Accurate Quantification of Anthocyanin in Red Flesh Apples Using Digital Photography and Image Analysis

Eckhard Grimm,Felix Kuhnke,Jörn Ostermann,Moritz Knoche,Anna Gajdt

doi:10.3390/horticulturae8020145

Eckhard Grimm, Felix Kuhnke + Show 3 more

Open Access

https://doi.org/10.3390/horticulturae8020145

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Abstract

Red fleshed apples (Malus × domestica Borkh.) differ in colour intensity between cultivars, seasons and sites. The objective of this study was to develop a procedure for predicting anthocyanin content from digital images of flesh discs. Flesh cylinders of uniform colour were excised, scanned and their colours determined in the R, G and B and the L*a*b* colour spaces. Anthocyanin content was also quantified chemically. A calibration line was constructed to predict anthocyanin content of flesh discs of varying colour from a scan or a photograph in the studio or outdoors. Anthocyanin concentration was linearly related to the logarithms of G, B and L*. From these relationships, the anthocyanin content of a flesh disc was predicted, pixel by pixel. Colour corrections were applied using a reference colour chart included in all images. The Finlayson algorithm was most effective for correcting the G parameter obtained by a flatbed scanner. For variable imaging methods (scanning or photography), the Vandermonde algorithm for correcting the L* parameter and the Finlayson algorithm for correcting the G parameter were most effective in predicting anthocyanin content. The procedure allows accurate prediction of anthocyanin content of red fleshed apples from simple colour scans or photographs.

Highlights

Academic Editor: Jianwei QinMany apple cultivars (Malus domestica Borkh.) have anthocyanins in their skin where they are responsible for the red blush
Increases in the anthocyanin concentrations of flesh cylinders excised from the different apple cultivars were correlated with decreases in R, G and B in the RGB colour space (Figure 2a–c)
It was possible to predict the absorbance of flesh extracts and, the anthocyanin content based on flesh colour

Summary

Introduction

Many apple cultivars (Malus domestica Borkh.) have anthocyanins in their skin where they are responsible for the red blush. Anthocyanins have antioxidant, anticancer and anti-aging properties and are believed to decrease the incidence of cardiovascular disease. They are considered beneficial in the human diet [1,2]. Genotypes of apple have become available that have anthocyanins in the flesh. Red-fleshed apple cultivars are attractive to consumers due to their appearance and health-related benefits. A recent survey even established preference of Italian consumers for red-fleshed apples [3]

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