Kesan a Agar Daripada Rumpai Laut Merah Ke Atas Sifat Terma Dan Mikrostruktur Kanji Gandum

8/3/2019 Kesan a Agar Daripada Rumpai Laut Merah Ke Atas Sifat Terma Dan Mikrostruktur Kanji Gandum

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Sains Malaysiana 38(3)(2009): 341345

Effect of Red Seaweed Polysaccharides Agar (Gracilaria changii) on ThermalProperties and Microstructure of Wheat Starch

(Kesan Polisakarida Agar daripada Rumpai Laut Merah ( Gracilaria changii )ke atas Sifat Terma dan Mikrostruktur Kanji Gandum)

P. K HAIRUL FAIZAL, H . ROHASMIZAH, B. ABDUL SALAM& A .S. NORRAKIAH

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 werecarried out to determine the properties of gelatinization and retrogradation. Proximate analysis has been determined forisolated wheat starch and agar. Through SEM , interaction was rst observed at 64C 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 the addition of agar decreased the onset temperature (T o) of gelatinization signi cantly (p


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MATERIALS & METHODS

ISOLATION OF WHEAT STARCH THROUGHALKALINE EXTRACTION

100g of wheat our was suspended in 350 mL distilled

water and 350 mL of 0.5% NaOH solution for 60 minutesand then centrifuged. Centrifugation was done at 3000 g for10 minutes at 20C. Sediments were washed with 350 mLof distilled water for 30 minutes and again centrifuged andwashed with 60 mL of distilled water for 15 minutes. Aftercentrifugation, sediments were suspended in 80 mL of water, stirred for 10 minutes, neutralized using 1.0 M HCland centrifuged. The upper greyish layer was removed andstarch which is white in colour was suspended in 100 mLdistilled water and sieved through 38 mm with additionalof 300 mL distilled water. Starch sample was centrifugedand dried overnight, sieved through 250 mm using mortarand pestle (Schierbaum et al. 1991).

AGAR EXTRACTION

Agar from Gracilaria changii was extracted using alkalinetreatment based on Hurtado-Ponce & Umezaki (1988) withslight modi cation. 25 g of red seaweed was soaked in a1 L of 5% NaOH for 1 hour. After that, the sample wasneutralized with 750 mL of 0.5% acetic acid for 1 hour.Extraction started when the sample was boiling in distilledwater for an hour. The sample was then vacuum lteredto separate cellulose residues. Filtered liquid (agar) wasfrozen overnight and thawed the next day. Agar was re-

ltered to remove pigments on samples and dried at 60Cand ned to powder.

PREPARATION OF WHEAT STARCH-AGAR(GRACILARIA CHANGII) MIXTURE

The agar was mixed at 0.1%, 0.2%, 0.4% and 0.8% onsubstitution basis to 6% of wheat starch using 25 mLof distilled water. Sample preparation is simpli ed inTable 1.

PROXIMATE ANALYSIS

After the isolation process, agar and wheat starchunderwent a series of proximate analysis to determine themoisture, ash, protein and fat in accordance to the standard

procedure stated in MALAYSIAN STANDARD (1994) providedby SIRIM and AOAC (1990).

PREPARATION OF SAMPLE FOR DEFFERENTIALSCANNING CALORIMETRY (DSC)

Wheat starch-agar samples underwent gelatinizationand retrogradation using DSC 822 c, Mettler Toledo,Schwezenbach, Switzerland. About 102 mg mixture of samples were weighed in a 40 L pan and hermaticallysealed. Scanning was performed from 20C to 90C ata constant rate of 10C/minute. Empty pan was used asreference and DSC was calibrated using indium. Thermalchanges were reported as onset temperature ( T o), peaktemperature ( T p), conclusion temperature ( T c) and entalphy(H) was calculated using the software (Suphantharika& Chaisawang, 2005). Gelatinization range ( Rg) and peakheight index (PHI) were calculated using formula 2( T p-T o)and H /(T

p-T

o) respectively (Singh & Sandhu 2007).

Retrogradations of gelatinized samples were determinedafter 7 days of storage at 4C. Retrogradation range ( Rret)was calculated as 2( T p-T o) and retrogradation percentage(%R) was calculated using formula below:

Scanning Electron Microscope (SEM) Initially, sampleswere heated in the water bath at 64C. SEM observationwas done as described by Barrera et al. (2002) withmodi cations. Samples were xed in 2% glutaraldehydefor 24 hours and dried in a critical point dryer (modelCPD -030, BAL-TEC Company). Images were observedby SEM (Phillips XL-accelerated voltage was operatedat 10 kV).

