214: Fluorescence Absorbance Transmittance Excitation Emission Matrix (A-TEEM) Spectroscopy as a Rapid Sensing Tool for Quality Defects in Concord Grapes

Introduction

Grape juice production faces challenges from quality defects caused by plant disease and pest damage, such as downy mildew or grape berry moth. Traditional human inspection method has limitations of low throughput and subjectivity. Fluorescence A-TEEM, known for its sensitivity in mapping the changes in fluorescent molecules, offers a promising alternative for rapid defect detection.

Methods

Concord grapes samples with 5 defect levels (1%, 2%, 3%, 4%, and 5% weight percentage based on a USDA standard) were prepared, homogenized, filtered, then diluted to 500-fold using deionized water. Fluorescence fingerprints of the diluted samples were recorded within 200-600 nm (2-nm increment) excitation (Ex.) and 245-827 nm (2.33-nm increment) emission (Em.) wavelength ranges using a Horiba Aqualog UV-800-C spectroscopy with 0.2 s integration time. Signal pre-processing techniques, including background subtraction, interpolation, inner-filter-effect correction, and Rayleigh scattering masking were applied to the raw dataset before formal analysis. The absorbance spectra, excitation and emission wave bands of featured peaks, and their fluorescence intensities were recorded and correlates with defect levels using regression approaches.

Results

The absorbance of the analyte were under 1.0 unit and fluorescence intensities showed linear responses to concentrations. Two featured fluorescence peaks were consistently observed with some energy-shifts noted: Peak 1 (Ex. 202 nm – Em. 315 nm) and Peak 2 (Ex.276 nm – Em. 315 nm), which may be attributed to the tannins, flavanols, procyanidins andanthocyanins in the grapes. The fluorescence intensities showed a decreasing trend from 5% to2% defect levels, and increased again at 1%. Such nonlinear trends highlighted the complexity of defect-related compositional changes and the need for further chemical analysis.

Significance

This study demonstrates the feasibility of fluorescence A-TEEM as a promising rapid and quantitative screening tool for grape quality defects. These findings provide a foundation for developing robust, scalable quality control methods for the grape juice industry, aimed at improving efficiency and safety.

Authors: Jiarui Xu, Jinhong Yu, Chang Chen