Effects of gamma radiation on the thermoanalytical, structural and pasting properties of black rice (Oryza sativa L.) flour Vivian Cristina Ito1 • Camila Delinski Bet1 • José Pedro Wojeicchowski1 • Ivo Mottin Demiate1 • Marta Helena Fillet Spoto2 • Egon Schnitzler1 • Luiz Gustavo Lacerda1 Received: 7 July 2017 / Accepted: 12 October 2017 / Published online: 23 October 2017 � Akadémiai Kiadó, Budapest, Hungary 2017 Abstract The effects of different doses of gamma radia- tion on the thermoanalytical, structural and pasting prop- erties of black rice (Oryza sativa L.) flour were studied using thermogravimetry and derivative thermogravimetry (TG–DTG), differential scanning calorimetry, X-ray diffraction (XRD), field emission gun–scanning electron microscopy (FEG–SEM) and pasting properties (RVA) analysis. The thermogravimetric curves showed four mass losses. A small displacement was observed for the second loss, which occurred for the irradiated flours, compared to the control sample. The irradiated samples showed a slight decrease in the thermal parameters: initial temperature (To), peak temperature (Tp) and gelatinisation enthalpy (4H). All the black rice flours exhibited A-type crys- tallinity pattern, and the gamma radiation did not change the XRD patterns or the degree of crystallinity. The micro- images obtained using FEG–SEM showed a composite of organic and heterogeneous material; after gamma radia- tion, some changes occurred, such as cracks, pores and smaller fragments. The pasting properties decreased sig- nificantly with irradiation. The decrease in setback and breakdown viscosity after irradiation suggested an indica- tion that it may be possible to improve the quality of food based on black rice flours. Gamma radiation can be a useful tool to modify rice flours in order to suit various func- tionalities and to help meet the growing demands of the food industry. Keywords Black rice � Irradiation � Thermal analysis � Gelatinisation � Morphology � Crystallinity Introduction Rice is one of the most widely consumed foods in the world, feeding almost one-third of the world’s population [1]; it represents a major source of energy owing to its high concentration of starch and proteins, as well as containing minerals and B vitamins [2]. In recent years, pigmented rice varieties, such as black rice, have received increased attention from researchers and have become popular with consumers, due to their health-promoting properties [3]. Black rice contains high amounts of phenolic com- pounds, such as anthocyanins, which are associated with numerous health benefits due to their antioxidant activity; they also help to reduce the risk of developing chronic diseases such as cardiovascular disease, type II diabetes, obesity and cancer [4]. The natural colourants found in black rice, which can be used in the food industry as synthetic dye replacements, are dark purple anthocyanin pigments. Consequently, this pigmented rice can be used as a valuable ingredient for gluten-free cereal products with higher nutritional value, thereby providing extra health benefits to consumers. Starch, which is the main carbohydrate present in rice, can be used to confer texture, structure and consistency to many food products. However, the uses of native starches are limited by their low solubility, high viscosity, thermal & Luiz Gustavo Lacerda lglacerda@uepg.br 1 Food Science and Technology Graduate Program, State University of Ponta Grossa (UEPG), Av. Carlos Cavalcanti 4748 Uvaranas Campus, Ponta Grossa, PR CEP 84030-900, Brazil 2 Centre for Nuclear Energy in Agriculture, State University of São Paulo (USP), Av. Centenário, Luiz de Queiroz Campus, 303, Piracicaba 13900-470, Brazil 123 J Therm Anal Calorim (2018) 133:529–537 https://doi.org/10.1007/s10973-017-6766-6 http://orcid.org/0000-0002-4689-5431 http://crossmark.crossref.org/dialog/?doi=10.1007/s10973-017-6766-6&domain=pdf http://crossmark.crossref.org/dialog/?doi=10.1007/s10973-017-6766-6&domain=pdf https://doi.org/10.1007/s10973-017-6766-6 decomposition and high retrogradation tendency [5]. Thus, conventional sources of flours and starches (such as wheat, corn and rice) are modified to suit the specific needs of industries by adapting their physicochemical and func- tional properties, which are not available in their native form [6, 7]. Chemical modification is commonly used but there is also a growing trend for the physical modification of starch [8]. Food irradiation represents an effective and environ- mentally friendly technology [9] that is aimed at improving food safety. In recent years, this technique has been widely researched. Its effects are known to preserve, reduce microbial load or