Rapid Assessment of Honey Quality and Authenticity via Electrochemical Determination of L-Proline and 5-Hydroxymethyl-2-Furfural Using Modified Pencil Graphite Sensors

Rapid and reliable quality control of honey is crucial for ensuring food safety and preventing food fraud. In this study, novel sensitive and selective molecularly imprinted polymer (MIP) sensors were developed for the direct and sequential determination of L-proline (L-Pro) and 5-hydroxymethyl-2-furfural (HMF). The sensors were fabricated via the electropolymerization of pyrrole (Py) on a pencil graphite electrode (PGE) surface, using L-Pro and HMF as template molecules. The linear working range for L-Pro and HMF using differential pulse voltammetry (DPV) is 10–1600 µM, with limits of detection determined as 5.39 µM and 4.81 µM, respectively. The MIP-PPy/PGEs demonstrated high selectivity against a 25-fold excess of structural analogues (response <25%). The sensors were highly reproducible (RSD 3.20–3.22%, n = 5) and repeatable (RSD 1.97–2.27%, n = 5), maintaining 81.5% stability over 15 days. The developed sensors successfully quantified native L-Pro and HMF levels in six real honey samples, monitoring thermal-stress-induced changes at 70 and 90 °C. Under increasing thermal stress, a consistent inverse relationship was observed, with L-Pro decreasing as HMF increased. The electrochemical results correlated strongly with standard UV and HPLC methods (RSD < 3%), offering a rapid, cost-effective, practical alternative for routine honey quality and authenticity control.