STATISTICAL ANALYSIS

The data reported in all tables are average of triplicateobservations and were subjected to one-way analysis of variance (ANOVA) and DUNCAN test. Statistical analyseswere performed using SAS version 9.1.

RESULT & DISCUSSION

In this study, 24.7% of agar was isolated from Gracilariachangii . Previous research on extraction of agar was

TABLE 1. Level of wheat starch with agar concentration

WS WS+A1 WS+A2 WS+A3 WS+A4

Wheat starch (%) 6 5.9 5.8 5.6 5.2Agar (%) 0 0.1 0.2 0.4 0.8

WS = Wheat starch only

WS+A1 = Wheat starch with 0.1 % agar

WS+A2 = Wheat starch with 0.2 % agarWS+A3 = Wheat starch with 0.4 % agar

WS+A4 = Wheat starch with 0.8 % agar


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reported to have the range of 12% to 25% (Phang et al.1996). Composition of agar and wheat starch is shownin Table 2. Moisture content obtained was higher thanpreviously reported by Selby and Wynne (1973) who alsostated that maximum moisture guideline for commercialagar is 20%. Solute such as agar affects the structure of the water. Interaction of water exists when special forcebetween solute and water molecules appears. Chargedions whether small or big create stronger solute-waterbond within the dipoles than water-water hydrogenbond (Fennema 1985). Lower ash (which referred to thepercentage of inorganic materials presence in samples)was observed as compared to Selby and Wynne (1973).Commercial agar usually has sodium ion and magnesiumbesides calcium. Protein and fat presented in lowerpercentage, as low as 1.01% and 0.12% respectively.Lower percentage of non agar compound such as nitrogenand fat was desired because those compounds could lead

to disruption of agar interaction with solvent and thusaffect agars properties during gelling. Maximum proteinnitrogen agreed is 0.32 % in commercial agar (Selby &Wynne 1973).

The amount of wheat starch obtained from alkalineextraction was slightly similar to the ndings reportedby Verwimp et al. (2004) namely 80.21%. Wheat starchextracted has low proximate value. The moisture contentobtained was 35.79%, higher than the moisture standard forstarch set by SIRIM , namely 12.0-13.0%. Protein content inwheat starch isolated is 0.67% which is higher than valuereported by Verwimp et al. (2004) (0.31%) in commercial

wheat our. The presence of protein on starch granulesaffects food product hardness (Thomas & Atwell 1999).

The fat content of wheat starch obtained was lowerthan 0.32% reported for commercial wheat our (Verwimpet al. 2004) and 0.90% for wheat starch (Davies 1995).Starch lipids are saturated in starch granules and the lipidstructure enable starch to form complexes by bonding fattyacids in the core of amylose helix (Fennema 1985). Ashcontent is higher in wheat starch isolated as compared toMALAYSIAN STANDARD (1994) and it maybe due to factorssuch as sources of raw material, farming methods, millingprocedure and chemical modi cation of starch (Thomas& Atwell 1999).

The addition of 0.4% of polysaccharide agar on wheatstarch caused formation of bridging by agar surroundingthe starch granules. Elevation of agar till 0.8 % showedan extensive bridging with more granules forming apacked structure as shown in Figure 1(c). The resultshows similarity with effect of 0.35% xanthan gum onstarch (Suphantharika & Chaisawang 2005). According to

Mandala et al. (2002), xanthan gum formed lm on tapiocastarch granules but no aggregation occurs. Starch dispersedin guar gum could adsorb more water which increasedswelling ability and viscosity of starch-guar gum complex.On the other hand, xanthan gum lowered the adsorption of water in starch which leads to lower swelling ability anda lower viscosity of starch (Mandala et al. 2002).

The gelatinization temperatures, enthalpy of gelatinization, peak height index and gelatinization rangefor mixtures measured using DSC are presented in Table 3.Signi cant changes (p


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the whole treatments shows uctuation in the uniformityof gelatinization. Sample with 0.8% agar exhibited thehighest Rgel (p


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P. Khairul FaizalDepartment of Food TechnologyMalaysian Institute of Chemical & Bioengineering Technology(MICET) Universiti Kuala LumpurTaboh Naning78000 Alor Gajah, MelakaMALAYSIA

H. Rohasmizah, B. Abdul Salam, A.S. Norrakiah*Food Science ProgrammeCentre of Chemical Sciences and Food TechnologyFaculty of Science and TechnologyNational University of Malaysia43600, UKM Bagi Selangor, D.E.MALAYSIA

*Corresponding author, email: [email protected]

Received: 18 January 2008Accepted: 15 September 2008

Kesan a Agar Daripada Rumpai Laut Merah Ke Atas Sifat Terma Dan Mikrostruktur Kanji Gandum

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