Blackberry (Rubus sp.) fruits are rich in phenolics (flavanols, anthocyanins, procyanidins, and chlorogenic acid), which are compounds that are highly active and have several health benefits; therefore, they are mostly used as dietary antioxidants (Moure et al., 2001; Reáteguia et al., 2014). Blackberries are mainly used as frozen, dried, or canned foodstuffs. Fruits are also processed into juice, jam, or jelly. Such processes prolong the storage duration and shelf life of these products (Rickman et al., 2007). Drying, which is the oldest method of preservation for various fruits, involves the process of reducing the moisture content or water activity of the fruits. The final quality is designated by the method of drying, the moisture level of the final product, packaging (regular or modified atmosphere packaging), and storage duration and conditions (Wu et al., 2010). In Turkey, there is an increasing demand for functional foods, especially for blackberries, because of the bioactive substance composition of these fruits.
Much of the weight of fresh fruit comes from its water content. Therefore, blackberry fruits have greater metabolic activity than other functional foodstuffs. Such metabolic activity, especially ethylene synthesis, continues after the harvest of the fruits, thus leading to their perishing and loss of flesh firmness within a short storage time (Atungulu et al., 2004). Therefore, the moisture content of fruits is reduced to prevent the growth and development of microorganisms, thereby prolonging storage duration and shelf life of the final products.
Drying is the basic process used to reduce moisture levels of the fruits; however, sun-drying is a difficult process because of undesired changes in weather that can occur and lead to differences in quality attributes of the final product (Maskan, 2000). The primary goal of drying is to reduce the moisture level of agricultural products to a certain extent to minimize ongoing reactions and prevent microbial deterioration (Krokida and Marinos-Kouris, 2003).
The primary goal of commercial blackberry producers is to obtain high-quality dried fruits by using different methods of drying. The method used for drying significantly influences the quality attributes of the final product. Sun-drying is the most common method used for drying blackberries. The sun-drying process takes longer than mechanical drying, and it involves the product being exposed to various contaminants, pests, and disease agents, such as dust, birds, rodents, and microorganisms. Such contaminants may result in significant reductions in the quality of the final product. Therefore, mechanical drying, especially hot-air-drying, is used to overcome the apparent problems of sun-drying. Hot-air-drying can be used reliably for blackberry drying in large quantities and shorter periods without any negative impacts on the final product quality because the method does not rely on weather conditions and the products are not exposed to external factors (Tunde-Akintunde et al., 2005).
The drying characteristics of biological materials should be well-comprehended to achieve the best results. A literature review revealed that there have been no studies of the drying characteristics of blackberry fruits or drying systems for blackberries. Therefore, the present study was designed to determine the drying characteristics of blackberry fruits. A convective hot-air dryer was used to calculate effective diffusivity, and the activation energy of the fruits and available models were used to fit the experimental data and identify the best model for representing the dry characteristics of blackberry fruits.
AgrawalY.C.SinghR.D.1977Thin layer drying studies on short grain rice. ASAE Paper No: 3531 ASAE St. Joseph MI
AOAC1990Official method of analysis. Association of Official Analytical Chemists (No. 934.06) Washington DC
AtunguluG.NishiyamaY.KoideS.2004Electrode configuration and polarity effects on physiochemical properties of electric field treated apples post-harvestBiosyst. Eng.87315461550
CrankJ.1975Mathematics of Diffusions. 2nd ed. Oxford University Press London
HendersonS.M.1974Progress in developing the thin-layer drying equation. Transactions of the ASAE 17:1167–1168/1172
LahsasniS.KouhilaM.MahrouzM.IdlimamA.JamaliA.2004Thin layer convective solar drying and mathematical modelling of prickly pear peel (Opuntia ficus indica)Energy29215461550
MartinM.B.S.MateJ.I.FernandezT.VirsedaP.2001Modelling adsorption equilibrium moisture characteristics of rough riceDry. Technol.193&415461550
MoureA.CruzJ.M.FrancoD.DomıìnguezJ.M.SineiroJ.DomıìnguezH.José NúñezM.A.ParajóJ.C.2001Natural antioxidants from residual sourcesFood Chem.72215461550
ReáteguiaJ.L.P.MachadoA.P.F.BarberoG.F.RezendeC.A.MartínezJ.2014Extraction of antioxidant compounds from blackberry (Rubus sp.) bagasse using supercritical CO2 assisted by ultrasoundJ. Supercrit. Fluids94223233
RickmanJ.C.BarrettD.M.BruhnC.M.2007Review: Nutritional comparison of fresh, frozen and canned fruits and vegetables. Part 1. Vitamins C and B and phenolic compoundsJ. Sci. Food Agr.87930944
SacilikK.YurtluY.B.UnalH.G.2010Thin layer convective drying and mathematical modeling of einkorn. Conference Proceedings—4th International Conference TAE 2010: Trends in Agricultural Engineering Prague; Czech Republic; 7-10 Sept. 2010 p. 540–548
Tunde-AkintundeT.Y.AfolabiT.J.AkintundeB.O.2005Influence of drying methods on drying of bell-pepper (Capsicum annuum)J. Food Eng.68415461550
WuR.FreiB.KennedyJ.A.ZhaoY.2010Effects of refrigerated storage and processing technologies on the bioactive compounds and antioxidant capacities of ‘Marion’ and ‘Evergreen’ blackberriesLebensm. Wiss. Technol.43815461550
YagciogluA.DegirmenciogluA.CagatayF.1999Drying characteristics of laurel leaves under different drying conditions. In Proceedings of the 7th International Congress on Agricultural Mechanization and Energy 565–569 26–27 May Adana Turkey