Solvent-Free Stevia Extraction with Ultrasound

The conventional extraction of the sweet components such as stevioglycosides from Stevia rebaudiana uses toxic solvents. In order to obtain a healthy, high-quality food product, a solvent-free extraction method is required. The ultrasonic extraction technique avoids the use of solvents achieving very high extraction yields in a short processing time. Thereby, ultrasonic stevia extraction excels by outstanding efficiency and environmental-friendliness.

Healthy Extracts with Ultrasonic Extraction

Stevia sweeteners are supposed to be a health-beneficial product made from the leaves of the herb Stevia rebaudiana Bertoni and are used as a zero-calorie sweetener. The sweetness is caused by diterpenic glycosides that is approx. 300 times sweeter than sucrose.
The glycoside content of stevia rebaudiana Bertoni is composed from stevioside (5–10%), rebaudioside A (2–4%), rebaudioside C (1–2%), dulcoside A (0.5–1%), rebaudioside B, rebaudioside D, and rebaudioside E. Unlike the other glycosides, rebaudiana A is characterized by its non-bitterness. Therefore, rebaudiana A is the most targeted compound from the stevia leaves. Ultrasonic extraction assists the extraction of steviosides and rebaudiosides of high-purity. ultraääni uuttaminen of steviol glycosides can be easily carried out in water and gives high yields at a very high extraction rate. The relatively low extraction temperature between 60°C and 80°C is gentle so that a degradation of the extracts is prevented.

Since stevia is approved as sweetener, the demand for the natural sugar, calorie-free substitute increased significantly. To provide the demanded stevia products, capacities of commercial production must be expanded. Ultrasound is a proven method for extraction intensification.

Advantages of Ultrasonic Extraction:

• solvent-free, e.g. in water
• Korkeammat saannot
• high extraction rates
• Aikaa säästävä
• cost-saving
• Turvallinen
• ympäristöystävällinen
• batch or inline processing

Ultrasonic Stevia Extraction: Research Results

Carbonell-Capella et al. (2016) compared various extraction techniques for the extraction of steviosides and rebaudiosides. The highest recovery of stevioside was obtained applying ultrasonic extraction with the UP400S (see picture left) using water as solvent, being 3.5 times higher compared to the traditional diffusion method, and 1.5 times higher than ground Stevia samples. In this study, stevia leaves (6 g) were suspended in water (180 g) at 208C at a solid/liquid ratio of 1:30 (w/w). Ultrasonic extraction was performed using an ultrasonic processor UP400S (Hielscher GmbH, Germany), operating at 400 W and 24 kHz frequency. For the experiments, the research team of Carbonell-Capella set the amplitude at 100%, with a continuous sonication mode. A titanium sonotrode H22 with a diameter of 22 mm and a length of 100 mm was mounted in order to couple the ultrasound waves into the sample. The probe was submerged in a mixture containing 6 g of Stevia leaves suspended in 180 g of water or ethanol/water (50%) in a narrow-neck glass flask (holding capacity 1,000 mL). Samples were immersed in a cooling bath to avoid heating induced by sonication and temperature was kept always lower than 50ºC). Total specific energy input (W_spec, in kJ/kg) was calculated by multiplying the generator power (400 J/s) (Power) by the total treatment duration (sec) divided by the product mass (kg). Ultrasound energy was of 178 kJ/kg (for t_US = 80 sec.)
(cf. Carbonell-Capella et al. 2016)
Sic-Zlabur et al., (2015) investigated the extraction of steviol glycosides along with other functional ingredients from Stevia leaves and concluded that ultrasonic extraction is an environmental-friendly technology which may be used for the extraction of functional compounds from Stevia leaves with a significantly shorter treatment time and lower energy consumption in comparison to conventional extraction.

Liu et al. (2010) investigated the ultrasonic extraction of total carbohydrates from Stevia rebaudiana Bertoni. In order to maximize the yield of total carbohydrates from Stevia rebaudiana Bertoni, stevia from type LUYU-131 was used as samples. The response surface methodology (RSM) was employed to optimize the ultrasound-assisted extraction condition. The results indicated the optimal extraction conditions were an extraction temperature of 68°C, a sonic power of 60 W and an extraction time of 32 min. Using the ultrasound-assisted extraction, the yield of extracts increased by a factor of 1.5 at the alempi uuttolämpötila (68°C) and the extraction time (32 min.) substantially shortened compared with that of classical extraction. The components analysis of crude extracts revealed that the relative amount of rebaudioside A increased in the ultrasound-assisted extracts as compared with extracts obtained by classical process, and the ultrasound-assisted extracts had better quality.
Alupului and Lavric (2008) confirm in their study the superior efficiency of ultrasonic stevia extraction stating that ultrasound induced stevioside extraction of Stevia rebaudiana results in improved productivity over conventional soaking by two hundred times and also a lower treatment time. (cf. Alupului A., Lavric V., 2008)

Ultrasonic Post-Processing of Steviosides

Ultrasound is a reliable method for mixing, Sekoitus ja Homogenisoinnin, therefore ultrasonic is often used during formulating and compounding of the final product. When the stevia extract has to be dissolved in a liquid, ultrasound is a fast and efficient technique to prepare a homogeneous blend – regardless of the viscosity. Ultrasonic Liuottamalla allows for preparing highly saturated and even over-saturated solutions.

Ultrasonic Extraction Systems

Hielscher’s product range get you covered – whether you want to extract smaller and mid-size volumes for analysis and research or to extract on large commercial production scale. Our product range of ultrasonicators includes ultraäänilaboratoriolaitteet, bench-top systems for R&D and pilot plants as well as industrial high-power ultrasonic systems with up to 16 000 wattia per single unit, which can be easily clustered and containerized. Our broad selection of ultrasonic Tykötarpeet such as sonotrode, flow cells, reactors and boosters allows for the optimal configuration of the perfectly matching system for our customer’s needs.

Investment

All Hielscher ultrasonic devices are built for 24/7 operation meaning that our equipment allows for a fast Return on Investment (RoI). Alupului et al. (2009) found during their research that the fact of the economic justification of the high intensity ultrasound application as a relatively low-cost method not be neglected. Furthermore, ultraääni uuttaminen is a convincing technique due to its simple utilization and significant tehokkuus.