Effect of Preservation Methods on Physicochemical Quality, Phenolic Content, and Antioxidant Activity of Stevia Leaves

Abstract

The effect of freeze-drying and gamma irradiation at 0.5, 1, and 2 kGy on the physicochemical composition (moisture, fat, ash, mineral, and chlorophyll contents), microstructure, total phenolic content, and antioxidant capacity of stevia leaves was investigated in the present study. The results obtained indicated that freeze-drying and gamma irradiation treatments caused significant reduction ( p ≤ 0.05) of moisture and fat contents in comparison with those of commercial leaves, while ash content was not significantly affected. Mineral composition was analysed. Among the analysed elements, potassium and iron levels were higher in the freeze-dried and irradiated samples, respectively. The microstructure was analysed using a scanning electron microscope. Micrographs revealed that a higher porous size structure was obtained by freeze-drying, and degradation of cell wall structure was more clearly visualized by irradiation at 2 kGy. However, the main functional groups were stable as confirmed by Fourier transform infrared spectroscopy analysis. The effects on chlorophyll content, phenolic profile, and antioxidant properties were evaluated before and after ten months of storage. In terms of chlorophyll contents, the freeze-dried leaves exhibited the highest content. Chlorophylls a and b decreased when storage progressed for freeze-dried leaves as well as for gamma-irradiated leaves. Both preservation methods gave significant advantages in increasing the total phenolic content and DPPH scavenging activity. Moreover, a significant increase of bioactive compounds and antioxidant activity was observed as the gamma irradiation dose increased. In addition, the storage time increased the amounts of polyphenols and DPPH scavenging activity. After 10 months of storage, gamma-irradiated leaves had the highest total phenolic content as well as the DPPH scavenging activity followed by freeze-dried leaves. The results indicate that freeze-drying and gamma irradiation at the studied doses could be effective postharvest methods for preservation of stevia leaf quality.

Formulation of functional gummy candies containing natural antioxidants and stevia

“…4 b) is indicated by the peak at 3420.85 cm −1 to C– O –H bending vibrations, and the peak at 2936.05 cm −1 , which corresponds to the asymmetric and symmetric stretching vibrations of –CH, CH 2 , CH 3 . Additionally, peaks at 1727.15 cm −1 and 1577.21 cm −1 are assigned to the stretching vibration of the –C O band, which is due to the presence of steviol glycosides and is also a characteristic band [ 32 ]. The FTIR spectra of the sample also showed bands around 1205.58 cm −1 , 1076.52 cm −1 , and 1037.94 cm −1 , which are characteristic absorption bands of the steviol glycosides [ 33 ].…”

Assessment of the Quality Characteristics of Stropharia rugosoannulata Subjected to Five Different Drying Methods

“…The contents of Ca and P were highest in the MD and RSD samples, respectively. The significant differences in mineral content among S. rugosoannulata dried by different methods may not be the effect of the drying process, but due to the heterogeneous distribution of the minerals in the analyzed samples [43]. Anyway, dried S. rugosoannulata was a good source of minerals that are essential for numerous body processes by serving as important cofactors for many enzymes.…”

A Review on the Biorefinery Approach and Marketing Strategy of Leafy Biomass

“…For example, freeze drying causes significant changes in the microstructure of the final dried product making it more porous so that solvents can easily penetrate the sample and thus extract more phytochemicals [36][37][38][39]. Several drying methods have been practiced with leaves aiming for extraction of phenolic compounds such as freeze drying [40][41][42][43][44][45][46][47], microwave drying [34,40,42,44,[48][49][50], oven drying [41,44,49], spray drying [51], sun drying [40,42,44], vacuum drying [40], shade drying [43], among others.…”