Abstract

Five types of starches isolated from cereal cultivars (gray millet, white creamy millet, wheat, rice and corn) were used in a comparative study with respect to their physico-chemical and morphological properties. Physico-chemical properties, such as chemical composition, water and oil absorption capacity, swelling power, solubility and syneresis attributes showed significant differences among the resulted starches. Amylose content of starches isolated from gray millet, white creamy millet, wheat, rice and corn was 21.35, 21.70, 19.32, 22.77 and 24.77%, respectively. White creamy millet possessed the highest swelling power 15.96 g.g^-1 at 90°C. The granule size varied from 3.6 to 13.1 and 2.8 to 12.3 µm for gray and white creamy millet, respectively. Rice starch had the smallest granules size, it ranged from 1.5 to 8.9µm. Granule sizes of wheat and corn varied from 6.9 to 34.8 and 2.4 to 9.8 µm, respectively. Rice starch showed a slower increase (76.79- 79.0%) in syneresis up to five day of storage at 4°C, followed by white creamy millet starch paste (77.7-82.0%). In addition, wheat starch paste showed a sharper increase (68.07-75%). While peak, break down, final and set back viscosity were in ranges of 2920-5190, 608-2964, 3781-4421 and 1469-2414 RVU, respectively.

1. Introduction

Cereals belong to the family Poaceae (formerly Gramineae) are particularly important crops to humans because they are staple food crops in many areas of the world. Cereal grains provide about 50% of the daily calories ingested by people throughout the world. The most extensively cultivated grains are wheat, rice, corn or maize, barley, oats, rye and millets. Wheat, rice and maize are the most important cereals grains in . They are the main source of carbohydrate ¹.

Starch is the major dietary source of carbohydrates and is the most abundant storage polysaccharide in plants. Amylose and amylopectin are two macromolecular components of starch granules ². Isolated starch is used in the food industry to impart functional properties, modify food texture, consistency and so on. Not only the amount of starch is important for the texture of a given product, but also the type of starch is critical ³.

The different botanical sources of starches are cereal, legume, root, tuber and unripe fruit. Starch granules occur in all shapes and sizes (spheres, ellipsoids, polygon, platelets and irregular tubules). Amylose has a high tendency to retrograde and produce tough gels and strong films. In contrast, amylopectin, when dispersed in water, is more stable and produces soft gels and weak films ⁴.

Wheat is one of the most important cereals for direct human consumption. Its textural properties determine the end product quality. Wheat has a unique trimodal distribution of starch granules i.e. A- (diameter 10–50 μm), B- (diameter 5–9.9 μm) and C granules (diameter <5μm) ^{5, 6}.

Starch from rice, millet and corn are non-allergenic, because of the hypoallergenicity of the associated protein. Rice starch granule being very small in size provides a texture perception similar to that of fat ⁷. Corn starch occupies an important place in the preparation of pies, puddings, salad dressings and confections. It is incorporated into cakes, cookies, icings and fillings to increase moisture retention and retard crystal growth. Recent uses of starch include their use as delivery vehicles that protect pharmaceutically active proteins from digestion ⁸, such as microencapsules for small molecules ⁹ and biodegradable films ¹⁰. Among several millet crops, proso millet, known as hershey, broom corn, or hog millet, is planted in some African countries as a food crop ¹¹. Interestingly, in the United States, millet is consumed as a puffed or cooked breakfast cereal or replacement for up to 30% of wheat flour in certain baked products and other household recipes ¹². The increasing price of wheat and its shortage in many less developed countries prompted to study replacing part of the wheat flour used in food industry and bakery products ¹³.

Due to the importance of starch in food processing, the present investigation was performed to study the physical and chemical properties of millet starch as a new source of starch in a comparative study with traditional cereal starches i.e. wheat, rice and corn.

2. Materials and Methods

Gray Egyptian proso millet (Panicum miliaceum ) Shandawel 1, wheat (Triticum aestivum) Seds 6 and rice (Oryza sativa) Giza 18 were obtained from Crop Research Institute, Agricultural Research Center Organic white creamy millet was purchased from local market produced by USA. Corn starch was obtained from Egyptian Starch and Glucose Manufacturing, Torah Cairo, Egypt.

Starch was isolated from the two tested millet varieties (gray and white creamy millet). Millet, wheat and rice were inspected for and cleaned from impurities and foreign matter then prepared for extraction the starch by using Wet Milling process. One kilogram of the sample was soaked in 4 L of distilled water containing diluted alkali (o.1 ) and kept at 4 °C for 12 h. The grains were pulverized along with water for 5 min in a blender.

