Global demand for naturally sourced, zero-calorie sweeteners has increased significantly over the last decade as consumers have become increasingly health conscious. But according to new research published in Current Opinion in Biotechnology, further growth to the natural sweeteners category is potentially limited by agricultural sustainability, undesirable taste qualities, perceived safety and commercial viability.
Led by Ryan Philippe from Manus Biosynthesis in the USA, the new review suggests that biotechnological production platforms for natural sweeteners can help to address supply and scalability limitations associated with plant-based production “while increasing sustainability of the overall endeavour.”
Indeed, the team noted that the ‘limitation and risks’ inherent in large-scale agricultural production, in addition to the costs associated with extracting and purifying the desired sweeteners from plant material, “can together work to limit the potential growth and development of these molecules and the products containing them.”
“In order to achieve the scale of production required to provide a go-to alternative for sucrose, these plant-derived sweeteners need to be produced via biotechnological fermentation of bulk sugars.”
“In terms of a fully sustainable production system, high-potency sweetener supply can be satisfied by biotechnological production while synergistically generating beneficial side-effects,” said Philippe and his colleagues. “Land can be used to produce high yielding crops such as sugarcane or corn, whose sugar can be converted via plant cell culture or microbial fermentation to natural high-potency sweeteners, instead of relying on variable potency plant formulations.”
“In addition, the development of plant or microbial cell-based production platforms can allow for the rapid modification of pathway enzymes to generate novel sweeteners with fewer or no negative taste attributes,” wrote the team.
The authors suggested that plant sources of sweeteners are limited – both in the total area that can be cultivated, and in total productivity on a per weight basis.
“Additionally, it can be difficult or impossible to produce superior but minor products using plant-based methods,” they said. “For example, while rebaudioside D has enhanced sweetening potential and taste profile compared to stevioside and rebaudioside A, it accumulates at much lower levels than the two latter compounds and thus its total production is limited.”
Indeed, the team argue that for any natural sweetener to reach the commercial scale to be seen as a realistic alternative to sugar, it is necessary to develop sustainable biotechnological production methods such as plant cell or microbial fermentation for its stable manufacture.
However, relatively few sweet-tasting plant-derived natural products have been commercially launched to date, they said.
“But those numbers are rapidly increasing,” wrote Philippe and his colleagues. Indeed, a recent partnership between Cargill and Evolva has seen the development of fermentation technologies that can produce natural steviol glycocides.
The biotech challenge
While the benefits of biotechnological production of natural sweeteners are numerous, the successful achievement of the goal is not without technical challenges, they noted.
“Ideally, if it is possible to produce the compound of interest via cell cultures of a critical plant, efforts can be limited to maximizing sweetener yield without requiring detailed knowledge about the biochemistry and biochemical pathway,” they said.
In the absence of this however, there still remains the potential for metabolic engineering of plant or microbial cells for production of the sweeteners – for example using fermentation techniques.
“In the past decade, metabolic engineering of microbial systems has demonstrated astonishing progress, and several tools and methods are now in place for manipulating biosynthetic pathways to enable scalable production of specialized natural products.”
For example, there is a ‘considerable’ amount of information available for steviol glycosides in S. rebaudiana, while other work has yielded candidate genes for every unknown step in the pathway to produce mogrosides, but biochemical function has not yet been verified.
“Taken together, a great deal of efforts — identifying genes responsible for biosynthesis, metabolic engineering, protein engineering, fermentation and downstream processing — is yet needed to develop sustainable manufacturing processes for naturally derived zero-calorie sweeteners,” they said.
Source: Current Opinion in Biotechnology
Volume 26, April 2014, Pages 155–161, doi: 10.1016/j.copbio.2014.01.004
“Biotechnological production of natural zero-calorie sweeteners”
Authors: Ryan N Philippe, Marjan De Mey, Jeff Anderson, Parayil Kumaran Ajikumar