Effect of Microwave and Conventional Heat Treatment on Total Phenolic Compounds, HPLC Phenolic Profile, and Antioxidant Activity of Leptadenia pyrotechnica (Forssk.) Decne Stem

Abstract

Leptadenia pyrotechnica is considered a wild herb used to enhance the palatability of food, particularly in the Gulf region. The effect of microwave (5, 8, and 10 min at 900 W) and hot-air heating (60, 120, and 180 min at 100 °C) on the phenolic compounds and antioxidants of L. pyrotechnica stems was investigated. The results showed that microwave heating gave high values of the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant properties, while the control sample was inferior in all these attributes. Moreover, microwave heating, particularly for 8 min, produced the highest TPC, TFC, and DPPH values (significant at p < 0.05) and reduced power in the L. pyrotechnica stem. However, prolonging the heating time caused adverse effects on the bioactive potential of the samples. The HPLC analysis indicates that both processes caused a significant increment in the phenolic compounds of the sample. Tannic acid, vanillin, and acetyl salicylic acid were found to be higher in the microwaved-treated samples than in those heated with hot air. The tannic acid was found to be high after microwave heating for 8 min at 116.06 mg/100 g, while the higher value of acetylsalicylic acid 119.08 mg/100 g was observed after microwave heating for 5 min. The partial least regression (PLS) validation model revealed that microwave heating, particularly at an 8 min application time, offered better results, and owing to its short processing time, which might be adopted for heating the L. pyrotechnica stems in the food industry, and it can be useful for preparing functional foods.