The obtained slurry was then diluted to ten times (volume/volume) with distilled water. The slurry was continuously mixed by a magnetic stirrer for one hour, and then filtered through a 75 μm mesh sieve to separate the fiber. The filtered slurry was then centrifuged at 236g for 30 min. The obtained sediment was scraped off from the surface and the lower white portion was washed three times with distilled water and over night allowed to sediment at the refrigerated temperature (4°C).

This sediment was recovered as starch. The starch was dried at 40°C in an air convection oven till dryness ¹⁴.

The method of hydrothermal starch was carried out according to Sievert and Pomeranz, ¹⁵. Starch sample (200 g) was weighed into a 1000-ml beaker and mixed with 700 ml of distilled water. The starch-water suspension was autoclaved at 121°C/20 min. After autoclaving, the sample was dried at 40°C in an air convection oven till dryness.

Moisture, protein, fat, crude fiber and ash contents of the raw cereal grains and their starches were determined according to the method of AOAC ¹⁶.

Total carbohydrate was calculated by difference. Amylose content was determined using the method outline by Juliano, ¹⁷. Amylopectin was calculated by following equation:

Water absorption capacity (WAC) and oil absorption capacity (OAC)

Starch (2.5 g dry weight basis db) was mixed with 20ml distilled water or corn oil in a preweighted centrifuge tube, then stirred for 2 min on vortex mixer and allowed it to stand for 30 min at 25°C, centrifuged at 236g for 10 min and the supernatant was decanted. Gain in weight was expressed as water or oil absorption capacity, respectively ¹⁸.

Water solubility (WS) and Swelling power (SP)

Water solubility (WS) and Swelling power (SP) determination of the starches were carried out using the methods described by Ali et al., ¹ with some modifications. The water solubility (WS) and swelling power (SP) were calculated according to Kibar et al. ¹⁹ as follows:

(1)

(2)

Starch suspensions (2%, w/w) were heated at 90°C for 30 min in a water bath with constant stirring. The starch samples, in separate tubes, were stored for 1, 2, 3, 4 and 5 days at 4°C. Syneresis was measured as percentage amount of water released after centrifugation at 236g for 10 min ¹.

The pasting properties of the starches were measured using a Rapid Visco Analyzer (RVA) (Tech Master, Pertain Instruments Warriewood, Australia) using the method described by Wani et al. ²⁰.

Scanning Electron Microscopic (SEM) Examination

Morphology of untreated (native) and hydrothermal treated cereal grain starches were examined using Scanning Electron Microscope (SEM), at central laboratory, Agriculture faculty, according to Dronzek et al. ²¹. Samples were sputter-coated (SPI- Module TM Sputter Coater, USA) with gold at vacuum evaporator then examined using SEM (JEOL, JSM- 5200, Tokyo, Japan) at 25 kV accelerating voltage with different magnification power at,1000, 3000 and 50X.

For the analytical data, mean values and standard deviation are reported. The obtained data were subjected to one-way analysis of variance (ANOVA) at P < 0.05. It was performed and the results were separated using the Multiple Range Duncan’s test using the SAS ²² statistical software.

3. Results and Discussion

Chemical composition of gray millet, white creamy millet, wheat and rice grains flours is shown in Table 1. Statistical analysis of the results showed significant differences in protein content of the tested raw materials. Protein content of cereals ranged from 7.0 to 14.39%.It recorded 12.01, 11.02, 14.39 and 7.04 % for gray millet, white creamy millet, wheat and rice, respectively. The fat content of gray millet, white creamy millet, wheat and rice were 7.20, 4.00, 1.56 and 0.56%, respectively. There were significant differences in fat where gray millet recorded the highest fat content, in contrast rice flour had the lowest value.

The ash content recorded 1.95, 2.48, 0.82 and 0.44% in gray and white creamy millet, wheat and rice flour, respectively. Statistical analysis for ash content of the four cereals showed significant differences, where white creamy millet had the highest ash content (2.48%). The fiber content of the four cereals was 3.00, 2.99, 1.22 and 0.54, respectively. Statistical analysis of the results showed significant differences among the four cereal in their crude fiber content. Carbohydrate content of the four cereals flour showed high values (75.84, 79.51, 82.01 and 91.42%, respectively). It was previously found that protein content in pearl millet varied from 8.96 to 10.36% while fat content was in the range of 3.11- 3.505% and the ash content ranged between 2.08-2.54% ²³.

