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In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch
Accepted Manuscript In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch Asima Shah, Farooq Ahmad Masoodi, Adil Gani, Bilal Ahmad Ashwar PII: DOI: Reference:
S0308-8146(16)30912-8 http://dx.doi.org/10.1016/j.foodchem.2016.06.019 FOCH 19360
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
11 March 2016 7 June 2016 7 June 2016
Please cite this article as: Shah, A., Masoodi, F.A., Gani, A., Ashwar, B.A., In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch, Food Chemistry (2016), doi: http://dx.doi.org/10.1016/j.foodchem. 2016.06.019
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In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch Asima Shah, Farooq Ahmad Masoodi*, Adil Gani, Bilal Ahmad Ashwar Department of Food Science and Technology, University of Kashmir, Srinagar, India-190006.
*authors for correspondence Email: [email protected] Ph: +91-9419135876
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Abstract Starches isolated from three different varieties of oat were modified with dual autoclavingretrogradation treatment to make modified food starches with high contents of type 3 resistant starch (RS3). FT-IR spectroscopy showed increase in the ratio of intensity of 1047 cm-1 /1022 cm-1 on treatment. Morphology of the oat starches changed into a continuous network with increased values for onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc). XRD showed an additional peak at 13° and increase in peak intensity at 20° inclusive of the major X-ray diffraction peaks which reflects formation of amylose–lipid complex from dual autoclaving-retrogradation cycle. Peaks at 13° and 20° are the typical peaks of the V-type pattern. Rheological analysis suggested that retrogradated oat starches showed shear thickening behavior as revealed from Herschel-Bulkely model and frequency sweep. Keywords: Resistant starch, Rheology, Microstructure.
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1. Introduction Oat starch is considered distinct among other cereal starches being smaller in size, high lipid content, and well developed granular surface. Besides it, oat starch is more viscous, less prone to retrogradation, offers some resistance to digestion due to starch-lipids complex in comparison to wheat starch which has raised interest among many food processors (Berski et al., 2011). However native oat starch has certain limitations to be used as food or an ingredient in foods, due to less shear stress resistance, thermal decomposition, high viscosity and low gel clarity. On the basis of glucose released during enzymatic hydrolysis, starch has been classified into three fractions, rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) and in most of the cereal products rapidly digestible starch predominates. In today’s scenario, people are having a sedentary life style with increased risk factors of various diseases like diabetes, hypercholestromia, cancers, obesity etc. So they are looking for such type of food that has low glycemic index (GI) and profound health benefits (Zhou & Lim, 2012; Simsek, & El, 2012; Han, & BeMiller, 2007). Different modifications of starch have been employed for improving the functionality and resistance to digestive enzymes, dual autoclaving- retrogradation treatment is one such. The knowledge of functional properties of starch like viscosity, swelling power, texture, gel clarity could be helpful for predicting its use for commercial purposes. The study of its rheological characteristics is important to anticipate its use as gelling and thickening agent and as well as the stability of end products (Wang et al., 2012). The present study was carried to evaluate the effect of dual autoclaving- retrogradation treatment on resistant starch development (RS3) and techno-functional properties from three different cultivars of oat found in the Indian Himalayan region. This comprehensive study will help to expand the utilization of oat
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starch for both domestic and industrial purpose for making second generation functional cereal foods. 2. Materials and methods 2.1. Materials Three oat varieties were procured form Sher-e-Kashmir University of Agricultural Sciences and Technology (SKAUST), Shalimar, Srinagar, J&K, India. Resistant starch content was assessed using GOPOD Assay Kit (Megazyme International, Ireland, Ltd). Amyloglucosidase (Aspergillus niger, 3300 U/mL) and pancreatin (porcine pancreas, 8×USP) were obtained from SigmaAldrich, St. Louis, USA. All the other chemicals used were of analytical grade. 2.2. Starch extraction Starch was isolated according to the method described by Gani et al. (2012) with certain modifications. Milled oat flour was diluted with distilled water (ten times), pH was adjusted to 9 (0.2 N NaOH) and the slurry obtained was mixed intermittently for 1 hour. After filtration slurry was centrifuged at 3000 × g for 15 min at 5οC (Eppendorf 5810 R, Germany). The sediment obtained was scraped off from the surface and the lower white portion was washed with distilled water three times and allowed to sediment at refrigerated temperature (4οC). The starch was dried at 40οC in oven. 2.3. Preparation of resistant starch from oat starch Dual autoclaving-retrogradation cycle was carried out for the preparation of resistant starch. Oat starch (15 g) was mixed with 60 mL of distilled water and the mixture was then pressure-cooked in an autoclave at 121οC for 30 min. The autoclaved starch paste was allowed to cool to room temperature and then stored at 4οC for 24 h. The autoclaving- retrogradation cycle was repeated two times. Finally the samples were oven dried at 45οC and ground using a mortar and pestle.
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2.4. Chemical composition of starch Moisture, protein, fat and ash were determined according to the AOAC, 1990. Apparent amylose contents of the starch samples were determined according to method described by Williams, Kuzina, Hlynka, 1970. 2.5. Color attributes Color of the starch was determined using Color Flex Spectrocolorimeter (Hunter Lab Colorimeter D-25, Hunter Associates Laboratory, Ruston, USA). The instrument was calibrated with black and white tile before colour measurement. The ‘L’ value indicates the lightness, 0 – 100 representing dark to light. The ‘a’ value gives the degree of the red – green colour with a higher positive ‘a’ value indicating more red. The ‘b’ value indicates the degree of the yellow – blue colour, with a higher positive ‘b’ value indicating more yellow. Whiteness index (WI) was determined using below equation: WI = 100-[(100-L)2 + a2 + b2]½ Where, L, a, and b are Hunter values. 2.6. Granule morphology and light microscopy of oat starches The freeze dried starch sample was placed on an adhesive tape attached to a circular aluminum specimen stub and then coated vertically with gold. Granule morphology was studied using scanning electron microscope (Hitachi S- 300H-Tokyo, Japan) at an accelerator potential of 5 kV. Further samples were stained with iodine solution (0.2% I2/KI for 10 s) and examined under a light microscope at 40x (LMI, Leedz Micro Imaging Ltd, UK). 2.7. ATR-Fourier transforms infrared (FTIR) spectroscopy The ATR-FTIR spectra of starches were recorded on an ATR- FTIR Spectrophotometer (CARY 630, Agilent Technologies, USA) at room temperature. The spectra were recorded within the
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range of 600-4000 cm-1 using Agilent Resolution-Pro MicroLab software (version B.05.2, Agilent Technologies). 2.8. XRD analysis X-ray patterns of the samples were recorded with a wavelength of 0.154 nm using X-ray diffractometer (X’Pert PRO, Panalytical, Netherlands). The diffractometer was operated at 40 kV and 35 mA. Diffractograms were acquired at 25οC over a 2 Ø range of 4ο - 40ο with a step size of 0.02 and sampling interval of 10 s. The relative crystallinity (RC) of starch was calculated as described by Rabek (1980) by the equation: RC (%) = (Ac/(Ac + Aa)100; where Ac is the crystalline area; Aa is the amorphous area on the X-ray diffractograms. 2.9. Determination of resistant starch Resistant starch content was assessed using GOPOD Assay Kit (Megazyme International, Ireland, Ltd), following the approved AACC method (2000). 2.10. Rheological measurement Starch dispersion (6 g/100 mL H2O) were heated up to 90οC with mild stirring for 20 min and the gel was left to cool at room temperature for 1 hr. Rheological measurements were made at 25 ± 0.1◦C with on a controlled stress rheometer (MCR 102, Anton Paar) using a parallel plate geometry (CP50-1; diameter: 50 mm). The flow properties were determined with increasing shear rate, from 0.1-500 s-1 and the delay time was 10 s. The experimental data was evaluated by fitting the data to a Herschel-Bulkley model τ = τ0 + Kγn τ (Pa) is the shear stress, τ0 (Pa) is the yield stress, K is the consistency index (Pa sn), and n is the flow behavior index.
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The viscoelastic range was determined through stress sweep tests at constant frequency of 1 Hz with a logarithmic increase of shear stress from 0.01 to 100 Pa. Frequency sweep tests at constant stress were carried out to obtain mechanical spectra. The appropriate shear stress was chosen after analyzing the LVE-range (Linear viscoelastic range) of the samples from the above experiment. Frequency was logarithmically decreased from 100 to 0.1 Hz at a constant shear stress of 1 Pa. 2.11. Swelling power & solubility index Swelling power and solubility index of the starch samples were determined with slight modifications to the method of Gani et al. (2012). Starch (0.6 g) (M0) was mixed with 30 mL of distilled water and heated at 90 °C in a water bath with occasional shaking. After 30 min stirring, the mixture was centrifuged at 1500×g for 30 min. The supernatant was carefully removed, and the swollen starch sediment was weighed (M1). The supernatant was evaporated and dried at 105 °C in an oven until constant weight (M2). Swelling power and solubility was calculated from the equations given below. Swelling power (g/g) = M1/M0 Solubility (g/g) = M2/M0 2.12. Light transmittance Light transmittance was determined by dissolving 1 g of starch (db) in 100 mL of distilled water and heating in a water bath at 90οC for 30 min with constant stirring then, cooled for 1 h at 30οC. The samples were stored for 5 days at 4οC in a refrigerator, and transmittance was determined after every 24 h at 640 nm against water as blank. 2.13. Bile acid binding capacity The bile acid-binding capacity of starch was determined by colorimetric method (Shah et al., 2016).
