A Single-Source Pilot Study of Machine Learning-Assisted Microwave S-Parameter Screening for Glucose Syrup and Water...

Grape molasses, known as pekmez in Turkish, is a traditional concentrated fruit product that may be adulterated with cheaper sweeteners or water. This study evaluated broadband microwave S-parameter measurements as a rapid, non-destructive screening approach for detecting glucose syrup substitution and water dilution in grape molasses. Nine physical mixture groups were prepared, including pure grape molasses, glucose syrup-substituted mixtures at 5-30%, pure glucose syrup as an endpoint reference, and water-diluted mixtures at 10-30%. For each group, five consecutive technical measurements were recorded using a Libre vector network analyzer connected to a WR-229 waveguide-based two-port setup over 3.30-4.90 GHz. All mixtures were prepared from a single commercial grape molasses source and a single glucose syrup source; the results should therefore be interpreted as pilot-scale, single-source evidence rather than a generalizable screening method. Glucose syrup substitution produced a systematic upward shift in S₁₁ resonance frequency. In the practical 0-30% range, S₁₁ resonance frequency showed a strong linear relationship with glucose syrup content on the calibration data (R² = 0.9955; inverse prediction error = 0.72 percentage points), though this reflects calibration fit rather than independently validated prediction accuracy. Water dilution produced stronger S₂₁ attenuation. The detection principle is based on the complementary use of S₁₁ resonance behavior for glucose syrup substitution and S₂₁ transmission loss for water dilution. In group-blocked point-wise classification, the Ensemble Bagged Trees classifier achieved 88.79% accuracy and a macro-F1 score of 0.874. These results indicate that S₁₁ and S₂₁ provide complementary proof-of-concept indicators for controlled-mixture screening of grape molasses adulteration.