The Effect of Drying Processes on the Nutritional and Phytochemical Levels of Chia Leaves (Salvia hispanica L.) at Different Stages of Growth

Chia leaf (Salvia hispanica L.) is an underutilized low-cost source of nutrients. The leaf is currently not widely utilized as compared to the chia seeds which have wide use in the food industry. The present study investigated the effect of solar-drying and oven-drying chia leaves harvested at different stages of growth on their nutritional and phytochemical composition. The chia leaves were harvested at four stages of early vegetative stage, late vegetative stage, budding stage and flowering stage. Oven drying was done at45 ^ºC for 24hours, and solar dried in a solar drier until a constant weight was achieved. The results indicated significant differences (p<0.05) between treatments and stages of maturity. Results also showed that solar dried had better nutritional and phytochemical retention over oven dried chia leaves. Crude protein was highest in solar dried leaves at early vegetative stage (FS1) 4.48%, compared to 4.44% for oven dried chia leaves. The fiber content increased from the fresh leaf at 12.4% to high content in solar dried leaf at the early vegetative stage at 23.33%, while oven dried leaves had high content at the flowering stage at 22.09%. There were minimal changes in fat content of the dried chia leaves compared to fresh sample at 5.908%, with high fat levels noted for oven dried leaf at the early vegetative stage (FS3) at 5.68% and solar dried leaves at 4.71% at the budding stage. The difference in fat content could be attributed to degradation during the drying processes. Ash content on the other hand showed difference at different stages of growth from raw samples for both solar- and oven dried leaves. Highest retention of phenolic content was recorded at 147.62 mg/GAE for solar dried leaves at the budding stage (FS3). However, oven dried leaf samples recorded high phenolic content at 124.06 mg/GAE at the late vegetative stage. The flavonoid levels were recorded highest for solar dried leaves at the budding stage at 299.8 mg/CE, compared to high content for oven dried leaves at the budding stage recorded at 270.4 mg/CE. Scavenging activity was highest recorded for solar dried samples at the budding and flowering stages at 100 µg/100g compared to oven dried leaves at 80.85 µg/100g at the late vegetative stage. Solar drying is the simplest and convenient low-cost technology for preserving the nutritional quality and retention of phytochemical ranges of chia leaves which will enhance their utilization when abundantly available.