Introduction

Pulses and grain legumes are the cheapest sources of fibers, proteins, minerals, and vitamins along with various phytochemicals that provide health benefits¹. The management of diabetes, cancer, heart disease, healthy aging, irregular bowel movements, obesity, and diabetes are among the chronic disorders for which the legume diet is advised². Most of the legumes are used to enhance technological properties and nutritive value in various modern and traditional foods like snacks, pasta, breakfast food, soups etc^3-4. Legumes are a rich source of carbohydrates mainly resistant starch, and fiber, devoid of allergic gluten proteins, so can be used in dietetic and gluten-free foods⁵. Legumes have a higher concentration of resistant starch than other conventional starches like cassava, corn, rice, and potatoes, which makes them useful for use in the creation of anti-diabetic diets⁶.

Vigna umbellata is an underutilized and multipurpose legume commonly named rice bean, mambi bean, climbing mountain bean and oriental bean⁷. In certain regions of India and Southeast Asia, people consume this legume as food⁸. It grows well in humid subtropical regions as well as temperate (warm and chilly) climates, and can withstand the conditions of drought. Therefore, it can be cultivated by the poor farmers at low cost and in a low fertile soil⁹.  Rice bean is used as a biological barrier of the living fence, as a cover crop and as green manure¹⁰. Because of fibrous mucilage, the rice bean seeds cannot be easily processed to dhal. As a result, hulling and cotyledon separation are more difficult with this legume than with other common sources like mung beans, peas, cowpeas, etc. ¹¹. Its seeds are rich source of proteins, starch, and fiber. In general, starch in rice bean mostly varies between 52-57% and amylose content generally ranges from 20-60%¹². The amylose content in rice bean is higher than other conventional sources (Cereals and tubers) of starch that makes it more important in the food industry because amylose affects various physicochemical parameters of starch¹².

Starch is a complex carbohydrate polymer and semi-crystalline in nature. It is an abundant carbohydrate reserve stored in a variety of plants¹³. It is used in food industry to improve various qualities like texture, quality, consistency, and thickening to enhance the overall quality and acceptability of food¹⁴. It is also used to develop biodegradable materials like edible coatings and polymers¹⁵. The various properties of starch like gelation, swelling power and solubility, water absorption capacity, oil absorption capacity, emulsification properties, etc further depend on chemical composition and major constituents of starch¹⁶. Because of the desired characteristics, starch is also used in polymer industries, and biomedical and pharmaceutical industries^17-19.  Starch from conventional sources like cereals, rhizomes and tubers has been extensively studied to date¹⁹ but the non-conventional starch sources (legumes) still need to be studied because they are the cheapest source sources of starch.  

As little is known about the properties of rice bean starch, it has not been exploited economically and is hence still underutilized. The physicochemical characteristics of rice bean starch are poorly understood¹² because the less research has been conducted by the researchers on this. Consequently, since food industries only rely on traditional sources of starch like grains and tubers, extensive research is required to examine its varied qualitative attributes and expand its applicability in food sector. Further, the cultivation of this legume may play a role for livelihood of poor farmers. Therefore, the present study was conducted to observe the physicochemical characteristics of native rice bean starch.

Material and Methods

Materials

The rice bean legume was purchased from Haryana Agriculture University, Hisar, Haryana. All the chemicals used i.e., toluene, sulphuric acid, hydrochloric acid, potassium iodide, dimethyl sulfoxide (DMSO), n-propanol, etc. for the research were of analytical grade from Himedia, Sigma-Aldrich and Merck.

Isolation of Rice bean starch

Isolation of starch from rice beans was carried out by the method of Schoch and Maywald²⁰. The seeds were soaked in distilled water for a night with 0.5% toluene (to prevent fermentation during soaking) and washed properly with distilled water. Slurry was prepared by using Waring blender and passed from a nylon cloth (60-mesh size). The slurry was filtered again through a screen (220-mesh size) after washing with distilled water. The process of double sieving provided better starch yield. The slurry was allowed to stand for 1 hour. The upper pale layer was scrapped off and the remaining white layer was re-suspended in distilled water and centrifuged (Laboratory centrifuge-REMI) for 5 minutes at 4000 revolutions per minute. The process was repeated 4 times to obtain clear white layer of starch. It was dried in a convection oven at 40˚ C for 24 hours,  ground with pestle mortar,  sieved (80-mesh size) and stored in an air-tight container for further analysis.

