The pink color of the shell and flesh of cold-water prawns is due to the presence of astaxanthins, a red-orange carotenoid pigment from the xanthophyll family. Prawns acquire astaxanthins through their diet, consisting of plankton and other marine organisms. While this color might seem straightforward to assess, the details involved in grading by color in cold-water prawns present a unique set of challenges that the seafood industry grapples with. The following sections will address some of the current challenges and potential solutions for grading cold water prawns.
The vibrant hues of pink found in cold-water prawns (Pandalus borealis) are not only a feast for the eyes but also a crucial indicator of quality in the seafood industry. Color is used in grading seafood products to obtain a high-quality product, meet consumer expectations, and get better prices.
1. Natural variability: Cold water prawns have unique characteristics such as non-uniform color distribution, size, and shape. These intrinsic characteristics are influenced by diet and environmental factors such as temperature, and water quality, among others. This natural variability in cold water prawns makes it difficult to measure the “pink color” with accuracy and reproducibility by using equipment and increases the risk of inconsistent grading by quality operators.
2. Visual grading: Color assessment is inherently subjective, varying from person to person. What might appear as a desirable intensity of pink to one observer could be perceived differently by another. In the seafood industry, quality operators grade cold water prawns by the intensity of pink color and compare them with a standard. However, they often lack experience or the correct training, which leads to inconsistent visual grading. This process is time-consuming and labor-intensive. Moreover, color grading is not a quantitative process and it can be biased by features in the sample. For example, a cold-water prawn with a more saturated pink color (easy-to-find differences) and/or more spread in a sample can influence visual judgment.
3. Objective measurement: Currently, colorimeters and spectrophotometers are used to assess the color of cold-water prawns. Colorimeters have been claimed to be less successful in obtaining accurate color representation and consistent reproducibility in foods with non-uniform characteristics, like cold water prawns. In addition, the process is time-consuming due to the point-by-point measurements to compensate for the heterogeneity of the product and provide an average color. Also, spectrophotometers (UV-Vis) and other spectral technologies like multispectral and hyperspectral are commonly used for compositional analysis, such as pigment content in food products. However, they require space to operate and demand specialized training for sampling preparation and data analysis. In both cases, colorimeters and spectrophotometers might not represent what humans see in the color of a product.
Furthermore, colorimeter and spectrophotometer equipment possess a small sample area which might lead to needing several measurements to ensure a color representation of the entire lot.
Image analysis as an automatic tool for grading the “pink” color in cold-water prawns
Image analysis is a prominent choice to obtain reliable quantification of color. This technique allows the extraction and analysis of information from images captured with devices such as digital cameras, scanners, etc. For example, we at Quality by Images, have developed an image analysis algorithm to grade cold-water prawns using a flatbed scanner as an acquisition device (see technical note at www.qualitybyimages.dk). This can overcome the challenges of a non-uniform product to obtain a reliable quantification of pink color with a high degree of reproducibility. To compare color information between images, a color reference is used to ensure color constancy when changes in light conditions occur. In addition, our solution provides a better representation of color due to a bigger sample area. Flatbed scanners capture a sample area 600 times larger than colorimeters.
Thus, image analysis can overcome the disadvantages of colorimeters and spectrophotometers to measure color and, it can be used for several applications such as measuring size, shape, defects, texture, and appearance. In addition, cost, versatility, maintenance, ease of operation, and setup are factors important to favor its use for online automatic applications. We at Quality by Images empower mobile technology, cloud service, and the internet, together with cost-efficient image acquisition devices (e.g., smartphones, tablets, scanners) that can be tailored to the customers’ specific needs.
In conclusion, the pink color of cold-water prawns is the complexity of nature’s processes. While this color serves as a visual indicator of quality and freshness, measuring and grading it in an objective and cost-efficient manner presents a series of challenges that Quality by Images can solve.