drying have a significant effect on water absorption capacities (WAC) of dried samples except the fig. The highest value of oil absorption capacities (OAC) and swelling capacity was noticed in oven dried samples followed by the sun dried samples. All sun dried samples have low foaming properties compared with oven dried samples. The drying techniques did not significantly (P>0.05) affect the bulk density of drying samples. Dried vegetables and fruits showed low emulsion properties in which oven drying slightly improved the emulsion activity and emulsion stability over sun drying. Sun drying samples formed gel quickly at low concentration while oven dried samples formed gel at high concentration. The highest gelatinization temperature was observed for oven dried samples and the lowest for sun dried samples.
Key words: sun and oven drying, quality characteristics, WAC, OAC.