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2.14. Pasting properties and gel texture analysis The pasting properties of the starches were measured using a Rapid Visco Analyzer (Tech Master, Perten Instruments Warriewood, Australia) as determined by Ashwar et al. (2016a). After RVA analysis, the gel obtained was stored at 4οC for 24 h. The gel texture was analysed with a Texture Analyser (TA.XT2 plus, Stable Micro Systems). The gel was compressed at 1.0 mm/s for a distance of 5.0 mm using a cylindrical probe (P/75). 2.15. Thermal properties The thermal characteristics of oat starch were studied with a Mettler Toledo DSC1STAR System. Starch samples (3.5 mg) were weighed into platinum pans and deionized water (8 µl) was added. The pans were kept at room temperature overnight before analysis. The samples were heated from 20 to 200°C at 10 °C/min. An empty platinum pan was used as a reference. 2.16. Statistical analysis Results are expressed as the mean ± standard deviation of triplicate experiments. Data were analyzed by two-way analysis of variance (ANOVA), followed by Duncan’s multiple range tests at 5% significance level (p< 0.05) using a commercial statistical package SPSS (IBM statistics 22). 3. Results and discussion 3.1. Chemical composition and color attributes of oat starch Chemical compositions of oat starch from three different varieties are presented in Table 1. Compared to other cereal starches, oat starch contains highest amounts of lipids (Zhou et al., 1998). Almost similar values for chemical composition have been seen in the reports of Mirmoghtadaie, Kadivar, & Shahedi (2009). The apparent amylose content was found in the range of 26.96-25.81% for oat starches. Comparable values of the amylose content have been
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reported earlier in canadian oat cultivars (19 to 33 %) (Hoover, Smith, Zhou, & Ratnayake, 2003). However, the amylose content of oat obtained from Breeding Station in Strzelce Krajenskie in Poland was found comparatively lower (Berski et al., 2011). Such difference in amylose content could be ascribed due to varietal difference, environmental condition, method of starch extraction, or method used for its estimation. On dual autoclaving-retrogradation process the amylose content showed a significant (p<0.05) decrease at same moisture content (dry basis). The Hunter lab values (L) of native starches from Sabzaar, SKO20, and SKO90 were 92.65, 94.96, and 91.02, a values were 0.65, 0.32 and 0.48 and b values were 6.3, 2.8 and 4.3, respectively. However, after modification the values for lightness (L) got decreased significantly (p<0.05) whereas those of “a” and “b” values were found to increase as represented in Table 1. The change in color values might be caused by the maillard reaction at high temperature. Similar decrease in color values were obtained for rice flour due to heat moisture treatment (Lorlowhakarn, & Naivikul, 2006). Whiteness index of starch is an important parameter that determines its applicability in food systems. Whiteness index (WI) decreased from 90.29 to 73.80, 94.19 to 68.80, and 90.03 to 65.15 in retrograded starches of Sabzaar, SKO20, and SKO90, respectively. 3.2. Granule morphology and light microscopy of oat starches Granule morphology and light microscopy of oat starches are shown in Fig.1. Oat starch samples showed presence of small granules with varying dimensions, oval or irregular shape with smooth surface and some damaged starch. Average granule size of oat starch was within the range of 1.55.33 µm in Sabzaar, 1.1-5.2 µm in SKO20, and 1.7-6.66 µm in SKO90. However dual autoclaving-retrogradation process resulted in disruption of granules and formation of continuous network microstructure with minimum small starch granules. Light microscopy also revealed
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formation of irregular granular aggregations. This solid network with increased density of RS3 crystallites offers resistance to enzyme attack (Dundar and Gocmen 2013). 3.3. ATR-FTIR spectroscopy The FTIR spectrum of native and modified oat starches is shown in Fig.2. All samples displayed absorption peaks at 3400, 2929, 1500, 1600 and 620-527 cm-1, which correspond to the functional groups of poly -OH, –CH2, C –O- C (skeletal vibrational mode of α-1,4 glycosidic linkage), carboxylate ion (COO), and skeletal modes of pyranose ring, respectively (Ashwar et al., 2016b). Dual autoclaving-retrogradation resulted in broading of peaks at 3400 cm-1 suggesting increase in the crystalline region (Garcia-Rosas et al., 2009). Further, FTIR spectrum may also be used to determine crystallinity of starch. Band at 1022 cm-1 is characteristic to an amorphous fraction whereas band at 1047 cm-1 is sensitive to crystallinity (Gani et al., 2016). Ratio of intensity of 1047 cm-1 /1022 cm-1 can be used to express the degree of order in starch. Table 2. shows the ratio of intensity (R=1047/1022 cm-1) of native and retrograded oat starches. Ratio for native starch was found in the range of 0.65-0.67 that increased to 0.73-1.12 upon treatment which might be due to close parallel alignment of disrupted crystals on retrogradation. 3.4. X-ray diffraction pattern Fig.3 shows the X-ray diffractograms of native and retrograded oat starches and corresponding peak intensities and relative crystallinity (RC) are given in Table 2. In native oat starches peaks were observed at 15° and 23°, doublet peak at 17° and 18°, and small peak at 20° of 2θ which are characteristic of a A-type pattern. However dual autoclaving-retrogradation process resulted in starches that showed an additional peak at 13° and increase in peak intensity at 20° inclusive of the major X-ray diffraction peaks which reflects formation of amylose–lipid complex. A typical amylose–lipid complex contains a hydrophobic fatty acid tail, which is buried inside an amylose
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helix that helps to develop further entanglement among starch molecules and thereby increasing resistance to digestive enzyme breakdown (Dupuis et al., 2014). Peaks at 13° and 20° are the typical peaks of the V-type pattern resulting from dual autoclaving- retrogradation treatment (Thomas & Atwell, 1999). Also increase in crystallinity on treatment is due to reorientation of double helical chains in a closer fashion, providing a more stable and crystalline structure (Zavareze & Dias, 2011). Liu et al., 2014 reported that higher the crystallinity of starch, higher is the resistance offered to digestion. 3.5. Resistant starch content Resistant starch content of native oat starches ranged from 17.14 % to 23.9 %. The differences in the resistant starch content among the varieties might be due to the following factors: source of starch, granular size, amylose-amylopectin ratio, branch length in amylopectin, percent crystallinity, amylose lipid complex, and pores within the granules (Ashwar et al., 2016a; Dupuis, Liu, & Yada, 2014). On dual autoclaving-retrogradation process the type 3 resistant starch content (RS3) of oat varieties increased significantly to the range of 25.81-38.88 % (Table 2). Increase in RS3 content may be attributed due to following reasons: (A) Recrystallisation of linear amylose polymers on cooling into double helices that form tightly packed structures which are stabilized by hydrogen bonds (Dundar, & Gocmen, 2013). (B) Higher amount of amylose–lipid complex which is resistant to digestive enzyme breakdown (Hasjim, Ai, & Jane, 2013). Results were in consistent with XRD analysis that revealed higher amylose–lipid complex (peaks at 13° and 20°) in retrograded starches compared to their native counterparts (Table 2). The modified starches therefore offers resistance to enzymes and thus could be helpful to lower plasma cholesterol, absorption of a number of minerals, for the control of obesity, improve glucose tolerance (Morita et al., 2005).
