* To whom correspondence should be addressed.
EFFECT OF DEFATTING AND OIL ADDITION ON THE GELATINIZATION PROPERTIES OF WHEAT, RICE
AND SAGO FLOUR
SALMA, M.Y., *MASKAT, M.Y. and WAN AIDA, W.M.
Food Science Program
School of Chemical Sciences and Food Technology Faculty of Science and Technology
Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor
ABSTRACT
Effect of defatting and addition of oil on the thermal properties of wheat, rice and sago flour were studied using Differential Scanning Calorimetry (DSC). To determine the effect of defatting, batter solutions were prepared by mixing wheat, rice or sago flour with water at a ratio of 1:1.2 (flour:water) and were then freeze-dried for 15 hr.
Defatting was done by Soxhlet extraction using hexane as solvent for 2 hr. For determining the effect of oil addition, batter solutions were prepared by mixing wheat, rice or sago flour with water at a ratio of 1:1.2 (flour:water). Five mg of frying oil was added to each batter solution which were then freeze-dried for 15 hr. Untreated and treated samples were analyzed by Differential Scanning Calorimetry (DSC) in the range of 25°C – 120°C at a scanning rate of 10°C/min. Parameters recorded were onset, peak and end temperatures along with enthalpy during gelatinization.
In each of the wheat, rice and sago flour, it was shown that defatting and oil addition to the batter did not result in any major effects on the onset (To), peak (Tp) and end (Te) temperatures and also enthalpy of gelatinization (ΔH).
ABSTRAK
Kesan langkah nyahlemak dan penambahan minyak kepada cecair penyalut terhadap tepung gandum, beras dan sagu telah dikaji menggunakan Kalorimeter Pembias Kebedaan (DSC). Bagi penentuan kesan langkah nyahlemak, cecair penyalut telah disediakan dengan mencampurkan tepung gandum, beras atau sagu kepada air pada nisbah 1:1.2 (tepung:air) dan kemudian dikenakan pengeringan sejuk-beku selama 15 jam. Langkah nyahlemak dijalankan menggunakan pengekstrakan Soxhlet selama 2 jam dengan heksana sebagai pelarut. Bagi penentuan kesan penambahan minyak, cecair penyalut telah disediakan dengan mencampurkan tepung gandum, beras atau sagu kepada air pada nisbah 1:1.2 (tepung:air). Sebanyak 5 mg minyak masak ditambah ke dalam cecair penyalut tersebut dan dikenakan pengeringan sejuk-beku selama 15 jam. Sampel kawalan dan sampel yang dikenakan perlakuan dianalisis menggunakan Kalorimeter Pembias Kebedaan (DSC) dalam julat 25°C – 120°C pada kadar pemanasan 10°C/min.
Parameter yang direkodkan adalah suhu awal, puncak dan akhir pengelatinan serta entalpi pengelatinan ternormal.
Bagi setiap jenis tepung yang digunakan, langkah nyahlemak dan penambahan minyak kepada cecair penyalut tidak memberi kesan yang besar terhadap suhu awal (To), puncak (Tp), akhir (Te) dan entalpi pengelatinan (ΔH).
Key words: defatting, gelatinization
INTRODUCTION
Wheat, rice and sago flour are commonly being used as raw material in the food industry. Many aspects of flour gelatinization have been extensively studied in the past since this phenomenon is encountered in many food
processes such as baking and cereal production.
Starch gelatinization refers to the disruption of the molecular order within starch granules when they are heated in the presence of water. It is a physical phenomenon involving the disaggregation of starch granules within an aqueous environment at a suitable temperature (Zanoni et al., 1995).
Evidence for the loss of an organized structure includes irreversible granule swelling, loss of
birefringence and crystallinity. Gelatinization is an energy-absorbing process that can be followed by differential scanning calorimetry (DSC) (Whistler
& BeMiller, 1997) and has been used to study starch (Bizot et al., 1997; Donovan et al., 1983;
Ghiasi et al., 1982; Rolee & LeMeste, 1999; Yu
& Christie, 2001).
Gelatinization behavior varies with the type of starch because of differences in composition and structure (Liu et al. 2002). At 50-70°C, depending on the type of starch and its origin, water swells the starch granules, and a homogenous gel is formed. It is understood that gelatinization not only depends mainly on the starch/water ratio but also on many processing parameters such as temperature, heating rate and size of starch granules (Sakonidou et al. 2003).
Coating used in deep-fat fried food, commonly consist of flour as its main component.
During frying, coated food undergoes a drying process and is cooked through contact with hot oil which involves simultaneous heat and mass transfer. Macroscopically, a dynamic state sets in where water evaporates in the form of steam bubbles and migrates from center to surface (Aguilera et al., 2001). Starch in coatings will gelatinize and sets the coating by the formation of an outer dry crust by dehydration and infiltration with oil.
