Influence of combined modification on digestion profile and physicochemical properties of sago (Metroxylon Sagu) starch

• Main Author: Ng, Jia Qin
• Format: Thesis
• Language: English
• Published: 2019
• Subjects: TX341-641 Nutrition. Foods and food supply
• Online Access: https://eprints.ums.edu.my/id/eprint/25230/1/Influence%20of%20combined%20modification%20on%20digestion%20profile%20and%20physicochemical%20properties%20of%20sago.pdf; https://eprints.ums.edu.my/id/eprint/25230/

This study was divided into two phases, aimed to elucidating the effect of combined modification of acid methanol treatment, hydrothermal treatment and subsequently autoclaving-storage in enhancing the formation of resistant starch (RS) in sago starch. Glycemic index (GI), thermal behaviour, pasting profile, crystallinity and morphology were examined. In the first phase, starch was acid methanol treated (AMT) with 1 and 2 ml of HCI at 35 and 40 °C, respectively prior to heat moisture treatment (HMT) (15 and 20% moisture content) or annealing (ANN) (24 and 72 hours). Starch with the highest RS content in both raw and gelatinised state was selected to further modified with autoclaving and subjected to isothermal ( 4 °C) and temperature-cycled (4/30 °C) storage in the second phase. Results of the first phase showed that AMT­ANN (especially sample treated with 1 ml acid at 40 °C followed by annealing for 72 hours, 140 AMT-ANN 72h) had more pronounced effect in increasing the RS content than AMT-HMT in both raw and gelatinised form (P < 0.05). 1 40 AMT-ANN 72h had successfully increased the RS content in raw starch by 15.8% while the RS that remained after gelatinisation was two times higher than gelatinised native starch, owing to its greater thermal stability (P < 0.05). The enhancement in thermal stability also enable 1 40 AMT-ANN 72h to retain higher amount of RS after autoclaving. RS was found to be correlated with GI in raw starch (r = -0.953, P < 0.01) but not in gelatinised starch. AMT-HMT and AMT-ANN increase the relative crystallinity of starch (P < 0.05), but these combined modifications severely reduced the pasting viscosities and caused granular surface erosion. After autoclaving, storage at 4 °C and 4/30 °C increased the relative crystallinity, SDS (slowly digestible starch) and RS content of sago starch (P < 0.05), in which the increment was more prominent in SDS content than in RS content. Both SDS and RS were negatively correlated with GI in autoclaved-stored samples (r = -0.925, P < 0.01). Pasting profile and morphology of starch were greatly altered when subjected to autoclaving-storage process. This study demonstrated that acid methanol treatment-annealing in combination with autoclaving-storage reduced the digestibility of sago starch by increasing both SDS and RS content.