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3.6. Rheological measurement Flow curves of native and modified oat starches, displaying changes in viscosity with increase in applied shear stress, are shown in Fig. 4A(a, b, & c). Native starch solutions exhibited shearthinning behavior over entire measured shear rates. Whereas modified starch dispersions showed increase in viscosity with the increase in shear rate, reached a maximum value, and then decreased as the shear rate increased. Such a behavior is typical of shear thickening fluids. Also modified starches showed higher shear stress than that of their native counterparts indicating their higher resistance to structure breaking at same shear rate. Moreover, shear thickening behavior can be characterised by a Herschel-Bulkely model and results of these fits are presented in Table 3. Flow behavior index (n) was found within the range of 0.42-0.50 in native starches which on dual autoclaving-retrogradation increased to 1.053-59019 (greater than unity) confirming that modified oat starch solutions exhibited shear-thickening behaviors. Consistency index (K) which gives an indication about structural strength of solution, was found greater for modified oat starches with SKO90 showing highest value (789805.1) than SKO20 (380507.92). However Sabzaar variety showed a contradictory trend. Decrease in K value may be due to increased amylose leaching in sabzaar than SKO20 and SKO90 during the dual autoclaving-retrogradation process. Dual autoclaving-retrogradation of starches results in the formation of gel-like clusters when dissolved in water. Such dispersions when subjected to shear-stress results in the breakdown of clusters, increasing the viscosity of solution and we observe shear thickening behavior. Above a critical shear rate, the solution becomes homogenous and its viscosity decreases with the increase in shear rate (Wang et al., 2011). Shear-thinning behavior of native starches is attributed due to the formation of a homogenous solution when dispersed in water and
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the disintegration of polymer entaglements at a faster rate than their reformation at the high shear rates (Salamone, 1996). Oscillatory experiments were carried to measure viscoelastic properties of native and modified oat starches (Fig.4d). In all samples storage modulus (G′) was higher than loss modulus (G″) at low shear rate, which is typical gel behavior. At certain point called flow point (τF) storage modulus becomes equal to loss modulus (G′ = G″) and this point is the intersection of G′ (elastic behavior) and G″ (viscous behavior). Further increase in shear rate G″ becomes higher than G′ and displays the viscous behavior of the solution. Flow point and yield point was observed lower for modified starches. Loss factor (Tan δ) is the ratio of viscous modulus (G") to elastic modulus (G') and a useful parameter to determine the extent of elasticity in a fluid. Tan (δ) values of native and modified starches were found within the range of 0.07-0.11 and 0.12-0.18, respectively. Tan (δ) values of modified starch pastes were found higher than that of native starches but lesser than unity (Table 3). A small tan δ indicates that the starch gel is stiff, reflecting its solid-like behavior; whereas a large tan δ reflects that the starch gel behaves more like a liquid. Similar kind of observation was reported in heat moisture treated pearl millet starch (Sharma et al., 2015). Frequency sweeps was measured in linear viscoelastic region over the frequency range (0.1 to 100 Hz) to determine frequency dependence of viscous modulus (G") and elastic modulus (G'). The G′ was greater than G″ in both native and modified starches throughout the frequency range (Fig. 4e) which is typical weak gel behavior. Such gels under small deformation behave as strong gels but as strain is increased their network structure breakdowns. Greater the difference between G′ and G″ for a gel, predominant is its elastic-behavior. 3.7. Swelling power & solubility index
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The results of swelling power and solubility index of oat starches, determined at 90°C, are shown in Table 4. Dual autoclaving-retrogradation resulted in significant (p<0.05) decrease in swelling power and solubility index. This decrease has been attributed to transformation of amylose into a helical form, higher interaction between amylose and amylopectin molecules, and further strengthing of intramolecular bonds and assuming more ordered configuration during repeated autoclaving-retrogradation treatment (Gunaratne, & Hoover, 2002). Similar observations have recently been made on sweet potato starch due to repeated heat-moisture treatments (Huang et al., 2016). 3.8. Light Transmittance Clarity values of starch samples during five days of refrigerated storage are shown in Table 4. The modified starch pastes showed significantly (p<0.05) higher gel clarity than native starch, which might be due to breakdown of granules during dual autoclaving-retrogradation treatment (Craig, Maningat, Seib, & Hoseney, 1989). The light transmittance of starch pastes showed time dependence and was found to decrease up to 3rd day of storage and then remained almost constant. Similar reduction in transmittance with time has already been reported in multiple studies (Ashwar et al., 2014; Ashwar et al., 2016a). Decrease in light transmittance of starch pastes with the increase in storage time is attributed to recrystallization of starch (re-association of originally broken bonds within the granule). 3.9. Bile acid binding capacity Resistant starch like dietary fiber entraps bile salts in the viscous matrix and increases its fecal bile excretion resulting in lowering of blood cholesterol level, controlling obesity, and subsequently reducing the risk of cardiovascular diseases (Rahim, Haryadi, Cahyanto, Pranoto, 2012). Data indicated that the affinity of oat starches to bile acid increased significantly (p ≤ 0.05)
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due to dual autoclaving-retrogradation cycles as shown in Table 4. Similar increase in bile acid binding capacity of taro starch after enzymatic modification was reported by Simsek, & Nehir, 2012. The high bile acid binding capacity of modified oat starches suggests their possible health improving potential. 3.10. Pasting characteristics and gel texture characteristics The pasting properties of native and modified oat starches are summarized in Table 4. Significant increase in pasting temperature after modification supports the fact that repeated autoclavingretrogradation cycles tends to increase the region of crystallinity, as a result of reorientation and increased interaction between the starch chains. Due to the presence of strong intragranular forces, the starch requires more heat for structural disintegration and paste formation (Adebowale, Henle, Schwarzenbolz, & Doert, 2009). However peak, breakdown, and setback viscosity was significantly (p<0.05) reduced by dual autoclaving-retrogradation treatment. The breakdown value is the ease with which the swollen starch can be broken down by heating and physical agitation. The compact organization of the modified starches tends to be more resistant to the effect of shearing force and heat as it is seen from the breakdown values. The tendency of starch to retrogradate is measured by set-back value. Due to limited starch swelling and amylose leaching, there is minimum amylose reassociation and hence low set back values. This kind of pasting behavior was also reported in rice, cassava, and pinhao starches (Klein et al., 2013). Texture properties of the retrograded oat starch gels presented lower hardness and higher values of adhesiveness as compared to native starch suspensions (Table 4). This decrease in hardness of gel might be due to partial gelatinization of starch that causes breakdown of structure, resulting in low rigid gel. Also, the retrograded starch showed lesser swelling power, and thus formed weaker starch gel. Also significantly lower values for springiness, and cohesiveness were obtained for
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modified starch gels. Similar decrease in hardness, springiness, and cohesiveness due to heat moisture treatment has also been seen in potato starch (Zavareze et al., 2012). 3.11. Thermal properties Dual autoclaving- cooling cycles of starches leads to increase in the onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) with decrease in transition temperature range (Tc-To) and gelatinisation enthalpy (∆H) (Table 3). Higher transition temperatures are due to continuous network of starch chains as revealed in SEM analysis and increased crystallinity (XRD analysis). During dual autoclaving-retrogradation process, the starch granules are disrupted, gelatinized, and then rearranged in a such a manner that there is increased association between starch chains which inturn increases the resistance of starch for disruption of helical order leading to increased To, Tp, and Tc (Zavareze, & Dias, 2011). The decrease in transition temperature range (Tc-To) indicates increased homogeneity within the starch. Klein et al., 2013 also reported decrease in transition temperature range in rice and cassava starches with both single and dual heat moisture treatment. Reduction in gelatinisation enthalpy (∆H) due to autoclaving-cooling treatment proposes that in retrograded starch re-association of the chains forms a weaker matrix or network that requires lesser energy to melt the crystalline structure (Ovando-Martinez et al., 2013). Conclusion Dual autoclaving-retrogradation treatment resulted in starch with high resistant starch (RS3), good bile acid binding capacity, improved pasting properties, better thermal stability, and increased crystalline perfection. Shear-thickening behavior of modified starches depicts that it cannot find applications in many food processing techniques like homogenization, spraying, pumping etc as it will block the equipment. However in foods where viscosity is the main criteria,
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we can use such type of modified starches as an additive to get the desired viscosity at minimum concentration. Moreover, the increased resistance of modified starch to enzyme digestibility could make its use as an encapsulating agent for controlling drug delivery systems in pharmaceutical industries. Acknowledgements The authors are thankful to the Department of Biotechnology, Government of India for their financial support (Grant number: D.O.BT/PR6701/FNS/20/674/2012).
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Huang, T. T., Zhou, D. N., Zheng, Y. J., Xu, X. M., & Chen, H.Q. (2016). Effect of repeated heatmoisture treatments on digestibility, physicochemical and structural properties of sweet potato starch. Food Hydrocolloids, 54, 202-210. Ovando-Martinez, M., Whitney, K., Reuhs, B. L., Doehlert, D. C., & Simsek, S. (2013). Effect of hydrothermal treatment on physicochemical and digestibility properties of oat starch. Food Research International, 52, 17–25. Klein, B., Pinto, V. Z., Vanier, N. L., Zavareze, E. R., Colussi, R., Evangelho, J. A., Gutkoski, L. C., & Dias, A. R.G. (2013). Effect of single and dual heat-moisture treatments on properties of rice, cassava, and pinhao starches nd dual heat–moisture treatments on properties of rice, cassava, and pinhao starches. Carbohydrate polymers, 98, 1578-1584. Liu, H., Liang, R., Antoniou, J., Liu, F., Shoemaker, C. F., Li, Y., & Zhong, F. (2014). The effect of high moisture heat-acid treatment on the structure and digestion property of normal maize starch. Food Chemistry, 159, 222–229. Lorlowhakarn, K., Naivikul, O. (2006). Modification of rice flour by heat moisture treatment (HMT) to produce rice noodles. Kasetsart Journal (Natural Science), 40, 135–143. Mirmoghtadaie, L., Kadivar, M., & Shahedi, M. (2009). Effects of cross-linking and acetylation on oat starch properties. Food Chemistry, 116, 709–713. Morita, T., Hayashi, J., Motoi, H., Yagishita, T., Takeya, K., Sugiyama, K., & Kiriyama, S. (2005). In vitro and in vivo digestibility of recrystallized amylase and its application for low glycemic foods. Journal of Food Science,70, 179 – 185. Rabek, J. F. (1980). Experimental methods in polymer chemistry: Applications of wide angle Xray diffraction (WAXD) to the study of the structure of polymers. Chichester: Wiley Interscience.
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Rahim, A., Haryadi., Cahyanto, M. N., & Pranoto, Y. (2012). Structure and functional properties of resistant starch from butyrylated arenga starches. African Journal of Food Science, 6, 335-343. Salamone, J. C. (1996). Polymeric materials encyclopedia. Boca Raton, FL: CRC Press. Shah, A., Masoodi, F. A., Gani, A., & Ashwar, B. A. (2016). Newly released oat varieties of himalayan region -Techno-functional, rheological, and nutraceutical properties of flour. LWT Food Science and Technology, 70, 111–118. Sharma, M., & Yadav, D. N., Singh, A. K., & Tomar, S. K. (2015). Rheological and functional properties of heat moisture treated pearl millet starch. Journal Food Science Technology, 52, 6502–6510. Simsek, S., & El, S. N. (2012). Production of resistant starch from taro (Colocasia esculenta L. Schott) corm and determination of its effects on health by in vitro methods. Carbohydrate Polymers, 90, 1204– 1209. Simsek, S., & Nehir, S. (2012). Effect of boiling time on chemical composition and physicofunctional properties of flours from taro (Colocasia esculenta cvfouê) corm grown in Cote d’Ivoire. Carbohydrate Polymers, 90, 1204– 1209. Sun, Q., Han, Z., Wang, L., & Xiong, L. (2014). Physicochemical differences between sorghum starch and sorghum flour modified by heat-moisture treatment. Food Chemistry, 145, 756–764. Thomas, D. J., & Atwell, W. A. (1999). Starches. St. Paul, MN: Eagan Press. pp. 1–48. Wang, B., Wang, L. J., Li, D., Wei, Q., Adhikari, B. (2012). The rheological behavior of native and high-pressure homogenized waxy maize starch pastes. Carbohydrate Polymers, 88, 481– 489. Wang, B., Wang, L. J., Li, D., Zhou, Y. G., & Ozkan, N. (2011). Shear-thickening properties of waxy maize starch dispersions. Journal of Food Engineering, 107, 415–423.