Chemical composition of isolated starch

The moisture, ash, lipid, protein, and fiber content of isolated rice bean starch were analyzed by using the Official Methods of Analysis-(AOAC)²¹.

Amylose content

Total and apparent amylose percent were analyzed by the method of Hoover and Ratnayake²².

Total amylose content

Defatted native starch (20 milligram starch) was taken in a 10 millilitre screw-cap reaction vial  and dissolved in 8 millilitre of 90% Dimethyl sulfoxide (DMSO). It was mixed with a Spinix vortex shaker ( Tarsons, India) for 2 minutes and heated at 85^oC in a water bath for 15 minutes with intermittent shaking. It was allowed to cool at room temperature. The content was diluted to 25 millilitre in a volumetric flask. 1 millilitre of this solution was taken in a test tube and mixed with 40 millilitre water and 5 millilitre I₂/KI solution (0.0025 m I₂ and 0.0065 M KI). The final volume was adjusted to 50 millilitre. This was then left for 15 minutes at room temperature and absorbance was measured at 600 nanometre (nm) by double beam spectrophometer (ELICO, India).

Apparent amylose content

The apparent amylose content of starch was estimated by the above same procedure except starch was taken without defatting. Further, the amylose content was estimated by drawing a standard curve with standard potato amylose (conc. 0.2. 0.4, 0.6, 0.8, and 1.0 mg/ml) (range 0-100% amylose). A line of calibration was plotted. The amount of apparent and total amylose was calculated using a regression equation

(Y=absorbance at 600 nm; X= % amylose).

This was done to correct the overestimation of both types of amylose because of the complex formation between I₂ (Iodine)and the amylopectin’s outer branches.

Amylose complexed with lipids

This was observed after obtaining apparent and total amylase content and calculated by a formula as under Hoover and Ratnayake²².

Effect of temperatures on amylose leaching

The effect of various temperatures on amylose leaching was assessed by the method of Ambigaipalan et al.,²³. In a test tube 20 mg starch and 10 ml of distilled water was taken. The content was heated to different temperatures (65, 75, 85, and 95 ^oC) in a boiling water bath for 30 minutes while being shaken intermittently. The tubes were cooled at room temperature and centrifuged for 10 minutes at 2000xg. Now, 1 milliliter of its supernatant was withdrawn, and the Hoover and Ratnayake²² method was used to assess the amylose content as before.

Least gelation concentration (LGC)

The Adebowal and Lawal²⁴ method was used to assess the LGC of rice bean starch. The sample of starch was dissolved in 5 milliliters of distilled water to get concentrations of 2, 4, 6, 8, 10, 12, and 14% (w/v). The tubes were cooled to room temperature after 30 minutes at 90 ^oC in a water bath. All of the suspensions were stored in a refrigerator at 10±2^oC for 2 hours. By inverting the tube, the coagulum’s strength was assessed. The gelation end point, or least gelation concentration, was defined as the sample concentration at which no longer formed a stable gel and remained in an inverted test tube.

Emulsion capacity and emulsion stability

Analysis of emulsion capacity and emulsion stability was done by using Kinsella²⁵ method. 5 millilitres of distilled water was added to half a gram of starch (0.5 g) in an Erlenmeyer flask. It was mixed with a magnetic stirrer (TARSONS, India) at 1000 rpm for 15 minutes. Over a 5-minute period, 5 ml of refined soybean oil was added and the mixture was agitated at 1000 rpm. The suspension was transferred to a centrifuge tube treated in a shaking water bath ( NSW-100, India) maintained at 85^˚C for 15 minutes. This was cooled for 15 minutes in a water bath at 25^o

C and then centrifuged at 3500 rpm till the height of the oil was constant. Results were expressed as a percent of emulsion after separating the upper layer from the emulsion.

