rebaudioside-c and steviol

To improve the conversion efficiency of rebaudioside C, this study screened the Paenarthrobacter ilicis CR5301 from soil samples and identified it by 16S rRNA. The conversion experiment proved that P. ilicis CR5301 was capable of converting rebaudioside C. The effects of initial pH, temperature, inoculation amount, and substrate concentration on rebaudioside C conversion rate were investigated. The results showed that the conversion rate of rebaudioside C reached up to 100% when CR5301 was incubated in a conversion medium with an initial pH of 7.0 for 8 h at 28°C and 270 rpm. The conversion time was reduced by at least 16 h compared with previous studies. The conversion product was analyzed and identified as steviol by high performance liquid chromatography, ultra performance liquid chromatography-triple-time of flight mass spectrometer, and Fourier transform infrared spectroscopy methods. In addition, stevioside, rebaudioside A, dulcoside A, and some unknown components in steviol glycosides byproduct were all efficiently converted to steviol. These findings provide an efficient approach to the conversion of rebaudioside C and byproduct to steviol to simplify the subsequent industrial process and improve the reuse value of steviol glycosides.

Topics: Diterpenes, Kaurane; Glucosides; Glycosides; RNA, Ribosomal, 16S; Stevia

Transcriptome analysis revealed the potential mechanism of nitrogen regulating steviol glycosides synthesis via shifting of leaf carbon metabolic flux or inducing certain transcription factors. Nitrogen (N) plays key regulatory roles in both stevia (Stevia rebaudiana) growth and the synthesis of its functional metabolite steviol glycosides (SGs), but the mechanism by which this nutrient regulates SGs synthesis remains to be elucidated. To address this question, a pot experiment was performed in a greenhouse where stevia plants fertilized with N (the control as CK plants) and compared with plants without the supply of N. Physiological and biochemical analyses were conducted to test the growth and metabolic responses of plants to N regimes. Our results showed that N deficiency significantly inhibited plant growth and leaf photosynthesis, while increased leaf SGs contents in stevia (49.97, 46.64 and 84.80% respectively for rebaudioside A, stevioside, and rebaudioside C), which may be partly due to "concentration effect". Then, transcriptome analysis was conducted to understand the underlying mechanisms. A total of 535 differentially expressed genes were identified, and carbon metabolism-related events were highlighted by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes. Many of these genes were significantly upregulated by N-deficiency, including those involved in "phenylpropanoid biosynthesis", "flavonoid biosynthesis" and "starch and sucrose metabolism". Our study also analyzed the expression patterns of SGs synthesis-related genes under two N regimes and the potential transcription factors linking N nutrition and SG metabolism. N-deficiency may promote SGs synthesis by changing the carbon metabolism flux or inducing certain transcription factors. Our results provide deeper insight into the relationship between N nutrition and SGs synthesis in stevia plants.

Topics: Carbon; Diterpenes, Kaurane; Gene Expression Profiling; Gene Expression Regulation, Plant; Glucosides; Glycosides; Nitrogen; Oligosaccharides; Plant Leaves; Plant Proteins; Reproducibility of Results; Stevia; Transcription Factors

Steviol glycosides are a family of compounds found in Stevia rebaudiana Bertoni that are responsible for sweetness capacity. The antihyperglycemic effect of the two major steviol glycosides, Rebaudioside A and Stevioside, has been studied and it has been found that despite having the same common structure, only Stevioside exerts an antihyperglycemic effect. Although other steviol derivatives are found in smaller amounts (minor steviol glycosides) in S. rebaudiana, whether or not they possess antihyperglycemic activity has not been evaluated. The aim of this study was to evaluate the antihyperglycemic effect of minor steviol glycosides in normoglycemic and diabetic (streptozotocin/nicotinamide) Wistar rats. Rats were subjected to an intraperitoneal glucose tolerance test (IPGTT) both before and after chronic treatment (28 days). After 6 h of fasting, IPGTT was conducted in pentobarbital-anesthetized rats using 1 g/kg of glucose plus 20 mg/kg of the minor glycoside (Dulcoside A, Rebaudioside B, C, D, or Steviolbioside) or control treatment (distilled water, glibenclamide, or metformin); the blood of the tip of the tail was collected at time 0, 15, 30, 60, and 120 min.; and blood glucose was measured, and its net area under the curve (AUCnet) was calculated. After 28-day chronic oral administration, IPGTT was again performed. Differences were considered significant at P < .05 by one-way ANOVA. Acute intraperitoneal or chronic oral administration of 20 mg/kg of minor steviol glycosides had no antihyperglycemic effect in normoglycemic or induced-diabetic Wistar rats. Considering the dose tested, it is unlikely that these glycosides have an effect on glucose in diabetic or normoglycemic humans.

Topics: Animals; Area Under Curve; Blood Glucose; Diabetes Mellitus, Experimental; Diterpenes, Kaurane; Glycosides; Hypoglycemic Agents; Male; Oligosaccharides; Phytotherapy; Plant Extracts; Rats, Wistar; Reference Values; Stevia; Trisaccharides

This study was aimed at identifying the effect of harvest time, experimental site and crop age on the no-calorie sweetener steviol glycosides (SG) and on the antioxidant properties of stevia leaf extracts. The experiment was conducted over two growing seasons at two sites in the northeastern plain of Italy.. The results showed that all analysed factors played an important role in defining the SG profile and the antioxidant properties of stevia extracts. A high level of phenols (78.24 mg GAE g⁻¹ DW by Folin-Ciocalteu method) and high antioxidant activity (812.6 µmol Fe²⁺ g⁻¹ DW by FRAP assay) were observed. The inhibition of DPPH free radicals was evaluated and an IC₅₀ mean value of 250 µg mL⁻¹ was obtained. Significant relationships among the total antioxidant capacity and the analysed compounds were found.. The results showed the possibility of obtaining, in the tested environments, very high SG yields thanks to the long-day conditions during the spring/summer season. The harvest time played a key role in determining the stevia quality, influencing the rebaudioside A/stevioside ratio. The strong antioxidant properties make very interesting the possibility of using stevia extracts to improve functional food properties.

Topics: Antioxidants; Chromatography, High Pressure Liquid; Crops, Agricultural; Diterpenes, Kaurane; Food Additives; Glucosides; Glycosides; Italy; Non-Nutritive Sweeteners; Oligosaccharides; Phenols; Phytochemicals; Plant Extracts; Plant Leaves; Seasons; Soil; Spatio-Temporal Analysis; Stevia