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Williams, P. C., Kuzina, F. D., & Hlynka, I. A. (1970). A rapid colorimetric procedure for estimating the amylose content of starches and flours. Cereal Chemistry, 47, 411–420. Zavareze, E. R., & Dias, A. R. G. (2011). Impact of heat-moisture treatment and annealing in starches: A review. Carbohydrate Polymers, 83, 317–328. Zavareze, E. R., Pinto, V. Z., Klein B., Halal S. L. M., Elias, M. C., Prentice-Hernandez C., & Dias, A. R. G. (2012). Development of oxidized and heat-moisture treated potato starch film. Food Chemistry, 132, 344-350. Zhou, M., Robards, K., Glennie-Holmes, M., & Helliwell, S. (1998). Structure and pasting properties of oat starch. Cereal Chemistry, 75, 273–281. Zhou, X., & Lim, S. (2012). Pasting viscosity and in vitro digestibility of retrograded waxy and normal corn starch powders. Carbohydrate Polymers, 87, 235–239.
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A
D
G
J
B
C
E
F
H
I
K
L
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Fig.1.Granular morphology of native and modified oat starches; (A&G) Native Sabzaar (B&H) Native SKO20 (C&I) Native SKO90 (D&J) Modified Sabzaar (E&K) Modified SKO20 (F&L) Modified SKO90.
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Fig.3. ATR-FTIR analysis of native and modified oat starches (A) Sabzaar (B) SKO20 (C) SKO90.
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Fig.3. XRD pattern of native and modified oat starches (A) Sabzaar (B) SKO20 (C) SKO90.
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Figure.4A. Flow curves of native ( ) and modified ( ) starch pastes; (A) sabzaar, (B) SKO20 and (C) SKO90. Dashed lines are fitted with Herschel-Bulkley model measured at 25oC.
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Figure.4B. Oscillatory (d) and mechanical spectra (e) measured as function of storage modulus (G′) and loss modulus (G″); native sabzaar ( 1G′ 1G″) & modified sabzaar ( 4G′ 4G″); native SKO20 ( 2G′ 2G″) & modified SKO20 ( 5G′ 5G″); native SKO90 ( 3G′ 3G″) & modified SKO90 ( 6G′ 6G″).
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Table.1. Chemical composition, and color attributes of oat starches (n=3). Sabzaar SKO20 SKO90 Native Modified Native Modified Native Modified 10.63±0.32b 10.99±0.46b 10.03±0.04a Moisture (%) 0.34±0.0a 0.32±0.01a 0.33±0.00a Protein (%) b a a 0.44±0.02 0.25±0.01 0.25±0.00 Lipid (%) b a a 0.57±0.03 0.46±0.02 0.42±0.02 Ash (%) 26.97±0.53c 25.91±0.05b 26.13±0.01b 25.43±0.09a 25.81±0.19ab 25.45±0.15a Amylose content (%) Color values L 92.65±0.10b 74.77±2.5b 94.96±0.61d 73.17±0.3b 91.02±0.40a 68.09±1.83a b b a ab b a 0.64±0.03 1.82±0.6 0.32±0.10 0.99±0.3 0.48±0.03 1.76±0.02b e a b b d b 6.30±0.04 6.4±2.5 2.84±0.08 15.8±0.6 4.31±0.07 13.6±2.52b d c e b d 90.29±0.06 73.80±2.56 94.19±0.50 68.80±0.42 90.03±0.39 65.15±1.17a Whiteness Index Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05).
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Table.2. R 1047/1020 cm-1, Peak intensities, RC (%), and Resistant starch content of oat starches (n=3). R 1047/1022 Peak intensity RC (%) RS cm-1 13.0οC 15.0οC 17.0οC 18.0οC 20.0οC 23.0οC Oat starch Sabzaar Native 0.65 1361 1520 1526 1233 1224 23.90±0.06c 23.9±1.27b f Modified 0.8 1059.68 1073 1263 1178 1380 890 28.07±0.02 38.88±1.00e SKO20 Native 0.65 1601 1795 1811 1389 1429 23.67±0.06b 17.39±0.57a e Modified 0.73 1164.77 1335 1478 1443 1444 1087 26.77±0.01 29.14±0.61d SKO90 Native 0.67 1675 1880 1866 1383 1539 23.19±0.11a 17.14±0.06a d Modified 1.12 1009.43 1160 1304 1306 1394 1014 28.83±0.09 25.81±1.04c Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05). R 1047/1022 cm-1; spectral ratio representing the crystalline to amorphous phase RS = resistant starch. RC = relative crystallinity.
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Table.3. Rheological parameters of oat starches (n=3). Sabzaar SKO20 SKO90 Native Modified Native Modified Native Modified Herschel-Bulkely model fitted parameters 12.02 57.83 -0.001 -380456.02 1.615 789714 τo [Pa]a 5.65 -0.02 0.758 380507.92 3.36 789805.1 Ka 0.42 1.16 0.502 1.033 0.43 59019 na LVR parameters 73.88 81.6 250.6 55.6 172.1 371 G′ 8.23 12.2 22.08 6.93 13.69 68 G″ 8.97 6.68 11.34 8.02 12.57 5.45 G′/G″ 12.64 0.30 8.23 0.19 8.32 0.30 τY [Pa] 44.58 2.07 36.96 2.07 33.51 1.28 τF [Pa] 0.28 0.14 0.22 0.09 0.24 0.23 τY /τF 0.11 0.14 0.08 0.12 0.07 0.18 Tan (δ) a Parameters obtained by fitting the curve by the Herschel-Bulkley equation. τo = yield stress; K = consistency index; n = flow behavior index; G′ = elastic modulus; G″ = viscous modulus; τY = yield point; τF = flow point; Tan (δ) = Loss factor
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Table.4. Physicochemical and functional properties of oat starches (n=3). Sabzaar SKO20 Native Modified Native Modified d b c 12.69±0.2 11.4±0.35 12.04±0.07 10.69±0.32a Swelling power (g/g) b a ab 0.41±0.02 0.29±0.07 0.37±0.02 0.27±0.00a Solubility index(g/g) Transmittance (%) 0h 0.61±0.00ar 1.55±0.05br 2.35±0.06ds 2.53±0.08es aq dr er 24 h 0.51±0.01 1.49±0.00 2.06±0.05 2.18±0.01fs 42 h 0.51±0.01aq 1.30±0.01cr 1.68±0.01fq 2.06±0.05es ap bq dp 72 h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00er ap bp cp 96 h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00fq ap bp cp 120h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00fp a e b 2.53±0.02 27.93±0.77 4.67±0.06 17.61±0.53d Bile binding capacity (%) Pasting properties Peak viscosity (cp) 3107.00±4.35d 2541±7.21a 3931.66±3.0f 2917.66±1.15c f c d Trough viscosity (cp) 2219.33±2.08 1515±3.60 1562.33±3.2 1831.33±2.08e a b f Breakdown (cp) 887.66±5.85 1026±10.81 2369.00±6.0 1086.33±1.52c f b d Final viscosity (cp) 3776.33±3.78 2859±10.44 3188.00±2.0 2876±3.60c d c e Setback viscosity (cp) 1557.00±5.00 1344±7.21 1625.66±4.0 1044±2.08a ο b b ab Pasting temperature ( C) 90.26±4.82 89.88±1.02 87.20±1.38 85.59±0.36b Texture profile analysis Hardness (g) 927.01±4.79d 865.18±1.17a 961.57±1.99e 893.32±6.86c b e b Adhesiveness (g×s) -33.25±1.47 -556.07±0.74 -31.33±1.88 -142.144±1.26d d b c Springiness (mm) 0.98±0.01 0.806±0.00 0.95±0.02 0.59±0.000a d b c Cohesiveness 0.87±0.01 0.483±0.01 0.86±0.00 0.32±0.00a Thermal properties TO (○C) 73.38±1.17c 89.07±0.02d 68.64±0.02b 91.95±0.03f
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SKO90 Native 11.95±0.10bc 0.34±0.04ab
Modified 10.23±0.09a 0.27±0.00a
1.46±0.05cs 1.3±0.00dr 1.2±0.00eq 1.1±0.00bp 1.1±0.00bp 1.1±0.00bp 4.9±0.09b
1.85±0.05cr 1.38±0.03cq 1.36±0.01cq 1.2±0.00dp 1.2±0.00dp 1.2±0.00dp 16.45±0.09c
3825.33±2.0e 1490.66±2.0a 2334.66±2.8e 3673.33±2.5e 2182.66±0.5f 87.00±0.79ab
2787.66±4.9b 1508±1.00b 1279.66±5.85d 2746.66±9.81a 1238.66±10.69b 85.2±0.70a
954.90±3.57e -21.36±1.91a 0.94±0.01c 0.86±0.00cd
875.85±1.10b -133.36±0.50c 0.58±0.00a 0.31±0.00a
63.45±0.05a
90.95±0.03e
Tp(○C) Tc (○C) TC -TO (○C) ∆H (J/g)
108.98±0.01f 91.94±0.03a 98.49±0.47e 96.32±0.00d 93.56±0.18 b 95.32±0.00c f c e a d 118.31±0.46 104.54±0.02 112.09±1.18 100.33±0.01 110.57±0.31 101.33±0.01b d c d a e 44.93±1.64 15.47±0.04 43.45±1.18 8.27±0.16 47.11±0.3 10.37±0.04 b d b d a c 12.34±0.02 2.87±0.01 12.35±0.00 1.66±0.02 12.13±0.02 1.65±0.02a Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05). TO = onset temperature; Tp = peak temperature; Tc = conclusion temperature; TC -TO = transition temperature
range; ∆H = gelatinisation enthalpy.
