Got Wood?

Wood could be Food

When we walk across a green field or wander through a forest, we are surrounded by the plant polymers which give the vegetable kingdom its many forms. Cellulose, the most prevalent organic polymer on the planet, is a structural and flexible element in all plant cell walls. A polysaccharide formed of many hundreds of glucose molecules linked together, it is the dominant fiber in plants such as the grasses; and in rayon, cotton and paper. 

Hemicellulose, a variant of cellulose, contains other sugars as well as glucose and is the third most common naturally occurring polymer. It is processed in various ways to make agar, curdlan, xanthan and other compounds used to improve the texture of various foods, but is not consumed in significant amounts. 

In between cellulose and hemicellulose in the polymer league table is lignin. It is the major fiber in wood, and unlike the other two it is a polyphenol. The fiber that gives wood its rigidity and structural strength, it is primarily used at this time as a building material and renewable energy source.

When we eat unprocessed plant foods we consume significant amounts of cellulose and hemicellulose, and trace amounts of lignin. We cannot digest them so they simply pass through, providing regularity on the way. Nevertheless, plant polysaccharides are hugely important in human nutrition. Starch derived from cereals or roots and tubers is a food staple in every culture, and plant fibers such as inulin, 1-3, 1-4 beta glucans and resistant starch are prebiotics we must eat to maintain a heathy microbiome. But these are minority compounds, way down the pecking order of global plant polymer production. Most plant polysaccharides end up as waste.

But suppose it didn’t have to be like that. If we could eat cellulose and hemicellulose (and from here on in I’ll refer to them both as cellulose), food production would increase dramatically. Every ton of harvested grain is accompanied by 2 to 3 tons of cellulose-rich scrap. We eat corn but not the cob, olive fruits but not the leaves, sugar but not the bagasse, apples but not (usually) the cores … and there are many billions of tons more of cellulose produced in inedible plants and weeds grown on marginal lands that require no irrigation, fertilizer or pesticides. 

If these waste streams could be converted to glucose and then alcohol or starches, food shortages would disappear, the grain weapon would lose its power, and food crops such as corn and sugar cane would no longer be required for biofuel. World economics – and therefore politics – would be transformed. 

If you’re the kind of person who studies food labels you’ll know that food manufacturers already put cellulose in food, but that’s only to enhance texture or reduce calorie density. Commonly listed as carboxymethylcellulose, microcrystalline cellulose, or MCC, it is perfectly safe to eat but has zero nutritional value for us. 

Some animals, however, can convert cellulose into calories. Sheep and goats, horses, cows and camels, elephants and antelopes (and termites) live on cellulose because their microbiomes contain symbiotic bacteria that break down cellulose to simple sugars. For ruminants, cellulose is a prebiotic fiber and a fuel. If only we could be more like sheep …

Seven years ago, a paper was published in the august Proceedings of the National Academy of Science (1) which showed that we could indeed be like sheep, at least by proxy. A team of scientists at Virginia Polytechnic Institute and State University took genes from various bacteria and soil fungi that break down cellulose, and other genes from plants such as the potato that produce starch, and introduced them into E coli. This bacterial work-horse promptly started to eat cellulose and churn out starch, the biological equivalent of transmuting lead into gold. The system converted cellulose to amylose with an efficiency of about 30%, which was a promising start but not yet commercial.

Five years later, a collaboration by five Japanese research centers announced the production of significant amounts of clean glucose and ethanol from cedar wood (2), using a combination of mechanical and enzymatic means rather than the harsh chemicals that had previously been used but produced unacceptable levels of contaminants. 

Another Japanese group working with similar technology reported almost complete enzymatic conversion of cellulose to glucose (3); and an Indian team reported success using a fermentation system to produce sugar from bamboo (4), the most rapidly growing source of cellulose and a hugely efficient transducer of solar energy. The prospect of food and energy independence in the tropics and sub-tropics is positively disruptive, and would transform the economies of Jamaica, Java and Japan. (And that’s just the J’s).

A year later again, researchers from the Max Planck Institute for Coal Research in Mülheim, Germany reported a significantly more efficient approach to cellulose digestion (5). Their technology utilises a combination of ionic solvents and solid-state acidic resins to generate sugar from cellulose from almost any source, including wood. The process is efficient but expensive due to the costs of the solvents used, so it is not yet commercial; but you can see that the race to produce cheap sugar from plant waste is approaching the finish line. It is a green gold rush which will eventually replace black gold as the world’s primary energy source. (The technical complexity of fusion and thorium cycle systems make them harder to predict).

A fourth industrial group, the EU-funded start-up Arbiom, utilises a different approach to turn wood into edible protein (6, 7). It is basically a fermentation process. They use a yeast which is related (distantly) to the fungi you often see growing on trees, and which uses similar enzymes to digest cellulose and turn it into biomass. 

