Comparison between Hyperspectral Imaging and Chemical Analysis of Polyphenol Oxidase Activity on Fresh-Cut Apple Slices

Boris Kulig,Roberto Moscetti,Barbara Sturm,Oliver Hensel,Elke Pawelzik,Luna Shrestha,Riccardo Massantini

doi:10.1155/2020/7012525

Abstract

The assessment of the quality of fresh-cut apple slices is important for processing, storage, market value, and consumption. Determination of polyphenol oxidase activity (PPO) in apples is critical for controlling the quality of the final product (i.e., dried apples and juices). Hyperspectral imaging (HSI) is a nondestructive, noncontact, and rapid food quality assessment technique. It has the potential to detect physical and chemical quality attributes of foods such as PPO of apple. The aim of this study was to investigate the suitability of HSI in the visible and near-infrared (VIS-NIR) range for indirect assessment of PPO activity of fresh-cut apple slices. Apple slices of two cultivars (cv. Golden Delicious and Elstar) were used to build a robust detection algorithm, which is independent of cultivars and applied treatments. Partial least squares (PLS) regression using the 7-fold cross-validation method and method comparison analysis (Bland–Altman plot, Passing–Bablok regression, and Deming regression) were performed. The 95% confidence interval (CI) bands for the Bland–Altman analysis between the methods were −4.19 and 13.11, and the mean difference was 3.7e−12. The Passing–Bablok regression had a slope of 0.8 and an intercept of 7.6. The slope of the Deming regression was 0.8 within the CI bands of 0.56 and 1.10. These results show acceptable performance and no significant deviation from linearity. Hence, the results demonstrated the feasibility of HSI as an indirect alternative to the standard chemical analysis of PPO enzyme activity.

Highlights

Processed foods such as fresh-cut and dried apples are becoming more popular due to their nutritional, functional, and convenience properties
The occurrence of browning reactions can lead to aesthetically unappealing final products. e development of brown pigments during processing is an important criterion in the determination of the quality of fresh-cut apples and dried apple slices [2]. e colour, occurring on the product surface, can be attributed to the activities of polyphenol oxidase (PPO) and peroxidase (POD) enzymes and the presence of other pigments such as chlorophyll and carotenoids [3, 4]
Characteristics of Spectral Profiles of Apple Slices. e average reflectance spectra extracted from regions of interest (ROIs) of apple slices treated with different treatments are shown in Figure 3 in the wavelength range of 500–1000 nm

Summary

Introduction

Processed foods such as fresh-cut and dried apples are becoming more popular due to their nutritional, functional, and convenience properties. To the best of our knowledge, no research comparing the HSI method and the standard chemical analysis method in measuring PPO activity in fresh-cut apples has been documented. Is study assessed the agreement between HSI and the standard chemical analysis method of determining PPO activity in apple slices of Golden Delicious and Elstar cultivars subjected to several antibrowning treatments.

Results

Conclusion