| To develop high-quality, healthy and delicious tilapia surimi paste products aimingat different groups of consumers, the gelation properties of low-salt tilapia surimiproduced by different methods of washing, microwave heating, and oil-addition wereinvestigated here. The study covered the following four parts:1. Aiming at good understanding the properties of the recent fish paste productssold on the market in Japan and making a basis for designing foods for the elderly (so-called elderly foods), rheological properties of typical fish paste products wereinvestigated and those with elastic properties were compared with results obtained fromfish-meat-based elderly food. According to the Ministry of Health, Labor and Welfare ofJapan, the gel strength of elderly foods should be lower than2×10~4N/m~2for seniorcitizens who have chewing and swallowing problems. In this report, it was shown thatelderly foods, which indicated “Nursing foods” or “Medicare foods,” bought from themarket had lower breaking gel strength (GS value) than1.5×10~4N/m~2. However,various traditional and common fish paste (kamaboko) showed high GS value above4×10~4N/m~2. The average GS value of them was10times higher than that designed forelderly foods. This fact suggests the reasons for limited consumption for the elderlywith chewing problems. While fish pastes combined with egg yolks or soybean curdshowed lower GS values than common kamaboko level. It was supposed that elderlypeople with masticatory dysfunction select those soften fish paste products that applyingwith non fish additives into the fish paste.2. The gelling properties of low-salt tilapia surimi produced by different washingprocesses were investigated. The result showed that washing had great effects on thegelling properties of low-salt tilapia surimi. The highest gel strength was obtained byconventional washing treatment, followed by alkaline-saline washing method and theunwashed method, respectively. The higher gel-forming ability was generally associatedwith both the lowered TCA-soluble peptide content and the protein solubility of allkinds of surimi gels. The SDS-polyacrylamide gel electrophoresis (SDS-PAGE)revealed the higher myosin heavy chain (MHC) band intensity in conventional washingprocess. Microstructure of gels received washing treatments showed more compactednetwork structure than the unwashed one. Therefore, the applying of conventional waterwashing treatment could effectively improve the properties of low-salt gel products from tilapia.3. The influence of microwave heating on the gel-forming ability of low-salt tilapiasurimi paste was studied. Different gel properties could be gained via different heating.Generally, the microwave heated low-salt surimi gels had lower gel strength than that ofwaterbath-heated suirmi gels. By heating under the middle microwave power intensity(15W/g) for30seconds,927g of gel strength for low-salt surmi gel was obtained. Andthe SDS-PAGE protein pattern of surimi gel predigested by pepsin revealed the gooddigestability of low-salt tilapia surimi gels produced by microwave heating.4. The effects of four common edible oils (bean oil, olive oil, rice oil and lard oil)addition upon the gelation properities of low-salt tilapia surimi were compared. Thesepecies and the amount of oil-addition could alter the quality of surimi gels. Gel-forming ability of the low salt tilapia surimi increased to some extent when mixed withvegetable oils. Results showed that gel strengths of the heat-induced gel significantlyincreased about1.16,1.14,1.07times when mixed at2%of all the three vegetable oils,respectively. However, gel strength of each gel declined with increasing levels ofvegetable oils when exceeding2%addition. Lard oil-addition decreased the gel strengthof low-salt tilapia surimi gel and the effect was concentration dependent. Furthermore，ω-3fatty acids aboundant in these oils may contribute to oxidation problems for thesurimi products. |
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