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Highlights Dual autoclaving-retrogradation resulted in modified food starches with high contents of RS4 and good bile acid binding capacity. Confirmational studies by SEM, XRD, ATR-FTIR and DSC. Dual autoclaving-retrogradation of oat starches resulted in shear thickening behavior as characterised by Herschel-Bulkely model.
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S0308-8146(16)30912-8 http://dx.doi.org/10.1016/j.foodchem.2016.06.019 FOCH 19360
To appear in:
Food Chemistry
Received Date: Revised Date: Accepted Date:
11 March 2016 7 June 2016 7 June 2016
Please cite this article as: Shah, A., Masoodi, F.A., Gani, A., Ashwar, B.A., In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch, Food Chemistry (2016), doi: http://dx.doi.org/10.1016/j.foodchem. 2016.06.019
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In-vitro digestibility, rheology, structure, and functionality of RS3 from oat starch Asima Shah, Farooq Ahmad Masoodi*, Adil Gani, Bilal Ahmad Ashwar Department of Food Science and Technology, University of Kashmir, Srinagar, India-190006.
*authors for correspondence Email: [email protected] Ph: +91-9419135876
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Abstract Starches isolated from three different varieties of oat were modified with dual autoclavingretrogradation treatment to make modified food starches with high contents of type 3 resistant starch (RS3). FT-IR spectroscopy showed increase in the ratio of intensity of 1047 cm-1 /1022 cm-1 on treatment. Morphology of the oat starches changed into a continuous network with increased values for onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc). XRD showed an additional peak at 13° and increase in peak intensity at 20° inclusive of the major X-ray diffraction peaks which reflects formation of amylose–lipid complex from dual autoclaving-retrogradation cycle. Peaks at 13° and 20° are the typical peaks of the V-type pattern. Rheological analysis suggested that retrogradated oat starches showed shear thickening behavior as revealed from Herschel-Bulkely model and frequency sweep. Keywords: Resistant starch, Rheology, Microstructure.
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1. Introduction Oat starch is considered distinct among other cereal starches being smaller in size, high lipid content, and well developed granular surface. Besides it, oat starch is more viscous, less prone to retrogradation, offers some resistance to digestion due to starch-lipids complex in comparison to wheat starch which has raised interest among many food processors (Berski et al., 2011). However native oat starch has certain limitations to be used as food or an ingredient in foods, due to less shear stress resistance, thermal decomposition, high viscosity and low gel clarity. On the basis of glucose released during enzymatic hydrolysis, starch has been classified into three fractions, rapidly digestible starch (RDS), slowly digestible starch (SDS) and resistant starch (RS) and in most of the cereal products rapidly digestible starch predominates. In today’s scenario, people are having a sedentary life style with increased risk factors of various diseases like diabetes, hypercholestromia, cancers, obesity etc. So they are looking for such type of food that has low glycemic index (GI) and profound health benefits (Zhou & Lim, 2012; Simsek, & El, 2012; Han, & BeMiller, 2007). Different modifications of starch have been employed for improving the functionality and resistance to digestive enzymes, dual autoclaving- retrogradation treatment is one such. The knowledge of functional properties of starch like viscosity, swelling power, texture, gel clarity could be helpful for predicting its use for commercial purposes. The study of its rheological characteristics is important to anticipate its use as gelling and thickening agent and as well as the stability of end products (Wang et al., 2012). The present study was carried to evaluate the effect of dual autoclaving- retrogradation treatment on resistant starch development (RS3) and techno-functional properties from three different cultivars of oat found in the Indian Himalayan region. This comprehensive study will help to expand the utilization of oat
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starch for both domestic and industrial purpose for making second generation functional cereal foods. 2. Materials and methods 2.1. Materials Three oat varieties were procured form Sher-e-Kashmir University of Agricultural Sciences and Technology (SKAUST), Shalimar, Srinagar, J&K, India. Resistant starch content was assessed using GOPOD Assay Kit (Megazyme International, Ireland, Ltd). Amyloglucosidase (Aspergillus niger, 3300 U/mL) and pancreatin (porcine pancreas, 8×USP) were obtained from SigmaAldrich, St. Louis, USA. All the other chemicals used were of analytical grade. 2.2. Starch extraction Starch was isolated according to the method described by Gani et al. (2012) with certain modifications. Milled oat flour was diluted with distilled water (ten times), pH was adjusted to 9 (0.2 N NaOH) and the slurry obtained was mixed intermittently for 1 hour. After filtration slurry was centrifuged at 3000 × g for 15 min at 5οC (Eppendorf 5810 R, Germany). The sediment obtained was scraped off from the surface and the lower white portion was washed with distilled water three times and allowed to sediment at refrigerated temperature (4οC). The starch was dried at 40οC in oven. 2.3. Preparation of resistant starch from oat starch Dual autoclaving-retrogradation cycle was carried out for the preparation of resistant starch. Oat starch (15 g) was mixed with 60 mL of distilled water and the mixture was then pressure-cooked in an autoclave at 121οC for 30 min. The autoclaved starch paste was allowed to cool to room temperature and then stored at 4οC for 24 h. The autoclaving- retrogradation cycle was repeated two times. Finally the samples were oven dried at 45οC and ground using a mortar and pestle.
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2.4. Chemical composition of starch Moisture, protein, fat and ash were determined according to the AOAC, 1990. Apparent amylose contents of the starch samples were determined according to method described by Williams, Kuzina, Hlynka, 1970. 2.5. Color attributes Color of the starch was determined using Color Flex Spectrocolorimeter (Hunter Lab Colorimeter D-25, Hunter Associates Laboratory, Ruston, USA). The instrument was calibrated with black and white tile before colour measurement. The ‘L’ value indicates the lightness, 0 – 100 representing dark to light. The ‘a’ value gives the degree of the red – green colour with a higher positive ‘a’ value indicating more red. The ‘b’ value indicates the degree of the yellow – blue colour, with a higher positive ‘b’ value indicating more yellow. Whiteness index (WI) was determined using below equation: WI = 100-[(100-L)2 + a2 + b2]½ Where, L, a, and b are Hunter values. 2.6. Granule morphology and light microscopy of oat starches The freeze dried starch sample was placed on an adhesive tape attached to a circular aluminum specimen stub and then coated vertically with gold. Granule morphology was studied using scanning electron microscope (Hitachi S- 300H-Tokyo, Japan) at an accelerator potential of 5 kV. Further samples were stained with iodine solution (0.2% I2/KI for 10 s) and examined under a light microscope at 40x (LMI, Leedz Micro Imaging Ltd, UK). 2.7. ATR-Fourier transforms infrared (FTIR) spectroscopy The ATR-FTIR spectra of starches were recorded on an ATR- FTIR Spectrophotometer (CARY 630, Agilent Technologies, USA) at room temperature. The spectra were recorded within the
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range of 600-4000 cm-1 using Agilent Resolution-Pro MicroLab software (version B.05.2, Agilent Technologies). 2.8. XRD analysis X-ray patterns of the samples were recorded with a wavelength of 0.154 nm using X-ray diffractometer (X’Pert PRO, Panalytical, Netherlands). The diffractometer was operated at 40 kV and 35 mA. Diffractograms were acquired at 25οC over a 2 Ø range of 4ο - 40ο with a step size of 0.02 and sampling interval of 10 s. The relative crystallinity (RC) of starch was calculated as described by Rabek (1980) by the equation: RC (%) = (Ac/(Ac + Aa)100; where Ac is the crystalline area; Aa is the amorphous area on the X-ray diffractograms. 2.9. Determination of resistant starch Resistant starch content was assessed using GOPOD Assay Kit (Megazyme International, Ireland, Ltd), following the approved AACC method (2000). 2.10. Rheological measurement Starch dispersion (6 g/100 mL H2O) were heated up to 90οC with mild stirring for 20 min and the gel was left to cool at room temperature for 1 hr. Rheological measurements were made at 25 ± 0.1◦C with on a controlled stress rheometer (MCR 102, Anton Paar) using a parallel plate geometry (CP50-1; diameter: 50 mm). The flow properties were determined with increasing shear rate, from 0.1-500 s-1 and the delay time was 10 s. The experimental data was evaluated by fitting the data to a Herschel-Bulkley model τ = τ0 + Kγn τ (Pa) is the shear stress, τ0 (Pa) is the yield stress, K is the consistency index (Pa sn), and n is the flow behavior index.
