Optimization of spray drying process for recovery of onion-stevia leaf hot water extract powder using response surface methodology.

It is important to optimize the drying process, along with the concentration of drying aid and the inlet air temperature, in order to obtain products with better physicochemical properties. Onion-stevia leaf hot extract powders were prepared using gum arabic (GA) and whey protein concentrate (WPC). Inlet air temperature and carrier concentrations were optimized using response surface methodology. The drying yield of powdered extracts was 14.39-74.32%, L*- value was 52.66-66.98, bulk density was 0.36-0.75 (g/cm3), moisture content was 2.40-11.57%, water solubility index was 30.32%-97.46%, and mean particle size D[4,3] was 9.13-88.01 (µm). For both GA- and WPC-based powders, optimal inlet air temperatures and carrier concentrations were 148.81 and 144.62°C, and 11.58 and 12.03% (w/v), respectively. GA powders had a higher glass transition temperature (76.49°C) as compared to WPC powders (48.12°C) or maltodextrin as control (55.49°C). Sweetness (5.0/7.0) and overall acceptability (4.3/7.0) scores were higher for GA powders as compared to WPC powders (3.7/7.0 and 3.4/7.0), respectively. Conclusively, GA is a better carrier than whey protein for preparing spray-dried onion-stevia powder that can be used as a natural sweetener.

Influence of salt concentration on Kimchi cabbage (Brassica rapa L. ssp. pekinensis) mass transfer kinetics and textural and microstructural properties during osmotic dehydration.

The effect of salt concentration (3%, 6%, and 9%) on the mass transfer kinetics of Kimchi cabbage during osmotic dehydration was investigated, including its influence on textural and microstructural properties and salt distribution. First, kinetics was analyzed using diffusion theory to determine the impact of the factors on moisture and salt transfer. Subsequently, using the Peleg, Azuara, Henderson-Pabis, and Page models, mathematical modeling of mass transfer (water loss and salt gain) was investigated. According to the statistical analysis, the Peleg model provided the best fit for the experimental results under the operating conditions. In addition, a novel viewpoint was proposed in which the salt content of Kimchi cabbage may be indirectly forecasted by monitoring solution salinity during osmotic dehydration. Higher salt concentration resulted in decreased hardness, gumminess, and chewiness in Kimchi cabbage. Scanning electron microscopy and energy-dispersive X-ray mapping images showed an intensification of moisture and salt transport with increasing salt content, which were confirmed using modeling studies. The results could be applied in the prediction of the target salinity of Kimchi cabbage during the salting process and could facilitate the improvement of final Kimchi product quality by producing salted Kimchi cabbage with uniform salinity.