The Impact of Starch Properties on Noodle Making Properties of Indian Wheat Flours

Abstract

The physico-chemical and noodles making properties of flour milled from three bread (PBW-154, PBW-343, and PBW-373) and one durum (PDW-233) wheat cultivars were studied. Noodles were evaluated for cooking and textural properties. The starches were also separated from these cultivars and investigated for morphological, thermal, rheological, and retrogradation properties. Protein, ash, SDS sediment value, and swelling power of flour milled from different varieties varied between 10.0–10.9%, 0.53–0.71%, 19.5–33.5 mL, and 7.4–9.8 g g⁻¹, respectively. Falling number values of flours indicate that the flour had been milled from sound wheat. PDW-233 grains showed highest fracture force while flour from PBW-154 cultivar showed highest SDS value (33.5 mL). The noodles prepared from PBW-154 flour showed lowest cooked weight, highest oil absorption, and highest amylose content. The amylose content of starches separated from different wheat cultivar varied between 20.5 and 29.2%. The starches from all the wheat cultivars had a granule size ranging between 8 and 25 µm and granules shape varied from oval to spherical. PBW-373 starch had largest average granule size while PBW-343 starch showed the smallest average granule size. The transition temperatures, enthalpy of gelatinization (ΔH _gel), enthalpy of retrogradation (ΔH _ret), peak height index (PHI) and range were determined using differential scanning calorimetry (DSC). PBW-343 starch showed highest onset temperature, peak temperature, and conclusion temperature of 61.4, 65.3, and 70.1°C whereas PDW-233 starch showed the least values of 58, 62.1, and 67.6°C, respectively. The ΔH _ret of gelatinized starch from all wheat cultivars was determined after 2 weeks of storage at 4°C. PBW-373 starch showed the highest ΔH _gel and ΔH _ret while PBW-343 showed lowest values for the same. The retrogradation (%) was observed to be highest in PDW-233 starch and lowest in PBW-343 starch. The synersis (%) was observed to be highest for PBW-343 starch, which increased during storage of starch pastes from all the varieties. The swelling power of flour was observed to be associated with noodle textural properties. The flour showing lower swelling power and small starch granules resulted into noodles having higher hardness, chewiness, cohesiveness, and packability.

Keywords:

• Turbidity
• Amylose
• Noodles
• Texture
• Wheat starch

Introduction

Starch is an important structural component in many foods. The starch is present in the form of granules that are insoluble in water at room temperature. The granules contain ordered regions, which are semi-crystalline and show birefringence. Most starches consist of a mixture of two polysaccharides, amylose and amylopectin. The molecular weights and the fine structure of amylose and amylopectin vary with the botanical source. Heating starch granules in excess of water results in melting of starch granules, with loss of x-ray crystallinity. This phenomenon depends upon temperature, amount of water present, agitation during heating and is called as gelatinization. Starch transition temperatures and gelatinization enthalpies by differential scanning calorimetry (DSC) had been related to characteristics of starch granules, such as degree of crystallinity by Krueger et al.1 It causes melting of starch granules, granules swell many times their original size, depending upon space available. These changes in starch granules are accompanied by separation of amylose and amylopectin, which results in leaching of amylose out of granules. Stevens and Elton2 applied DSC in many studies of thermal properties of starch, since its first use. Differential scanning calorimetry has been frequently used in the study of phase transitions of starch. The results have shown to be dependent on the water content, the ratio of components in the mixture, and the heating rate in the calorimeter scan. During cooling and storage, the structure of most products with a high degree of starch content also changes, mostly resulting in a decrease in quality. These changes are jointly known as retrogradation. Starch retrogradation has been extensively investigated in relation to starch gels using DSC. Starch retrogradation is divided in two kinetically different processes: first the amylose fraction undergoes rapid gelation, implying formation of double helices in various chain segments and second amylopectin short chains recrystallize at a much lower rate compared with amylose. Differential scanning calorimetry has been used to study the gelatinization behavior for many different starches, but so far there has been no extended study to relate the DSC parameters with the end use quality of starch.

