Food protection methods assessed by Surface Enhanced Raman Spectroscopy

Importance of the Topic

Maintaining the quality and safety of meat products is a critical challenge for the food industry. Lipid oxidation not only degrades flavor, aroma and texture but also generates potentially harmful compounds. Innovative analytical methods that enable rapid, sensitive monitoring of oxidation are therefore essential. Surface-Enhanced Raman Spectroscopy (SERS) offers high specificity and signal amplification, making it a promising tool to assess packaging strategies aimed at slowing oxidation in fresh meat.

Objectives and Study Overview

This study evaluated the protective performance of conventional low-density polyethylene (LDPE) packaging versus an active packaging film containing oregano extract. A homemade SERS substrate and a custom cooling system were used to monitor lipid oxidation in ground pork over 16 days. Key objectives included:

• Comparing conventional Raman and SERS signal intensities for lipid oxidation markers.
• Quantifying oxidation rates under different packaging conditions.
• Demonstrating the efficiency of a homemade SERS substrate for routine quality control.

Methodology and Instrumentation

Sample Preparation and Storage:

• Fresh ground pork (22 g) placed in polystyrene dishes, covered with either conventional LDPE or active oregano-infused film, and stored at 5 °C.
• Lipid extraction from samples after 0, 7, 9, 11, 14 and 16 days using n-hexane/diethyl ether (1:1).

SERS Analysis:

• Homemade substrate: silver nanoparticles deposited on glass Petri dishes.
• Custom cooling stage maintained -2 °C during measurements.
• Thermo Scientific DXR3 Raman Microscope with 532 nm laser, 10× objective (NA 0.40), 900 lines/mm grating, 5 mW power, 20×30 s exposures.
• Data processing with OMNIC™ v.9.2 software.

Oxidation Monitoring:

• Peak ratio between 1655 cm⁻¹ (C=C stretch) and 1439 cm⁻¹ (CH₂ scissoring) used to calculate relative change of unsaturation (RCU%).

Main Results and Discussion

SERS vs. Conventional Raman:

• SERS provided a signal enhancement factor of ~1×10⁷ for both 1439 cm⁻¹ and 1655 cm⁻¹ bands, enabling clear detection of oxidation markers.
• Conventional Raman spectra showed minimal differences between packaging types, whereas SERS spectra revealed pronounced changes in unsaturation after 7 days.

Oxidation Trends:

• RCU% increased steadily over time, accelerating after day 7 for both packaging types.
• Active packaging samples consistently exhibited lower RCU% values compared to LDPE, confirming the antioxidant effect of oregano extract.

Benefits and Practical Applications

The combined use of a SERS substrate and cooling stage offers:

• Rapid, sensitive detection of early oxidation events.
• Minimal sample preparation and handling.
• Potential integration into quality assurance workflows for meat and other lipid-rich foods.

Active packaging with natural antioxidants can extend shelf life and improve product quality without synthetic additives.

Future Trends and Potential Applications

Advancements may include:

• Optimization of SERS substrates for portability and cost-effectiveness.
• Extension of the approach to other food matrices (dairy, oils, seafood).
• Automated inline monitoring systems in processing lines.
• Development of multifunctional packaging combining barrier and sensing capabilities.

Conclusion

This work demonstrated that a home-made SERS substrate coupled with a low-temperature measurement setup can sensitively track lipid oxidation in packaged ground pork. The approach outperformed conventional Raman by a factor of ~10⁷, revealing clear differences between standard LDPE and oregano-infused active packaging. Such tools hold strong promise for rapid, high-throughput quality control and for guiding the design of innovative antioxidant packaging solutions.

Reference

1. Morrissey PA, Buckley DJ, Sheehy PJA, Monahan FJ. Vitamin E and meat quality. Proc Nutr Soc. 1994;53(2):289–295.
2. Brewer MS, Ikins WG, Harbers CAZ. TBA values, sensory characteristics, and volatiles in ground pork during long-term frozen storage: effects of packaging. J Food Sci. 1992;57(3):558–564.
3. Formanek Z, Kerry JP, Higgins FM, Buckley DJ, Morrissey PA, Farkas J. Addition of synthetic and natural antioxidants to α-tocopheryl acetate supplemented beef patties: effects of antioxidants and packaging on lipid oxidation. Meat Sci. 2001;58(4):337–341.
4. Nerín C, Tovar L, Salafranca J. Behaviour of a new antioxidant active film versus oxidizable model compounds. J Food Eng. 2008;84(2):313–320.
5. Camo J, Beltrán JA, Roncalés P. Extension of the display life of lamb with an antioxidant active packaging. Meat Sci. 2008;80(4):1086–1091.
6. Sharma B, Frontiera RR, Henry AI, Ringe E, Van Duyne RP. SERS: materials, applications, and the future. Mater Today. 2012;15(1–2):16–25.
7. Le Ru EC, Blackie E, Meyer M, Etchegoin P. Surface enhanced Raman scattering enhancement factors: a comprehensive study. J Phys Chem C. 2007;111(37):13794–13803.
8. Wrona M, Lours J, Salafranca J, Joly C, Nerín C. Innovative surface-enhanced Raman spectroscopy method as a fast tool to assess the oxidation of lipids in ground pork. Appl Sci. 2023;13(9):5533.