Amount of Fish, Type of Starch and Steaming Duration on the Quality of Fish Cracker ("Keropok")

The effect of steaming duration on the linear expansion of "keropok" in relation to microstructure of starch in "keropok" gel was investigated . Tapioca starch (Manihot esculen tus), sago starch (Metroxylon sagu) and wheat starch (Triticum aestivum) were used . Linear expansion of "keropok" was best when the starch granules were fully gelatinized and expanded to their largest sizes. It was found that 20 to 30 minutes steaming was sufficient to cook the gel (40 mm diameter). When starch granules swell, water is absorbed. The entrapped water molecules contribute to higher linear expansion, due to the steam released from water in the starch granules during frying in oil. "Keropok" made from tapioca starch gave the best expansion at 20-30 minutes steaming, and prolonged steaming led to reduced expansion due to fragmentation of the starch granules. The protein contents of native starches and flours were negatively correlated to swelling power of starches and linear expansion of "keropok". Among the six varieties of starches and flours, swelling power and solubility of tapioca starch and flour and sago starch were relatively higher than that of cereal starches (wheat starch , wheat flour and rice flour), and gave better linear expansions. There was positive correlation between amylose/amylopectin leaching and linear expansion of "keropok". The ratio of amylose and amylopectin did not contribute to expansion . The centre of the "keropok" gel containing 0-10% fish did not gelatinize after steaming for 2 hr. This may be due to the effect of water movement during steaming. The water-holding capacity (WHC) of "keropok" dough increased with increasing fish content. WHC of the dough with 1 5% fish was significantly (P<0.05) higher than that of the dough with 1 0% fish. Consequently, water movement may be limited by the fish protein-starch network in the "keropok" dough with high fish content. This was supported by moisture profile analyses. Scanning electron microscopy results showed that the fish-protein network started to build up at a fish : starch ratio of 1 5:85. Rheological properties changed markedly with different fish : starch ratios. The value of storage modulus (G'),loss modulus (G") and complex viscosity (11*) in the doughs containing 15% fish and above were noticeably higher than that containing 10% fish due to the fish protein network formation.

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