Calcium ascorbate (CaAsc), effectively inhibits browning and decay in fresh fruits and vegetables, preserving the quality of horticultural products. This study investigated the effects of pre-harvest foliar application of CaAsc on the growth, photosynthetic pigments, secondary metabolites, and nutritional value at the harvest time (Part I) and physiological parameters, biochemical responses, and antioxidant enzyme activities at the post-harvest periods (Part II) of basil microgreens. Basil seeds were germinated for four days in a controlled dark environment with a relative humidity of 80% ± 5%. The germinated seedlings were then moved to a glasshouse and exposed to sunlight, where the average air temperature was 23/18°C ± 2 °C and relative humidity was 60 ± 5%. Once the basil plants were established, foliar application with different concentrations of CaAsc began. The experimental treatments comprised four concentrations of CaAsc: 0 mM (as control), 10, 20, and 40 mM. The foliar application was implemented in three stages on the 5th, 8th, and 11th days after sowing using a hand sprayer. Plants were harvested 14 days after sowing, and various parameters related to quantity and nutritional quality were measured. Results showed that the highest fresh and dry weight (FW and DW), dry weight% (DWP), pigments, total phenolic (TPc), total flavonoid (TFc), ascorbic acid (AsA), and total antioxidant capacity (TAC) were observed in basil microgreens treated with 40 mM and 20 mM CaAsc, respectively. Furthermore, plants sprayed with 40 mM CaAsc exhibited 46.09% and 36.58% higher potassium (K) and calcium (Ca) content compared to the control. The highest phosphorus (P) and manganese (Mn) content was observed in the 10 mM CaAsc treatment. Results indicated that weight loss percentage (WLP), malondialdehyde (MDA), electrolyte leakage (EL), polyphenol oxidase enzyme activity (PPO), and browning index (Bi) increased with extended shelf life. However, treatments with 40 mM and 20 mM CaAsc significantly reduced these parameters on the eighth and twelfth days of shelf life. Catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) enzyme activities increased during shelf life compared to the control, with the highest activity levels observed in the 40 mM and 20 mM CaAsc treatments. Conclusions: In general, 40 mM and 20 mM CaAsc foliar applications effectively maintained the quality, nutritional value, and extended the physiological and biochemical responses of basil microgreens both at harvest and during shelf life. Therefore, these treatments are recommended for optimal basil microgreen production and preservation.
