ORIGINAL RESEARCH article
Front. Soft Matter
Sec. Foams
This article is part of the Research TopicFood Foams: Where Do We Stand? Recent Advances and Emerging ApplicationsView all articles
Foam Cleaning in Closed Circuits: Effect of surfactant type on foam structure and Bacillus subtilis spore removal from stainless steel surfaces
Provisionally accepted
- 1EPLEFPA - ENILV, La Roche sur Foron, France
- 2Universite de Lille, Lille, France
- 3Université de Caen Normandie, Caen, France
- 4ACTALIA, Saint-Lô, France
- 5Universite Polytechnique Hauts-de-France Bibliotheque Universitaire du Mont Houy, Valenciennes, France
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Foam cleaning represents an environmentally and economically attractive alternative to conventional cleaning-in-place (CIP) processes for removing microbial contamination in food and bioprocessing industries. This study systematically compared three surfactants, sodium dodecyl sulfate (SDS), Ammonyx® LO, and Capstone® FS-30, to understand how surfactant type influences foam structure and cleaning performance. Stainless steel coupons contaminated with Bacillus subtilis 98/7 spores were cleaned under identical flow conditions using foam generated at a nominal air fraction of 0.5 and a mean velocity of 1.8 cm·s⁻¹. SDS achieved the highest spore removal (1.9 log₁₀ reduction after 20 min), with superior kinetic detachment (K₁ = 114.75 s⁻¹; f = 98.2%), while Ammonyx® LO (0.83 log₁₀) and Capstone® FS-30 (0.55 log₁₀) performed significantly worse. These differences were attributed to foam structural properties: SDS produced fine, stable bubbles persisting for 24 hours, while Ammonyx® LO and Capstone® FS-30 collapsed after 8 and 3 hours, respectively. Image analysis revealed local air fractions of 0.88 (SDS), 0.79 (Ammonyx), and 0.96 (Capstone) in the test section, confirming dry foam behavior. Theoretical analysis using Bretherton's model and microscopic observations showed that SDS's low capillary number promotes strong Marangoni stabilization and thin lamellae, generating sustained wall shear stress fluctuations essential for spore detachment. This study demonstrates that foam cleaning efficiency is primarily determined by surfactant-controlled variations in bubble size, foam stability, and interfacial properties. SDS provides the optimal balance for achieving efficient and sustainable foam-based cleaning.
Keywords: B. subtilis spores, capillary number, Cleaning kinetics, Foam cleaning, sds, shear stress, surfactants
Received: 20 Nov 2025; Accepted: 05 Feb 2026.
Copyright: © 2026 AL SAABI, DALLAGI, JHA, ALOUI, BENEZECH and FAILLE. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
* Correspondence: Heni DALLAGI
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