Water and Oil absorption capacity

Analysis of water and oil absorption capacity was done by the method of Beuchat²⁶. 10 ml of distilled water and oil was added to 1.0 gm of starch sample in different test tubes. The content of both the tubes were mixed properly. It was let to stand at 21˚C for 30 minutes. The material was centrifuged at 5000xg  for 30 minutes,  A 10 milliliter graduated cylinder was used to record the volume of supernatant. The mass of oil/ water absorbed is expressed as g/g starch on a dry weight basis.

Color analysis

Hunter Colorlab ( 45/0 LAV) was used to measure the color of the isolated starch in terms of whiteness, and L*, a*, and b* values were anticipated. A sample cup was used, and it was set on the port plate to hold the sample cup. The sample cup was covered with an opaque cover and the color value was measured directly that was displayed on the screen.

Effect of temperatures on swelling power and solubility of starch

The solubility and swelling power of starch was determined at concentrations of 1%, 2%, 3%, and 4% by the method of Lauzpnet et al.,²⁷. The starch suspension—0.25, 0.50, 0.75, and 1.0g of starch, respectively, in 25 milliliters of distilled water—was heated for 30 minutes at various temperatures (55, 65, 75, 85, and 95⁰C), while being continuously shaken. This was followed by a quick cooling period to room temperature and 15-minute centrifugation at 1900xg. The % solubility and swelling power were then calculated by the standard formula.

Effect of temperature and concentration on freeze-thaw stability

The method of Hoover and Ratnayake²⁸ was used to study freeze-thaw stability of starch. It was conducted at three concentrations for rice bean starch (6%, 8%, and 10%) and stability was checked for five freezing cycles (day 1-5). For sixteen hours, starch gels were kept at 4 ^oC for 16 hours. The gels were further kept in frozen storage for a full day at -16^oC. The gel tubes were centrifuged at 2000xg for 20 minutes after being frozen for 6 hours at 25 ^oC. The amount of water (ml) removed from each tube was calculated.

Effect of storage and temperature on paste clarity of starch

The Peera and Hoover²⁹ approach was used to determine it. The starch suspension (1% starch solution in distilled water) was boiled in a boiling water bath for an hour while being continuously stirred. It was then cooled to room temperature in the two different test tubes. The tubes were stored for 1-7 days at 4^oC and 30^oC. The paste clarity was assessed by obtaining absorbance values of suspensions  displayed on the UV Spectrophotometer (ELICO, SL-177 Scanning mini spec) at 640 nm against distilled water taken as blank. The observation was continued for 7 days to study the storage effect on the clarity of starch paste.

Statistical analysis

All the results were reported in triplicates for all the properties and their mean values ±SD (standard deviation of mean) were predicted. Statistical software (SPSS 19.0) was used for statistical analysis. One way analysis of variance (ANOVA) at a significant difference level of p˂0.05 was used to analyze the data.

Results and discussion

Chemical composition

The isolated starch from legume was analyzed for the chemical composition and the results were displayed in Table 1. The values are presented as mean±SD. The extraction yield of starch was 25.79% (Table 1) It was comparatively higher than beach pea (12.30%) legume starch previously studied³⁰  but lower compared to starches extracted from black gram (45%), pea (40%), and red bean (46%) and this may be attributed to the compact association of granules of starch with other biomolecules³¹. It is challenging to extract the starch from legume seeds because they include fine fiber and flocculent proteins, which sedimented as a brown layer with the starch during separation.²⁰. The dilute alkali has been used by some investigators for more efficient isolation of starch³².

Table 1: Chemical composition of rice bean starch

The values are depicted as the mean ±SD of three independent determinations

The moisture, protein, and fiber were found to be 9.56%, 0.69%, and 0.33% respectively (Table 1). The low moisture level of the starch (0–10%) made it safe for storage and subsequent analysis without running the risk of fatty acid microbial degradation. ³³. The ash content of rice bean starch was 0.35%. The “Fine fibers” are components that contribute to the greater ash content of starch and also affect the whiteness of starch.³⁴. The present study shows the lipid content in starch was 0.21%. Similar results were also reported for ash content (0.24-0.36%) and crude fat content (0.15 to 0.54%) of starches isolated from Nigerian legume starch³⁵. The total carbohydrates (sum of moisture, ash, lipid and protein) were found to be 89.19% in rice bean starch. The quantity of fiber, fat, protein, and ash is usually considered as the purity index of legume starches. The less quantity of these components contribute to the purity of isolated starch³⁶.  