sterilise, thereby increasing the shelf life of products and above all maintaining food quality. Its efficacy and safety are proven by official agencies includ- ing the Food and Agricultural Organisation (FAO), Inter- national Atomic Energy Agency (IAEA) and the World Health Organisation (WHO) [10]. Furthermore, irradiation has been used as a physical method to modify flours and starches in order to replace chemical or enzymatic modifications. According to Bhat and Karim [11], gamma radiation can alter the molec- ular structures, mainly of starch, causing its fragmen- tation by the penetration of ionising energy into the granules [12]. Starch plays an important role in the properties of rice and rice products. Gamma irradiation can provide different characteristics for rice flour, which need to be studied according to the final properties obtained. To date, there are few studies in the literature regarding the effect of irradi- ation on the degree of crystallinity, morphology, viscosity and thermal properties of pigmented rice varieties. Thus, the aim of this study was to understand the effects of gamma radiation on the thermoanalytical, structural and pasting properties of black rice flour. Experimental Materials and sample preparation The black rice used in the experiments was purchased in the local supermarket in the city of Curitiba (25� 250 4000 S 49� 160 2300 W), Paraná, Brazil. The samples were ground and sieved through 60 mesh (particle size up to 250 lm) to obtain the black rice flour (BRF). This flour was separated and vacuum-packed in samples of about 200 g in small non-toxic metallic polyester bags with hermetic sealing and with light protection. The BRF had 10.64% moisture, 76.20% carbohydrate, 9.61% protein, 2.15% fat, 4.32% total dietary fibre and 1.41% ash, based on dry matter. All the samples were stored at 25 �C for further analysis. Radiation of the BRF The black rice flour was subjected to gamma radiation at doses of 0, 1, 2 and 3 kGy at 0.221 kGy h-1 dose rate. The irradiation source was Cobalt 60 (Gammacell Excell 220 - MDS Nordion), which was located in the Centre for Nuclear Energy in Agriculture at the University of São Paulo, Brazil (CENA/USP). Harwell Amber 3042 dosimeters were used to measure the radiation dose, and the uncertainty dose was less than 1% [13]. Thermal analysis The thermogravimetric and derivative thermogravimetric curves (TG/DTG) were obtained as previously described [14] using a TGA-50 thermal analysis system (Shimadzu, Japan) under an oxidative atmosphere (synthetic air) flow of 150 mL min-1 with a heating rate of 10 �C min-1 from 30 to 600 �C. The initial sample mass was about 6 mg, which was weighed in open alumina crucibles. All the mass loss percentages were determined using TA-60WS data analysis software. The DSC curves were recorded according to Hornung et al. [15], using a DSC-Q200 model thermal analysis system (TA-Instruments) under airflow of 50 mL min-1 and at a heating rate of 10 �C min-1. Each sample (approximately 2.5 mg) was weighed directly in an aluminium crucible, and a volume of distilled water was added (1:4 w/v) using a micropipette. The crucible was hermetically sealed and allowed to equilibrate for 60 min before testing. In order to obtain the DSC curves, the instrument was calibrated with 99.99% purity standard indium, m.p. = 156.6 �C, DH = 28.71 J g-1, and an empty aluminium crucible was used as reference. TA Universal Analysis 2000 software was used to analyse the main endotherm of the DSC curves for the initial (To), peak (Tp) and conclusion (Tc) temperatures, as well as the gelatinisation enthalpy (4H). The measurements were performed in triplicate. Morphological analysis The micro-images were obtained using a field emission gun–scanning electron microscope (FEG–SEM) (MIRA 3, Tescan, Czech Republic). The parameters were as follows: reading scale of 5 and 50 lm with a tension of 15 kV of field emission gun, which was generated by a lamp with a tungsten filament. The black rice flour samples were pul- verised over a carbon tape. As flour is not conductive, it was necessary to metallise the samples with gold and palladium to promote the passage of electrons and to obtain the images using Image J software (Image J 1.47 to Win- dowsTM) [16]. 