Acrylamide, Plant Genomics and the Food Industry
Posted 30th December 2019 by Liv Sewell
Ahead of the 8th Plant Genomics and Gene Editing Congress, we asked keynote speaker Nigel Halford, Principal Research Scientist at Rothamsted Research, UK, to share with us the background to his research…
At Rothamsted Research, we have been working for a long time on the processing contaminant acrylamide. It is not present in raw crop materials, but forms during high temperature cooking and processing: frying, baking, roasting, and toasting. It affects cereal and fried potato products as well as other products made from beans, tubers, storage roots, and any grains.
It is a serious problem for the food industry because acrylamide is a probable human carcinogen. We know it causes cancer in rodents and it is likely to cause cancer in humans. It also has developmental effects and effects on the nervous system and fertility in high doses. It is a highly undesirable chemical to have in a food product.
All in the Chemistry: the Maillard reaction and the acrylamide problem
Acrylamide forms within the Maillard reaction. Whereas acrylamide was only discovered in food in 2002, the Maillard reaction has been known about since 1912. It is an important reaction for the food industry: a reaction between amino groups, principally those of free (soluble, nonprotein) amino acids, and reducing sugars like glucose, fructose, and maltose.
It’s complicated chemistry, and no enzymes are involved. Initially the reaction produces sugar degradation products called carbonyl compounds. These are highly reactive and can react again with free amino acids. This will produce a plethora of compounds, many of which impart flavour, colour and aroma to the product. These reactions and the compounds produced are therefore key to product quality and the differentiation between various product types and brands.
In the case of free asparagine, however, the product is acrylamide. That makes it all the more difficult because you then have correlations between flavour formation, colour formation and acrylamide formation, because they involve similar chemical pathways.
Free asparagine and reducing sugars can be regarded as precursors for acrylamide. In fact, the carbon skeleton for the acrylamide that forms is derived entirely from asparagine. In cereal products, it’s free asparagine concentration which is the determinant for the acrylamide-forming potential of the crop.
A Shifting Regulatory Landscape
At Rothamsted, our target is to reduce the acrylamide-forming potential of wheat grain through gene editing.
This is timely. The regulations of acrylamide are becoming more difficult for the food industry. In April 2018, new regulations were brought in which require all food businesses to mention monitor the amount of acrylamide in their products and follow compulsory codes of practice to ensure the acrylamide level is as low as possible.
Along with those regulations came a threat of introducing maximum levels for acrylamide: levels above which it would be illegal to sell a food product. This would be a difficult situation for the food industry.
It’s important that everything is done to make sure the food industry and its supply chain can comply with regulations and the evolving regulatory scenario. In light of this, we are targeting asparagine synthesis.
We’ve done a genomics study on the asparagine synthetases, the enzymes which make asparagine and glutamate from glutamine and aspartate. These are at the heart of the asparagine metabolic network. We’ve identified five genes, called 1, 2, 3.1, 3.2, and 4. Because wheat is a hexaploid, that gene family structure is found in all three genomes.
We found that asparagine synthetase-2 is the most highly expressed in the grain and not highly expressed anywhere else. This has become our target using both CRISPR/Cas9 and old-fashioned chemical mutagenesis.
In the past year we have been developing the CRISPR/Cas9 project, and some wheat plants have come through the editing process. We now have asparagine data on those plants, and there is one line in particular in which asparagine concentration has been greatly reduced compared to the wild type and in which the trait is not segregating.
There are other lines in which the trait is still segregating, but in which some of the individual plants also have a very low asparagine level. We are taking these forward to look further at the asparagine levels as well as trying to get support for a field trial, probably in 2021-22.
At the same time, we’re also stacking the chemically induced mutations with our partners in the plant breeding industry. We have mutations in each gene, and they have to be stacked by conventional crossing. We may have an A genome negative from that process in time for the 2021-22 field trial, if that is funded.
We have data which shows that the A genome ASN2 gene is much more highly expressed than the D genome gene, while the B genome gene is missing altogether in some varieties. This is interesting because it means we have three different types of mutation in the project: mutations induced by CRISPR/Cas9, mutations induced by chemical mutagenesis, and what appears to be a spontaneous mutation that has taken out the whole of the B genome ASN2. The spontaneous mutation is a much bigger event than anything we’re doing artificially.
Regulatory Barriers in Europe
Ironically, no regulation applies to that much bigger genetic event or to chemical mutagenesis. But currently in Europe, plants carrying the CRISPR/Cas9-induced targeted mutation have to be treated and risk assessed as if they were GM plants.
The regulatory situation is a massive disincentive for anyone to invest in gene editing and gene editing technologies in Europe. We do have support from five plant breeders, but commercialisation of our work in Europe, if it goes ahead, will probably involve the plants carrying chemically-induced mutations rather than gene edits if the regulatory situation continues, even if that approach turns out to be less effective. Europe’s over-regulation of crop biotechnology is, therefore, compromising our efforts to improve food safety.
Nigel Halford, Principal Research Scientist, Rothamsted Research will be presenting on ‘Genomics and gene editing for ultra-low acrylamide wheat’ at the 8th Plant Genomics and Gene Editing Congress.
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