Noodles differ widely in many aspects such as ingredients, method of preparation, color, and texture. Both cooking time and protein content of samples significantly influenced cooking loss as observed by Dexter et al.3 Most noodles are made from flours of 8–10% protein and 0.36–0.40% ash. Good surface appearance, favorable texture, minimal cooking loss, and high yield are important noodle quality characteristics associated with flour. Kruger et al.4 reported a decrease in raw noodle brightness and an increase in yellowness when using flours of decreasing flour refinement. Cooked noodle properties on the other hand are not affected much to a large extent by difference in flour refinement. Cooking loss is also an important factor for evaluating starch noodles. Starch structure of noodles is maintained as a ramified three-dimensional network that is interlinked by amylose based crystallites as reported by Mesters et al.5 Amylose networks swell during boiling in water due to hydration of amorphous regions. Matsuo et al.6 reported that proteins act as an essential structural component in noodles during cooking causing noodle strands to integrate and maintain their form during cooking. Lipids form an amylose–lipid complex, minimizing cooking losses. Toyokawa et al.7 reported a correlation between hardness of cooked noodles and amylose content and observed that primary starch fraction of flour appeared to be most responsible for the desirable viscoelastic texture of cooked noodles. Oh et al.8 found out that the protein content of flour influenced the chewiness of cooked noodles. Oh et al.9 reported that gluten fraction most influenced the cooked noodle strength and surface and that the primary starch and water-soluble fractions did not effect any noodle quality factors. The objective of present study was investigate noodle making properties of flours of different wheat cultivars as well as to compare morphological, thermal, and retrogradation properties of starches separated from three Indian bread and one durum wheat cultivars.

Materials and Methods

Sample Procurement

Three bread wheats (PBW-154, PBW-343, PBW-373) and one durum wheat (PDW-233) variety was procured from Punjab Agricultural University, Ludhiana, India from the 2000 harvest.

Fracture Force of Wheat Kernels

The fracture force was measured on Instron Universal Testing Machine. A speed of 50 mm min⁻¹ was used for fracturing the kernel using a load cell of 500 N. The wheat kernel was placed with its crease facing the platform of the testing cell. The maximum force observed during the snapping of kernel into two halves was measured as fracture force.

Milling of Wheat

The moisture content of wheat samples was determined using MG53 Halogen Moisture Analyzer (Mettler Toledo). Wheat was conditioned to 13.5% moisture level by adding required amount of water. The wheat was conditioned in refrigerator for 24 hours to equilibrate moisture content. Then milling of wheat cultivars was done in a Brabender Quadrametric Junior Mill (Duisberg, Germany). The flour obtained was stored in airtight containers till further use under ambient conditions.

Flour Properties

The flour obtained from four wheat cultivars was analyzed for protein (%), ash (%), falling number, SDS sedimentation value, water solubility index, and water absorption capacity and swelling index. Protein, ash, and falling number were determined by using AACC method.10 SDS sedimentation value was determined using method of Axford et al.11 Water solubility index and water absorption index was determined using method of Anderson et al.12 13

Swelling power was determined by taking 1 g of flour sample to which 30 mL distilled water was added. The mixture was heated at 90°C for 30 min with constant stirring. The sample was transferred to centrifuge tubes after cooling to 25°C, the sample was centrifuged at 1000×g for 20 min, and supernatant was removed using a pipette. The swelling power (g g⁻¹) was calculated as the weight of sedimented gel divided by the original weight of flour.

Noodle Making

The dough was prepared by mixing 200 g flour with desired quantity of distilled water by mixing in a three-pin mixer (National Man. Com., Lincoln, Nebraska) for 3 min. The dough was removed from mixer and rested for 15 min in a bowl at 30°C.

The noodles were prepared by extruding 200 g of dough through a hand operated extruded machine fitted with 1.5 mm die. Immediately after extrusion, the noodles were dried and fried in cottonseed oil, heated to a temperature of 190°C for 14 s in electrically operated frier (Kenwood). After frying, noodles were placed over filter paper to remove excess oil and were cooled to room temperature.

Noodle Cooking Properties

Gruel Solids Loss

Ten gram noodles were cooked to optimum cooking time in 200 mL of distilled boiling water in a 250-mL beaker, determined in preliminary experimentation by squeezing noodles between two glass slides at different cooking times until the disappearance of white core in noodles. The beaker was covered with aluminum foil to minimize evaporation losses. The cooked noodles were drained and rinsed with distilled water in Buchner funnel for 1 min. Gruel solids loss was determined by drying an aliquot of cooking water in an oven at 110°C for 12 hours in a preweighed petridishes. The residue was weighed after cooling petridishes in a dessicator.

