Assessment of the bioactive compounds in gamma irradiated stevia (Stevia rebaudiana Bertoni) leaves

Stevia is a potential alternative sweetener for individuals with diabetes. Gamma radiation is one technique that can alter a plant's physiological traits or phytochemical makeup without producing any dangerous byproducts or chemical initiators. Therefore, the aim of the current study was to determine the effect of gamma radiation (0, 3, 5, 7, and 10 kGy) on the bioactive compounds of dry stevia leaves. In comparison to non-irradiated samples, it is clear that all gamma radiation doses raised the percentages of carbohydrates, total steviosides, total sugar, reducing sugar, crude protein, and nitrogen, while decreasing the percentages of fat, ash, and fiber. The irradiation of stevia leaves at a dose of 7 kGy resulted in the most significant increase in carbohydrates by 57.7%, total steviosides by 32.8%, total sugars by 38%, reduced sugars by 66.8%, and crude protein by 21.9% when compared to non-irradiated samples. In contrast, the percentages of fat, ash, and fiber decreased by 23.2%, 10.8%, and 11.9%, respectively. According to the HPLC profile chromatogram, stevia leaves exposed to 3, 5, and 7 kGy had higher concentrations of all identified phenolic compounds than non-irradiated leaves; 5 kGy was outperformed by 3 and 7 kGy, while 10 kGy resulted in a decrease in these compounds. While apigenin and ellagic acid only disappeared from leaves exposed to 10 kGy, kaempferol was seen to disappear from all irradiated leaves. Furthermore, cinnamic acid was detected at radiation doses of 5, 7, and 10 kGy (0.50, 0.90, and 0.14 µg.ml^{- 1}, respectively), whereas it was absent at the non-irradiated and 3 kGy radiation doses. The Fourier Transform Infrared (FTIR) spectra of the irradiated and non-irradiated stevia samples displayed a comparable band profile. In conclusion, gamma irradiation of dried stevia leaves increased the levels of carbohydrates, steviosides, sugars, crude protein, and phenolic compounds, while reducing the levels of fat, ash, and fiber, with no observable differences in the FTIR spectra between the irradiated and non-irradiated samples. The optimal radiation dose was 7 kGy, which resulted in the most significant enhancement in biologically active compounds, along with the emergence of cinnamic acid.