Unlike most tree fungi, however, Torula yeast is edible and has an impressive nutritional profile, combining 60% protein, 25% carbohydrates and 2% fat. 60% protein beats soy concentrate, matches whey protein concentrate and is comparable in cost. It is a better source of the amino acids lysine, methionine, and threonine than other plant protein concentrates, making it eminently suitable for animal feed, body building and human foods in general. With the typical umami flavour you find in many yeast hydrolysates, it would require minimal processing to produce Marmite (Vegimite for my Oz friends), which some people regard as food.

Arbiom are working with sawdust and other waste streams from the paper, pulp and wood processing industries, so their method is environmentally sound as well as cost-effective. The finished product will be appearing in foods and protein powders circa 2023, and will be listed on the label as ‘inactive dried yeast’ or possibly ‘Sylpro’. The word ‘Sylpro’ derives from sylvan protein which, as any language geek will tell you, is a mash-up of Latin and Greek meaning ‘first from the forest’. So ‘Arbiom’, which is a similar mash-up linking trees and either biomass or microbes, get a blue ribbon for neology too.

Their Torula technology is enough, if it is capitalised on, to bridge the global protein gap. It is not the answer to the global calorie gap, but this milestone is not far off. If we get there intact, despite the best attempts of the current crop of political buffoons and blowhards, there is a real possibility that the sociopathy of the centralised state will dissolve into a more diffuse and more human- and eco-friendly system.

And lignin? That, too, looks promising (8). Potential high value applications include anti-bacterial (9) and anti-retroviral (10) compounds, plus a host of lower value (but still commercially very relevant) applications in bioplastics (11) and bio-oils (12), agriculture, composite and building materials, and industrial emulsifiers and dispersants. The Max Plank Institute are major players in this sector too (12), and are among the growing number of experts who see the wood and the trees.

The forest may not come to Dunsinane, but it will soon be coming to dinner.

References

1. You C, Chen H, Myung S, Sathitsuksanoh N, Ma H, Zhang XZ, Li J, Zhang YH. Enzymatic transformation of nonfood biomass to starch. Proc Natl Acad Sci U S A. 2013 Apr 30;110(18):7182-7.
2. Navarro RR, Otsuka Y, Nojiri M, Ishizuka S, Nakamura M, Shikinaka K, Matsuo K, Sasaki K, Sasaki K, Kimbara K, Nakashimada Y, Kato J. Simultaneous enzymatic saccharification and comminution for the valorization of lignocellulosic biomass toward natural products. BMC Biotechnol. 2018 Dec 12;18(1):79.
3. Asada C, Sasaki C, Hirano T, Nakamura Y. Chemical characteristics and enzymatic saccharification of lignocellulosic biomass treated using high-temperature saturated steam: comparison of softwood and hardwood. Bioresour Technol. 2015;182:245-250.
4. Pandey RK, Chand K, Tewari L. Solid state fermentation and crude cellulase based bioconversion of potential bamboo biomass to reducing sugar for bioenergy production. J Sci Food Agric. 2018 Sep;98(12):4411-4419.
5. Rechulski K, Daniel M, Käldström M, Udo R, Schüth F, Roberto R. (2015). Mechanocatalytic Depolymerization of Lignocellulose Performed on Hectogram and Kilogram Scales. Industrial & Engineering Chemistry Research. 54. 10.1021/acs.iecr.5b00224
6. Øverland M, Skrede A. Yeast derived from lignocellulosic biomass as a sustainable feed resource for use in aquaculture. J Sci Food Agric. 2017 Feb;97(3):733-742.
7. Chen M, Li Q, Zhang Y, Li H, Lu J, Cheng Y, Wang H. Xylo-oligosaccharides enriched yeast protein feed production from reed sawdust. Bioresour Technol. 2018 Dec;270:738-741.
8. Graichen F.H.M., Grigsby W.J., Hill S.J., Raymond L.G., Sanglard M., Smith D.A., Thorlby G.J., Torr K.M., Warnes J.M. Yes, we can make money out of lignin and other bio-based resources. Ind. Crops Prod. 2017;106:74–85.
9. Oeyen M, Noppen S, Vanhulle E, Claes S, Myrvold BO, Vermeire K, Schols D. A unique class of lignin derivatives displays broad anti-HIV activity by interacting with the viral envelope. Virus Res. 2019 Dec;274:197760.
10. Nada AMA, El-Diwany AI, Elshafei AM. Infrared and antimicrobial studies on different lignins. Acta Biotechnol. 1989;9:295–298.
11. Jang J, Ching YC, Chuah CH. Applications of Lignocellulosic Fibers and Lignin in Bioplastics: A Review. Polymers 2019, 11(5), 751
12. Wang G-H, Cao Z, Gu D, Pfänder N, Swertz A-C,  Spliethoff B, Bongard H J, Weidenthaler C, Schmidt W, Roberto R, Schüth F. (2016). Nitrogen-Doped Ordered Mesoporous Carbon Supported Bimetallic PtCo Nanoparticles for Upgrading of Biophenolics. Angewandte Chemie International Edition. 128. 10.1002/ange.201511558.