Proximate composition of the investigated cereal starches are shown in Table (2). The protein contents of the five starches extracted from gray millet, white cream millet, wheat, rice and corn were 0.60, 0.62, 0.57, 0.48 and 0.62%, respectively. It was found that protein percent contents were 0.58, 0.55 and 0.31% in wheat, millet and rice, respectively, and it was also found that, the fat contents in the corresponding samples were 0.85, 0.83 and 0.77%, respectively ²⁴. The average of protein content of starches in rice and corn ranged from 0.35% to 0.52% as reported by Ali et al. ¹. The fat contents in the corresponding five starches is 0.15, 0.16, 0.18, 0.10 and 0.17%, respectively. Analysis of variance showed non significant differences among the four extracted starches in their fat contents, except of rice starch. The protein and fat content values of the corn starch agree with that obtained by Jiranuntakul et al. ²⁵ who reported that protein and fat contents of rice starches were 0.61 and 0.15%, respectively. Another study showed, also, that the fat content average of starches in rice and corn varieties ranged from 0.25% to 0.67% ¹.

Ash contents recorded 0.18, 0.18, 0.19, 0.24 and 0.38% in gray millet, white creamy millet, wheat, rice and corn starches, respectively. Rice and corn starches showed significant differences in ash content, while there were non significant differences among the other three starch types. The present results were in agreement with the values reported by Hassan et al. ²⁴. It was, also, reported that ash content of the rice and corn starches recorded 0.26 and 0.42, respectively ²⁵.

Amylose content of isolated starches was ranged from 19.32 to 24.77%. The highest value was observed in case of corn starch while the lowest value recorded in wheat starch. The two varieties of millet, Nearly, had a similar amylose content (21.35 and 21.70 for gray and white creamy, respectively. In addition, rice grain starch had 22.77% amylose content (Table 2). Statistical analysis revealed that the cereal starches are significantly different in their amylose content. Such observation was confirmed by a study stated that amylose content of wheat, sorghum, millet, rice and cassava starches recorded 30.94, 28.66, 22.60, 22.88 and 23.59%, respectively ²⁴. Beleia et al. ²⁶ showed that the quantitative determinations of amylose in pearl millets ranged from 20 to 22%, while, Ali et al. ¹ found that the amylose content ranged from 4.9 to 6.33 and from 7.52 to 8.09% in Indian rice and corn cultivars, respectively. However, Badi et al. ¹³ reported a low amylose content in millet starch (17%), but the current data indicated, that the millet starches contained amylose content as do as normal cereal starches. The amylose content of starch has been reported to vary with the botanical source of the starch and is affected by the climatic and soil conditions during grain development ²⁷.

Results revealed that the cereal starches had significant differences in their amylopectin content (Table 2). Amylopectine content of isolated starches ranged from 75.23 to 80.67%. The highest value was observed in wheat starch meanwhile, the lowest value recorded in corn starch. Gray millet, white millet and rice starches recorded 78.65, 78.30 and 77.23%, respectively.

Syneresis, an index for the degree of starch retrogradation at low temperatures, is an undesired property in both food and non food applications. White creamy millet showed the highest value (77.7%) of Syneresis, while corn and wheat starch paste showed the lowest value (68 and 68.07%) on the zero day of storage (Table 3). Further storage increases the syneresis of different starches. Rice starch paste showed a slower increase from (76.79 to 79%) in syneresis followed by white creamy millet starch paste (77.7- 82%) after 5 days of storage.

Wheat starch paste showed a sharper increase (68.07 to 75%) than corn and gray millet starch paste (68-73.25% and 75.09-81%), respectively. Generally, there are differences among different types of starch and different millet varieties. The syneresis of different cereal starches increased in the order of wheat > gray millet > corn > white creamy millet > rice. Indian rice starch paste showed a slower increase (80.1-81.5%) of syneresis whereas the corn starch paste showed a sharper increase (68.4-76.8%) as reported by Ali et al. ¹.

Upon cooling, starch molecules reassociate in a complex recrystallization process known as retrogradation, which is often associated with water separation from the gel (syneresis) ²⁸. These changes may result in textural and visual gel deterioration ²⁹.