Oil Absorption

Soxhlet apparatus was used to determine fat absorbed by noodles. Extraction of fat was carried out for 10–12 hours using petroleum ether by AACC method.10

Textural Properties

Textural properties of noodles were determined using Back Extrusion Test. A stainless steel cylinder with a flat base plunger having a diameter of 40 mm and an annular gap of 2 mm was used to conduct Back Extrusion Test. Cooked noodles (50 g) were cooled to 25°C and were placed in the test cylinder. Before conducting the test, the noodles were pressed with 150 g weight for 30 seconds. The test was conducted on Instron Universal Testing Machine (Model 4464, Buckling, Hampshire, UK) using 500 N load cell at cross head speed of 100 mm min⁻¹. A force distance curve (Fig. 1) was obtained from the test and following texture parameters determined:

1.	Packability (mm): It is the distance traveled by plunger before an average linear slope is reached.
2.	Hardness (N mm−1): It is the average slope of the initiate linear portion of the curve.
3.	Cohesiveness (N): It is the force required to initiate shear and extrusion.
4.	Maximum force (N): It is the maximum force observed during back extrusion of noodles.
5.	Chewiness (N mm): It is the area under the force distance curve.

Figure 1. Typical force–displacement curve for noodles prepared from PBW-343 flour during back extrusion testing.

Starch Isolation

Uniform sized grains were selected from each cultivar before starch isolation. The initial moisture content was determined and water added to bring final moisture content to 13.5% in each cultivar. The grains were left undisturbed for 24 hours and milled in Brabender Quadrumatic Junior Mill, Germany. The flour obtained was used for preparation of dough. A stiff dough was prepared by mixing 100 g of flour with 45–55 mL of distilled water in laboratory mixer (National Manufacturing, USA). The dough ball was covered with moist cheese cloth and rested at 30°C for 1 hr. Starch was washed from dough ball by kneading under a stream of distilled water, dough being kneaded by hand over nylon bolting cloth (No. 20 XX) drawn over the mouth of 2-L beaker. Cloth with mesh openings of 70 µ will pass all starch granules but will hold most of the cell wall and gluten particles. Starch slurry in beaker was wet sieved twice through bolting cloth; bran and endosperm cell-wall impurities were retained on the cloth together with a small amount of starch in a gelatinous of impurities. Starch in slurry was packed down firmly by centrifuging in 250 mL wide-mouthed polyethylene bottles at relative centrifugal forces of 2500×g for 10 min. The upper pigmented fraction was carefully removed by scraping with metal spatula. Resuspending in distilled water, centrifuging, and again scrapping off any tailings remaining further purified the prime starch thus separated. Four such purification cycles were carried out. The prime starch was dried in a cabinet hot air drier at 40–45°C. During drying, clumps were broken manually to prevent formation of hard masses.

Amylose Content

Amylose content of the isolated starch was determined by using method of Williams et al.14

Swelling Power and Solubility

Swelling power and solubility were determined in triplicate using 2% aqueous suspension of the starch by the method of Leach et al.15

Turbidity

Turbidity of starches from different cultivars was measured as described by Perera and Hoover.16 The aqueous starch suspension (2%) from different wheat cultivars was heated in a boiling water bath for 1 h with constant stirring. The suspension was cooled for 1 h at 30°C. The samples were stored for 5 days at 4°C in a refrigerator and turbidity was determined every 24 h by measuring absorbance at 640 nm against a water blank with a Shimadzu UV-1601 spectrophotometer (Shimadzu Corporation, Kyoto, Japan).

Scanning Electron Microscopy

Scanning electron micrographs were obtained at 1000× with a scanning electron microscope (SEM) (Joel JSM-6100, Jeol Ltd., Tokyo, Japan). Starch samples were suspended in ethanol to obtain a 1% suspension. One drop of the starch–ethanol solution was applied on an aluminum stub using double-sided tape and the starch was coated with gold–palladium (60:40). An accelerating potential of 10 kV was used during micrography.

