US Standard Methods for Measuring Surimi Functional Properties

Surimi – the refined fish protein paste behind products like imitation crab, fish cakes, and kamaboko – must meet precise quality standards before it reaches any production line. But how do manufacturers know whether a batch will hold together under heat, look appealingly white on the shelf, or taste clean and neutral? The answer lies in a set of standardized US methods specifically designed to measure surimi’s functional properties. These tests cover everything from gel strength and color to sensory attributes like flavor and odor, and together they give processors a reliable, reproducible picture of how surimi will actually perform.

Why standardized testing matters 🔗

Surimi is only as good as the final product it produces. Without consistent testing protocols, manufacturers would have no reliable way to compare batches, predict processing outcomes, or maintain product quality across shifts and facilities. The current ISO 23855:2021 standard sets out baseline requirements for frozen surimi and quality control test methods for both raw and gelled specimens – but in the United States, the industry has also developed its own standardized functional testing procedures that are widely adopted across seafood processing plants. These methods are specifically designed to simulate commercial processing conditions, so that laboratory results translate directly into production reality.

Preparing the model test product 🔗

Before any measurement can take place, technicians must prepare a standardized model test product. This step is foundational – the test product must replicate the conditions of actual manufacturing as closely as possible. The process begins with thawing frozen surimi blocks under controlled refrigeration temperatures to prevent protein degradation. Once fully thawed, the surimi is carefully weighed and portioned to ensure consistency across all samples.

Standardized amounts of salt – typically around 2-3% by weight – are then incorporated through mechanical mixing. This is not just a routine step: as the paste is mixed, myosin proteins begin to interact and develop the characteristic sticky, elastic texture that defines surimi’s gel-forming potential. Mixing time and intensity must be carefully controlled, since under-mixing leads to poor gel formation and over-mixing can damage protein structure.

The shaped portions are then subjected to a two-stage heating process that mirrors commercial production. The paste is first held at a lower temperature – around 40°C – to allow protein setting, followed by higher-temperature cooking at 85-90°C to achieve final gel formation. Research on surimi gel preparation confirms that two-step heating, with an initial setting phase before final cooking, consistently produces stronger, more elastic gels than single-step heating. This controlled thermal treatment ensures the test sample faithfully reflects how surimi will behave during actual processing.

Gel strength testing 🔗

Gel strength is the single most critical functional property of surimi, and measuring it accurately is the core of the US standard testing approach. It determines how well the final product holds together, how firm and elastic it feels, and how it will perform during handling, packaging, and consumption.

The penetration test method 🔗

The punch or penetration test is the most widely used gel measurement technique in the surimi industry for evaluating gel strength. Although classified as an empirical test, it directly mimics the large deformations involved in chewing, and numerous studies have confirmed that puncture results correlate well with sensory perceptions of surimi gels.

The test uses a texture analyzer or viscometer fitted with a standardized probe – typically a 5 mm ball or cylindrical probe – which descends into the gel sample at a controlled, consistent speed (usually around 1 mm per second). As the probe penetrates the gel surface, sensors continuously record the resistance encountered. The probe descends until the gel structure fractures or yields. Two key values are captured: the breaking force (in grams) and the breaking distance (in centimeters, measured to the point of rupture). Gel strength is then calculated as the product of breaking force multiplied by breaking distance, expressed in g·cm.

Premium surimi typically delivers gel strength values above 500 g·cm, with top-grade material often exceeding 1000 g·cm. Lower-grade surimi produces measurably weaker values. Beyond peak strength, the test also reveals information about elasticity and fracture behavior. Some gels reach high peak strength but break suddenly; others yield more gradually. This distinction matters for predicting how a product will respond during commercial handling. Researchers have proposed complementary measures such as “energy to failure” – the total mechanical work required to fracture the gel – to give a more complete characterization of gel toughness beyond the standard single-point measurement.

What gel strength reflects at the protein level 🔗

The numbers produced by gel strength testing are not arbitrary – they reflect real structural changes in surimi’s proteins. During heating, myosin molecules unfold and form cross-links with one another, building a three-dimensional protein network that traps water and creates the gel matrix. Research shows that β-sheet protein conformations make the primary structural contribution to gel strength, while the elasticity of the gel is largely associated with the polymerization of myofibrillar proteins. High-quality surimi, with its well-developed protein network, produces dense, uniform gel structures – and this is precisely what the penetration test captures.

