A Chinese research team has developed an innovative method to produce starch from CO2 through a chemo-enzymatic system. An upcycling process with 8.5 times higher yield than current methods of starch synthesis in corn. (1)
The prospect is to absorb a greenhouse gas to derive the biotech equivalent of a raw material whose demand is growing-for a wide variety of industrial uses, from bioethanol to bioplastics, food and feed, etc. – Is still competing with food.
Starch, characteristics and categories
Starch is a reserve carbohydrate consisting of several glucose units, synthesized by different plants (green leaves, tubers, and cereals). It consists of two units, amylose and amylopectin, in proportions that vary in different plant species and affect different functionalities such as strength, solubility, and gelatinization. (2)
The various categories of starches are distinguished by the number of glucose units and levels of digestibility, measured as the time it takes for enzymes to convert to glucose:
– glucose units. 1. Type A (23-29, cereals), type C (26-29, legumes), type B (30-44, tubers),
– Digestibility of starches. It can be fast (20m), in cooked foods such as potatoes and bread, or slow (>100m) in starches with complex structure. Resistant starches (>120m), on the other hand, are those that promote the development of the gut microbiota. (3)
Industrial applications
Chemical and physical modifications to native starch, by altering the structure of amylose and amylopectin, result in distinctive textures suitable for different uses. (4) In the food sector, as seen, modified starch has similar functionalities to some additives. Thickener, stabilizer, gelling and coating agent in a variety of baked goods but also sauces, soups, desserts, ice cream, etc. (5)
The applications of starches in areas other than food are countless and sometimes involve the use of native starch from different plants. GM maize, rather than other starchy species (e.g., rice, potato, wheat. See footnote 6). For ‘biofuels’ and bio-polymers, the paper industry, animal feed, detergent drugs, cosmetics, etc.
Starch from CO2
Biotech starch was obtained through the combined use of computational models and protein engineering, through the use of specific enzymes capable of catalyzing the reaction. The researchers then experimented with 62 enzymes, in 11 pathways, to find the optimal reaction with methanol obtained from the conversion of CO2.
The selected pathway, ASAP 1.0(Artificial Starch Anabolic Pathway), resulted in greatly increased yields and reduced process intermediates.
The entire process requires only 11 main reactions, compared to the 60 that occur in nature. And it makes it possible to obtain-in 2-4 hours, at a concentration of 1.3-1.6 g/l-a starch with characteristics almost identical to natural starch.
Advantages and disadvantages of the method
Chemo-enzymatic catalysis is a combination of the processes of chemocatalysis and biocatalysis, which allows for a combination of their main advantages. In essence saving resources, time and cost. As well as reducing unstable intermediate compounds and the number of process reactions.
However, the transition from experimental to industrial stage is not immediate. In fact, chemocatalysis and biocatalysis reactions tend to mutually inactivate each other. Therefore, a solution must be developed that can optimize the combination of the two types of catalysis. (7)
Interim conclusions
Chinese technological innovation looks very promising for obtaining starch with significant savings in essential and limited resources such as soil and water. The fine-tuning of the system will make it possible to produce a very versatile product suitable for multiple uses with greater efficiency than in the wild.
The availability of biotech starch may relieve pressure on the agricultural sector to produce corn varieties with non-food fates. With a potentially favorable impact on the supply of safe and nutritious food to the planet’s population. #SDG2(Stop Hunger), #SDG12(Sustainable production and consumption), #SDG15(Life on land).
Dario Dongo and Andrea Adelmo Della Penna
Notes
(1) Cai et al. (2021). Cell-free chemoenzymatic starch synthesis from carbon dioxide. Science 373:1523-1527, https://doi.org/10.1126/science.abh4049
(2) Bashir et al. (2019). Physicochemical, structural and functional properties of native and irradiated starch: a review. J. Food Sci. Technol. 56(2):513-523, https://doi.org/10.1007/s13197-018-3530-2
(3) Magallanes-Cruz et al. (2017). Starch Structure Influences Its Digestibility: A Review. Journal of Food Science 82(9):2016-2023, https://doi.org/10.1111/1750-3841.13809
(4) Ostrander (2019). Maize Starch for Industrial Applications. In: Industrial Crops – Breeding for BioEnergy and Bioproducts. Springer, ISBN 978-1-4939-1447-0
(5) Egharevba (2019). Chemical Properties of Starch and Its Application in the Food Industry. Intechopen , http://doi.org/10.5772/intechopen.87777
(6) Beckles et al. (2014) Use of Biotechnology to Engineer Starch in Cereals. Encyclopedia of Biotechnology in Agriculture and Food, https://doi.org/10.1081/E-EBAF-120051354
(€) Xu et al. (2021). Recent advance of chemoenzymatic catalysis for the synthesis of chemicals: Scope and challenge. Chinese Journal of Chemical Engineering 30:146-167, https://doi.org/10.1016/j.cjche.2020.12.016
Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.
Graduated in Food Technologies and Biotechnologies, qualified food technologist, he follows the research and development area. With particular regard to European research projects (in Horizon 2020, PRIMA) where the FARE division of WIISE Srl, a benefit company, participates.
