By Eben van Tonder, 5 July 2025

Introduction: Trees from Air, Fibre from Fire

What holds a tree upright? What makes its body firm, its growth rise from the soil as if by magic? What compound in this great green alchemy defied microbial decay long enough to become coal? And why did nature, over millions of years, select such materials that now bind our sausages, gel our fruit jams, and clean our intestines?

This article traces the journey of plant bulking agents like lignin, cellulose, hemicellulose, and pectin from their evolutionary origins in prehistoric forests, through their chemical transformations and microbiological resistance, to their modern applications in food and meat processing. It explores how trees are built from air, how carbon is stored in fibre, and how dietary bulking agents—from the natural to the modified—serve health, structure, and sustainability.

1. The Strength of Trees: Lignin and Cellulose

Lignin and cellulose form the core of a tree’s strength. Cellulose—a linear polymer of glucose—is the most abundant organic polymer on Earth. It forms rigid, cable-like microfibrils within plant cell walls. Lignin, a complex aromatic polymer, infiltrates the spaces between these cellulose fibrils, creating a water-resistant, rot-resistant matrix. Together, these give wood its rigidity and resilience.

The evolutionary appearance of lignin during the Devonian–Carboniferous periods (~400–300 million years ago) allowed plants to grow tall and upright. But this strength came with an unintended consequence: lignin was almost indigestible to early microbes. Thus, fallen trees did not decompose but were buried in anaerobic conditions, leading to the massive coal beds of the Carboniferous era.

It wasn’t until around 290 million years ago that white rot fungi evolved enzymes like lignin peroxidase and manganese peroxidase, initiating the microbial digestion of lignin and ending large-scale coal formation. This represents a major shift in Earth’s carbon cycle, from burial to respiration.

2. Photosynthesis: Building Bulk from Air

The bulk of a tree does not arise from soil. Rather, it is photosynthesis that drives the accumulation of biomass:

6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2

The glucose (C6H12O6) produced is polymerised into cellulose and other structural carbohydrates. The tree exhales oxygen and retains carbon—fixing the gas of the air into the wood of its body. About 50 percent of wood’s dry mass is carbon drawn from atmospheric CO2.

When a tree is burned, or when coal is combusted, this carbon re-combines with oxygen to form CO2, releasing the stored energy of ancient sunlight. Thus, the carbon cycle comes full circle—from photosynthesis to fire.

3. Evolution of Plant Cell Wall Polymers

Plants evolved a composite wall made of:

• Cellulose: tensile strength
• Hemicellulose: cross-links cellulose, flexible
• Lignin: structural glue, hydrophobic barrier
• Pectin: gel-like matrix, cell adhesion, especially in fruits

These polymers likely co-evolved with the complexity of plant tissues. Pectin, in particular, became critical in angiosperms (~125 million years ago), enabling soft tissues in fruit that could harden (unripe) and soften (ripe) to control seed dispersal.

Unripe fruits are firm due to proto-pectin, which gradually degrades via polygalacturonase during ripening. This makes the fruit attractive for animal consumption, ensuring seed dispersal. Once pectin is degraded, the fruit softens and the seed can be released.

4. Coal, Fibre, and the Gut: Human and Animal Nutrition

What was once resistant to decay became known in modern times as dietary fibre. Humans lack enzymes to digest cellulose, lignin, or most hemicelluloses, so these pass through the gut undigested, acting as bulking agents:

• Insoluble fibre: cellulose, lignin (adds bulk, speeds transit)
• Soluble fibre: pectins, some hemicelluloses (forms gels, slows absorption, feeds gut microbes)

These fibres retain water, improve stool consistency, regulate blood sugar, and modulate cholesterol. In animal health, particularly in monogastrics, fibre stimulates mucosal activity and improves gut motility. In ruminants, microbes digest cellulose for energy, but lignin remains largely inert.

