Nondestructive Discrimination of Lead (Pb) in Preserved Eggs (Pidan) by Near-Infrared Spectroscopy and Chemometrics

Lu Xu,Xiao-Ping Yu,Si-Min Yan,Chen-Bo Cai

doi:10.1155/2014/253143

Abstract

A major safety concern with pidan (preserved eggs) has been the usage of lead (II) oxide (PbO) during its processing. This paper develops a rapid and nondestructive method for discrimination of lead (Pb) in preserved eggs with different processing methods by near-infrared (NIR) spectroscopy and chemometrics. Ten batches of 331 unleaded eggs and six batches of 147 eggs processed with usage of PbO were collected and analyzed by NIR spectroscopy. Inductively coupled plasma mass spectrometry (ICP-MS) analysis was used as a reference method for Pb identification. The Pb contents of leaded eggs ranged from 1.2 to 12.8 ppm. Linear partial least squares discriminant analysis (PLSDA) and nonlinear least squares support vector machine (LS-SVM) were used to classify samples based on NIR spectra. Different preprocessing methods were studied to improve the classification performance. With second-order derivative spectra, PLSDA and LS-SVM obtained accurate and reliable classification of leaded and unleaded preserved eggs. The sensitivity and specificity of PLSDA were 0.975 and 1.000, respectively. Because the strictest safety standard of Pb content in traditional pidan is 2 ppm, the proposed method shows the feasibility for rapid and nondestructive discrimination of Pb in Chinese preserved eggs.

Highlights

Preserved egg or pidan has been one of the most popular traditional alkali-treated egg products in South and East Asian countries, including China, South Korea, Thailand, and Japan
Ten batches of 331 preserved eggs produced by lead-free processing and six batches of 147 preserved eggs produced with traditional processing with usage of PbO were purchased from domestic markets
Considering the limit of detection (LOD) (0.66 μg/L) and practical quantification limit (PQL) (80 μg/L) of Inductively coupled plasma mass spectrometry (ICP-MS) analysis, ICP-MS is sufficient as a reference method, because the cutoff value of Pb content for pidan is 2 ppm

Summary

Introduction

Preserved egg or pidan has been one of the most popular traditional alkali-treated egg products in South and East Asian countries, including China, South Korea, Thailand, and Japan. It has been shown that alkali treatment improves the extractability, solubilization, gelation, and dispersibility for preparing texturized products in recent years [3]. This process is effective in destroying toxins, such as aflatoxin and protein inhibitors, which is advantageous for food processing [3, 4]. Produced by the reaction of sodium carbonate (Na2CO3), water (H2O), and calcium oxide (CaO) of pickle or coating mud, NaOH penetrates the eggshell and membrane into an egg, leading to physical and chemical changes, color changes, and gelation of the protein [1, 5,6,7,8]

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