530 V. C. Ito et al. 123 X-ray diffractometry (XRD) The X-ray diffractograms (XRD) were obtained using an X-ray diffractometer (Ultima IV, Rigaku, Japan) with CuKa radiation (k = 1.5418 Å), a tension of 40 kV and an electric current of 30 mA. The analysis was performed at 20 8C in an angular range of 5–408 (2h), scanning speed of 28 min-1 and a step of 0.028. Equation (1) was used to calculate the relative crystallinity [7]. Xc ¼ Ap ðAp þ AbÞ � 100 ð1Þ where Xc refers to the relative crystallinity; Ap refers to the crystallinity area of the X-ray diffractogram and Ab refers to the amorphous area of the diffractogram. Pasting properties Prior to determining the pasting properties of each sam- ple, it was necessary to determine their moisture content in order to calculate the exact amount of dry matter to prepare a suspension with 8% of flour. An infrared moisture analyser (Sartorius AG, MA35 M, Germany) was used for the moisture determination. The pasting properties of the black rice flour samples were determined using a RVA-4 viscoamylograph (Newport Scientific Pvt. Ltd., Australia). A total mass of 28 g of the flour sus- pension was submitted to a controlled heating and cooling cycle under constant stirring, where it was held at 50 �C for 2 min, heated from 50 to 95 �C at 6 �C/min and held at 95 �C for 5 min, cooled to 50 at 6 �C/min and held at 50 �C for 2 min [17]. Statistical analysis The results are expressed as the mean ± standard deviation and were analysed using STATISTICA 10 software (Stat- Soft Inc., Tulsa, OK, USA). One-way analysis of variance was used to study the effect of the gamma radiation on DSC, X-ray diffraction and pasting properties. Tukey’s tests were conducted to determine differences between the means at 95% confidence level (p\ 0.05). Pearson’s products (r) were used to evaluate the strength of correla- tion between the response variables [10]. Results and discussion Thermogravimetry and derivative thermogravimetry (TG/DTG) Thermogravimetry is a thermoanalytical technique where the mass variation of a substance that is subjected to a controlled temperature variation is evaluated. The data that are obtained make it possible to study the decomposition of the matter and the periods of thermal stability [18]. The TG/DTG curves are presented in Fig. 1. Flour is a complex mixture of different components, such as starch, non-starch polysaccharides, lipids, sugars, minerals and proteins, which influence its industrial use [19]. In addition, black rice flour contains a high content of fibres, minerals and phytochemicals, which are mainly flavonoids and anthocyanins [4]. These components present specific temperature ranges of thermal decom- position; thus, it is possible degradation occurs during different mass loss steps, which are detected by thermogravimetry. Four mass losses were detected for the black rice flour samples, different from the characteristic behaviour of thermal decomposition of starches, which usually involves only three steps [16, 17]. A slight displacement was observed for the second loss which occurred for the irra- diated flours, compared to the control sample (0 kGy). The values obtained from the TG/DTG curves are shown in Table 1. The first loss occurred at similar temperatures for all the samples and corresponded to the loss of water and volatile compounds, as discussed by Bet et al. [16]. A slight increase in the thermal stability range was observed for the irradiated sample at a dose of 2 kGy (until 189 8C). The second loss, with a mass loss between 4.01 and 4.56%, started soon after the stability and was related to the thermal-oxidative decomposition, mainly of lipids [20]. The peak temperatures calculated by DTG were between 213 and 216 8C, corresponding to the maximum rate of loss. Darfour et al. [21] reported that after the irradiation of cowpea meal at doses between 0.25 and 1.5 kGy, the flour had a greater capacity to absorb oil. In the present study, this may have been associated with the second loss, where there was an increase in the temperature range in which this event occurred in relation to the control sample. The third and fourth losses referred to the decomposition and oxidation of organic matter, as reported by Lopes et al. [22], and occurred at similar temperatures for the control flour and the flours subjected to gamma irradiation. Corradini et al. [23] have suggested that the degradation of compounds such as fibres, proteins, cellulose (310–360 8C) and hemicellulose (240-310 8C) occurs during the third step. In addition, as pointed out by Beninca et al. [24], the depolymerisation of the starch chains that make up the flours occurs. The final residue contents after the thermal decomposition (ash) of the black rice flour were 1.41% for the control sample (0 kGy) and 1.48, 1.40 and 1.68% for the samples submitted to gamma radiation at doses of 1, 2 and 3 kGy, respectively. Effects of gamma radiation on the thermoanalytical, structural... 