Relationship Between Optical Properties and Internal Quality of Potatoes During Storage

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The College of Agricultural Engineering and Food Science at Shandong University of Technology, China, conducted a study to evaluate and predict the internal quality of stored potatoes based on their optical characteristics. Below is the abstract of the study, followed by the introduction, key points from the results and discussion, and the conclusion. A flowchart of the materials and methods is also provided.

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Abstract

The researchers conducted a study of potatoes stored at 25°C, focusing on two main areas: the optical properties of the potatoes, such as their absorption and scattering coefficients, and their internal quality, which includes firmness, moisture content, and soluble solids content. They also observed the ultrastructure of the potato tissue, which changes significantly over time and affects its optical properties.

The study found that the absorption coefficient is closely related to the moisture content and soluble solids content of potatoes. In contrast, the scattering coefficient correlates more with the firmness of the potatoes. To improve the accuracy of their predictions of these characteristics, the researchers used a method known as competitive adaptive reweighted sampling (CARS), along with partial least squares regression (PLSR) and support vector regression (SVR) models.

The results were promising, showing high accuracy in predicting the internal quality of potatoes based on their optical properties. This suggests that optical properties could be a reliable means of assessing the quality of stored potatoes without the need for invasive testing.

Introduction

Potatoes play a critical role as a primary ingredient in the food processing industry, and their quality is essential for the production of various products such as crisps, mash, and dehydrated forms. Traditionally, potato quality is assessed by measuring moisture content, firmness and soluble solids content — factors that influence both the nutritional value and taste of the final product. However, conventional methods for determining these qualities are often destructive and costly. In response, visible/near-infrared (NIR) spectroscopy has emerged as an effective, non-destructive alternative that provides rapid assessments of the internal quality of various agricultural products.

This research builds on previous studies that have successfully applied NIR spectroscopy to predict internal quality metrics in fruits and vegetables by examining the optical properties of potato tissue-specifically, absorption and scattering coefficients related to chemical composition and physical structure. While existing research has demonstrated the potential of optical properties in quality assessment, their application to potato quality has been less explored, with a limited understanding of the relationship between these optical properties and the internal quality of potatoes.

The study aims to fill this gap by investigating the correlation between optical properties and internal quality of stored potatoes, including moisture content, firmness, and soluble solids content. Through a combination of visible/NIR spectroscopy and advanced predictive modeling, the research aims to establish a non-destructive method for assessing potato quality, offering potential improvements in food processing and quality control. The results show a promising relationship between the measured optical properties and potato quality, suggesting that this method could provide a viable alternative for predicting the internal quality of potatoes during storage. This study not only contributes to the field by improving the accuracy of quality predictions through optical assessments, but also underscores the broader applicability of NIR spectroscopy in the agricultural sector.

Materials and methods

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Results and discussion

• System Validation Accuracy: The integrating sphere system demonstrated high accuracy in measuring the optical properties of pure water and Intralipid 20% solution, with relative errors within acceptable limits, validating the reliability of the system for further experiments.
• Homogeneity of Potato Samples: Throughout the storage test, potato samples exhibited consistent thickness and only minor variations in weight and size, providing a consistent basis for assessing changes in internal quality and optical properties.
• Internal quality changes over time: Potatoes showed a progressive decrease in firmness index (FI), relatively stable moisture content (MC) with slight fluctuations, and a decreasing trend in soluble solids content (SSC), highlighting the impact of storage on potato quality.
• Variations in optical properties: Significant absorption peaks were identified in the absorption spectra (μa) of potato tissues, correlating with specific molecular vibrations and water content, while reduced scattering coefficient (μs′) values increased with storage time, indicating changes in tissue structure.
• Correlation between optical properties and internal quality: There were significant correlations between μa and both MC and SSC, and between μs′ and FI, suggesting that optical properties may be indicative of the chemical composition and structural integrity of potato tissues.
• Ultrastructural changes: SEM images revealed degradation of cell structure over time, which correlated with the observed changes in optical properties and internal quality, especially FI and μs′, highlighting the impact of storage on cell integrity.
• Internal quality prediction models: Partial Least Squares Regression (PLSR) and Support Vector Regression (SVR) models developed to predict FI, MC, and SSC from optical properties showed varying levels of accuracy, with some models performing better than others depending on the preprocessing method and specific quality metric.
• Model Optimization with CARS: The use of Competitive Adaptive Reweighted Sampling (CARS) for characteristic wavelength extraction significantly improved the accuracy of the prediction models, demonstrating the potential of targeted spectral analysis for internal quality assessment.
• Validation of prediction models: The optimized models showed strong linear fits between predicted and measured values of FI, MC, and SSC, validating the effectiveness of using optical properties for quantitative prediction of potato internal quality.

Conclusion

Exploring the intricate relationship between the optical properties, internal quality, and ultrastructure of potatoes during storage reveals significant shifts in quality and structural integrity over time. Research identified four key absorption peaks within the μa spectra that correlated with MC and SSC, and highlighted a nuanced interaction between these factors and FI. Increased storage time not only altered the internal structure of potatoes, but also improved their scattering properties, as evidenced by a monotonic increase in the reduced scattering coefficient (μs′). The study carefully established that μa spectra have strong correlations with MC and SSC, but a weaker relationship with FI. Conversely, the predictive power of μs′ spectra was more aligned with FI, showing a complex web of weak to significant correlations with MC and SSC across different spectral regions.

Advanced modeling techniques, including PLSR and SVR, were used to navigate these relationships using raw and pre-processed spectral data. In particular, the use of the CARS algorithm to extract characteristic wavelengths significantly improved model accuracy. This meticulous approach resulted in accurate prediction of internal quality metrics, with μs′ spectra excelling in predicting FI and μa spectra demonstrating superior performance in predicting MC and SSC.

This research underscores the profound relationship between the optical properties of a potato and its internal quality, paving the way for the development of sophisticated non-destructive testing techniques. By providing a comprehensive understanding of how storage affects potatoes at the molecular level, this research offers invaluable insights into maintaining quality and extends a fundamental reference for future studies in the field of agricultural and food science.

Source: Xiao, Z., Xu, Y., Wang, X., Wang, Y., Qu, J., Cheng, M., & Chen, S. (2024). Relationship between optical properties and internal quality of potatoes during storage. Food Chemistry, 441, 138334. https://doi.org/10.1016/j.foodchem.2023.138334

For more research on potato storage, click here: https://bit.ly/3u8OCtU.