Sains Malaysiana 38(3): 341-349(2009)

Effect of Red Seaweed Polysaccharides Agar (Gracilaria changii) on

Thermal Properties and Microstructure of Wheat Starch

(Kesan Polisakarida Agar daripada Rumpai Laut Merah (Gracilaria changii)

ke atas Sifat Terma dan Mikrostruktur Kanji Gandum)

P. Khairul Faizal

Department of Food Technology

Malaysian Institute of Chemical & Bioengineering Technology (MICET)

Universiti Kuala Lumpur, Taboh Naning

78000 Alor Gajah, Melaka, Malaysia

H. Rohasmizah, B. Abdul Salam, A.S.Norrakiah*

Food Science Programme

Centre of Chemical Sciences and Food Technology

Faculty of Science and Technology, National University of Malaysia

Bangi, 43600, Selangor, Malaysia

Received: 18 January 2008 / Accepted: 15 September 2008

ABSTRACT

This study has been carried out on the mixture of Gracilaria changii agar (0.1 %, 0.2 %, 0.4 % and 0.8 %) with wheat starch. Scanning electron microscopy (SEM) was performed for morphology observation, and starch thermal analysis were carried out to determine the properties of gelatinization and retrogradation. Proximate analysis has been determined for isolated wheat starch and agar. Through SEM, interaction was first observed at 64˚C for 0.4 % agar but at 0.8 % of agar, a more extensive bridging was formed which enveloped the starch granules.  Differential scanning calorimetric (DSC) result shows that as the addition of agar decreased the onset temperature (T_o) of gelatinization significantly (p<0.05) but increased the gelatinized enthalpy (ΔH_gel), gelatinized temperature range (R_g) and Peak Height Index (PHI) significantly (p<0.05). Agar lowered the retrogradation enthalpy (ΔH_ret), retrogradation range (R_ret) and retrogradation percentage (%R) of wheat starch significantly (p<0.05).

Keywords: Agar; gelatinization; Gracilaria changii;  retrogradation; starch granule

ABSTRAK

Kajian  telah dijalankan terhadap campuran agar Gracilaria changii (0.1 %, 0.2 %, 0.4 % dan 0.8 %) dengan kanji tepung gandum. Kajian ini meliputi mikroskopi pengimbas elektron (SEM) untuk pemerhatian morfologi. Analisis terma kanji juga dikaji bagi melihat sifat pengelatinan dan retrogradasi. Melalui SEM pada suhu 64°C, interaksi mula dilihat pada aras 0.4 % agar tetapi pada aras 0.8 %, agar membentuk jejambat yang lebih ekstensif dan bertindak menyaluti granul kanji. Melalui kalorimetrik pengimbas perbezaan (DSC), penambahan agar merendahkan suhu permulaan penggelatinan (T_o) secara signifikan (p<0.05) sementara meningkatkan nilai entalpi penggelatinan (ΔHgel), julat penggelatinan (R) dan Indeks Ketinggian Puncak (PHI) dengan signifikan (p<0.05). Agar juga merendahkan entalpi retrogradasi (ΔHret), julat retrogradasi (R) dan peratusan retrogradasi (%R) kanji gandum secara bererti (p<0.05).

Kata kunci: Agar; Gracilaria changii; penggelatinan; retrogradasi; granul kanji

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*Corresponding author; email: norra@ukm.my