Hyperspectral fluorescence imaging for shelf life evaluation of fresh-cut Bell and Jalapeno Pepper

Authors: Delwiche, Stephen - Steve; Stommel, John; Kim, Moon; ESQUERRE, CARLOS - University College Dublin

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2018
Publication Date: 6/1/2019
Citation: Delwiche, S.R., Stommel, J.R., Kim, M.S., Esquerre, C. 2019. Hyperspectral fluorescence imaging for shelf life evaluation of fresh-cut Bell and Jalapeno Pepper. Scientia Horticulturae. 246:749-758.

Interpretive Summary: Fresh-cut fruits and vegetables refer to those that are trimmed, peeled, or cut and then packaged for retail or food service sales. Unlike many of the popular fresh-cut leafy vegetables whose decay becomes apparent in wilting and browning, fresh-cut pepper undergoes more subtle visible changes as tissue decays and these changes may not be easily detected. Analytical laboratory measurements used to monitor quality of fresh-cut pepper are laborious. The current study investigated fluorescence imaging techniques based on selected light wavelengths as an alternative to monitor the decay of sliced pepper during cold storage. Various statistical modeling techniques were tested to identify relationships between imaging parameters and analytical measures of tissue decay. We found that a statistical analysis termed linear discriminant analysis was successful in assessing tissue decay based upon image analysis. These results will be useful to food technologists and other scientists conducting research to evaluate and improve fresh-cut fruit and vegetable quality.

Technical Abstract: Fresh-cut fruits and vegetables refer to those that are trimmed, peeled, or cut, utilizing all or nearly the entire product and then packaged for retail or food service sales. Unlike many of the fresh-cut popular leafy vegetables whose decay becomes apparent in wilting and browning, fresh-cut pepper (Capsicum spp.) undergoes more subtle visible changes. As a result, shelf life of pepper is more accurately determined through monitoring the leakage of electrolytes from the cells injured during the slicing operation. The current study investigated hyperspectral fluorescence imaging as an alternative to monitor the decay of sliced pepper rings in cold storage (5 deg. C, 0 to 21 days). Five accessions of bell-type pepper and an equal number of jalapeno pepper accessions were harvested from replicated field plots, prepared by routine fresh-cut operation and placed in cold storage. At weekly increments, pepper samples were scanned by UV-excited (365 nm) fluorescence hyperspectral imaging (464-799 nm response range), whereupon quantitative and qualitative modeling was subsequently performed in trials to respectively model a) electrolyte leakage percentage by partial least square (PLS) regression, and b) compare storage days by linear discriminant analysis (LDA). In each modeling approach, the images were reduced to collections of individual pixel spectra irrespective of pepper ring size and shape, with mean spectral subsequently calculated for PLS modeling and histograms of the fluorescence intensities at three selected wavelengths (688, 724, and 740 nm) for LDA analysis. Whereas electrolyte leakage percentage models were poor and ineffective, two-class LDA-based classification models of the structure storage day x vs. storage day y were generally successful, with the greatest contrast occurring when x = 0 days. As with previous studies on the physiological effects of slicing peppers, the fluorescence response was variable across accessions within pepper type and between the two pepper types studied, which we attribute to the complicating effects of cell injury response and genotypic differences that influence suitability for fresh-cut applications among the accessions evaluated.