Surimi is a Japanese term for mechanically deboned fish flesh that has been washed with water and mixed with cryoprotectants for a good frozen shelf life. It is used as an intermediate product for a variety of fabricated seafoods such as crab legs and flakes.
In this practical, we are asked to produce surimi from two types of local fish species which are sardine and kerisi and commercial surimi. Sardine is dark-flesh fish whereas kerisi is white-flesh fish. Theorically, there is some different between the white-flesh (low fat content <>4%) fish. Besides, research showed that sardine have low gel-forming ability due to large quantity of lipids and myoglobin in the muscle tissue and kerisi (threadfin bream) meat is white with very good flavour and a strong gel forming ability since theirs myofibrillar proteins are highly stable in frozen storage and its makes a very high-quality surimi.
Firstly, we must make sure that we used fresh fish to get the good quality of surimi.
1. We weight the raw fish for making the surimi (60kg each).
2. The fresh fish were de-heading, the internal organs were removed and the scales of the fish were removed manually. The viscera must be removed completely as small portion of the viscera may influence the appearance and gel-forming properties of the surimi produced or low quality surimi will be produced. The results of gutted fish for kerisi (threadfin bream) is 4079g and for sardine is 4176g( kerisi lower than sardine).
3. Then, the gutted fish were washed in cool water that less than 10oC to remove contaminants and unwanted materials in order to maintain the gel-forming ability of fish. Besides, the fish were washed by using cold water to prevent the protein denaturation of the fish.
4. Minced fish, on the other hand, is a mechanically separated flesh that has not been washed and does not have good freeze storability. Bones, fin and skin from the fish were removed mechanically in a fish bone separator. The fish were forced through the holes to the inside of the drum. The diameter of the drum holes will influence the subsequent leaching and dewatering processes as well as the yield and the quality of the surimi. From the results, for kerisi (threadfin bream) is 1970g and for sardine is 1887g.
5. After that, the step is leaching process. It is to remove water-soluble matter, lipid and blood from the minced meat to improve the color and flavor as well as to increase gel strength of the surimi.
a. The rate at which this undesirable soluble are leached from the minced meat depends on the water quality, water temperature, degree of agitation and the contact time between water and meat particles. It is recommended that the pH of wash water be adjusted to that of fish meat (6.5-7.0) to ensure maximum functional performance of fish protein. Temperature of fresh water used in leaching should be in the range from 3 to 10oC. Above this temperature, myofibrillar protein will be denatured and loses its gel forming ability. Low water temperature can reduce microbial multiplication. Two washing cycles with water-to-meat ratio 3:1 was required. In each cycle, the water-meat mixture was agitated for two minutes and was let to settle for five minutes. After washed with iced water, the minced fish was sieved with commercial sieve to remove excessive water. The washing treatment removes water soluble sarcoplasmic muscle proteins which do not forms gel, enzymes (protease), pigment/blood, lipids compounds that are causing lipid oxidation which leads to protein denaturation. More importantly, increases the concentration of myofibrillar protein (actomyosin), thereby improving gel strength and elasticity, essential properties for surimi based products.
6. After the second washing cycle, the remaining water in the minced fish was squeezed out by using cotton cloth and hand press machine. Then, the raw surimi was weighed to calculate the amount of cryoprotectants to be used. Cryoprotectants such as sucrose, sorbitol and sodium pyrophosphate were added and blended with the minced meat so that they were uniformly dispersed and dissolved before the meat was frozen. The purpose of addition of cryoprotectants is to stabilize the fish proteins from freeze denaturation during frozen storage. The cryoprotectant molecules will interact and bond with the protein molecules via functional groups of the surfaces. Water molecules are hydrated onto the other remaining functional groups of cryoprotectants, thus each protein molecule is covered by hydrated cryoprotectant molecules. Consequently, the frequency of mutual contact between protein molecules is lowered, resulting in increased hydration and decreased aggregation of the proteins.
7. Finally, the surimi was filled into the plastic containers and freeze in the blast freezer until the temperature reached -25ºC. From the result we obtained for surimi, we found that kerisi (threadfin bream) has the highest value of percentage yield followed by sardine.
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