The syneresis of starches progressively increased with the increase in storage duration. The increase in % syneresis during storage has been attributed to the interaction between leached amylose and amylopectin chains which leads to development of functional zones ³⁰ or leading to gel shrinkage ³¹, degree of polymerization of amylose, amylopectin chain length, proportion of short chains or shrink back of partially disintegrated granules to their original size during cooling ¹⁴. Starch retrogradation occurs when starch molecules begin to reassociate in an ordered structure ³². Amylose aggregation and crystallization have been reported to be complete within the first few hours of storage while amylopectin aggregation and crystallization occur during later stages ³³.

Water absorption capacity (WAC) is an important parameter that determines the ability of starch to use in products manufacturing. It affects functional properties such as viscosity, which is a very important indicator of bulking and consistency of products ³⁴. Water absorption capacity represents the ability of a substance to associate with water under a limited water condition. Water absorption capacity (WAC) of gray millet, white creamy millet, wheat, rice and corn starches are shown in Table 4. WAC found to be 74.48, 75.02, 62.87, 87.39 and 73.39 ml.100gm^-1 , respectively.

Rice starch gave the highest value (87.39 ml.100gm^-1), while wheat starch had the lowest WAC value (62.87 ml.100gm^-1).

Statistical analysis of the result showed significant differences among the starch samples. OAC or FAC is the ability of the dry starch to physically bind fat by capillary attraction and it is of great importance, as fat acts as flavor retainer and also increases the mouthfeel of foods ¹. The oil absorption capacity of starches was 77.57, 77.41, 65.75, 91.40 and 77.59 ml.100gm^-1 for gray, white creamy millet, wheat, rice and corn starch, respectively. Statistical analysis of the result showed no significant differences between corn starch and gray millet starch, while significant differences among other starches were observed. Data in Table (4) showed that, rice starch had the highest OAC value (91.40 ml.100 gm^-1) while wheat starch had the lowest value (65.75 ml.100gm^-1).The two millet varieties and corn had nearly the same values (77.57, 77.41 and 77.59 ml.100gm^-1 respectively). These results are agreed with Ali et al. ¹ who found that, the oil absorption capacity in rice cultivars was significantly higher than corn cultivars. The differences in WAC of starches extracted from cereals different types could probably be attributed to the variation in their granule structure. The engagement of hydroxyl groups to form hydrogen and covalent bonds between starch chains lowers WAC ³⁵. The loose association of amylose and amylopectin molecules in the native starch granules has been observed to be responsible for high WAC ³⁶.

The ability to swell in excess water and solubility of the starches extracted from cereal grains showed significant differences. Figure 1 showed the water solubility (WS) of different cereal starches (gray millet, white creamy millet, wheat, rice and corn) at various temperatures from 60°C to 90°C. Data showed that solubility was increased with increasing temperature. Solubility of rice and white creamy millet starches at 90°C showed the highest value which recorded 14.33 and 14.26g.g^-1, respectively, followed by corn and gray millet, where as the wheat starch showed the lowest solubility at that temperature (90°C). Water solubility (g.g-1) of grain starches showed low degree of solubility at 60°C while at 70°C an increase in solubility was noticed for grain starches. This data agreed with Bhupender et al. ³⁷, who found that solubility behavior of pearl millet starches at 60°C to 90°C increased with increasing the temperature. The solubility could imply to the amount of amylose leaching out from starch granule when swelling, therefore the higher the solubility the higher will be the amylose leaching ³⁸. Difference in solubility could also be attributed to different chain length distribution in the starch ³⁹.

The swelling power of starch indicates the degree of water absorption of starch granules and solubility As well as reflects the degree of dissolution during the starch swelling procedure ⁴⁰. The swelling power at different temperatures (60°C to 90°C) for the tested five grain starches are presented in (Figure 2). Swelling power of different starch samples varied from 2.76 to 15.96 g.g^-1 with changed the temperature from 60°C to 90°C. Data in such Figure cleared that, the swelling capacity was a function of temperature and the average value of swelling capacity was significantly increased with increasing the temperature. Consequently, the current study showed that starch extracted from white creamy millet possessed the highest swelling power (15.96 g.g^-1) at 90°C followed by rice starch (15.93 g.g^-1). The lowest swelling power (12.89 g.g^-1) was detected in wheat at that temperature. The swelling power and solubility depend on the interaction between starch chains and crystalline domains. Ali et al. ¹ observed that swelling index of rice cultivars varied from 8.67 to 9.23 g.g^-1 and in corn cultivars, it was in the range of 8.33 to 8.50 g.g^-1, confirmed another study ⁴¹.

