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Article

Functionalization of Sodium Caseinate for Production of Neat Films: Effects of Casein Crosslinking Induced by Heating at Alkaline pH or Light Exposure

by
Paolo D’Incecco
*,
Stefano Gerna
,
Marta Sindaco
,
Luisa Pellegrino
,
Alberto Barbiroli
,
Veronica Rosi
and
Sara Limbo
Department of Food, Environmental and Nutritional Sciences (DeFENS), Università degli Studi di Milano, Via G. Celoria 2, 20133 Milan, Italy
*
Author to whom correspondence should be addressed.
Foods 2025, 14(16), 2764; https://doi.org/10.3390/foods14162764
Submission received: 27 June 2025 / Revised: 5 August 2025 / Accepted: 6 August 2025 / Published: 8 August 2025
(This article belongs to the Special Issue Effect of the Application of Novel Processes to Food Proteins on Structure, Physicochemical Properties and Modifications)
Versions Notes

Abstract

This study explored the functionalization of sodium caseinate (NaCas) using environmentally friendly approaches to improve the mechanical and structural properties of the derived films. NaCas functionalization was achieved through casein crosslinking using two approaches: (i) thermal treatment at an alkaline pH to induce the formation of lysinoalanine (LAL) and (ii) riboflavin-mediated photo-oxidation to induce the formation of di-tyrosine (di-Tyr). Starting from NaCas (not functionalized, control) obtained from pasteurized milk, three functionalized NaCas samples were prepared: one sample crosslinked by LAL, and two samples crosslinked by di-Tyr formed under LED light either with or without riboflavin. The amount of crosslinking was evaluated in the acid hydrolysates through HPLC methods using either fluorescence (di-Tyr) or MS (LAL) detection. Heat treatment at pH 9 induced the formation of up to 3540 µg of LAL/g casein, whereas LED light exposure in the presence of riboflavin promoted the formation of up to 500 µg of di-Tyr/g casein. The formation of crosslinks at the intermolecular level, which resulted in protein aggregation, was detected by SDS-PAGE. Films were obtained by mixing the water solutions of the four NaCas samples with glycerol as the plasticizer and casting them. The FTIR spectra revealed that the formation of crosslinks also induced changes in the secondary structure of NaCas, which were conserved in the derived films. Mechanical testing demonstrated that di-Tyr crosslinks enhanced film ductility, while LAL crosslinks increased tensile strength and stiffness.
Keywords: sodium caseinate; crosslinking; di-tyrosine; lysinoalanine; caseinate film; thermal treatment; FTIR; mechanical properties sodium caseinate; crosslinking; di-tyrosine; lysinoalanine; caseinate film; thermal treatment; FTIR; mechanical properties

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MDPI and ACS Style

D’Incecco, P.; Gerna, S.; Sindaco, M.; Pellegrino, L.; Barbiroli, A.; Rosi, V.; Limbo, S. Functionalization of Sodium Caseinate for Production of Neat Films: Effects of Casein Crosslinking Induced by Heating at Alkaline pH or Light Exposure. Foods 2025, 14, 2764. https://doi.org/10.3390/foods14162764

AMA Style

D’Incecco P, Gerna S, Sindaco M, Pellegrino L, Barbiroli A, Rosi V, Limbo S. Functionalization of Sodium Caseinate for Production of Neat Films: Effects of Casein Crosslinking Induced by Heating at Alkaline pH or Light Exposure. Foods. 2025; 14(16):2764. https://doi.org/10.3390/foods14162764

Chicago/Turabian Style

D’Incecco, Paolo, Stefano Gerna, Marta Sindaco, Luisa Pellegrino, Alberto Barbiroli, Veronica Rosi, and Sara Limbo. 2025. "Functionalization of Sodium Caseinate for Production of Neat Films: Effects of Casein Crosslinking Induced by Heating at Alkaline pH or Light Exposure" Foods 14, no. 16: 2764. https://doi.org/10.3390/foods14162764

APA Style

D’Incecco, P., Gerna, S., Sindaco, M., Pellegrino, L., Barbiroli, A., Rosi, V., & Limbo, S. (2025). Functionalization of Sodium Caseinate for Production of Neat Films: Effects of Casein Crosslinking Induced by Heating at Alkaline pH or Light Exposure. Foods, 14(16), 2764. https://doi.org/10.3390/foods14162764

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