Mulberry Feasibility Study

2.1. Sample Preparation
Fruits of black mulberry (Morus nigra) at a commercially mature stage were crashed and mixed with a blender. A sieve was used to eliminate the seeds. The juice with 17% of total soluble solid (TSS) was rapidly cooled and frozen at −25 ºC to use for further experiments.
Ice cream mixes were prepared by adjusting the fat ratio of pasteurized milk to 6% with cream addition and other ingredients were in the following order: 5% 12DE maltodextrin (Tongaat Hulett starch, South Africa), 0.8% salep (provided locally, Kordestan, Iran) and 0.1% k-carrageenan (Sigma Co., St. Louis, MO), 10% skim milk powder (provided locally, Karaj, Iran), 10% sugar, and black mulberry juice at three concentration of 15, 30, and 45%. Black mulberry

The purge gas used was dry nitrogen (25 mL/min). Indium and zinc (Perkin-Elmer standards) were used for temperature and heat flow calibration. The samples were cooled to desired temperature (−25 °C) by fast cooling to reach temperature equilibrium at this temperature. Two to four mg of ice cream powders were scanned in a hermetically sealed 50 μL DSC aluminum pans (Perkin Elmers). An empty aluminum pan was used as a reference. The tests were conducted −50 °C to 200 °C with a heating rate of 10 °C/min. The transfer of samples from container to DSC pan was done in a sealed “Dry box” containing silica gel with regular N2 flushing, to avoid moisture absorption by the sample.

2.9. Scanning electron microscopy (SEM)
The microstructure of the ice cream powders was examined using a scanning electron microscope (XL-30, Philips, Amsterdam, The Netherlands). To obtain SEM images, small amount of powders were taken from well mixed powder samples and coated with very thin layer of gold under high vacuum conditions, to provide a reflective surface for the electron beam. Gold coating was carried out in a sputter coater BIO-RAD E-5200 (Bio-Rad Laboratories Ltd., London, UK) under a low vacuum in the presence of inert argon gas. The gold-coated samples were subsequently viewed under the microscope.

2.10.

1 shows the influence of inlet air temperature, feed flow rate, and black mulberry concentration on the spray drying process yield. Increase in inlet air temperature from 120 to 140°C induced a significant increase in yield, which can be attributed to the greater efficiency of heat and mass transfer processes and decreasing the probability of hitting the inadequate drying particles to the drying chamber wall. Similar results were reported by Tonon et al. [21] and Goula and Adamopoulos [19]. But increasing inlet air temperature to 160 °C showed a negative effect especially for samples containing higher amount of black mulberry juice. It is due to the stickiness problem and the low glass transition temperature of components. The same results were shown by Papadakis et al. [22] for spray drying of raisin juice.
Increasing feed flow rate led to lower process yield because higher feed rate reduced the contact time between feed and the drying air and caused a decrease in the rate of heat and mass transfer. This is in agreement with the results published by Toneli et al. [23] and Tonon et al. [21] working with spray drying of tomato pulp and acai,