These differences in swelling power and solubility may also be attributed to the differences in amylose content, viscosity patterns and weak internal organization resulting from negatively charged phosphate groups within the rice starch granules ⁴². Swelling behavior of cereal starches has primarily been reported that a property of their amylopectin content, amylose acts as an inhibitor of swelling, especially in the presence of lipid ⁴³. The swelling behavior of starch depends on the amylose content, structure of amylose and amylopectin, and presence of non-carbohydrate substances, especially in the presence of lipids which acting as an inhibitor of swelling ⁴³. The increasing in both the swelling power and solubility in oxidized and thinned hybrid maize starch was due to the increase in mobility of starch molecules, which facilitated easy percolation of water ⁴⁴.

Pasting properties are determined to give a picture of the functional behavior of starch during heating and cooling periods during processing ⁴⁵. The RVA profiles of grain starches are summarized in Table 5. Corn starch showed the lowest pasting temperature (75.8°C), while white creamy millet had the highest value (80.8°C). With respect to the peak viscosity rice starch had a higher peak viscosity (5190 RVU)) than the other four grain starches. Wheat starch presented a lower peak viscosity (2920 RVU). These variations can be attributed to the granule swelling, starch crystallinity, amylose content and chain length distribution ⁴⁷.

It has been reported that low swelling factor, stronger crystalline structure and a large amount of relative crystallinitye, cause a low peak viscosity in starch ⁴⁶.

Regarding to breakdown viscosity, wheat starch had the lowest break down viscosity (608 RVU), Rice starch had the highest break down viscosity (2964 RVU) followed by white creamy millet starch (2348 RVU). High break down viscosity reflects the granular swelling that makes the starch granules more susceptible to shear ⁴⁸. This indicates that rice and millet starches have more susceptibility to disintegration. Set back viscosity ranged from 1469 to 2414 RVU. Corn starch had higher set back viscosity fillowed by rice starch. Where as white millet and gray millet starch had 2137 and 2121, RUV, respectively. Final viscosity of starches ranged from 3781 to 4421 RVU. Rice starch had the highest value 4421 RVU followed by gray millet 4302 RVU. In addition wheat starch had the lowest final viscosity (3781RVU). This parameter is used to indicate the ability of starch paste to retrograde and form a strong gel after cooling ⁴⁹. Sorghum starch gelatinization temperature ranges from 67-73°C have been reported for sorghum grown in South Africa and 71-81°C for sorghum grown in India ⁵⁰ and 73.2°C for Korean waxy sorghum ⁵¹. High temperature gelatinization can be considered as an indication of the higher stability of starch crystallites in starch molecules ⁵². Starch gelatinization temperature is influenced by many factors; in particular, the lengths of the various chains in the amylopectin molecule with gelatinization temperature which increasing with longer chain length ⁵⁰. Moorthy ⁵² reported that, gelatinization enthalpy depends on number of factors such as cristallinity intermolecular bonding, and it also depends on genetic and environmental factors, so it can be deduced that hyper arid environment has affected gelatinization properties of sorghum starch by increasing peak temperature. Similar observation was previously done for wheat and other species but gelatinization enthalpy was found increasing ⁵³.

Starch naturally occurs as discrete particles called granules. Scanning electron micrographs (SEM) estimation was used to investigate the morphology of starch extracted from different cereal grains before and after thermal treatment as shown in Figure 3.

SEM for starch granules extracted from millet grain varieties (gray and white creamy) mostly presented as smooth surface, polygonal or spherical shape without clear differences between them in the shape and with smooth surface. Native corn and rice starch granules also showed angular shape and rather uneven surface characteristics (Figure 3) although entirely smooth ones were also observed. The wheat starch granules exhibited the disc-like lenticular shape and the smallest granules were roughly spherical or oval and irregular or cuboidal in shape. After thermal treatment, few starch granules became puckered, curved or irregularly shaped and a remarkable degree of swelled (Figure 3). Table 6 showed that, the granule size of white creamy millet starch varies between 2.8 and 12.3 μm and the value of the pigmented millet (gray) varies from 3.6 to 13.1 μm. The size of starch granules of wheat, rice and corn was ranged from 6.9 to 34.8, 1.5 to 8.9 and 2.4 to 9.8 μm, respectively. Little differences in native gray and white creamy millet granules size was observed when viewed by SEM (Figure 3). The wheat granules size ranged from 6.9 to 34.8 μm, in generally, the granule size of millet is nearly similar to those of corn so industrially millet starches can replace the starch of corn in the processes, since there are no influences related to the other functional characteristics.