Although starch gelatinization has been extensively studied, limited material can be found in the literature regarding gelatinization in fried coating systems. As the food coating also contains oil, it is of concern during thermal analysis whether the thermal properties of the oil would affect the results of the thermal analysis. Also, gelatinization properties may be affected by the presence of oil, due to the fact that such phenomenon of oil absorption is inevitable during frying.
Vasanthan and Hoover (1992) reported that the literature is replete with conflicting information in regards to the effect of defatting on starch form functionality. Hoover and Vasanthan (1994) and Vasanthan and Hoover (1992) have shown that defatting and heat- moisture treatment alter the structural arrangement of starch chains within the amorphous and crystalline regions of starch granules. Mahsa et al. (2003) reported there are several reports showing the effect of defatting on the structure and physicochemical properties of starch. However, defatting has also been reported to not significantly affect the gelatinization temperatures of wheat, corn and cassava starches (Vasanthan & Hoover, 1992). Due to the conflicting reports and the limited literature on gelatinization in fried foods, attempts were made
in this study to determine the effect that the removal and addition of oil would have on gelatinization.
Thus, the objective of this study was to determine the gelatinization properties of wheat, rice and sago flour as affected by defatting and oil addition.
MATERIALS AND METHODS
Low-protein wheat flour (Sauh Brand, Federal Mills Berhad, Klang, Malaysia) was obtained from Pasaraya Desanika, Bandar Baru Bangi, Selangor, Malaysia. Rice flour (Erawan Brand, Tiga Gajah Cho Heng Sdn Bhd, Penang, Malaysia) was obtained from Rajan Enterprise, Ipoh, Perak, Malaysia, meanwhile sago flour was purchased from Nee Seng Ngeng & Sons Sdn.
Bhd., Sarawak, Malaysia.
Effect of defatting
Each flour type of wheat, rice and sago was mixed with water at a ratio of 1:1.2 (flour: water) and then freeze-dried (Heto Freeze Dryer CD 8, Heto Lab Equipment A/S, Denmark) for 15 hr.
About 2 g dried sample was then defatted using a Soxhlet apparatus for 2 hr (AOAC 1990) with hexane as the solvent. Non-defatted samples of each flour type were used as control.
Effect of oil addition
Each wheat, rice and sago flour was mixed with water at a ratio of 1:1.2 (flour: water). Five mg of oil was added in each batter solution and freeze-dried for 15 hr. Native flour of each wheat, rice and sago was used as control.
Differrential Scanning Calorimetry (DSC)
Control and treated samples were analyzed by Differential Scanning Calorimetry (DSC). DSC gelatinization temperatures and enthalpy changes were estimated using a Mettler-Toledo DSC 822e (Switzerland)instrument. The STARe software was used to analyze the results. About 5 mg of each control, defatted and oil-added sample from wheat, rice and sago was used in each experiment and placed in an aluminium pan. The pans were hermetically sealed and heated in the range of 25°C – 120°C at a scanning rate of 10°C/min. An empty pan was used as reference material.
Parameters recorded were onset, peak and end temperatures along with enthalpy during gelatinization.
Statistical analysis
Statistical analyses were done using t-test. In all analyses the probability level used was P=0.05
(SAS 1998). Each treatment was analyzed in 3 replications.
RESULTS AND DISCUSSION Effect of defatting
Typical thermograms corresponding to control and defatted flour of wheat, rice and sago are depicted in Figure 1. A single endothermic peak associated with gelatinization was typically observed in the DSC thermograms for each control and defatted sample. It was clearly observed that sago flour gelatinized over a broader range than did the other flours. In this study, a heating rate of 10°C/min was used.
Warne (1992) reported that a heating rate in the region of 10°C/min is generally acceptable.
Apparently, no major differences were observed for the thermograms between the control and defatted samples of each flour type.
The gelatinization peak properties of control and defatted samples are as presented in Table 1.
Results showed that defatting did not significantly affect (p>0.05) the onset (To), peak (Tp) and end temperatures (Te) along with enthalpy of gelatinization (ΔH) for wheat and sago flour. The present findings corroborate with those reported by Takashi and Seib (1988) who found that extraction of wheat starches with 75% ethanol did not cause any significant change in their gelatinization temperatures. Similar observations were also reported by Lorenz (1983) for defatted
wheat starch. Rice flour also did not show any significant difference between control and defatted samples for To and Tp. However, defatted rice flour produced a significantly (p<0.05) lower end temperature (Te) compared to control rice flour (Table 1). The end temperature (Te) of rice flour decreased after defatting from 81 to 80.75°C.