531 123 Differential scanning calorimetry (DSC) Starch is an ingredient widely used in food systems to impart better texture, consistency and viscosity; it is the main component found in rice and confers important characteristics in the use of this cereal in a process known as gelatinisation [12]. This phenomenon can be studied using DSC to study the temperatures and the enthalpy involved in this endothermic event. 100 80 60 40 20 0 100 80 60 40 20 0 100 80 60 40 20 0 100 80 60 40 20 0 0 100 200 300 400 500 600 0 100 200 300 400 500 600 0 100 200 300 400 500 600 0 100 200 300 400 500 600 0,00 –0,01 –0,02 0,00 –0,01 –0,02 0,00 –0,01 –0,02 0,00 –0,01 –0,02 Temperature/°C Temperature/°C Temperature/°CTemperature/°C M as s/ % M as s/ % M as s/ % M as s/ % D T G /m g m in –1 D T G /m g m in –1 D T G /m g m in –1 D T G /m g m in –1 Control sample 1 kGy 3 kGy2 kGy TG DTG TG DTG TG DTG TG DTG Fig. 1 TG/DTG curves of untreated and irradiated samples of black rice flour Table 1 TG/DTG results of untreated and treated samples of black rice flour Samples TG results DTG results Step Dm/% DT/�C Tp/�C Control sample 1st 10.64 30–148 67.13 Stability – 148–186 – 2nd 4.01 186–238 214.06 3rd 61.79 238–406 313.93 4th 22.15 406–593 488.06 1 kGy 1st 9.08 30–144 71.00 Stability – 144–183 – 2nd 4.56 183–244 213.56 3rd 62.64 244–404 313.51 4th 22.24 404–592 487.64 2 kGy 1st 9.14 30–146 67.35 Stability – 146–189 – 2nd 4.32 189–247 216.21 3rd 61.75 247–394 314.60 4th 23.39 394–593 472.41 3 kGy 1st 10.07 30–145 69.03 Stability – 145–184 – 2nd 4.41 184–240 215.38 3rd 61.35 240–400 313.54 4th 22.49 400–597 472.29 Dm mass loss/%, DT temperature range, Tp peak temperature 40 50 60 70 80 90 Temperature/°C H ea t f lo w /m W 1 Exo up Control sample 1 kGy 2 kGy 3 kGy Fig. 2 DSC curves of untreated and irradiated samples of black rice flour 532 V. C. Ito et al. 123 The DSC curves of the black rice flour samples are presented in Fig. 2. All the samples showed slight changes in the thermal parameters (To, Tc, Tp, and 4H). For the irradiated samples (1, 2 and 3 kGy), Tc remained unchan- ged (p[ 0.05), whereas To, Tp and 4H displayed a slight decrease when compared to the control sample (0 kGy) (Table 2). The dose of 1 kGy showed the lowest To (62.1 �C) and Tp (68.4), whereas the control sample (0 kGy) displayed the highest To (62.5 �C) and Tp (69.7 �C). Regarding the behaviour of 4H, it decreased continuously with the increase in the irradiation dose (p\ 0.05). Bao et al. [12] also concluded that the 4H decreased in white rice flour after gamma irradiation. The enthalpy value was reported to decrease in wheat starches [25]. Rombo et al. [26] studied different flours and concluded that a decrease in required energy may have been due to the difference in starch granule sizes, or possibly to a difference in polymer chain lengths of the starch. In the present study, the gamma irradiation caused a rupture in the black rice flour components, promoting a small variation in the gelatinisation temperature of the starch fraction. The samples submitted to 1 and 2 kGy presented a slight decrease in the onset temperature (To). The reduction in the gelatinisation temperature is due to the cleavage of the amylopectin, which results in short chains and a reduction in the crystalline phase [27]. A slight decrease in the crystallinity, although without significant difference (p[ 0.05) in relation to the non- irradiated flour shown by XRD (Table 2), may also have influenced the decrease in the gelatinisation enthalpy that was observed for the irradiated samples, which was due to the loss of the crystalline domain and double helices [6]. Furthermore, the 4H and crystallinity parameters showed a positive correlation (r = 0.84), suggesting that 4H was influenced by the crystallinity of the starch [28]. X-Ray diffractograms (XRD) The X-ray diffractograms (Fig. 3) were used to verify the main peaks and to calculate the relative degree of crys- tallinity (%) of each sample (Table 2). All the samples had clear A-type diffraction patterns with main reflections at 2h & 15�, 17�, 18� and 23�. Minor peak intensities were also observed at 2h & 20� and 27�. According to Ocloo et al. [29], this peak observed at 2h & 20� indicates the presence of some V-type starch crystals in rice varieties. In the present study, the gamma irradiation did not change the XRD patterns of the black rice flours, which was in agreement with other studies, such as [12] with white rice flour [29], with rice cultivars from Ghana [6], with rice starch and [5, 30] with cornstarch. The non-irradiated flour showed a relative crystallinity higher than values reported for rice flour by Yu et al. [31]. Those authors reported that the differences found in the degree of relative crystallinity could have been associated with the presence of other components in the flour, such as proteins and