Amylose content

In the present study, apparent amylose content and total amylose content of native rice bean starch were 37.62% and 40.83% respectively (Table 1) which was within the range (21.19% – 60.14%) as previously studied for rice bean starch grown in Himalyan region by Kaur et al., ¹². Total amylose content refers to the defatted amylose content, while apparent amylose content is the assessed amylose before defatting. Amylose content significantly affects starch properties, impacting food characteristics. High and low amylose starches display different structures, affecting physicochemical characteristics (pasting, swelling, texture etc) during various applications.³⁷–³⁸. Colorimetric techniques based on iodine complex production can be used to estimate amylose. However, amylopectin interference may cause an overestimation. Consequently, propanol should be used to defatt starch prior to the final evaluation of amylose.³⁹. The amylose content in legume starches ranged from 24%-88% as reported previously in various legumes³⁴. Moreover, during the studies of mung bean starch  the researchers reported amylose content varying from 37-42%⁴⁰.  It is preferable for the starches to have a higher amylose content while making noodles. ⁴¹. The lipids that are bound to amylose are called as amylose-lipid complex. The rice bean starch contains 7.90% of amylose-lipid complex. Amylose-lipid complexes are insoluble in water and require higher energy for dissociation, while amylose bonded with lipids remains intact within starch granules.^42-43.

Effect of temperature on amylose leaching

Fig. 1 illustrates the amylose leaching of rice bean starch and the impact of temperature on leaching. As the temperature increased from 65°C to 95°C, there was a significant variation in the leaching of amylose (p ˂ 0.05), ranging from 6.56% to 9.50%. Below 65°C, there was no amylose leaching, indicating that the starch molecules in the structure had strong bonds with one another²⁸. Legumes have high amylose concentration, reducing swelling and amylose leaching at low temperatures (˂ 65°C) ⁴⁴. However, at 90°C, amylose leaching increases due to crystalline amylopectin swelling in water, causing the suspension to leach out⁴⁵. Heat can weaken amylopectin structures, releasing amylose, potentially affecting gelatinization properties of starch⁴⁶. Relationship between swelling power, starch solubility, and amylose leaching may exist. ^47-49. Similar results of amylose leaching were also observed in the previous studies for navy beans and northern bean as 3.5%-9.0% and 3.8%-9.50% respectively⁴⁷. Amylose leaching is influenced by the apparent amylose content, bound lipids, and interactions between amylose-amylopectin and amylose-amylose chains, with a higher amylose lipid complex causing less leaching.⁵⁰.

Figure 1: Effect of temperature on amylose leaching of rice bean starch Click here to view Figure

Gelation properties

The least gelation concentration of native rice bean starch was observed at 8.0% (Table 2). At this concentration, a soft, complete gel was seen to develop. However, as the concentrations increased higher, the gel hardened and fractured. In previous studies the LGC of a legume (Jack bean, Nigeria) was observed at 8% similar to the present study and gel become harder at increased concentrations⁵¹.  Since the LGC and water absorption capacity of starches are connected, the high water absorption capacity of starches contribute to good gel forming ability⁵¹. Moreover, it  is affected by the physical competition of water for its availability in starch gelatinization and protein gelation⁵².The gelation temperature is the point at which starch takes on the consistency of gel, whereas the least gelation concentration is the lowest concentration of starch required to make a soft gel⁵³. Starch absorbs water during gelation, which causes the granules to enlarge and ultimately create a three-dimensional structure through the process of gelatinization. It occurs due to the formation of the structural network in the starch granules by H-bonding as intergranular binding⁵⁴.

