Solvent-Free Stevia Extraction with Ultrasound
- The conventional extraction of the sweet components such as stevioglycosides from Stevia rebaudiana uses toxic solvents.
- To obtain a healthy, beneficial food product, a solvent-free extraction method is required.
- The ultrasonic extraction technique avoids the use of solvents achieving very high extraction yields.
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 then 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
Liu et al. (2010) investigated the ultrasonic extraction of total carbohydrates from Stevia rebaudiana Bertoni using Hielscher’s ultrasonic device UP400S. 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.
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.
- 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.
- Toboc, Ani (Alupului); Lavric, Vasile (2012): Artificial Neural Network Modelling of Ultrasound and Microwave Extraction of Bioactive Constituents from Medicinal Plants. Revista Chimica 63/7, 2012. 743-748.
- Wang L.; Weller C.L. (2006): Recent advances in extraction of nutraceuticals from plants. Trends in Food Science and Technology 17, 2006. 300-312.
- 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.
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.