5. Fibre in Meat Processing: Binding, Firming, Hydration

Food technologists harness fibre for more than nutrition. In meat and plant-based products, bulking fibres improve texture, juiciness, yield, and reduce cost. Examples include:

• Cellulose: added to sausages for water binding and bulk
• Citrus fibre: rich in pectin, used in burgers and frankfurters
• Cacao husk fibre: high in lignin, increases emulsion stability

These fibres absorb water (up to 5–10 times their weight), stabilise emulsions, and provide structure. They reduce cooking loss and simulate fat’s texture without its calories.

6. Pectin in Jam and Fruit Processing

Pectin forms gels under acidic, high-sugar conditions. That’s why jam sets. Unripe apples, quince, and citrus peels are pectin-rich and traditionally used to make pectin stock for jams.

In ripening fruit, pectin chains are enzymatically cleaved, reducing gelling capacity. Thus, green apples are prized for jam because they retain more intact pectin.

7. Methylcellulose: From Chemistry Lab to Veggie Burger

Methylcellulose (MC) is a human-made cellulose ether, first synthesised by Theodor Suida in 1905. It is produced by treating cellulose with methyl chloride in alkali conditions. The result: a cold-water-soluble fibre that gels when heated, typically between 50–60°C.

• Cold water: dissolves into a viscous liquid
• Heating: forms a thermo-reversible gel
• Cooling: returns to liquid

This unique property is used in:

• Plant-based meat (heat-induced firmness)
• Gluten-free baking (structure)
• Fibre supplements (bulk laxative)

MC is not found in nature but is derived from plant cellulose. It’s safe, non-digestible, and approved in most jurisdictions as food additive E461.

8. Hydration and Thermal Behaviour of Bulking Agents

Agent Hydration Temp Max Water Binding Gelling Temp Digestibility Cellulose Any (50°C ideal) 3–10× weight None Indigestible Lignin Insoluble Minimal None Indigestible Pectin ~100°C (boiling) ~100× in jams Cools to gel Partly fermentable Methylcellulose Dissolve <40°C 20×+ 50–60°C Indigestible Hemicellulose 40–70°C Variable Some gel Variable

Hydration improves with moderate heat (~50°C) for most fibres due to reduced water viscosity and polymer unfolding. Overheating can denature or prematurely gel some fibres. Proper hydration is key to uniformity in food matrices.

Conclusion: A Cycle of Strength, Health, and Innovation

From the first trees that defied gravity to the food innovations of the twenty-first century, plant bulking agents have shaped ecosystems, energy storage, digestion, and diet. They evolved to resist rot, built empires of carbon, and now fortify our diets and reformulated meat products.

What once made coal, now makes fibre. What once held a fruit firm until the time was right, now holds your vegan burger together on the grill.

And at the heart of it all is air—fixed by light, hardened by chemistry, transformed by fungi, and repurposed by food scientists into a better future.

References

1. Biello, D. (2012). Scientific American. White Rot Fungi and the End of Coal.
2. Harvard T.H. Chan School of Public Health – Nutrition Source on Dietary Fibre.
3. Cirmaci, M., et al. (2022). Functional Properties of Dietary Fibres in Meat Products. Foods, 11(6).
4. Saladino, F. et al. (2017). Fruit Ripening and Cell Wall Disassembly. Front. Plant Sci.
5. Wikipedia: Methylcellulose; Cellulose Derivatives History; E461.
6. OrchardNotes.com. Traditional Jam Recipes with Green Apples.
7. Penn State Extension. Tree Carbon Storage and Photosynthesis.
8. Food Hydrocolloids Handbook – Functional Properties of Methylcellulose.
9. IFT.org: Role of Dietary Fibre in Functional Food Design.
10. Britannica.com: Hemicellulose and Plant Cell Wall Components.
11. National Institutes of Health (NIH): Fibre and Gut Health.

Copyright © 2025 by Eben van Tonder, EarthwormExpress. All rights reserved.