Egg Freshness Safety and Detection Techniques: A Comprehensive Review and Future Perspective

Globally, annual egg production has steadily increased, and liquid eggs are gradually replacing shell eggs, with the potential to become the dominant form of future egg consumption. However, current freshness evaluation systems mainly focus on shell eggs, with almost no global standard for liquid eggs. Beginning with deterioration mechanisms of egg freshness, this review systematically summarizes traditional and novel techniques for egg freshness detection, covering principles, attributes (accuracy, cost, model, duration, sample integrity), and potentials (online and automated detection), with particular emphasis on applicability to shell eggs and liquid eggs. Among traditional techniques, Haugh unit and candling are authoritative but limited to shell eggs. Among novel techniques, Raman spectroscopy has proven effective for evaluating liquid egg yolk freshness, and electrochemical-chemometric detection has been applied to liquid egg white. In addition, low-field nuclear magnetic resonance characterizes water distribution in liquid eggs, olfactory sensors monitor volatile compounds during storage, and machine vision and microwave near-field imaging also show potential for evaluating liquid egg freshness. Meanwhile, all above techniques are nondestructive and show strong potential for online, continuous, and automated detection. For modeling: deep learning, machine learning, and stacking ensemble strategies have enabled hyperspectral imaging and dielectric spectroscopy to achieve 100% accuracy. In context of Food Industry 4.0, future research should integrate diverse models with promising techniques to enhance applicability to both shell and liquid eggs and improve practicality, thereby providing critical references for establishing global standards on liquid egg freshness.