Thermal Properties

Thermal properties of isolated starches were analyzed using a DSC-821 (Mettler Toledo, Switzerland) equipped with a thermal analysis data station. Starch (3.5 mg, dwb) was weighed into a 40-µL capacity aluminum pan (Mettler, ME-27331) and distilled water was added with the help of a Hamilton microsyringe to achieve a 70% starch–water suspension. Samples were hermetically sealed and allowed to stand for 1 h at room temperature before heating in DSC. The DSC analyzer was calibrated using indium and an empty aluminum pan was used as a reference. Sample pans were at a rate of 10°C min⁻¹ from 20°C to 85°C. Onset temperature (T _o), peak temperature (T _p), conclusion temperature (T _c), and enthalpy of gelatinization (ΔH _gel) were calculated automatically. Besides the peaks were symmetrical, the gelatinization range (R) was computed as (T _c−T _o) as described by Vasanthan and Bhatty.17 Enthalpies were calculated on starch dry basis. The peak height index (PHI) was calculated by the ratio ΔH/(T _p−T _o) as described by Krueger et al.1

After cooling, the samples were stored in the refrigerator at 4°C for 7 days. Retrogradation was measured by reheating the sample pans containing the starches of four cultivars at the rate of 10°C min⁻¹ from 20°C to 85°C. The enthalpy of retrogradation (ΔH _ret) was calculated automatically and percentage of retrogradation (%R) was calculated from the ratio of ΔH of retrogradation to ΔH of gelatinization.18

Statistical Analysis

The data of the parameters except fracture force observed are average of triplicate observations. The fracture force data observed is average of 10 observations. The data was subjected to statistical analysis using Minitab Statistical Software (State College, PA).

Results and Discussion

Fracture Force of Wheat Kernels

The fracture force of grain from different wheat cultivars varied between 93 and 187 N. The fracture force of 93, 120, 131, and 187 N for PBW-343, PBW-154, PBW-373, and PDW-233, respectively, was observed. These differences may be attributed to variation in starch granule sizes and occurrence of friabilin. The smaller granules have larger surface area available for noncovalent bonding with the endosperm protein matrices. They also pack more efficiently by producing harder endosperm as observed by Gaines et al.19 Texture of wheat cultivars has been related to starch granule sizes and occurrence of friabilin.20 21

Flour Properties

The physico-chemical properties of flours milled from different wheat cultivars are presented in Table 1. PBW-154 flour showed highest SDS value of 33.5 mL while PDW-233 flour showed a lowest value of 19.5 mL. The falling number was highest for PDW-233 (702 sec) and PBW-154 showed the lowest falling number value (588). PDW-233 flour showed highest ash content (0.71%) followed by PBW-343 flour (0.62%) while PBW-154 flour showed least ash content (0.53%). The protein content for PDW-233 flour (10.9%) was followed by PBW-154 flour (10.6%), PBW-373 flour (10.2%), and PBW-343 flour (10.0%). WAI was highest for PDW-233 flour and lowest for PBW-343 flour. WSI was highest for PBW-343 flour (6.3%), followed by PDW-233 (5.4%), PBW-154 (4.7%), and PBW-373 flour (4.6%), respectively. The swelling power was highest for flour from PBW-154 (9.8%) cultivar and least for PDW-233 (7.4%) respectively.

Table 1 Physico-chemical properties of flour from different wheat cultivars

Physical/chemical tests	PDW-233	PBW-154	PBW-343	PBW-373
SDS sedimentation (mL)	19.5	33.5	28.75	29.75
Falling no. (s)	702	588	608	655
Moisture (%)	12.7	13.2	12.3	12.6
Ash (%)	0.71	0.53	0.62	0.61
Protein content (%)	10.9	10.6	10.0	10.2
WAI (g g^−1)	2.01	1.96	1.82	2.05
WSI (%)	5.4	4.7	6.3	4.6
Swelling power (g g^−1)	7.4	9.8	8.7	7.5

Table 2 Cooking properties and textural parameters of noodles prepared from flours of various wheat cultivars