Previous work done by Biliaderis and Tonogai (1991) had reported that gelatinization temperature of rice starch decreased on extraction with 85% methanol. However, in this study, the onset (To) and peak (Tp) temperatures (Te) of the rice samples were not significantly affected by defatting. The statistically significant effect of defatting on the end temperature (Te) most probably will not have a significant effect on the overall gelatinization process. This is due to the very small difference (0.75) between the end temperature of control and defatted samples.
Furthermore, as have been mentioned, the gelatinization temperatures of To and Tp, along with the gelatinization enthalpy did not show any significant differences between the control and defatted samples. Thus, defatting, as performed in this study, most possibly will not produce any significant effect that may affect the thermal analysis of gelatinization using DSC.For sago flour, although an overall effect of defatting, where a slightly increasing trend of gelatinization temperatures (To, Tp, Te)and enthalpy (ΔH) compared to control samples can be seen, these changes were not significantly different (p>0.05).
Fig. 1. Comparison of Differential Scanning Calorimetry curves recorded at a heating rate of 10°C/
min corresponding to – NW (native wheat), DW (defatted wheat), NR (native rice), DR (defatted rice), NS (native sago) and DS (defatted sago).
Effect of oil addition
The gelatinization peak properties of control and oil added flour samples are as presented in Table 2. Results showed that addition of oil did not significantly affect the onset (To), peak (Tp) and end temperatures (Te) of gelatinization peak for wheat flour. However, oil-added rice flour produced a significantly (p<0.05) lower peak (Tp) and end temperatures (Te) compared to its control. The end temperature (Te) of sago flour also decreased significantly (p<0.05) for oil added samples from 78.04 to 77.07°C. However, gelatinization enthalpy (ΔH) did not differ significantly (p>0.05) between control and oil added samples for all types of flour. As discussed
for defatted rice flour, the observed differences in Tp and/or Te values were small and did not result in any significant change in the gelatinization enthalpy (ΔH).
Thus, these results suggest that addition of oil as performed in this study had a minor influence on wheat, rice and sago flour gelatinization properties as observed using DSC. However, in the actual frying system, there are many other factors involved such as frying temperature and pressure, which may contribute to a varying amount of oil absorption which may not be covered in this study. In addition, lipids from the food itself may also increase the fat content in the fried coating.
Table 1. Gelatinization properties of control (native) and defatted wheat, rice and sago flour using Differential Scanning Calorimetry (DSC)
Types of flour Gelatinization property
To (°C) Tp (°C) Te (°C) ΔH (J/g) Wheat
control 54.03 ± 0.12 a 60.71 ± 0.16 a 66.92 ± 0.14 a -0.93 ± 0.01 a defatted 53.95 ± 0.61 a 60.72 ± 0.33 a 67.05 ± 0.20 a -0.92 ± 0.27 a Rice
control 73.22 ± 0.16 a 77.09 ± 0.08 a 81.00 ± 0.09 a -1.59 ± 0.44 a defatted 73.09 ± 0.10 a 76.97 ± 0.09 a 80.75 ± 0.07 b -1.48 ± 0.17 a Sago
control 66.93 ± 0.41 a 72.15 ± 0.36 a 77.73 ± 0.63 a -2.59 ± 0.08 a defatted 69.01 ± 4.23 a 74.22 ± 4.04 a 79.10 ± 3.54 a -2.91 ± 0.04 a
Note: To,Tp,Te,ΔHindicate the temperatures of the onset, peak and end of gelatinization and gelatinization enthalpy respectively.
a Means with the same letter within the same column and flour type denotes no significant difference (p>0.05).
Table 2. Gelatinization properties of control (native) and oil-added wheat, rice and sago flour using Differential Scanning Calorimetry (DSC)
Types of flour Gelatinization property
To (°C) Tp (°C) Te (°C) ΔH (J/g) Wheat
control 54.64 ± 1.38 a 60.57 ± 0.23 a 66.37 ± 0.78 a -0.63 ± 0.13 a addition of oil 54.38 ± 0.26 a 61.11 ± 0.26 a 67.37 ± 0.50 a -0.97 ± 0.09 a Rice
control 73.27 ± 0.36 a 77.12 ± 0.17 a 80.95 ± 0.32 a -1.44 ± 0.45 a addition of oil 73.11 ± 0.28 a 76.95 ± 0.01 b 80.74 ± 0.15 b -1.45 ± 0.10 a Sago
control 66.88 ± 0.37 a 72.30 ± 0.36 a 78.04 ± 0.34 a -2.76 ± 0.14 a addition of oil 66.57 ± 0.42 a 71.89 ± 0.11 a 77.07 ± 0.32 b -2.75 ± 0.12 a
Note: To,Tp,Te,ΔHindicate the temperatures of the onset, peak and end of gelatinization and gelatinization enthalpy respectively.
a-b Means with different letters within the same column and flour type denotes significant difference (p<0.05).
