Food protection methods assessed by Surface Enhanced Raman Spectroscopy

Importance of the topic

Lipid oxidation represents a critical challenge for the meat industry, leading to flavor deterioration, off-odors and the formation of harmful compounds such as malondialdehyde and cholesterol oxidation products. Consumers’ demand for natural preservation solutions has driven interest in active packaging systems that release antioxidant agents directly into the food environment. Rapid and sensitive analytical methods are necessary to evaluate and optimize such packaging for quality control and product safety.

Objectives and study overview

This study aimed to compare conventional low-density polyethylene (LDPE) packaging with an active film containing oregano extract for preserving ground pork meat. The investigation focused on monitoring lipid oxidation over a 16-day storage period at 5 °C by applying a home-made Surface-Enhanced Raman Spectroscopy (SERS) substrate and cooling system.

Methodology and sample preparation

• Fresh ground pork was portioned into 22 g samples in 5 cm Petri dishes.
• Samples were covered with either an active oregano-extract film or a standard LDPE film and stored under normal atmosphere at 5 °C.
• Lipids were extracted using a n-hexane/diethyl ether mixture (1:1) at days 0, 7, 9, 11, 14 and 16.
• A home-made SERS substrate consisting of silver nanoparticles deposited on glass was used for enhanced detection.
• Analyses were conducted at –2 °C on a Thermo Scientific DXR3 Raman Microscope with a 532 nm laser, 10× objective, 5 mW power and 20 × 30 s exposures.
• Lipid oxidation was quantified by the area ratio between the 1655 cm⁻¹ (C=C stretch) and 1439 cm⁻¹ (CH₂ scissoring) bands.

Used instrumentation

• Thermo Scientific DXR3 Raman Microscope (532 nm, 900 lines/mm grating, 50–3500 cm⁻¹ range, 10×/NA 0.40).
• Home-made SERS substrate with silver nanoparticles on glass Petri dishes.
• Custom cooling system enabling measurements at –2 °C.

Key results and discussion

SERS measurements yielded an enhancement factor on the order of 10⁷ for both 1439 cm⁻¹ and 1655 cm⁻¹ bands, significantly improving sensitivity and reducing acquisition times. The relative change of unsaturation (RCU%) increased progressively, with a marked acceleration after day 7. Across all time points, samples in active packaging exhibited consistently lower RCU% values than those in conventional LDPE, confirming superior protection against lipid oxidation.

Benefits and practical applications

• Highly sensitive detection of oxidative changes with minimal sample preparation.
• Rapid data acquisition enabled by strong SERS signal enhancement.
• Validation of oregano‐based active films as effective natural antioxidant packaging.

Future trends and applications

Advancements may include integration of portable SERS devices for in-field quality control, development of standardized and reproducible SERS substrates, extension to other food matrices and real-time in-line monitoring systems within production environments.

Conclusion

The combination of a home-made silver nanoparticle SERS substrate and a cooling system demonstrated rapid, sensitive monitoring of lipid oxidation in ground pork. Active packaging containing oregano extracts effectively delayed oxidation compared to conventional LDPE. This approach offers a valuable tool for optimizing natural preservation technologies.

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