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Is this melon sweet? A quantitative classification for near-infrared spectroscopy

https://doi.org/10.1016/j.infrared.2021.103645Get rights and content

Highlights

  • Vis/NIRS quantified sweetness of ‘honey’ melons.

  • Direct classification quantifies sweetness better than indirect classification.

  • With indirect classification the accuracy is 80.2%.

  • With direct classification the accuracy is upto 88.12% for two classes.

Abstract

Melons are nutritious, healthy, and one of the most eatable summer fruits in South Asia, especially in Pakistan. A melon is delicious if it is sweet, however, the gauge of its sweetness depends on the individual taste buds. In this paper, a direct sweetness classifier is proposed as a quantitative measure, to predict the sweetness of melon as opposed to indirect measure of soluble solid content (SSC/°Brix) based thresholding for near-infrared (NIR) spectroscopy. To provide guidance for fruit sweetness classification, sensory test was conducted, and sweetness standards were established as; very sweet (with °Brix over 10), sweet (with °Brix between 7 and 10), and flat (with °Brix below 7) class. NIR spectral data obtained using F-750 produce quality meter (310–1100 nm) was analyzed to build SSC prediction model and direct sweetness classification model. The best SSC model was obtained using multiple linear regression on second derivative of spectral data (for wavelength range 729–975 nm) with correlation coefficient = 0.93, and root mean square error = 1.63 on test samples. Sweetness of test samples were obtained using °Brix thresholding with an accuracy of 55.45% for three classes. The best direct sweetness classifier was obtained using K nearest neighbor (KNN) on second derivative of spectral data (for wavelength range 729–975 nm) with an accuracy of 70.3% for three classes on test samples. It was further observed that classification accuracy for sweet and flat melon can be improved by combining sweet and very sweet class samples into one ‘satisfactory’ class (with °Brix over 7). For °Brix thresholding-based classification the accuracy was improved to 80.2% and for KNN based direct sweetness classification the accuracy was improved to 88.12%. Extensive evaluation validates our argument that modeling a direct sweetness classifier is a better approach as compared to °Brix based thresholding for sweetness classification using NIR spectroscopy.

Section snippets

Introduction:

Melons (Cucumis Melo) are nutritious, sweet, and amongst the most refreshing summer fruits in Pakistan. Honey melons are cultivated in Sindh, Punjab, and some parts of Kyber Pakhtun Khaw province of Pakistan, harvested from April till June. These are not the same as honey dew melons although they have little resemblance in appearance. Honey melons have creamy net patterns on their skin with a strong fragrant aroma. Melons come under the class of non-climacteric fruits i.e. once harvested they

Melon samples preparation

For the experiment, a total of 101 honey melon samples were purchased from local market in five different batches (20 melons each) covering one full season of melons i.e. on 17 April, 1 May, 15 May, 29 May and 12 June 2020. All samples were elliptic and individual fruit weight was around 0.5–1.5 kg. Average rind thickness was 6.68 mm. All samples were transported to a local laboratory (Islamabad, Pakistan) and stored at room temperature (25 °C) for 24 h to minimize the influence of sample

Vis /NIR spectroscopy analysis

Vis/NIR spectroscopy (range 350–2500 nm) records response of O-H, C-H, C-O and N-H bonds in fruits. Hence these organic molecules absorb energy as they vibrate because of NIR radiation exposure, which is translated into absorbance spectrum by NIR spectrometer. Short wave NIR radiation i.e. 750–1300 nm is considered as the absorbance band of high overtones i.e. 3rd and 4th overtone while common NIR (after 1300 nm) belongs to 1st or 2nd overtone.

The raw absorbance spectra of 101 melons within

Conclusion

We proposed direct classification based quantitative measure to predict melons sweetness intensity using NIR spectroscopy. An extensive evaluation was conducted on “honey melon” variety, which is grown in Pakistan. A total of 101 melons with average rind thickness 6.68 mm, were scanned from four sides at equator position. The industry standard F-750 spectrometer employing interactance optical geometry was used to collect spectral data. After spectra collection, destructive testing was performed

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This research is supported by Pakistan Agriculture Research Council, Agriculture Linkage Program.

Grant numbers: AE-007. Ministry of Education – Kingdom of Saudi Arabia. National Center of Robotics and Automation, Robot Design and Development Lab Grant numbers: DF-1009-31.

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