Influence of air-drying temperature on the quality and bioactive characteristics of dried galega kale (Brassica Oleracea L. Var. Acephala)

Drying processes are often applied to preserve and increase the shelf life of vegetables. These products contain an extensive collection of phytochemicals known to provide health benefits. However, these compounds generally undergo significant degradation during drying because of their sensitivity to heat, light, oxygen, as well as to leaching phenomena. Thus, increased attention has been given to the concerns regarding the quality degradation of vegetables during drying. Galega kale was selected, since this leafy vegetable, often included as soups ingredient, presents high amounts of vitamins and micronutrients. The objective of this work was to evaluate the drying characteristics and the effect of drying temperature on quality characteristics of Galega kale, without any pretreatment. Drying times of 330, 162, 78 and 51 min provided minimal moisture contents, using temperatures of 35, 50, 70 and 85 ⁰C, respectively. Increasing air-drying temperatures originated significant changes in color and nutritional parameters. The L* and a* values diminished, and b* increased, originating increasing values of chroma, total colour difference and browning index, as well as decreasing values of hue angle. A pronounced effect on the retention of total phenolic compounds was observed. Regarding antioxidant capacity and vitamin C, losses of 51.7±7.5- 69.6±3.7 and 4.8±9.7-55.5±7.4% were obtained, respectively. Chlorophyll a content decreased with increasing drying temperatures, with losses between 8.9±6.7 and 35±5.6%, while degradation of chlorophyll b was negligible. In conclusion, the air-drying of Galega kale without any pretreatment resulted in considerable deterioration of its quality characteristics and nutritional value.