Physical properties of spray dried pitaya (original) (raw)

Studies of fruits obtained from a wide variety of cactus have revealed bio-active compounds with a high antioxidant capacity. Encapsulation methods have been used to conserve betalains, the principle bio-active compounds in the juice, which is highly susceptible to degradation in a fresh state. The encapsulation conditions (temperature and encapsulant matrix) affect the physical properties of the dry powders, which in turn influence the retention capacity of bio-active compounds. The objective of this work is to evaluate the effect of the spray dried encapsulation conditions on the following physical properties: color, glass transition temperature (Tg) and adsorption isotherm. The color was determined using a spectrocolorimeter with a L*,a*,b* color scale, Tg was calculated using a DSC Q2000 and the adsorption isotherms, at 25 °C, were measured with a VTI-SA + . The experimental data was fitted to the GAB (Guggenheim-Anderson-DeBoer) using non-linear regression. Micrographs of the structure were analyzed. Pitaya fruit (Stenocereus griseus) were selected, washed and pealed. The juice was obtained with manual extrusion and filtered through a metallic sieve. The encapsulation method was spray drying. A 2 2 factorial design was used to evaluate the effect of the independent variables: inlet air temperature (150-180 •C) and feed flow rate (1.635 -2.148 L/h) on the powder properties. The atomization speed was kept constant (28,000 rpm). A maltodextrin/pectin combination was used as the encapsulant matrix in a 40/20% ratio based on the total solids concentration. The highest variation was found in the parameter b*, which represents changes of the color yellow. This change is associated with the loss of betaxanthin, a highly thermolabile compound. A type III adsorption isotherm was found. The constants of the GAB equation were determined with a fit of R 2≥ 0.99. Tg between -26.21 y 32.68°C were found for water activity in the range of 0.11 and 0.53. A test of SEM micrographs shows polydisperse powder particles. These particles were observed to be sphere-like with some sections exhibiting compaction of agglomerated particles. The application of different encapsulation conditions and encapsulant matrix ratio no affect significantly the physical properties of pitaya juice powder. A humidity content ≤ 10% and water activity of 0.4 are required to maintain the stability of the powder at room temperature.