CRC Sugar Industry innovation through biotechnology : final report 2B8
Date
2010Metadata
Show full item recordAbstract
Sugarcane has a highly effective carbohydrate biosynthetic and storage metabolism
that has facilitated its use for the production of sucrose. Sugars are increasingly seen
as low-cost, renewable organic resources which can be modified to produce food
ingredients and industrial raw materials. For the sugar industry, alternative sugars
offer a means of diversification in an area close to the existing core business.
However a major restriction to development of alternative products has been
ownership of enabling intellectual property by third parties. This project aimed to
identify alternative sugars with desirable commercial properties and capture the IP to
enable their production. The initial phase of the project was a scoping study to identify novel, naturally occurring sugars and enzyme systems that may be involved in their manufacture by
collating information from the literature and patent databases. Sugars that occur
naturally in sugarcane and closely related species were also examined for potential as
higher value products. Preferred candidates were simple modifications of sucrose
where the gene sequences encoding the enzymes were available and no prior IP
existed. Four sugars with potential applications as alternative sweeteners or chemical
feedstocks were identified. Two of the candidate sugars could be either purchased directly or made by chemical
synthesis from a purchased precursor. The remaining two candidate sugars were not
available commercially and could not be synthesised easily. We proposed to make
these sugars by cloning and expressing the genes that encode the enzymes from
their native sources and then using the enzymes to synthesise the novel sugars in
vitro. Two enzymes were expressed and characterised. Although neither of these
enzymes carried out the predicted reactions, both enzymes were new; one is a
dehydrogenase and the other is a glucosidase acting on gluco-oligosaccharides. The potential value of any novel sugar depends on its physical and sensory
properties. For application as an alternative sweetener, a novel sugar ideally needs to
be as sweet as sucrose but offer health benefits, particularly low cariogenicity (tooth
decay) and low calorie-yield. We developed methods that can be used in the
laboratory to test industry-relevant properties of sugars, specifically sweetness,
cariogenicity and digestibility. A set of commercially available sugars, including
several alternative sweeteners, was used to test the assays and provide a comparison
with the novel sugars. Sweetness relative to sucrose and glucose was determined by a two-way preference
ingestion assay with Drosophila melanogaster (fruit flies). Production of acid by the
oral bacterium Streptococcus mutans was used as an assay to detect potentially
cariogenic sugars. Calorie yield of sugars was measured by assays for digestibility by
yeast invertase and rat α-glucosidase/sucrase. We also tested whether the sugars
were able to inhibit the digestion of sucrose, and whether the sugars could promote
the growth of ‘healthy’ bacteria in the gut. The results showed that two alternative sugars derived from sucrose have the
properties required for an alternative sweetener. We also identified a disaccharide
which is sweet-tasting and able to inhibit the digestion of sucrose. Further research
will be required to develop an economic production system for these candidate
sugars. The tests developed in this project also identified some interesting
relationships between sugar structure and sensory or nutritive properties. Further
analysis of these relationships may allow design of new sweeteners with optimal
properties. The outcome of this work is an improved ability to develop new sugar derivatives as
alternative sweeteners. The information and tools developed by the project will assist
future efforts to exploit new options for diversification in the sugar industry.