Physical/chemical tests	PDW-233	PBW-154	PBW-343	PBW-373
Fat absorption (%)	21.4	24.2	20.4	21.6
Gruel solids loss (%)	0.49	0.87	0.42	0.34
Cooked weight (g)	24.0	22.0	24.3	24.4
Packability (mm)	32.0	21.3	18.9	24.2
Max force (N)	171	107	109	150
Cohesiveness (N)	151	100	92	107
Hardness (N mm^−1)	48.9	41.0	40.5	46.5
Chewiness (N mm)	3,321	2,779	2,707	3,699

Noodle Characteristics

The gruel solids loss was maximum for noodles prepared from PBW-154 flour (0.87%) whereas those prepared from PBW-373 showed minimum loss (0.34%) during cooking. The oil uptake by noodles from PBW-154 cultivar was highest as it had highest amylose content. The oil absorption by noodles is very important from both nutritional and cost aspects during commercial processing of noodles. The cooked weight of noodles from PDW-233, PBW-343, and PBW-373 did not differ significantly. PBW-154 noodles showed lowest cooked weight. This may be attributed to higher α-amylase activity of PBW-154 flour as indicated by its lowest falling number value.

Noodle Textural Properties

Figure 1 shows typical force–displacement curve for noodles prepared from PBW-343 flour during back extrusion testing. PDW-233 flour noodles showed highest packability, maximum force, cohesiveness, and hardness values where as PBW-154 flour noodles showed least values for these parameters. PBW-373 flour noodles showed highest chewiness and PBW-343 flour showed the least chewiness. The variation in texture parameters of noodles made from PBW-154 and PBW-343 flour did not differ significantly. The difference in textural parameters may be attributed to difference in flour swelling volume and protein content. The cultivar showing higher swelling power showed lower chewiness, maximum force, hardness, packability and vice-versa. Konik et al.22 related high swelling volume to less firm alkaline noodles. Ross et al.23 observed that noodle texture depends on both starch and protein component. They also observed a positive correlation between SDS sedimentation volume and noodle firmness, however, the magnitude of the correlation coefficient and level of significance were both lower than those observed for protein content. However, the influence of starch on noodle texture was best characterized by swelling volume of flour. Zeng et al.24 observed that low swelling starches of hard wheat produced hardened and elastic starch gels. The present work does not demonstrate any relationship between SDS value and noodle texture. The relation of other factors such as amylopectin/amylose ratio, molecular weight, and gluten on noodle structure cannot be ruled out. Their role in noodle texture needs to be addressed.

Amylose, Swelling Power, and Solubility

Amylose content of starches separated from different wheat cultivars ranged between 20.5 and 29.2%. PBW-343 starch showed least amylose content and PBW-154 starch showed highest amylose content, however amylose content among various starches did not differ significantly (Table 3). Biliaderis and Tonogai25 observed an amylose content of 23.8% in commercial wheat starch. Swelling power and solubility of different starches ranged between 15.0–15.9 g g⁻¹ and 1.35–1.85%, respectively. PBW-373 starch showed highest swelling power. Swelling power of PBW-343, PBW-154, and PDW-233 starch did not differ significantly. This suggests that amylose content is not the main factor affecting the swelling index. The factors such as granule crystallinity, amylopectin, phospholipids, and proteins have been observed to influence the swelling properties of starch by Sasaki and Matsuki.26

Table 3 Amylose content, swelling power, and solubility index of starches from different wheat cultivars

Cultivar	Amylose content (%)	Swelling power (g g^−1)	Solubility index (%)
PBW-343	20.5^a	15.2^a	1.45^a
PBW-373	25.1^b	14.0^b	1.55^ab
PBW-154	29.2^c	15.9^ab	1.35^a
PDW-233	25.9^b	14.2^a	1.85^b

Note: Values with similar superscripts in column do not differ significantly (p<0.05).

