Effect of orange sweet potato (ipomoea batatas) flour substitution on the pasting, rheological and textural properties of fish-flours mixture of extruded fish cracker / Noorakmar Ab. Wahab

Fish cracker or more commonly known as keropok in Malaysia is popular snack food among countries in the ASEAN region. The main starchy flour component used is tapioca starch {Manihot esculentd) that gives cracker expansion which was strongly correlated with consumer preference. Very few studies have been carried out on potential of other tuber sources to replace tapioca flour in formulation of fish crackers. Besides, the information on utilisation of freshwater fish in fish crackers was also limited. This study highlighted the potential usage of orange sweet potato (Ipomoea batatas) flour as an ingredient to substitute tapioca flour in fish cracker and as for types of fish, the red tilapia (Oreochromis niloticus) is used. Fish cracker manufacturing is mostly practised in small scale and extrusion cooking could simplify the process of stuffing and steaming. This stresses the importance of this work which studied the effect of orange sweet potato flour substitution to tapioca flour on the extruded fish cracker quality. The amount of orange sweet potato flour studied was at 20%, 30% and 50% of tapioca flour working range at fish contents of 20-70%. The physicochemical properties determined that orange sweet potato flour was lower in swelling power but higher in fat, protein and ash content and had higher gelatinisation temperature than tapioca flour. As a result, two endothermic gelatinisation temperatures were observed by differential scanning calorimetry (DSC) in fish-flours mixture with orange sweet potato flour substitution and the enthalpy gelatinisation was also low with orange sweet potato flour substitution. The DSC showed that the fish-flours mixture with 20% orange sweet potato substitution had lower gelatinisation temperature than fish-flours mixture with 50% orange sweet potato flour substitution. The rheology results indicated that the fish-flours gel with 20% orange sweet potato flour substitution had high G', low gradients and low tan 8 at all measured temperatures. The texture profile analysis (TPA) indicates that the fish-flours gel was also hard, cohesive and springy. The fried extruded fish cracker with 20% orange sweet potato flour substitution was high in linear expansion, oil absorption and water absorption index, and was low in hardness and water solubility index. The product was slightly yellow and the field emission scanning electron microscope revealed that this formulation had big air cells with thin cell walls. The fried extruded fish cracker with 20% orange sweet potato flour substitution had high crispiness score and was highly accepted by the trained panellists. In conclusion, partial substitution of tapioca flour with 20% orange sweet potato flour in fish-flours mixture was easier to gelatinise and the gel had better elasticity and texture. Hence, high quality of fried extruded fish cracker was achieved with the 20% orange sweet potato flour substitution.