Color measurement with a colorimeter 🔗

Color is the second major functional property assessed under US standard methods, and it plays a direct role in consumer acceptance. Premium surimi should be bright white, signaling that fat, blood, pigments, and sarcoplasmic proteins have been effectively removed during washing. Any yellowish or grayish tint indicates residual pigments or inadequate processing.

The CIE L*a*b* color system 🔗

Color is measured using a colorimeter or spectrophotometer based on the internationally recognized CIE L*a*b* color space, which encodes colors according to human visual perception. The system produces three values for each sample. L* measures lightness on a scale from 0 (black) to 100 (white); a* captures red-green coloration; and b* measures yellow-blue characteristics. For surimi, L* is the primary indicator of whiteness, while a high b* value signals unwanted yellowness from residual pigments. The a* value can also serve as an indicator of raw material freshness.

A widely used formula for calculating overall whiteness is: Whiteness = L* − 3b*, which accounts for the fact that yellowness is particularly penalized in surimi grading. This whiteness index is used across the industry as a composite measure of surimi color quality. High-grade surimi typically achieves L* values of 85 or above, with b* values kept as low as possible.

Sample preparation and measurement procedure 🔗

For accurate color measurement, the surimi gel is cut with sharp, clean blades to produce smooth, uniform surfaces free from irregularities that could scatter light inconsistently. Multiple readings are taken across different areas of each sample to account for natural variation. Colorimeters used in food processing are typically portable instruments that can accommodate paste, gel, and solid samples through dedicated accessory holders, making them practical for quality control on the processing floor as well as in the laboratory.

Color measurement is applied at multiple stages: during raw material intake to check incoming fish quality, throughout the washing process to monitor the reduction of yellowness, and at the final grading stage to confirm whiteness standards. In the food sector, colorimetric analysis using the CIE L*a*b* system has become the standard approach because it closely approximates human color perception and provides objective, repeatable data that visual inspection simply cannot deliver.

Sensory evaluation: texture, flavor, and odor 🔗

Instrumental measurements of gel strength and color give processors objective data – but they do not tell the full story. US standard methods also incorporate sensory assessment to capture the qualities that only human perception can reliably evaluate.

Texture assessment 🔗

Trained sensory panels evaluate surimi gels for springiness, chewiness, cohesiveness, and overall mouthfeel. These attributes complement the mechanical data from penetration testing. Studies have shown that texture analyzer results can be validated against descriptive sensory tests, with strong correlations between instrumental and panelist scores for attributes like hardness and chewiness. When both methods agree, manufacturers can rely on the faster, more cost-efficient instrumental test for routine quality control while using sensory panels for product development and shelf-life studies.

Flavor and odor assessment 🔗

Fresh, high-quality surimi should have minimal fishy odor and a clean, neutral flavor that does not interfere with seasoning or flavoring applied during downstream processing. Off-flavors or undesirable aromas are significant quality defects – they may indicate protein degradation, lipid oxidation, or microbial activity. The US FDA recognizes odor, flavor, and texture as core sensory parameters in seafood quality assessment, and trained analysts use standardized criteria to score these attributes consistently.

Sensory panels follow structured protocols aligned with internationally recognized sensory analysis frameworks, in which trained assessors evaluate each attribute individually using defined scales before reaching a consensus score. This structured approach removes subjectivity and ensures that results from one facility or testing session can be meaningfully compared to another.

How the tests work together 🔗

No single measurement fully characterizes surimi quality on its own. Gel strength confirms protein network integrity. Color confirms washing efficiency and raw material purity. Sensory evaluation catches off-flavors and textural anomalies that instruments may not flag. Together, these standardized tests form an integrated quality picture. Products made from surimi with optimal test results consistently demonstrate better shelf stability, maintain texture through freeze-thaw cycles, and earn higher scores in consumer acceptance studies. This predictive capability is the real value of the US standard methods – they give processors confidence in sourcing decisions and production parameters before a single gram of final product is manufactured.

Salt concentration, moisture content, pH, and thermal profiles are all standardized within the testing procedures to reflect typical commercial formulations. This attention to detail ensures that the laboratory faithfully mirrors the factory floor, so that passing a test is not a technicality – it is a genuine indicator of commercial performance.

What do you think? Given that gel strength and color testing are both well-established, should sensory panel evaluation be considered equally essential in routine quality control, or is it better reserved for product development and shelf-life studies? And as more surimi is produced from non-traditional fish species, how reliably do current US standard testing methods predict real-world performance across different protein profiles?

References

1. https://www.sciencedirect.com/science/article/abs/pii/S0268005X25009099
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