CONCLUSION
From this study, wheat, rice and sago flour did not show significant differences between control and defatted flour samples for onset (To), peak (Tp) and end (Te) temperatures except for the end temperature (Te) of rice flour which decreased significantly (p<0.05) after defatting. Addition of oil also did not produce significant differences except for peak (Tp) and end temperatures (Te) for rice flour and end temperature (Te) for sago flour (p<0.05) as compared to the control samples.
Gelatinization enthalpy for all flour types did not show any significant differences between control and treated samples either after defatting or addition of oil to the batter.
ACKNOWLEDGEMENTS
The authors would like to thank the Ministry of Science, Technology and Innovation of Malaysia (MOSTI) for its financial support of this study under the IRPA funds (03-02-02-0059-EA119).
REFERENCES
A.O.A.C. 1990. Official Method of analysis. 15th edition. Washington, DC: Association of Official Analytical Chemists. USA.
Aguilera, J.M., Cadoche, L., Lopez, C. &
Gutierrez, G. 2001. Microstructural changes of potato cells and starch granules heated in oil. Food Research International. 34: 939-947.
Biliaderis, C.G. & Tonogai, J.R. 1991. Influence of lipids on the thermal & mechanical properties of concentrated starch gels. J.
Agric. Food Chem. 39: 833-40.
Bizot, H., Le Bail, P., Leroux, B., Davy, J., Roger, P. & Bule´on, A. 1997. Calorimetric evaluation of the glass transition in hydrated, linear and branched polyanhydroglucose compounds. Carbohydrate Polymers. 32: 33–
50.
Donovan, J.W., Lorenz, K. & Kulp, K. 1983.
Differential scanning calorimetry of heat- moisture treated wheat and potato starches.
Cereal Chemistry. 60(5): 381–387.
Ghiasi, K., Hoseney, C. & Varriano-Marston, E.
1982. Gelatinization of wheat starch. III.
Comparison by differential scanning calorimetry and light microscopy. Cereal Chemistry. 59(4): 258–262.
Hoover, R. & Vasanthan, T. 1994. Effect of heat- moisture treatment on the structure and physicochemical properties of cereal, legume and tuber starches. Carbohydrates Research.
252: 33-53.
Liu, Q., Charlet, G., Yelle, S. & Arul, J. 2002.
Phase transition in potato starch-water system 1. Starch gelatinization at high moisture level.
Food Research International 35: 397-407.
Lorenz, K. 1983. Physicochemical properties of defatted heat-moisture treated starches.
Starch. 35: 123-9.
Mahsa, M., Arthur, J.R., Martin, C., Sandra, E.H. & Stephen, E.H. 2003. Partial fractionation of wheat starch amylase and amylopectin using zonal ultracenrifugation.
Carbohydrate Polymers 52: 269-274.
Rolee, A. & LeMestre, M. 1999. Effect of moisture content on thermomechanical behavior of concentrated wheat starch-water prep-arations. Cereal Chemistry. 76(3): 452–
458.
SAS. 1998. SAS Institute Inc., Cary, NC, USA.
SAS Software Release 6.12 TS020 Lousiana State University.
Sakonidou, E.P., Karapantsios, T.D. &
Raphaelides, S.N. 2003. Mass transfer limitations during starch gelatinization.
Carbohydrate Polymers. 1-9.
Takashi, S. & Seib, P.A. 1988. Paste and gel properties of prime corn and wheat starches with and without native lipids. Cereal Chemistry 65: 474-83.
Vasanthan, T. & Hoover, R. 1992. Effect of defatting on starch structure and physico- chemical properties. Food Chemistry 45: 337- 347.
Warne, S.S.J. 1992. Introduction in Thermal Analysis. Thermal Analysis Technique and Applications. 1-30. Royal Society of Chemistry, Cambridge.
Whistler, R.L. & BeMiller, J.N. 1997.
Carbohydrate Chemistry for Food Scientists.
St. Paul: Eagan Press, pp. 117–151.
Yu, L. & Christie, G. 2001. Measurement of starch thermal transitions using differential scanning calorimetry. Carbohydrate Polymers 46.
Zanoni, B., Schiraldi, A. & Simonetta, R. 1995.
A naïve model of starch gelatinization kinetics. Journal of Food Engineering 24: 25- 33.
