Influence of Talc Substitution with Starches from Different Botanical Origins on Rheological and Absorption Properties of Stiff Zinc Oxide Paste Formulations

Our plain-English summary of Influence of Talc Substitution with Starches from Different Botanical Origins on Rheological and Absorption Properties of Stiff Zinc Oxide Paste Formulations, by D. Zaklan, N. Davidović, J. Milutinov, et al (Pharmaceutics, 2025).

The study

• Authors: D. Zaklan, N. Davidović, J. Milutinov, D. Ćirin, V. Krstonošić, N. Pavlović
• Journal: Pharmaceutics
• Published: 2025;17(5)
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Zinc oxide paste is traditionally compounded and applied in the therapy of various skin conditions. However, prolonged use of talc, usually present in zinc oxide pastes, may pose health risks due to potential contamination with asbestos and quartz, highlighting the need for alternative excipients. This study aimed to examine the effects of starches from various botanical sources and their particle size on the rheological and absorption properties of zinc oxide paste. Methods: Eight zinc oxide paste formulations were prepared, containing 25% zinc oxide and 25% indifferent excipient (talc, tapioca, rice, or maize starch) in two particle sizes. Rheological properties were assessed using amplitude and frequency sweep tests, and water- and oil-absorption capacities were determined using a centrifugation-based method. Results: Amplitude sweep tests confirmed the predominant solid-like nature of zinc oxide pastes, with the elastic modulus (G') exceeding the viscous modulus (G″) in all formulations. Tapioca starch-based pastes exhibited the highest G' and G″ values, while talc-based pastes exhibited the lowest. Frequency sweep tests showed that pastes were resistant to structural changes under stress, with G' consistently dominating over G″ across the entire frequency range. Tapioca starch-based formulations exhibited the highest water-absorption capacity, while the talc-based formulations had the highest oil-absorption capacity. Reducing particle size improved both water- and oil-absorption capacities. Conclusions: Starches may be considered as alternatives to talc in zinc oxide pastes, due to their ability to modify the absorption and rheological properties of pastes. Future studies should assess the impact of starch substitution on sensory characteristics, shelf-life stability, and patient satisfaction.

In plain English

This was a laboratory study of pharmacy-made zinc oxide skin paste, not of people or asbestos exposure. The authors noted that talc, the paste's usual powder, often occurs with asbestos and quartz; they tested starches instead. The article does not report testing the talc for asbestos. Eight pastes each contained 25% zinc oxide, 25% talc or tapioca, rice or maize starch (sieved to 140 or 355 micrometres) and 50% soft paraffin. All pastes behaved mainly like solids. Talc pastes had the lowest elastic and viscous modulus values and significantly lower complex viscosity than starch pastes. Absorption was the weight of liquid retained, as a percentage of the weight of liquid added. Water absorption ranged from 1.6 to 4%, highest with tapioca starch and lowest with talc. Oil absorption ranged from 5.8% to 9.2% for olive oil and 7.2% to 12.2% for paraffin oil, highest with talc. The authors concluded that replacing talc with starches is justified in this context. They added that texture, sensory and stability testing is needed, and that microbiological stability was not tested.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory formulation experiment (pharmaceutical paste testing); no human or animal subjects
• Who was studied: Eight laboratory-made stiff zinc oxide paste formulations, using tapioca starch, rice starch, maize starch or talc, each in two particle sizes (140 and 355 micrometres)
• Exposure: Not an asbestos exposure study. The pastes contained talc (the conventional excipient) or tapioca, rice or maize starch at 25%, with 25% zinc oxide and 50% soft paraffin. The authors' stated motivation was that talc often co-occurs with asbestos and quartz. No asbestos testing of the talc is reported.
• Main results:
  • In all eight pastes the elastic (solid-like) properties dominated the viscous properties. The tangent of the phase angle (tan δ) stayed below one for all pastes; at 50 Pa it ranged from 0.2221 to 0.2946.
  • Elastic modulus (G′) plateau values ranged from 3.146 × 10^5 Pa (P8, talc, 355 micrometres) to 13.06 × 10^5 Pa (P1, tapioca starch, 140 micrometres).
  • The lowest elastic (G′) and viscous (G″) modulus values were recorded for the talc-based pastes (P7, P8).
  • Talc pastes (P7, P8) had significantly lower complex viscosity than the starch pastes.
  • Method for all absorption results: 0.50 g of paste was mixed with 5 mL of water or oil and centrifuged. Absorption capacity was the gain in sample mass divided by the mass of liquid (solvent) added, times 100. It was not a percentage of paste mass.
  • Water absorption capacity, as a percentage of the water added, ranged from 1.6 to 4%. It was highest for tapioca starch pastes (P1, P2) and lowest for talc pastes (P7, P8).
  • The paste with the smaller tapioca starch particles (P1) had significantly better water absorption than all other pastes (p less than 0.05).
  • Oil absorption capacity, as a percentage of the oil added, ranged from 5.8% to 9.2% for olive oil and from 7.2% to 12.2% for paraffin oil. Talc pastes absorbed the most oil.
  • Talc pastes had significantly higher olive oil absorption than three of the starch pastes (P2, P3, P4), and significantly higher paraffin oil absorption than all six starch pastes (P1 to P6).
  • For water absorption, the effect of particle size was statistically significant only for the tapioca starch pastes.
• The authors' conclusion: The authors concluded that substituting starches for talc is justified in this context. They said further textural measurements, sensory analyses and stability testing of raw materials and final preparations are needed.
• Limitations the authors state:
  • No textural or sensory analysis was performed, and there was no microbiological stability testing of the raw excipients or the final pastes.

Topics

Medical terms in this study, explained in our Lexicon: Talc.

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