Emulsion capacity and stability

The emulsion capacity and emulsion stability of native rice bean starch were 68.33% and 79.00% respectively (Table 2). The ability of proteins to produce a stable emulsion is referred to as emulsion capacity, and it is associated with the ability of proteins to absorb water and oil in the interfacial area of an emulsion. The stability of the emulsion is assessed by evaluating the proteins’ ability to fortify the emulsion’s resistance to alterations and stress. As a result, it is related to the interfacial area’s consistency throughout a certain time period.⁵⁵. The findings were in line with research conducted by Du et al., that the emulsion capacity of black beans, navy beans, and black eye beans was 67.82%, 66.94%, and 67.02%  respectively. Additionally, the pinto bean and red kidney bean emulsion stability was 84.15% and 86.54%, respectively. The researchers also observed that water and protein interactions occur in the polar amino acid areas of protein molecules⁵⁶. Most proteins have different polar side chains that contain peptide groups from parent chains. These chains result in hydrophobic areas that affect the molecules’ solubility and emulsification potential.⁵⁷.

Table 2: Hydration and physical properties of rice bean starch

The values are depicted as the mean ±SD of three independent determinations

Water and oil absorption capacity

The water and oil absorption capacity of native rice bean starch was found to be 2.60% and 2.54% respectively (Table 2). Water absorption capacity plays a crucial role in the preparation of food as it affects sensory attributes and other functional properties⁵⁸. It is the amount of water retained after compression or external centrifugal force whereas oil absorption capacity is a functional property related to the physical entrapment of oil⁵⁹. The ability of starch to retain oil is a measure of emulsifying property that is important to retain flavour and increase the mouth feel of the food product⁶⁰. Water absorption and retention are crucial for food system texture, with legume starches having lower water absorption capacity due to less amylose content⁶¹. It is affected by various parameters like conformational characteristics, size, shape, steric properties, fats and carbohydrates associated with proteins, hydrophilic-hydrophobic balance in starch molecules, thermodynamic properties of the system, solubility of the starch molecule and physicochemical environment etc⁶². The present results were comparable with the studies of Sathe & Salunke⁶³. They observed the water and oil absorption of great northen bean starch as 2.93g/g and 2.94 g/g respectively. The swelling power and the solubility of starch are inversely correlated with the water absorption capacity of legume starches⁶¹. Researchers  reported that raw legume starches had a water absorption capacity of less than 10 g/g^63–65. These findings were consistent with the findings of the current investigation.

Pigmentation

The L*, a*, and b* values of native rice bean starch were 94.23, 0.48 and 5.78 respectively (Table 2). The components like beta-carotene and polyphenolic compounds are present in plants and may influence the degree of whiteness in starch. Additionally, these phytochemicals affect the quality of starch, which may affect the final color of the product³⁶. To satisfy consumer preferences, it is essential that the starch must have a low chroma value (b*) and high lightness value (L*) The red-green color axis is quantified using the a* value. More red tones are present when a* has a positive value, while more green tones are present when a* has a negative value. Similarly, a metric for measuring the color axis that runs from yellow to blue is the b* value. More yellow tones are present when the b* value is positive, while more blue tones are present when the b* value is negative. Rice bean starch can be used in food applications i.e., pasta products⁶⁶.  The value of L* (94.23) in the present study showed that the value is very high towards the whiteness so the isolated starch is pure and light in color which further indicates its applications in various foods where the equality in color is predominant. Moreover, protein and ash in starch are negatively related to the lightness of starch⁶⁷.

Effect of temperature on swelling power and solubility

Swelling power and solubility depict the interaction within crystalline and amorphous regions within the starch chains⁶⁸. The swelling power and solubility at different temperatures (55 to 95°C) and the effect of concentration (1 to 4%) are shown in Fig. 2-3 and Table 3-4. The swelling power of rice bean starch significantly increased (p ˂ 0.05) as the temperature increased from 55- 95°C . It ranged 2.50 – 20.53g/g, 2.19 – 12.08g/g , 2.00 – 10.79g/g  and 1.94 – 9.80g/g at 1%, 2%, 3% and 4% starch concentrations respectively (Table 3). Similarly, solubility of native rice bean starch was in the range of 2.31% – 12.85%, 1.56% – 7.84%, 1.14% – 6.53% and 1.04% – 6.37% at 1%, 2%, 3% and 4% respectively with the elevated temperature from 55- 95°C (Table 4). The internal associative forces that keep the structure  of granule intact, diminished as temperature increased.⁶⁹

