How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Tuesday, 4 April 2017

Texture Analysis of Surimi Products: 1: Introduction; Gel Strength (Stiffness)

A predominant ingredient in the Orient is fish – used both fresh and comminuted as surimi fish mince.

Made for centuries by the Japanese and thought to date as far back as 1100AD, surimi is now spreading from Japanese to Western processed foods and is used to form extruded, shaped or cooked simulated shell-fish meat products such as crab, lobster, scallop or shrimp.

To gain consumer acceptance of imitation shell-fish, the texture, flavour and appearance of fresh shell-fish must be matched as closely as possible. This has successfully been achieved by Japanese processors who produce surimi as an economic alternative to fresh fillets and imitation shell-fish which are barely distinguishable from the real thing. 

However, in the emulation of this success and creation of products with an authentic shell-fish texture, especially using surimi from non-Japanese species of fish, European food manufacturers are challenged. Europeans have not had the history to develop their skills in discrimination sufficiently to equal the quality. Instead, they are using analysis techniques at R&D, production and quality control stages. 

At each stage in surimi product development, production and quality control, food manufacturers can quantify textural parameters using the TA.XT2i or TA.XTplus texture analyser and Windows-based software. This equipment can provide accurate data about, for instance, the effects of gel moisture content, salt concentration, cooking temperature and length of time heat is applied during processing which cuts out the guess-work.

Texture analysis is applicable both near-line and in individual laboratory tests for surimi manufacture, measuring specific toughness, elasticity and gel strength of surimi-type products.

Gel Strength or “Stiffness” using Penetration Tests

The importance of the gel forming ability in surimi is vital especially in the Japanese food Kamaboko. 

Strong gels can hold in water and maintain succulence and juiciness of the end-product. Loss of product quality, in the form of decreased gel-forming and water-holding capacity of surimi is attributable to two factors: temperature of heating and the addition of the incorrect level of cryoprotectants (added for the prevention of protein denaturisation during freezing). 

Figure 1: Although a 5mm ball probe
is typically used for surimi testing,
a range of cylinder and ball probe
diameters are available for use
on the texture analyser

The “punch” or penetration test, although considered an empirical test, is the single most popular gel measurement technique used in the surimi industry for evaluating “gel strength” or stiffness. The test imitates the large deformations to failure involved in mastication. 

Many studies have been reported that correlate puncture or penetration methods with the sensory properties of surimi gels. This attribute of the test, coupled with its convenience, has made it popular for quality control within the surimi industry.

By using a 5mm Ball Probe (Figure 1), the gel forming ability of surimi can be analysed by the penetration method. Surimi ‘Gel Strength’ is traditionally calculated by <Peak force (g) * Distance at the peak (cm)> (Figure 2). This Gel Strength does not provide significant meaning to the rheological properties of gels. 

Figure 2: Typical curve obtained
from a penetration test to
assess gel strength

However, it has been arbitrarily used in the surimi industry as a symbol of surimi quality. For instance, when this method is used on a range of different surimi samples (Figure 3) the results show significant differences in gel strength. A high gel strength value for example 1019gcm for ‘A’ grade surimi indicates a much higher degree of firmness compared to its ‘A’ grade counterparts.

This highlights the effect of adding ingredients to the product. The very high gel strength of suwari and the very low gel strength of modori when compared to the control surimi highlight the effect of processing time and temperature on the gel consistency of surimi. 

However, it is possible that five different gels could have the same gel strength but the protein quality of the gels is significantly different. When used as a single measurement, deformation indicates the quality of surimi proteins – the greater the deformation the higher is the quality.  

Figure 3: Typical curves obtained
from a penetration test to assess
gel strength of multiple samples
Force values depend on the quantity of proteins – a higher force indicating the least value surimi. Therefore, it is often wise to express force and deformation values individually to indicate the gel functionality of surimi and not solely in the form of gel strength.

The penetration method evalutes a small area, making it useful for showing differences due to location within a sample. However, because a ball probe is symmetrical about its central axis, it is not suitable for determining anisotropy which is better determined by a cutting/shearing test.

To see a summary of the types of testing possibilities that are available for the measurement of texture of your meat and fish products to ensure consistent quality and ultimately, consumer satisfaction, watch the video below...

View meat testing video

You can also visit our website's Meat and Fish Applications pages...

We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

TA.XTplus texture analyser with bloom jar The
TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

To discuss your specific test requirements click here...

Watch our video about texture analysis Replicating Consumer Preferences
 Texture Analysis applications

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