30: Citric Acid Is Not What You Think - How Form Concentration and Context Change Everything with Dr. Rob Karlinsey and Tami

What if citric acid is not inherently good or bad, but misunderstood because formulation context is rarely explained?

In this episode of Dental Formulator’s Playbook, Dr. Rob and co-host Tami take a deep, science-first look at one of the most widely used yet misunderstood ingredients in modern products: citric acid. Building on earlier episodes that examined citric acid’s role in foods and dental erosion, this conversation explores how citric acid is made, why it appears in everything from toothpaste to skincare to cleaners, and how its chemistry changes depending on form, concentration, and context.

Dr. Rob explains the critical distinction between citric acid and citrate, why hydration state matters for formulators, and how citric acid functions as a buffer, chelator, preservative, and flavor modifier. The discussion traces citric acid’s industrial production back to early fermentation research, its historical link to penicillin scale-up through Pfizer, and its foundational role in cellular energy via the Krebs (citric acid) cycle. The episode also examines citric acid’s use in cosmetics as an alpha hydroxy acid, in household cleaners, in laboratory sample preservation, and in encapsulated food applications.

Rather than framing citric acid as “good” or “bad,” this episode emphasizes understanding concentration, buffering, formulation design, and intended use to make informed decisions across oral care, food, skincare, and consumer products.

Key Topics Covered

The difference between citric acid and citrate in aqueous systems
Why citric acid and sodium citrate behave the same once dissolved in water
Hydration states of raw materials (anhydrous, monohydrate, dihydrate) and why they matter for formulation accuracy
How citric acid functions as a buffer in pharmaceuticals and oral care products
Why citric acid is considered a natural ingredient despite industrial-scale production
Fermentation-based production of citric acid using Aspergillus niger
The historical link between citric acid scale-up and penicillin mass production
Pfizer’s role in advancing fermentation technology during World War II
James Currie’s 1917 research and its lasting impact on microbial production methods
Why fermentation is still the dominant method for producing citric acid today
Citric acid’s role in metabolism through the Krebs (citric acid) cycle
Alpha hydroxy acids (AHAs) and citric acid’s role in skincare formulations
Concentration differences between dental products, foods, cosmetics, and cleaners
Why buffering citric acid is critical in oral care and pharmaceutical products
Citric acid use in household cleaners, including modern low-toxicity formulations
Encapsulated citric acid in food applications and controlled-release systems
Why formulation context matters more than ingredient labels alone

Highlights and Takeaways

Citric acid and citrate are chemically linked and convert based on pH once dissolved
Hydration state affects raw material weighing, not final function in solution
Fermentation, not fruit extraction, is how citric acid is produced at scale
Citric acid production enabled the industrial-scale manufacture of penicillin
The same citric acid found in foods, like lemons, is chemically identical to that produced by fermentation
Citric acid is central to cellular energy metabolism through the Krebs cycle
In oral care and pharmaceuticals, citric acid must be buffered for stability and safety
Concentration determines function, from gentle buffering to aggressive exfoliation
Lack of testing, not citric acid itself, creates risk in consumer products
Understanding chemistry allows better decisions across food, dental, skincare, and cleaning products

References

Fermentation of Citric Acid and Penicillin History