Figure 2: Effect of temperature on swelling power of rice bean starch Click here to view Figure

(1,2,3 and 4 shows the 1%, 2%, 3% and, 4% starch concentration respectively)

Figure 3: Effect of temperature on solubility of rice bean starch Click here to view Figure

(1,2,3 and 4 shows the 1%, 2%, 3% and, 4% starch concentration respectively)

Swelling power indicates water absorption, while solubility measures dissolution. Heat causes disruption in starch granules, causing hydroxyl groups to link with water molecules, increasing swelling and solubility.⁷⁰. The swelling power and solubility of starch are significantly influenced by factors such as amylose-to-amylopectin ratio, chain length distribution, phosphate concentration, amylose leaching, and amylose lipid complexes^71-72.

Furthermore, swelling power and solubility showed the reverse trend and decreased as the concentration of starch increased from 1% – 4%. The swelling power decreased to 1.93g/g as concentration increased to 4%  at 55°C. While, at the temperature  95°C the swelling power decreased to 9.65g/g  as concentration increased to 4%. A similar trend was observed for solubility. It decreased to 1.00%  as concentration increased to 4% at 55°C and at temperature  95°C it decreased to 6.39% as concentration increased to 4%.

Table 3: Effect of temperatures and concentrations on swelling power (g/g) of rice bean starch

The values are depicted as the mean ±SD of three independent determinations

Values in same column having different superscripts are different significantly (p<0.05)

Table 4: Effect of temperatures and concentrations on solubility (%) of rice bean starch

The values are depicted as the mean ±SD of three independent determinations

Values in same column having different superscripts are different significantly (p<0.05)

Effect of Storage and concentration on freeze-thaw stability

Freezing is one of the method used to enhance the shelf life of perishable foods and could be used as an indicator of tendency to retrograde starch ⁷³. In the present study the starch gels at 6%, 8% and 10% concentrations were stored in freezing conditions for 5 days. The gels were taken out each day, centrifuged and water released was measured in ml. The results in Table 5 depicted that the water leached out was significantly more (p<0.05) on the first day at all the concentrations and decreased till 3^rd day of storage. The expelled water was 9.80 ml,  1.67 ml, and 0.9 ml on 1^st, 2^nd and 3^rd day storage respectively (6% concentration) while it was 7.84 ml, 1.03 ml and 0.6 ml (8% concentration), and 4.34 ml, 0.98 ml and 0.42 ml (10% concentration)  on 1^st, 2^nd and 3^rd days of successive storage respectively. Moreover, there was no water expelled after 3^rd day of storage. This can be ascribed to the reason that the  water content of gels decreased after the first and second storage intervals due to its re-freezing after the first storage cycle⁷⁴.Temperature and storage changes can cause ice crystals in frozen food products, causing deterioration due to thermal fluctuations and water phase changes^74-75.

Moreover, retrogradation led to the removal of water from rice bean starch gels during the production of ice crystals when the gels were kept in a freezing conditions. These ice crystals melt to separate water as they thaw at room temperature. No syneresis on 4^th and 5^th day showed good freeze-thaw stability. Furthermore, the gels changed from a smooth structure to a sponge-like structure (rough textured porous gel) during the freeze-thaw cycles. The separated water was able to reabsorb due to rough and porous gel structure.⁷⁶. Therefore, there was no syneresis on the 4^th and 5^th day of gel storage.

The present study also observed the effect of concentration of starch on freeze-thaw stability (Table 5). The expelled water was significantly (p<0.05) more at 6% concentration. The increased concentration of starch in gels or pastes led to lower syneresis and long-term thermally reversible gel stiffness, attributed to amylopectin involved in crystallization⁷⁷. Additionally, in earlier research, the maximum amount of free water in both wheat flour paste and regular corn starch was 6% rather than 8% or 10% concentration. ⁷⁸. The extent of syneresis in legume starches depends on their higher amylose content as it leads to a higher extent of retrogradation⁷⁹.