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The viscoelastic range was determined through stress sweep tests at constant frequency of 1 Hz with a logarithmic increase of shear stress from 0.01 to 100 Pa. Frequency sweep tests at constant stress were carried out to obtain mechanical spectra. The appropriate shear stress was chosen after analyzing the LVE-range (Linear viscoelastic range) of the samples from the above experiment. Frequency was logarithmically decreased from 100 to 0.1 Hz at a constant shear stress of 1 Pa. 2.11. Swelling power & solubility index Swelling power and solubility index of the starch samples were determined with slight modifications to the method of Gani et al. (2012). Starch (0.6 g) (M0) was mixed with 30 mL of distilled water and heated at 90 °C in a water bath with occasional shaking. After 30 min stirring, the mixture was centrifuged at 1500×g for 30 min. The supernatant was carefully removed, and the swollen starch sediment was weighed (M1). The supernatant was evaporated and dried at 105 °C in an oven until constant weight (M2). Swelling power and solubility was calculated from the equations given below. Swelling power (g/g) = M1/M0 Solubility (g/g) = M2/M0 2.12. Light transmittance Light transmittance was determined by dissolving 1 g of starch (db) in 100 mL of distilled water and heating in a water bath at 90οC for 30 min with constant stirring then, cooled for 1 h at 30οC. The samples were stored for 5 days at 4οC in a refrigerator, and transmittance was determined after every 24 h at 640 nm against water as blank. 2.13. Bile acid binding capacity The bile acid-binding capacity of starch was determined by colorimetric method (Shah et al., 2016).
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2.14. Pasting properties and gel texture analysis The pasting properties of the starches were measured using a Rapid Visco Analyzer (Tech Master, Perten Instruments Warriewood, Australia) as determined by Ashwar et al. (2016a). After RVA analysis, the gel obtained was stored at 4οC for 24 h. The gel texture was analysed with a Texture Analyser (TA.XT2 plus, Stable Micro Systems). The gel was compressed at 1.0 mm/s for a distance of 5.0 mm using a cylindrical probe (P/75). 2.15. Thermal properties The thermal characteristics of oat starch were studied with a Mettler Toledo DSC1STAR System. Starch samples (3.5 mg) were weighed into platinum pans and deionized water (8 µl) was added. The pans were kept at room temperature overnight before analysis. The samples were heated from 20 to 200°C at 10 °C/min. An empty platinum pan was used as a reference. 2.16. Statistical analysis Results are expressed as the mean ± standard deviation of triplicate experiments. Data were analyzed by two-way analysis of variance (ANOVA), followed by Duncan’s multiple range tests at 5% significance level (p< 0.05) using a commercial statistical package SPSS (IBM statistics 22). 3. Results and discussion 3.1. Chemical composition and color attributes of oat starch Chemical compositions of oat starch from three different varieties are presented in Table 1. Compared to other cereal starches, oat starch contains highest amounts of lipids (Zhou et al., 1998). Almost similar values for chemical composition have been seen in the reports of Mirmoghtadaie, Kadivar, & Shahedi (2009). The apparent amylose content was found in the range of 26.96-25.81% for oat starches. Comparable values of the amylose content have been
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reported earlier in canadian oat cultivars (19 to 33 %) (Hoover, Smith, Zhou, & Ratnayake, 2003). However, the amylose content of oat obtained from Breeding Station in Strzelce Krajenskie in Poland was found comparatively lower (Berski et al., 2011). Such difference in amylose content could be ascribed due to varietal difference, environmental condition, method of starch extraction, or method used for its estimation. On dual autoclaving-retrogradation process the amylose content showed a significant (p<0.05) decrease at same moisture content (dry basis). The Hunter lab values (L) of native starches from Sabzaar, SKO20, and SKO90 were 92.65, 94.96, and 91.02, a values were 0.65, 0.32 and 0.48 and b values were 6.3, 2.8 and 4.3, respectively. However, after modification the values for lightness (L) got decreased significantly (p<0.05) whereas those of “a” and “b” values were found to increase as represented in Table 1. The change in color values might be caused by the maillard reaction at high temperature. Similar decrease in color values were obtained for rice flour due to heat moisture treatment (Lorlowhakarn, & Naivikul, 2006). Whiteness index of starch is an important parameter that determines its applicability in food systems. Whiteness index (WI) decreased from 90.29 to 73.80, 94.19 to 68.80, and 90.03 to 65.15 in retrograded starches of Sabzaar, SKO20, and SKO90, respectively. 3.2. Granule morphology and light microscopy of oat starches Granule morphology and light microscopy of oat starches are shown in Fig.1. Oat starch samples showed presence of small granules with varying dimensions, oval or irregular shape with smooth surface and some damaged starch. Average granule size of oat starch was within the range of 1.55.33 µm in Sabzaar, 1.1-5.2 µm in SKO20, and 1.7-6.66 µm in SKO90. However dual autoclaving-retrogradation process resulted in disruption of granules and formation of continuous network microstructure with minimum small starch granules. Light microscopy also revealed
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formation of irregular granular aggregations. This solid network with increased density of RS3 crystallites offers resistance to enzyme attack (Dundar and Gocmen 2013). 3.3. ATR-FTIR spectroscopy The FTIR spectrum of native and modified oat starches is shown in Fig.2. All samples displayed absorption peaks at 3400, 2929, 1500, 1600 and 620-527 cm-1, which correspond to the functional groups of poly -OH, –CH2, C –O- C (skeletal vibrational mode of α-1,4 glycosidic linkage), carboxylate ion (COO), and skeletal modes of pyranose ring, respectively (Ashwar et al., 2016b). Dual autoclaving-retrogradation resulted in broading of peaks at 3400 cm-1 suggesting increase in the crystalline region (Garcia-Rosas et al., 2009). Further, FTIR spectrum may also be used to determine crystallinity of starch. Band at 1022 cm-1 is characteristic to an amorphous fraction whereas band at 1047 cm-1 is sensitive to crystallinity (Gani et al., 2016). Ratio of intensity of 1047 cm-1 /1022 cm-1 can be used to express the degree of order in starch. Table 2. shows the ratio of intensity (R=1047/1022 cm-1) of native and retrograded oat starches. Ratio for native starch was found in the range of 0.65-0.67 that increased to 0.73-1.12 upon treatment which might be due to close parallel alignment of disrupted crystals on retrogradation. 3.4. X-ray diffraction pattern Fig.3 shows the X-ray diffractograms of native and retrograded oat starches and corresponding peak intensities and relative crystallinity (RC) are given in Table 2. In native oat starches peaks were observed at 15° and 23°, doublet peak at 17° and 18°, and small peak at 20° of 2θ which are characteristic of a A-type pattern. However dual autoclaving-retrogradation process resulted in starches that showed an additional peak at 13° and increase in peak intensity at 20° inclusive of the major X-ray diffraction peaks which reflects formation of amylose–lipid complex. A typical amylose–lipid complex contains a hydrophobic fatty acid tail, which is buried inside an amylose
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helix that helps to develop further entanglement among starch molecules and thereby increasing resistance to digestive enzyme breakdown (Dupuis et al., 2014). Peaks at 13° and 20° are the typical peaks of the V-type pattern resulting from dual autoclaving- retrogradation treatment (Thomas & Atwell, 1999). Also increase in crystallinity on treatment is due to reorientation of double helical chains in a closer fashion, providing a more stable and crystalline structure (Zavareze & Dias, 2011). Liu et al., 2014 reported that higher the crystallinity of starch, higher is the resistance offered to digestion. 3.5. Resistant starch content Resistant starch content of native oat starches ranged from 17.14 % to 23.9 %. The differences in the resistant starch content among the varieties might be due to the following factors: source of starch, granular size, amylose-amylopectin ratio, branch length in amylopectin, percent crystallinity, amylose lipid complex, and pores within the granules (Ashwar et al., 2016a; Dupuis, Liu, & Yada, 2014). On dual autoclaving-retrogradation process the type 3 resistant starch content (RS3) of oat varieties increased significantly to the range of 25.81-38.88 % (Table 2). Increase in RS3 content may be attributed due to following reasons: (A) Recrystallisation of linear amylose polymers on cooling into double helices that form tightly packed structures which are stabilized by hydrogen bonds (Dundar, & Gocmen, 2013). (B) Higher amount of amylose–lipid complex which is resistant to digestive enzyme breakdown (Hasjim, Ai, & Jane, 2013). Results were in consistent with XRD analysis that revealed higher amylose–lipid complex (peaks at 13° and 20°) in retrograded starches compared to their native counterparts (Table 2). The modified starches therefore offers resistance to enzymes and thus could be helpful to lower plasma cholesterol, absorption of a number of minerals, for the control of obesity, improve glucose tolerance (Morita et al., 2005).
