Production of raspberry fruit powder using foam-mat drying: Effect of convective hot air temperature

Raspberry fruit is a good source of various micronutrients, such as anthocyanins, polyphenols, ascorbic acid, fibers, proteins, and minerals. Due to high water content (75-90%), it is susceptible to enzymatic and microbial reactions. Raspberry, due to high amounts of antioxidant compounds, is resistant to free radical compounds, and it is very valuable. Drying of raspberry pulp will increase shelf life, reduce storage and transportation costs. Foam mat drying is an economical alternative to drum, spray, and freeze-drying for the production of food powders. Foam mat drying can be used for the large production of food powders because of its suitability for all types of food materials, rapid drying at a lower temperature, retention of nutritive value and bioactive compounds. The raspberry pulp is converted into a stable foam by adding ovalbumin (0.5%) as the foaming agent through whipping in the presence of methylcellulose (0.5%) as foam stabilizers and dehydrated by different convective hot air temperature (50, 60 and 70℃), with constant air velocity (3 m/s). By using the above concentrations, the foam density, foam porosity and foam overrun were obtained 0.383, 0.6087 and 155, respectively. The stable form of the raspberry foam, was consequently spread as a thin sheet to be exposed to the stream of relatively hot air until it is dried to desired moisture.Physicochemical properties such as water absorption index, water solubility index, bulkporosity, effective moisture diffusion coefficient, drying rate, and etc., were evaluated. Withincreasing temperatures from 50 to 60℃, the drying rate increased by 57% and with a rise intemperature from 60 to 70℃, its value dropped by 7%. Also, bulk porosity decreased withincreasing temperature from 50 to 70℃. The water solubility index in the 50, 60, and 70℃ were54.43%, 63.22% and 57.64%, respectively, and the water absorption index were 7.567, 8.197,and 7.694, respectively. The amount of effective moisture diffusion coefficient for temperaturesof 50, 60 and 70℃, were obtained 9.065× 10−5,1.64× 10−4, and 1.063× 10−4, respectively.

کلیدواژه ها:

Foam mat drying ، Temperature ، Raspberry ، D eff