Development of sago (Metroxylon sagu Rottb.) starch as an ingredient for functional food

Sago starch is extracted from the pith of Metroxylon sagu Rottb. It is considered as an underutilised starch when compared to other commercially available starches such as corn, tapioca, and rice starches. Therefore, modification of native sago starch is essential to improve its properties and will give addon value to the starch. The current study aims to develop an ingredient with functional food properties from native sago starch. In this study, the native starch was modified using three different methods with microwave heat treatment as the main treatment. The treatments were microwave heat treatment with different treatment durations (MHT) (5, 10, 15, or 20 min), microwave heat treatment with cooling cycles (CMHT) (1, 3, or 5 cycles), and pre-treated microwave heat treatment (PMHT). Modified starches with a highest resistant starch (RS) content from each series was subjected to fractionation of RS. The last part of this study focused on the formulation of food product (breakfast drinks). The formulation was done by replacing a portion of wheat flour with modified starches. Among the modification methods investigated, the CMHT showed potential in improving the functional food properties of the sago starch. The treatment showed an increasing pattern in RS content for uncooked starch samples up to 67.93% with five treatment cycles. It also increases the RS contents for cooked starch samples compared to the native starch (4.37%), especially for treatment with one (CMHT1, 8.58%) and three (CMHT3, 7.87%) cooling cycles. Furthermore, the CMHT3 (0.191 min–1) and CMHT5 (0.197 min–1) had their Lactobacillus casei growth rates higher than the native starch (0.173 min–1) for uncooked samples. Meanwhile, in the cooked samples, all CMHT starches (0.087 – 0.095 min–1) were higher than the native starch (0.065 min–1). Additionally, the food formulation using CMHT starches showed a higher RS content than the 100% flour formulation. It also had a low predicted glycaemic index (pGI) values among the food formulated especially the CMHT3 with pGI value lower than 55 for all flour:starch ratios used. They also lower the Escherichia coli growth rates (0.050 – 0.060 min–1) compared to the 100% flour (0.074 min–1) formulation. Fractionation of the RS from selected modified starches provided an insight on the importance of amylose/amylopectin ratio to resistance properties of RS against digestion. Moreover, the fractions exhibit pGI values between 52 – 65. Based on the study, it was also understood that the formation of double helix structures between amylopectin side chains may contributing to the resistance behaviour of the amylopectin group as suggested by the correlation study (r = 0.582, p < 0.001). Additionally, the amylopectin content was associated with the growth rates of the tested bacteria. Current work showed that the CMHT can be used in the development of sago starch as a functional food ingredient, especially for low pGI and high RS content food with potential prebiotic effects. Future work on functional food properties of the modified starches especially CMHT starches on in vivo study and clinical trials are required. Keywords: Glycaemic index; Metroxylon sagu Rottb.; microwave; prebiotic; physical modification; resistant starch

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