lipids. The relative crystallinity values obtained for the anal- ysed samples ranged from 19.7 to 23.1% (Table 1). All the irradiated flour samples (1, 2 and 3 kGy) had decreased crystallinity compared with that of the non-irradiated flour sample (0 kGy). Chung and Liu [30] found lower crys- tallinity values with increasing doses of gamma radiation, and they attributed this fact to breaks in the crystalline regions inside the starch granules. However, the present study did not find significant (p[ 0.05) effects of gamma irradiation on the relative crystallinity of the black rice flour samples. According to Polesi et al. [6], many studies have found varying results for crystallinity. Irradiation degrades both the crystalline structure and the amorphous region of the starch granules, which leads to an increase or decrease in crystallinity depending on which region is most affected by Table 2 DSC and relative crystallinity results of untreated and treated samples of black rice flour Sample DSC gelatinisation XRD To/�C Tp/�C Tc/�C DHgel/J g-1 Degree of relative crystallinity/% 0 kGy 62.5 ± 0.04a 69.7 ± 0.23a 77.8 ± 0.30a 4.4 ± 0.12a 23.1 ± 0.05a 1 kGy 62.1 ± 0.03b 68.4 ± 0.47b 77.3 ± 0.82a 3.7 ± 0.37b 22.5 ± 3.41a 2 kGy 62.2 ± 0.05b 69.7 ± 0.09a 77.6 ± 0.15a 3.3 ± 0.07b 21.2 ± 0.60a 3 kGy 62.5 ± 0.06a 68.6 ± 0.17b 77.1 ± 0.10a 3.3 ± 0.05b 19.7 ± 2.08a To ‘‘onset’’ initial temperature, Tp peak temperature, Tc ‘‘endset’’ conclusion temperature, DHgel gelatinisation enthalpy, the degree of crys- tallinity was calculated as a percentage, and peaks are determined in 2h Averages followed by the same letters in the same column do not differ statistically by Tukey’s test (p\ 0.05) Effects of gamma radiation on the thermoanalytical, structural... 533 123 each dose. In addition to the botanical source, the dose rate plays an important role in crystallinity because greater recombination occurs among the starch molecules at low dosage rates [30]. Field emission gun–scanning electron microscopy (FEG–SEM) The micro-images in Fig. 4 show an organic and hetero- geneous composition, with particle agglomerates present- ing irregular shapes and sizes that are characteristic of the samples of black rice flour. For the non-irradiated sample (0 kGy), the black rice flour was characterised by having a continuous structure with the starch granules surrounded by protein bodies and embedded in a cementing matrix [32]. Some changes occurred after gamma radiation such as cracks, pores and smaller fragments. In the control sample (0 kGy), the particles were larger, and surface cracking increased in line with increasing radiation doses; at the doses of 1, 2 and 3 kGy, there was an accumulation of smaller fragments, which resulted from cracks, pores and irregularities on the surface. Ashwar et al. [33] reported that cracks on the surface could be due to the effect of highly energetic and pene- trating gamma radiation. These changes were associated with free radicals generated by gamma irradiation cleaving the glycosidic linkages of the large starch molecules, and some starch granules were fractured along the cleaved molecules, which may contribute to the formation of dex- trin [34]. This kind of breakage resulted in increased numbers of small-sized particles in samples of the black rice flour. Pasting properties The pasting properties of the non-irradiated and irradiated black rice flour samples are presented in Fig. 5. Significant (p\ 0.05) differences in the pasting properties were found in terms of temperature, peak viscosity, setback, break- down and final viscosities in all the samples (Table 3). These results agreed with previous reports of the effects of irradiation on the pasting properties of flours made with rice cultivars [12, 29]. In the present study, the pasting properties decreased continuously with the increase in irradiation dose, except for the pasting temperature, which proportionally increased with the gamma radiation (Table 3). The pasting temper- ature was negatively correlated with peak, break, setback and final viscosity, which was in line with a previous study by Singh et al. [28]. Free radicals generated during the modification by irradiation of flour can promote the cleavage of the amylose and amylopectin glycosidic bonds, which are major components of starch, reducing its molecular mass and consequently decreasing the paste viscosity, thereby requiring higher temperatures for the formation of gel [6]. As found by Singh et al. [28], the pasting temperatures were higher than the To obtained by DSC. The decrease in these characteristic features (peak vis- cosity, setback, breakdown and final viscosities) of black rice flour samples after gamma