Application of Colorimeters in Non-Destructive Testing of Fruits and Vegetables Maturity and Freshness

Introduction: The "Visual Economy" and Quality Risk Control in the Global Fruit and Vegetable Supply Chain

In modern international food trade and smart agriculture, the "appearance color" of fruits and vegetables is not only the primary visual element to attract consumers, but also a "barometer" of their internal physiological state. From the greenness of immaturity to the redness or yellowness of full ripeness, subtle changes in color directly correspond to the synthesis and decomposition of internal pigments such as chlorophyll, carotenoids, and anthocyanins.

Traditional detection of fruit and vegetable maturity and freshness mostly relies on manual visual observation or destructive experiments (such as penetrometer indentation, chemical titration for sugar-acid ratio, etc.). Manual visual observation is highly susceptible to light sources, environment, psychology, and individual physiological differences, leading to high misjudgment rates and an inability to achieve standardization. On the other hand, destructive testing implies high losses and cannot achieve online screening for large-scale, full-volume production lines.

With the development of photoelectric detection technology, non-destructive testing (NDT) technology based on colorimeters and spectrophotometers has become a standard configuration for global fruit and vegetable warehousing, cold chain transportation, customs inspection, and deep processing enterprises.

I.Data-Driven Color: How Colorimeters "Read" the Maturity and Freshness of Fruits and Vegetables

A colorimeter does not simply take a picture, but converts complex color information into unified color space data of the International Commission on Illumination (CIE) (such as CIE L*a*b*, L*C*h*, etc.). Through these high-precision quantitative indicators, supply chain managers can accurately capture subtle physiological changes in fruits and vegetables during harvesting, ripening, and storage.

1. The Color Password of Fruit and Vegetable Maturity
During the ripening process of fruits and vegetables, the most significant change is shifting "from green to yellow" or "from green to red."

• The Jump of the a* Value: In the L*a*b* color space, the a* value represents redness-greenness (negative values for green, positive values for red). Taking tomatoes or apples as an example, as maturity increases, chlorophyll degrades, and lycopene or anthocyanins accumulate in large quantities, causing their a* value to quickly turn from negative to positive. By monitoring the critical point of the a* value, harvesters can accurately determine the "Harvest Window."
• The b* Value and Yellowing: The b* value represents yellowness-blueness (negative values for blue, positive values for yellow). Bananas, citrus, and other fruits show a significant increase in b* value when ripening, reflecting the appearance of carotenoids.

2. Fruit and Vegetable Freshness and Shelf-life Prediction
Freshness is often accompanied by water loss, browning, oxidation, and microbial invasion of fruits and vegetables.

• The Decline of the L* Value (Loss of Gloss and Brightness): L* represents brightness (0 for black, 100 for white). Freshly picked leafy vegetables or berries have high brightness and a wax layer on the surface. As storage and transportation time extends, respiration consumes organic matter and water is lost, leading to a continuous decline in the L* value, resulting in a dim appearance.
• Browning Index (BI) and Color Difference Variation (ΔE): Cut fruits and vegetables (such as fresh-cut apples, potatoes) or damaged fruits will turn yellow and black quickly under enzymatic browning. By calculating the overall color difference ΔE compared to the standard sample, the colorimeter can capture the early stages of browning that are difficult for the naked eye to detect within one second, thereby achieving advanced warning of shelf-life.

II.CHNSpec Fruit and Vegetable Non-Destructive Testing Product Line

Aiming at complex application scenarios in the domestic and foreign fruit and vegetable industries, CHNSpec has developed a variety of detection equipment featuring high precision, portability, and high cost-effectiveness to meet a wide range of usage scenarios from fields to professional laboratories.

1. ColorMeter Pro / DS-200 / DS-210 Series: "Pocket Gadgets" for Field Harvesting and Mobile Commercial Inspection
In orchards, greenhouses, or wholesale markets, inspectors need to move frequently, which requires extremely high environmental adaptability.

• Product Advantages: ColorMeter Pro (Colorimeter) and DS series portable colorimeters are lightweight and extremely easy to operate.
• Industry Applications: They support multiple measurement apertures (such as 6mm, 11mm), which can perfectly fit the curved surfaces of berries (such as blueberries, grapes) or large drupes (such as peaches, mangoes). Through Bluetooth connection to a mobile APP, quality inspectors can synchronize the measured  L*a*b* data to the cloud database in real time directly at the orchard site, achieving data archiving of origin maturity.

2. DS-700D Handheld Spectrophotometer: Suitable for Quantitative Analysis and Shelf-life Prediction
For large export enterprises or QA (Quality Assurance) departments of supermarket chains, it is necessary not only to look at color differences, but also to have more precise "spectral reflectance" to predict changes in internal chemical components.

• Product Advantages: DS-700D adopts a D/8 (diffuse illumination, 8° viewing) optical geometry structure, with a repeatability of ΔE*ab≤ 0.025, and a built-in camera for previewing, ensuring that every measurement is accurately focused on the representative area of the fruit.
• Industry Applications: It can output not only standard color indicators, but also yellowness, whiteness, and reflectance at specific wavelengths, making it suitable for color tracking of kiwifruit, refrigerated apples, and avocados in cold chain transportation. Through long-term accumulated color degradation curves, it directly correlates with fruit firmness and soluble solids content (SSC) to achieve non-destructive shelf-life prediction.

3. CS-820N / CS-821N Benchtop Spectrophotometer: Ideal Choice for Deep Food Processing, Scientific Research, and Teaching
In deep processing industries such as fruit juice, jam, and frozen fruit pieces, the color standardization of raw materials directly determines the brand consistency of the final product.

• Product Advantages: As a flagship model for laboratory use, CS-820N/821N possesses reliable measurement stability and high-precision color measurement performance. It supports both reflectance measurement (for solid fruit pulp) and transmittance measurement modes (for fruit juice, fruit vinegar, plant extracts).
• Industry Applications: In post-harvest storage quality control research of kiwifruit, citrus, etc. (such as evaluating the impact of different refrigeration temperatures on fruit quality), CS-820N can accurately establish a baseline color database and has been widely adopted by many agricultural universities and international quality inspection institutions.

4. Featured Extension: Application of Hyperspectral Cameras in Modern Intelligent Fruit Sorting Lines
With the comprehensive upgrade of smart agriculture, traditional single-point color measurement can no longer meet the high-speed sorting needs of several tons per second in large packing houses. The hyperspectral cameras launched by CHNSpec (such as the FS series, covering 400-1000nm) perfectly achieve the "combination of image and spectrum." It can not only capture large-area color features on the surface of fruits, but also utilize the near-infrared band to penetrate the fruit peel, directly online detecting internal sugar content, acidity, latent bruising, and moldy core. This technology has been applied to multiple intelligent fruit sorting lines around the world as one of the key modules for color and internal quality inspection.

III.Conclusion: Digital Color, Empowering the Global Green Supply Chain

Non-destructive testing is an important direction for the future development of agriculture and the food industry. The introduction of CHNSpec colorimeters and spectrophotometers transforms the rich experience accumulated over a long time by agronomy experts and growers into internationally accepted quantitative color data.

If you are looking for effective solutions to improve post-harvest quality control of fruits and vegetables, reduce international trade return rates, and establish a standardized food supply chain, CHNSpec will be a partner worth considering. Contact us to get a fruit and vegetable color detection solution tailored to your needs.