Adding Value To Surimi

In Japan there are documentary references to the seafood known as surimi going back to 1115, according to Jae W. Park’s third edition of “Surimi and Surimi Seafood” in 2014. Surimi, which means “ground meat” in Japanese, refers to a paste made from fish meat. White fish such as Alaska pollock and threadfin bream are gutted, filleted, deboned, refined and mixed with cryoprotectants before freezing to produce this paste.

In 2016, the global surimi market volume exceeded 1.5 million tons a year, with China, Vietnam and the US each contributing 20 percent to global production. Surimi and its products are a familiar part of Asian cuisine; Japan leads consumption, with around 500,000 tons per year.

While Asian markets remain the main drivers of consumption, surimi is becoming increasingly popular in other regions too. This development is accompanied by demands for higher quality, standardisation and additional health benefits like mineral fortification and sodium reduction.

Consumers are increasingly moving towards healthier lifestyles, with a focus on wellness and wellbeing. Conversely they want to spend less time preparing meals and more time doing things they value. Busy lifestyles, increasing number of women in the workforce, and ageing populations all influence consumer demand for processed food.

However, processed food usually contains high levels of sodium. A diet high in sodium and low in potassium adversely affects blood pressure and increases the risk of heart disease and stroke. According to the World Health Organisation, 2.5 million deaths could be prevented each year if global sodium consumption could be reduced to the recommended less than 2 g of sodium per day (corresponding to 5 g of salt). Yet global average consumption is currently 9-12 g of salt per day, and therefore twice the general recommendation.

In surimi, salt has a fundamental function. It not only imparts flavour; it also gives the paste its desirable smooth texture and gelling properties. Salt ions selectively bind to the negatively charged groups on protein surfaces and break the intermolecular ionic bonds, thus increasing the affinity of the proteins to water. This helps to disperse proteins and increases water-holding capacity.

Added salt contributes up to 80-90 percent of the total sodium in surimi. Thus raw surimi contains around 150 mg of sodium per 100 g, but adding the extra 1.5-3 percent of salt needed to produce processed surimi seafood products can take their levels up to 800–1,200 mg sodium per 100 g. Reducing the amount of salt in surimi reduces saltiness but it also affects extraction and stability, which in turn affects its cooked texture.

As such, there is a need for salt replacers, such as Jungbunzlauer’s sub4salt. This is a mixture of sodium chloride and potassium salts designed to reduce sodium content by up to 43 percent without compromising the taste and texture of products.

This salt replacer can be used to replace salt on a 1:1 basis, keeping the same saltiness and functionalities. Referring to Figure 1, replacing salt this way in a basic surimi sausage formulation leads to a 15-33 percent increase in hardness (expressed as breaking strength), and 5-13 percent increase in cohesiveness (expressed as distance to rupture).

This can be attributed to the potassium ions present which enhance protein solubility and gelation better than sodium ions. Using salt replacers not only have an impact on the healthiness of surimi products but can also improve their texture without compromising on taste.

Annually, osteoporosis causes more than 8.9 million fractures worldwide, according to the WHO Scientific Group on the assessment of osteoporosis at primary health care level in 2007. It was found that the risk of developing osteoporosis is strongly linked to low dietary calcium intake.

Osteoporosis is especially prevalent among Asians, whose consumption of dairy products is lower due to lactose intolerance. Surimi in the form of surimi sausages is a popular snack in Japan, South Korea and China. This wide acceptance and consumption makes it an ideal vehicle for effective calcium fortification to prevent calcium deficiency, in particular in children and elderly women.

The selection of the appropriate calcium source for a specific application depends on a number of factors, including functionality, taste and bioavailability. In taste comparisons, calcium salts such as carbonates and phosphates tend to produce a chalky mouthfeel, whereas calcium lactate may impart bitterness and astringency at high concentrations. The organic tricalcium citrate is considered to be very neutral tasting.

Furthermore, any nutrient’s effectiveness depends on its bioavailability. Various scientific studies have proven that organic calcium salts outperform inorganic calcium salts such as calcium carbonate and calcium phosphate in this respect. The intestinal absorption of tricalcium citrate is approximately 24 percent better than that of calcium carbonate, regardless of food intake.

Besides being a nutrient, additional benefits have been observed for micronised tricalcium citrate at 150 mg and 210 mg per 100 g calcium levels in a surimi sausage formulation. These include an increase in brightness and textural improvement. The ingredient gave the surimi sausages a whiter appearance—a desirable attribute. The same effect is usually achieved using titanium dioxide, but the use of titanium dioxide is restricted in the US and the ingredient is under scrutiny by the European Chemicals Agency because it is suspected of being carcinogenic when inhaled.

Trials have shown that when tricalcium citrate was added at 150 mg calcium level to surimi sausages, firmness increased by 26 percent and cohesiveness by 10 percent, as compared to controls (see Figure 2). Fortification with tricalcium citrate at the 210 mg calcium level increased the firmness of the sausages by 46 percent and cohesiveness by 23 percent. Using tricalcium citrate does not only fortify surimi with calcium but also improves the texture and colour of the end products.

Surimi is known to produce gels of very high strength and deformability. The gelation and water-holding ability of raw surimi can fluctuate depending on the different fish species used, spawning season, freshness of the fish before processing and even storage duration of frozen surimi.

Because of these variations, surimi formulations often need to be adjusted before production to balance the desired texture against costs. Protein solubility can be greatly affected by pH. Solubility increases at either extremely acidic or alkaline pH, and pH shifts from 5 to 4 or from 10 to 11 can increase solubility rapidly.

The use of glucono-delta-lactone (GdL) at 0.15 percent in surimi sausages doubles their firmness compared to control (Figure 3), while maintaining the cohesiveness. The addition of GdL lowers the pH of surimi sausages by 0.21 units, contributing to increased protein solubilisation and improved gelation.

GdL is a neutral cyclic ester of gluconic acid. It hydrolyses progressively to gluconic acid when added to an aqueous solution. This characteristic allows gentle acidification of food applications during processing. This is highly desirable in the preparation of surimi, as rapid acidification of the raw surimi would cause pre-gelation during comminution.

GdL preserves the soft sol texture of the surimi paste and only starts to release during the setting and cooking stage. Its mild taste sets it apart from other acidulants and it has a minimum impact on the neutral profile of surimi. Low level (0.15 percent) usage of GdL can increase gel strength to a staggering degree without imparting a sour taste. This makes GdL an ideal, economical ingredient to adjust texture when the quality of raw surimi fluctuates.

The usage of functional ingredients addresses the desire to improve the healthiness and texture of the seafood known as surimi. With a salt replacer like sub4salt, sodium content can be reduced without compromising taste while improving texture. Tricalcium citrate as a highly bioavailable calcium salt increases calcium content, whiteness and texture of surimi.

And finally, GDL offers an economical way of adjusting texture when surimi quality fluctuates. It can be added at the comminution stage causing no pre-gelation and effectively increasing the hardness of the surimi two-fold.