irradiation can be associ- ated with partial depolymerisation of the rice starch molecules due to chain ruptures [29]. This can be corre- lated with the results found by microscopy and X-ray powder diffraction analysis. According to Chung and Liu [30], a reduction in peak viscosity after irradiation might be due to the degradation of starch after irradiation, as well as the reduction in its swelling power. Liu et al. [5] reported that the breakdown viscosity provides an indication of the stability of starch pastes and the tendency of starch granules to resist shear force during the heating process. However, the higher breakdown vis- cosity of the irradiated flour samples might indicate a disruption or weakening of the bonding forces (hydrogen bonds) in the starch granules [35]. According to Bhat et al. [35], the decrease in setback and final viscosities mainly occurs due to the reordering or polymerisation of leached amylose and amylopectin. This might decrease due to the degradation, as well as the shortening of the amylopectin branch chains. It is worth noting that setback and final viscosities are important parameters for the food industry. The lower viscosities of the studied samples suggest that irradiated black rice flours could be used in infant foods, for example. 5 10 15 20 25 30 35 40 2θ 100 In te ns ity /c ou nt s. –1 Control sample 1 kGy 2 kGy 3 kGy Fig. 3 X-ray diffraction patterns of untreated and irradiated samples of black rice flour 534 V. C. Ito et al. 123 Conclusion The effects of gamma radioisotope 60Co on black rice flour were investigated considering thermoanalytical, structural and pasting properties. The thermogravimetric curves showed four mass losses. A small displacement was observed for the second loss, which occurred for the irra- diated flours compared to the control sample. All the samples showed slight changes regarding thermal param- eters (To, Tc, Tp and 4H). For the irradiated samples, the To, Tp and 4H displayed a small decrease. Fig. 4 FEG–SEM micro-images of untreated and irradiated samples of black rice flour Effects of gamma radiation on the thermoanalytical, structural... 535 123 All the black rice flours exhibited A-type crystallinity pattern, and the gamma radiation did not change the XRD pattern or the degree of crystallinity. The micro-images obtained using FEG–SEM showed a composite of organic and heterogeneous material: after gamma radiation, some changes occurred such as cracks, pores and smaller frag- ments. The pasting properties (viscosity) decreased sig- nificantly with irradiation. The decrease in setback and breakdown viscosities after irradiation suggested the pos- sibility of improving the quality of foods based on black rice flours. Gamma radiation can be a useful tool to modify rice flours to suit various functionalities and to help to meet the growing demands of the food industry. Black rice is known as a potential source of anthocyanins, as well as being used as a natural colourant. This study showed that flours from gamma-irradiated black rice have the potential to be used in food formulations that require low viscosity such as porridges and infant foods. However, it also can be a valuable ingredient in gluten-free, cereal products with higher nutritional value, thereby providing extra health benefits to consumers. Acknowledgements The authors are deeply grateful to the Coordi- nation for the Improvement of Personnel in Higher Level (CAPES), Fundacão Araucária for funding and C-LABMU-UEPG for the infrastructure. References 1. Hu Z, Tang X, Liu J, Zhu Z, Shao Y. Effect of parboiling on phytochemical content, antioxidant activity and physicochemical properties of germinated red rice. Food Chem. 2017;214:285–92. 2. Ziegler V, Ferreira CD, Goebel JTS, El Halal SLM, Santetti GS, Gutkoski LC, et al. Changes in properties of starch isolated from whole rice grains with brown, black, and red pericarp after storage at different temperatures. 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Effects of gamma radiation on the thermoanalytical, structural... 537 123 http://dx.doi.org/10.1007/s10973-016-5832-9 Effects of gamma radiation on the thermoanalytical, structural and pasting properties of black rice (Oryza sativa L.) flour Abstract Introduction Experimental Materials and sample preparation Radiation of the BRF Thermal analysis Morphological analysis X-ray diffractometry (XRD) Pasting properties Statistical analysis Results and discussion Thermogravimetry and derivative thermogravimetry (TG/DTG) Differential scanning calorimetry (DSC) X-Ray diffractograms (XRD) Field emission gun--scanning electron microscopy (FEG--SEM) Pasting properties Conclusion Acknowledgements References