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. Ultrasonic extraction 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
- higher yields
- high extraction rates
- time saving
- 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 (Wspec, 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 tUS = 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 lower extraction temperature (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, blending and homogenizing, 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 dissolving 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 ultrasonic lab devices, bench-top systems for R&D and pilot plants as well as industrial high-power ultrasonic systems with up to 16,000 watts per single unit, which can be easily clustered and containerized. Our broad selection of ultrasonic accessories such as sonotrode, flow cells, reactors and boosters allows for the optimal configuration of the perfectly matching system for our customer’s needs.
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, ultrasonic extraction is a convincing technique due to its simple utilization and significant efficiency.
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Literature / References
- Carbonell-Capella, Juana; Šic Žlabur, Jana; Rimac, Suzana; Barba, Francisco; Grimi, Nabil; Koubaa, Mohamed; Brncic, Mladen; Vorobiev, Eugene (2016): Electrotechnologies, microwaves, and ultrasounds combined with binary mixtures of ethanol and water to extract steviol glycosides and antioxidant compounds from Stevia rebaudiana leaves. Journal of Food Processing and Preservation 41, 2016.
- Žlabur, Jana Šic; Voća, Sandra; Dobričević, Nadica; Brnčić, Mladen; Dujmić, Filip; Karlović, Sven (2012): Possibilities of Using High Intensity Ultrasound Technology with Stevia – a Review. Croatian Journal of Food Technology, Biotechnology and Nutrition 7, 2012. 152-158.
- Petigny L., Périno-Issartier S., Wajsman J., Chemat F. (2013): Batch and Continuous Ultrasound Assisted Extraction of Boldo Leaves (Peumus boldus Mol.). International Journal of Molecular Science 14, 2013. 5750-5764.
- Alupului, Ani Toboc; Vasile, Lavric (2008): Artificial Neural Network Modelling of Ultrasound and Microwave Extraction of Bioactive Constituents from Medicinal Plants. Chem. Eng. Trans. 14, 2008. 83–90.
- Liu, Jie; Li, Jin-Wei; Tang, Jian (2010): Ultrasonically assisted extraction of total carbohydrates from Stevia rebaudiana Bertoni and identification of extracts. Food and Bioproducts Processing 88/ 2-3, 2010. 215-221.
- Wang L.; Weller C.L. (2006): Recent advances in extraction of nutraceuticals from plants. Trends in Food Science and Technology 17, 2006. 300-312.
- Dogan Kubra, P.K. Akman, F. Tornuk(2019): Improvement of Bioavailability of Sage and Mint by Ultrasonic Extraction. International Journal of Life Sciences and Biotechnology, 2019. 2(2): p.122- 135.
- Fooladi, Hamed; Mortazavi, Seyyed Ali; Rajaei, Ahmad; Elhami Rad, Amir Hossein; Salar Bashi, Davoud; Savabi Sani Kargar, Samira (2013): Optimize the extraction of phenolic compounds of jujube (Ziziphus Jujube) using ultrasound-assisted extraction method.
Facts Worth Knowing
Steviol glycosides are the substances, which are responsible for the sweet taste of the stevia leaves. These glycosides of steviol are a diterpene compounds. They have the chemical structure of a steviol molecule where its carboxyl hydrogen atom is replaced by a glucose molecule to form an ester, and a hydroxyl hydrogen with combinations of glucose and rhamnose to form an acetal.
The steviol glycosides found in S. rebaudiana leaves include (with approx. weight percentage):
- Stevioside (5–10%)
- Rebaudioside A (2–4%)
- Rebaudioside C (1–2%)
- Dulcoside A (0.5–1%)
- Rebaudioside B
- Rebaudioside D
- Rebaudioside E
Rebaudioside B, rebaudioside D, rebaudioside E are found only in minute quantities. Commercially available steviol glycoside mixture used as non-caloric sweetener extracted from the plant mostly are composed from approx. 80% stevioside, 8% rebaudioside A, and 0.6% rebaudioside C.
Ultrasonic tissue homogenizers are often referred to as probe sonicator/ sonificator, sonic lyser, ultrasound disruptor, ultrasonic grinder, sono-ruptor, sonifier, sonic dismembrator, cell disrupter, ultrasonic disperser, emulsifier or dissolver. The different terms result from the various applications that can be fulfilled by sonication.