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3.6. Rheological measurement Flow curves of native and modified oat starches, displaying changes in viscosity with increase in applied shear stress, are shown in Fig. 4A(a, b, & c). Native starch solutions exhibited shearthinning behavior over entire measured shear rates. Whereas modified starch dispersions showed increase in viscosity with the increase in shear rate, reached a maximum value, and then decreased as the shear rate increased. Such a behavior is typical of shear thickening fluids. Also modified starches showed higher shear stress than that of their native counterparts indicating their higher resistance to structure breaking at same shear rate. Moreover, shear thickening behavior can be characterised by a Herschel-Bulkely model and results of these fits are presented in Table 3. Flow behavior index (n) was found within the range of 0.42-0.50 in native starches which on dual autoclaving-retrogradation increased to 1.053-59019 (greater than unity) confirming that modified oat starch solutions exhibited shear-thickening behaviors. Consistency index (K) which gives an indication about structural strength of solution, was found greater for modified oat starches with SKO90 showing highest value (789805.1) than SKO20 (380507.92). However Sabzaar variety showed a contradictory trend. Decrease in K value may be due to increased amylose leaching in sabzaar than SKO20 and SKO90 during the dual autoclaving-retrogradation process. Dual autoclaving-retrogradation of starches results in the formation of gel-like clusters when dissolved in water. Such dispersions when subjected to shear-stress results in the breakdown of clusters, increasing the viscosity of solution and we observe shear thickening behavior. Above a critical shear rate, the solution becomes homogenous and its viscosity decreases with the increase in shear rate (Wang et al., 2011). Shear-thinning behavior of native starches is attributed due to the formation of a homogenous solution when dispersed in water and
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the disintegration of polymer entaglements at a faster rate than their reformation at the high shear rates (Salamone, 1996). Oscillatory experiments were carried to measure viscoelastic properties of native and modified oat starches (Fig.4d). In all samples storage modulus (G′) was higher than loss modulus (G″) at low shear rate, which is typical gel behavior. At certain point called flow point (τF) storage modulus becomes equal to loss modulus (G′ = G″) and this point is the intersection of G′ (elastic behavior) and G″ (viscous behavior). Further increase in shear rate G″ becomes higher than G′ and displays the viscous behavior of the solution. Flow point and yield point was observed lower for modified starches. Loss factor (Tan δ) is the ratio of viscous modulus (G") to elastic modulus (G') and a useful parameter to determine the extent of elasticity in a fluid. Tan (δ) values of native and modified starches were found within the range of 0.07-0.11 and 0.12-0.18, respectively. Tan (δ) values of modified starch pastes were found higher than that of native starches but lesser than unity (Table 3). A small tan δ indicates that the starch gel is stiff, reflecting its solid-like behavior; whereas a large tan δ reflects that the starch gel behaves more like a liquid. Similar kind of observation was reported in heat moisture treated pearl millet starch (Sharma et al., 2015). Frequency sweeps was measured in linear viscoelastic region over the frequency range (0.1 to 100 Hz) to determine frequency dependence of viscous modulus (G") and elastic modulus (G'). The G′ was greater than G″ in both native and modified starches throughout the frequency range (Fig. 4e) which is typical weak gel behavior. Such gels under small deformation behave as strong gels but as strain is increased their network structure breakdowns. Greater the difference between G′ and G″ for a gel, predominant is its elastic-behavior. 3.7. Swelling power & solubility index
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The results of swelling power and solubility index of oat starches, determined at 90°C, are shown in Table 4. Dual autoclaving-retrogradation resulted in significant (p<0.05) decrease in swelling power and solubility index. This decrease has been attributed to transformation of amylose into a helical form, higher interaction between amylose and amylopectin molecules, and further strengthing of intramolecular bonds and assuming more ordered configuration during repeated autoclaving-retrogradation treatment (Gunaratne, & Hoover, 2002). Similar observations have recently been made on sweet potato starch due to repeated heat-moisture treatments (Huang et al., 2016). 3.8. Light Transmittance Clarity values of starch samples during five days of refrigerated storage are shown in Table 4. The modified starch pastes showed significantly (p<0.05) higher gel clarity than native starch, which might be due to breakdown of granules during dual autoclaving-retrogradation treatment (Craig, Maningat, Seib, & Hoseney, 1989). The light transmittance of starch pastes showed time dependence and was found to decrease up to 3rd day of storage and then remained almost constant. Similar reduction in transmittance with time has already been reported in multiple studies (Ashwar et al., 2014; Ashwar et al., 2016a). Decrease in light transmittance of starch pastes with the increase in storage time is attributed to recrystallization of starch (re-association of originally broken bonds within the granule). 3.9. Bile acid binding capacity Resistant starch like dietary fiber entraps bile salts in the viscous matrix and increases its fecal bile excretion resulting in lowering of blood cholesterol level, controlling obesity, and subsequently reducing the risk of cardiovascular diseases (Rahim, Haryadi, Cahyanto, Pranoto, 2012). Data indicated that the affinity of oat starches to bile acid increased significantly (p ≤ 0.05)
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due to dual autoclaving-retrogradation cycles as shown in Table 4. Similar increase in bile acid binding capacity of taro starch after enzymatic modification was reported by Simsek, & Nehir, 2012. The high bile acid binding capacity of modified oat starches suggests their possible health improving potential. 3.10. Pasting characteristics and gel texture characteristics The pasting properties of native and modified oat starches are summarized in Table 4. Significant increase in pasting temperature after modification supports the fact that repeated autoclavingretrogradation cycles tends to increase the region of crystallinity, as a result of reorientation and increased interaction between the starch chains. Due to the presence of strong intragranular forces, the starch requires more heat for structural disintegration and paste formation (Adebowale, Henle, Schwarzenbolz, & Doert, 2009). However peak, breakdown, and setback viscosity was significantly (p<0.05) reduced by dual autoclaving-retrogradation treatment. The breakdown value is the ease with which the swollen starch can be broken down by heating and physical agitation. The compact organization of the modified starches tends to be more resistant to the effect of shearing force and heat as it is seen from the breakdown values. The tendency of starch to retrogradate is measured by set-back value. Due to limited starch swelling and amylose leaching, there is minimum amylose reassociation and hence low set back values. This kind of pasting behavior was also reported in rice, cassava, and pinhao starches (Klein et al., 2013). Texture properties of the retrograded oat starch gels presented lower hardness and higher values of adhesiveness as compared to native starch suspensions (Table 4). This decrease in hardness of gel might be due to partial gelatinization of starch that causes breakdown of structure, resulting in low rigid gel. Also, the retrograded starch showed lesser swelling power, and thus formed weaker starch gel. Also significantly lower values for springiness, and cohesiveness were obtained for
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modified starch gels. Similar decrease in hardness, springiness, and cohesiveness due to heat moisture treatment has also been seen in potato starch (Zavareze et al., 2012). 3.11. Thermal properties Dual autoclaving- cooling cycles of starches leads to increase in the onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) with decrease in transition temperature range (Tc-To) and gelatinisation enthalpy (∆H) (Table 3). Higher transition temperatures are due to continuous network of starch chains as revealed in SEM analysis and increased crystallinity (XRD analysis). During dual autoclaving-retrogradation process, the starch granules are disrupted, gelatinized, and then rearranged in a such a manner that there is increased association between starch chains which inturn increases the resistance of starch for disruption of helical order leading to increased To, Tp, and Tc (Zavareze, & Dias, 2011). The decrease in transition temperature range (Tc-To) indicates increased homogeneity within the starch. Klein et al., 2013 also reported decrease in transition temperature range in rice and cassava starches with both single and dual heat moisture treatment. Reduction in gelatinisation enthalpy (∆H) due to autoclaving-cooling treatment proposes that in retrograded starch re-association of the chains forms a weaker matrix or network that requires lesser energy to melt the crystalline structure (Ovando-Martinez et al., 2013). Conclusion Dual autoclaving-retrogradation treatment resulted in starch with high resistant starch (RS3), good bile acid binding capacity, improved pasting properties, better thermal stability, and increased crystalline perfection. Shear-thickening behavior of modified starches depicts that it cannot find applications in many food processing techniques like homogenization, spraying, pumping etc as it will block the equipment. However in foods where viscosity is the main criteria,
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we can use such type of modified starches as an additive to get the desired viscosity at minimum concentration. Moreover, the increased resistance of modified starch to enzyme digestibility could make its use as an encapsulating agent for controlling drug delivery systems in pharmaceutical industries. Acknowledgements The authors are thankful to the Department of Biotechnology, Government of India for their financial support (Grant number: D.O.BT/PR6701/FNS/20/674/2012).
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Dundar, A. N., & Gocmen, D. (2013). Effects of autoclaving temperature and storing time on resistant starch formation and its functional and physicochemical properties. Carbohydrate Polymers, 97, 764–771. Dupuis, J. H., Liu, Q., & Yada, R. Y. (2014). Methodologies for Increasing the Resistant Starch Content of Food Starches: A Review. Comprehensive Reviews in Food Science and Food Safety, 13, 1219–1234. Gani, A., Bashir, M., Wani, S. M., Masoodi, F.A. (2012). Modification of bean starch by γirradiation: effect on functional and morphological properties. LWT—Food Science and Technology, 49, 162–169. Gani, A., Jan, A., Shah, A., Masoodi, F. A., Ahmad, M., Ashwar, B. A., Akhter, R., & Wani, I.A. (2016). Physico-chemical, functional and structural properties of RS3/RS4 from kidney bean (Phaseolus vulgaris) cultivars. International Journal of Biological Macromolecules, 87, 514–521. Garcia-Rosas, M., Bello-Perez, A., Yee-Madeira, H., Ramos, G., Flores-Morales, A., MoraEscobedo, R. (2009). Resistant Starch Content and Structural Changes in Maize (Zea mays) Tortillas During Storag. Starch/Stärke, 61, 414–421. Gunaratne, A., & Hoover, R. (2002). Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches. Carbohydrate Polymers, 49, 425–437. Hasjim, J., Ai, Y., & Jane, J. (2013). Novel applications of amylose-lipid complex as resistant starch type 5. In: Shi YC, Maningat CC, editors. Resistant starch sources, applications and health benefits. Chapter 4. Chichester, United Kingdom: John Wiley & Sons, Ltd. p 79–94. Hoover, R., Smith, C., Zhou, Y., & Ratnayake, R. M. W. S. (2003). Physicochemical properties of Canadian oat starches. Carbohydrate Polymers, 52, 253–261.
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Williams, P. C., Kuzina, F. D., & Hlynka, I. A. (1970). A rapid colorimetric procedure for estimating the amylose content of starches and flours. Cereal Chemistry, 47, 411–420. Zavareze, E. R., & Dias, A. R. G. (2011). Impact of heat-moisture treatment and annealing in starches: A review. Carbohydrate Polymers, 83, 317–328. Zavareze, E. R., Pinto, V. Z., Klein B., Halal S. L. M., Elias, M. C., Prentice-Hernandez C., & Dias, A. R. G. (2012). Development of oxidized and heat-moisture treated potato starch film. Food Chemistry, 132, 344-350. Zhou, M., Robards, K., Glennie-Holmes, M., & Helliwell, S. (1998). Structure and pasting properties of oat starch. Cereal Chemistry, 75, 273–281. Zhou, X., & Lim, S. (2012). Pasting viscosity and in vitro digestibility of retrograded waxy and normal corn starch powders. Carbohydrate Polymers, 87, 235–239.