These results are in accordance with those of Kim et al. ¹² and Jobling, ⁵⁴ who estimated that, granule size of corn, wheat, potato and cassava was ranged from 2-30, 1-45, 5-100 and 4-34 μm, respectively. Many researchers suggested that as the amylose content increases, the irregularity of starch granule shape increases too ⁵⁵.

The most expanded and broken or damaged granules was observed after thermal treatment. Kaur et al. ⁵⁶ showed that physicochemical properties have been correlated with the granule size average of starches separated from different plant sources. Rice starch granules are the smallest known to exist in cereal grains with the size observed in range of 7 to 14 μm. Same findings were observed by Vandeputte and Delcour ⁵⁷. Wheat has a unique trimodel distribution of starch granules i.e. A-( dimater 10 -50 μm), B- ( diameter 5 – 9.9 μm) and C granules ( diameter < 5).

The average size of wheat starch granules ranges from 2–40 μm ⁵⁸, it is the larger granules. while some say 30–40μm ⁵⁹. After heat treatment, some of granules showed small fissures and depressions on the surface, whereas size of the wheat starch granules was ranging from 1.5 to 24.0 μm, and especially bigger ones, showed quite numerous small depressions (Figure 3) agreed with Lawal et al. ⁴⁴.

Kim et al. ¹² found that millet varieties starch granule sizes ranged from 4.3 to 8.9 μm. The variation in size and shape of starch granules may be due to their biological origin ⁶⁰. The morphology of starch granules also depends on the biochemistry of the chloroplast or amyloplast as well as physiology of the plant ⁶¹. The size of granule starch plays a significant role in food product quality and the properties of biodegradable plastic films ⁶². It is a characteristic of their botanical origin and can be affected by environmental temperature. Indeed, Matsuki et al. ⁵³ found that size granule reduced at the high temperature in barley. These granules have a smooth surface with angular, irregular and polygonal shapes. Starch properties depend on the physical and chemical characteristics such as mean granule size, granule size distribution, amylose/amylopectin ratio and mineral content ¹⁴.

The variation notably in granule size distribution and shape is associated with various functional properties in different food systems and the possibility of relating granule morphology to manufacturing processor nutritional qualities ⁶³. Generally it could be confirmed that granule size refers to the average diameter of the starch granule and the size of starch granules varies from cultivar to cultivar. Starch properties depend on the physical and chemical characteristics. The variation notably in granules size and shape is associated with various functional properties in different food systems and possibility of relating granule morphology to manufacturing processes or nutritional qualities.

White creamy millet starch is nearly reassembly in its physic chemical properties, to rice starch i.e. light color, syneresis and granules size. These unique properties could be made white creamy millet as a new source of starch that can share in decreasing corn exportation and increasing millet starch demand in food and pharmaceutical. So, it could be recommended to increase the cultivated area with white color millet in the cultivation of the 1.5 million fed project, due to its relatively drought tolerance compared to other cereals. It could be, also, due to that it can grow under very hard conditions such as the infertile soils and the excessive heat.

4. Conclusion

Starch is greatly varied in its form and functionality between and within botanical species, and even from the same plant cultivar grown under different conditions. Its different properties are possible utilized for making diverse food products. A growing demand for starches from the food industry has created the need for new sources of this polysaccharide. A potential new starch source is the proso millet. This grain has a high starch (710 g/kg) and protein (120 g/kg) content. The pasting properties are used in assessing the suitability of starch as a functional ingredient in food and other industrial products. The granules size of millet is nearly similar to those of corn so industrially millet starches can replace the starch of corn in processes. Corn starch showed the lowest pasting temperature while creamy millet had the highest value. Rice starch had the highest break down viscosity, thus rice and white millet starches have more susceptibility to disintegration than the other types of starch under study. More research is required to understand the relationship between environment and characteristics and end-product quality and extend the investigation on starch functional properties for other millet varieties. Scanning electron microscopy (SEM) was suitable tool to characterise the starch granules in different cereals. Millet contained a large number of small spherical granules. Gray and white creamy millet showed a high gelatinization temperature compared to corn, rice and wheat starches.

References