Table 5: Effect of concentration and storage on freeze-thaw stability of rice bean starch

The values are depicted as the mean ±SD of three independent determinations

Values in same column having different superscripts are different significantly (p<0.05)

Effect of storage and temperature on paste clarity (turbidity) of starch

Paste clarity is an important factor in determining the quality of starch paste as high reflection and less light intensity improve color in the finished product⁸⁰. The paste clarity of starch suspensions was evaluated at two temperatures (30°C and 4°C) (Table 6). The values for the starch paste clarity are given as the percentage absorbance read directly in a spectrophotometer. On the first day, it was found to 0.267 followed by 0.715, 1.002, 1.008, 1.022, 1.027 and 1.031 on successive days at 30°C. Similarly, the absorbance values increased from 0.0849 on the first day followed by 1.200, 1.211, 1.345, 1.418, and 1.534 on successive days at 4°C. It was depicted from the table that absorbance values increased with the storage time and more at refrigeration temperature than the room temperature . The rearrangement of solubilized starch chains and the retrograded starch formation at lower temperatures, there is a rise in turbidity in starch suspensions during cold storage⁸¹.

The effect of storage (1-7 days) on paste clarity was also observed (Table 6) in the present study. The extent of retrogradation of starch increased with the enhancement of storage period so gel became more and more cloudy as storage exceeded⁸². Starch gels stored at room temperature have less retrogradation tendency and better paste clarity compared to those stored in refrigeration⁸³. Polymer-polymer aggregation plays a significant role in a polymer-solvent system, with amylose chains causing crystallization within hours and amylopectin chains causing crystallization over longer storage days, resulting in increased light absorption^82,84-85.

Table 6: Effect of storage and temperature on paste clarity (turbidity) of starch

Conclusion

In the present study, we examined the physicochemical properties of rice bean starch. Various parameters like moisture, ash, fat, protein, fiber, carbohydrate content was evaluated. Further, water and oil absorption capacity, emulsion capacity and stability, least gelation concentration, amylose content, complexed amylose with lipids, and starch pigmentation properties were evaluated. The effect of temperature showed a positive relationship with amylose leaching. Similarly, there was a positive relationship between swelling power and solubility with temperature but a negative relationship with the concentration of starch. Moreover, freeze-thaw stability increased with the storage period and concentration of starch. The starch paste clarity was more at 30°C than at 4°C. Our experimental results would provide necessary information to the food industry making use of non-conventional source of starch rather than conventional starch sources like potato, corn, rice, cassava, chestnut, wheat, etc. Understanding the properties of this legume starch will provide valuable perspectives on the innovative application of legume starch. The rice bean starch can be used to modify the texture of food products such as soups, frozen foods, noodles, cookies, pasta, crackers, sauces and extruded snacks. The future food scientists may study the various properties of starch by blending of 2 or more starches (conventional or non-conventional) that may enhance the application of legume starch without going any kind of modification because modification leads to structural changes and sometimes affect health as some kind of enzymes or chemicals used in such starch modification process. Consuming native starch has no health issues. Therefore, this study may be helpful for future scientists to better understand its properties for various uses in food industries.

Acknowledgment

We acknowledge the Department of Food Technology, Maharshi Dayanand University, Rohtak for providing the infrastructure, chemicals, and continuous support during the research.

Conflict of Interest

There is no conflict of interest declared by the authors.

Funding Sources

The funding for the research was provided as the University Research Fellowship by Maharshi Dayanand University, Rohtak, Haryana, India.

Author’s contribution

Sapna Dhawan Munjal: Writing – original draft, Methodology, Conceptualization, Visualization, Data curation. Jyotika Dhankhar: Writing – review & editing. Alka Sharma: editing, and, Supervision. Prixit Guleria: Statistical analysis of results

Data Availability

Not applicable

Ethics Approval

Not applicable

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