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A
D
G
J
B
C
E
F
H
I
K
L
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Fig.1.Granular morphology of native and modified oat starches; (A&G) Native Sabzaar (B&H) Native SKO20 (C&I) Native SKO90 (D&J) Modified Sabzaar (E&K) Modified SKO20 (F&L) Modified SKO90.
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Fig.3. ATR-FTIR analysis of native and modified oat starches (A) Sabzaar (B) SKO20 (C) SKO90.
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Fig.3. XRD pattern of native and modified oat starches (A) Sabzaar (B) SKO20 (C) SKO90.
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Figure.4A. Flow curves of native ( ) and modified ( ) starch pastes; (A) sabzaar, (B) SKO20 and (C) SKO90. Dashed lines are fitted with Herschel-Bulkley model measured at 25oC.
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Figure.4B. Oscillatory (d) and mechanical spectra (e) measured as function of storage modulus (G′) and loss modulus (G″); native sabzaar ( 1G′ 1G″) & modified sabzaar ( 4G′ 4G″); native SKO20 ( 2G′ 2G″) & modified SKO20 ( 5G′ 5G″); native SKO90 ( 3G′ 3G″) & modified SKO90 ( 6G′ 6G″).
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Table.1. Chemical composition, and color attributes of oat starches (n=3). Sabzaar SKO20 SKO90 Native Modified Native Modified Native Modified 10.63±0.32b 10.99±0.46b 10.03±0.04a Moisture (%) 0.34±0.0a 0.32±0.01a 0.33±0.00a Protein (%) b a a 0.44±0.02 0.25±0.01 0.25±0.00 Lipid (%) b a a 0.57±0.03 0.46±0.02 0.42±0.02 Ash (%) 26.97±0.53c 25.91±0.05b 26.13±0.01b 25.43±0.09a 25.81±0.19ab 25.45±0.15a Amylose content (%) Color values L 92.65±0.10b 74.77±2.5b 94.96±0.61d 73.17±0.3b 91.02±0.40a 68.09±1.83a b b a ab b a 0.64±0.03 1.82±0.6 0.32±0.10 0.99±0.3 0.48±0.03 1.76±0.02b e a b b d b 6.30±0.04 6.4±2.5 2.84±0.08 15.8±0.6 4.31±0.07 13.6±2.52b d c e b d 90.29±0.06 73.80±2.56 94.19±0.50 68.80±0.42 90.03±0.39 65.15±1.17a Whiteness Index Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05).
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Table.2. R 1047/1020 cm-1, Peak intensities, RC (%), and Resistant starch content of oat starches (n=3). R 1047/1022 Peak intensity RC (%) RS cm-1 13.0οC 15.0οC 17.0οC 18.0οC 20.0οC 23.0οC Oat starch Sabzaar Native 0.65 1361 1520 1526 1233 1224 23.90±0.06c 23.9±1.27b f Modified 0.8 1059.68 1073 1263 1178 1380 890 28.07±0.02 38.88±1.00e SKO20 Native 0.65 1601 1795 1811 1389 1429 23.67±0.06b 17.39±0.57a e Modified 0.73 1164.77 1335 1478 1443 1444 1087 26.77±0.01 29.14±0.61d SKO90 Native 0.67 1675 1880 1866 1383 1539 23.19±0.11a 17.14±0.06a d Modified 1.12 1009.43 1160 1304 1306 1394 1014 28.83±0.09 25.81±1.04c Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05). R 1047/1022 cm-1; spectral ratio representing the crystalline to amorphous phase RS = resistant starch. RC = relative crystallinity.
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Table.3. Rheological parameters of oat starches (n=3). Sabzaar SKO20 SKO90 Native Modified Native Modified Native Modified Herschel-Bulkely model fitted parameters 12.02 57.83 -0.001 -380456.02 1.615 789714 τo [Pa]a 5.65 -0.02 0.758 380507.92 3.36 789805.1 Ka 0.42 1.16 0.502 1.033 0.43 59019 na LVR parameters 73.88 81.6 250.6 55.6 172.1 371 G′ 8.23 12.2 22.08 6.93 13.69 68 G″ 8.97 6.68 11.34 8.02 12.57 5.45 G′/G″ 12.64 0.30 8.23 0.19 8.32 0.30 τY [Pa] 44.58 2.07 36.96 2.07 33.51 1.28 τF [Pa] 0.28 0.14 0.22 0.09 0.24 0.23 τY /τF 0.11 0.14 0.08 0.12 0.07 0.18 Tan (δ) a Parameters obtained by fitting the curve by the Herschel-Bulkley equation. τo = yield stress; K = consistency index; n = flow behavior index; G′ = elastic modulus; G″ = viscous modulus; τY = yield point; τF = flow point; Tan (δ) = Loss factor
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Table.4. Physicochemical and functional properties of oat starches (n=3). Sabzaar SKO20 Native Modified Native Modified d b c 12.69±0.2 11.4±0.35 12.04±0.07 10.69±0.32a Swelling power (g/g) b a ab 0.41±0.02 0.29±0.07 0.37±0.02 0.27±0.00a Solubility index(g/g) Transmittance (%) 0h 0.61±0.00ar 1.55±0.05br 2.35±0.06ds 2.53±0.08es aq dr er 24 h 0.51±0.01 1.49±0.00 2.06±0.05 2.18±0.01fs 42 h 0.51±0.01aq 1.30±0.01cr 1.68±0.01fq 2.06±0.05es ap bq dp 72 h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00er ap bp cp 96 h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00fq ap bp cp 120h 0.41±0.01 1.00±0.00 1.3±0.00 1.9±0.00fp a e b 2.53±0.02 27.93±0.77 4.67±0.06 17.61±0.53d Bile binding capacity (%) Pasting properties Peak viscosity (cp) 3107.00±4.35d 2541±7.21a 3931.66±3.0f 2917.66±1.15c f c d Trough viscosity (cp) 2219.33±2.08 1515±3.60 1562.33±3.2 1831.33±2.08e a b f Breakdown (cp) 887.66±5.85 1026±10.81 2369.00±6.0 1086.33±1.52c f b d Final viscosity (cp) 3776.33±3.78 2859±10.44 3188.00±2.0 2876±3.60c d c e Setback viscosity (cp) 1557.00±5.00 1344±7.21 1625.66±4.0 1044±2.08a ο b b ab Pasting temperature ( C) 90.26±4.82 89.88±1.02 87.20±1.38 85.59±0.36b Texture profile analysis Hardness (g) 927.01±4.79d 865.18±1.17a 961.57±1.99e 893.32±6.86c b e b Adhesiveness (g×s) -33.25±1.47 -556.07±0.74 -31.33±1.88 -142.144±1.26d d b c Springiness (mm) 0.98±0.01 0.806±0.00 0.95±0.02 0.59±0.000a d b c Cohesiveness 0.87±0.01 0.483±0.01 0.86±0.00 0.32±0.00a Thermal properties TO (○C) 73.38±1.17c 89.07±0.02d 68.64±0.02b 91.95±0.03f
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SKO90 Native 11.95±0.10bc 0.34±0.04ab
Modified 10.23±0.09a 0.27±0.00a
1.46±0.05cs 1.3±0.00dr 1.2±0.00eq 1.1±0.00bp 1.1±0.00bp 1.1±0.00bp 4.9±0.09b
1.85±0.05cr 1.38±0.03cq 1.36±0.01cq 1.2±0.00dp 1.2±0.00dp 1.2±0.00dp 16.45±0.09c
3825.33±2.0e 1490.66±2.0a 2334.66±2.8e 3673.33±2.5e 2182.66±0.5f 87.00±0.79ab
2787.66±4.9b 1508±1.00b 1279.66±5.85d 2746.66±9.81a 1238.66±10.69b 85.2±0.70a
954.90±3.57e -21.36±1.91a 0.94±0.01c 0.86±0.00cd
875.85±1.10b -133.36±0.50c 0.58±0.00a 0.31±0.00a
63.45±0.05a
90.95±0.03e
Tp(○C) Tc (○C) TC -TO (○C) ∆H (J/g)
108.98±0.01f 91.94±0.03a 98.49±0.47e 96.32±0.00d 93.56±0.18 b 95.32±0.00c f c e a d 118.31±0.46 104.54±0.02 112.09±1.18 100.33±0.01 110.57±0.31 101.33±0.01b d c d a e 44.93±1.64 15.47±0.04 43.45±1.18 8.27±0.16 47.11±0.3 10.37±0.04 b d b d a c 12.34±0.02 2.87±0.01 12.35±0.00 1.66±0.02 12.13±0.02 1.65±0.02a Results are mean ± S.D. Means in the row and in the column within a particular parameter with different superscript are significantly different at (P < 0.05). TO = onset temperature; Tp = peak temperature; Tc = conclusion temperature; TC -TO = transition temperature
range; ∆H = gelatinisation enthalpy.
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Highlights Dual autoclaving-retrogradation resulted in modified food starches with high contents of RS4 and good bile acid binding capacity. Confirmational studies by SEM, XRD, ATR-FTIR and DSC. Dual autoclaving-retrogradation of oat starches resulted in shear thickening behavior as characterised by Herschel-Bulkely model.
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