The turbidity values of gelatinized suspensions of starches separated from the wheat cultivars did not differ significantly. The turbidity values of starch suspensions from all the wheat cultivars increased progressively during storage, however, increase was significant only after 120 hrs of storage. An increase in turbidity during storage has been reported16 that has been attributed to the interaction between leached amylose and amylopectin chains that led to development of function zones, which reflect or scatter a significant amount of light. Amylose aggregation and crystallization have been observed to be with in the first few hours of storage while amylopectin aggregation and crystallization occurs during later stages by Miles et al.27

Scanning Electron Microscopy

Figure 2 shows the scanning electron micrograph (1000×) of starches separated from different wheat cultivars. The starches isolated from different wheat cultivars differed significantly in granule size and shape. The granules size in different wheat starches ranged between 8 and 28 µm. PBW-154 starch showed the largest average granule size (28 µm) while PDW-233 starch showed the least average granule size (22 µm). PBW-373 showed narrow range of granule size while PBW-154 showed wider range of granule size. All wheat starches showed the presence of large and small granules. However, PDW-233 starch showed highest number of small starch granules followed by PBW-373 starch. Wheat starches from all the cultivars showed the presence of both spherical and oval shape granules, however, spherical granules were predominant. Biliaderis and Tonogai25 observed that size of 2–8 µm for spherical and 18–24 µm for lenticular granule for wheat starch. The variation in size and shape of starch granules may be due to difference in genotype as observed by Raeker et al.28 The morphology of starch granules depends on the biochemistry of the chloroplast or amyloplast, as well as physiology of the plant as stated by Badenhuizeb.29 Davis30 observed granule size between 25–40 µm for large lenticular and between 5–10 µm for small spherical granule. The differences in granule size may be related to the hardness of wheat varieties. PDW-233, being durum wheat had the hardest kernels and showed the greater number of small starch granules. PBW-343 and PBW-154 with minimum fracture force showed least number of smaller granules.

Figure 2. Scanning electron micrography of starches separated from different wheat cultivars (A) PBW-343, (B) PBW-373, (C) PBW-154, (D) PDW-233.

Thermal Properties

The results of DSC analysis of starches separated from different wheat cultivars are summarized in Table 4. Figure 3 presents gelatinization thermograms of starch separated from different wheat cultivars. The transition temperatures (T _o, T _p, and T _c), enthalpies of gelatinization (ΔH _gel) and PHI and range (T _c−T _o) of starches from different wheat cultivars differ significantly. T _o, T _p, and T _c of starches from different wheat cultivars ranged between 58–61.4, 62.1–65.3°C, and 66.7–70.2°C, respectively. PBW-343 starch had the highest T _o (61.4°C), followed by PBW-373 starch (59.2°C), while PDW-233 starch showed the lowest value (58°C). PBW-343 starch showed the highest T _p (65.3) and T _c (70.2°C) while PDW-233 starch showed the lowest T _p (62.1°C). Keetals et al.31 observed lower T _o and T _p value for wheat starch than the values observed in our study. These differences may be due to difference in environment and botanical origin. PBW-154 starch showed highest H _gel value (6.8 J g⁻¹) and PBW-373 showed the lowest ΔH _gel value (5.2 J g⁻¹). The ΔH _gel value observed in the present work fall in the range observed earlier.25 Lee et al.32 observed gelatinization enthalpy of 10.5 J g⁻¹ for normal starch having amylose content of 24% and 15.3 J g⁻¹ for waxy wheat starch. The differences in different starches may be attributed to difference in the proportion of crystallinity in the starch granules as described by Fujita et al.33 The ΔH _gel reflected the loss of double helical rather than crystalline and high transition temperatures have been observed,34 to result from a high degree of crystallinity, which provided structural stability and made the granule more resistant to gelatinization order. The differences in granule shape, percentage of large and small granules, and presence of phosphate esters have been observed to effect the gelatinization enthalpy values of starches and observed that the endothermic peak temperature was 3°C higher for the small granule starch than for large granules.2 Peak height index and R of different wheat starches differed significantly. PDW-233 starch showed highest PHI and R whereas reverse was observed for PBW-373 starch. These differences may be attributed to difference in size and uniformity in starch granules among various varieties. The difference in R-values among the starches from different wheat cultivars may be attributed to differences in crystalline regions in a starch granule as stated by Banks and Greenwood.35 The variation in T _o, ΔH, and R in starches from different cultivars may also be due to differences in amounts of longer chains in amylopectin. Yamin et al.36 observed that longer amylopectin chains require a higher temperature to dissociate completely than that required for shorter double helices.

Table 4 Effect of storage conditions on the absorbance of starches from different wheat cultivars

	Turbidity (absorbance at 640 nm)
Cultivar	0 hrs	24 hrs	48 hrs	72 hrs	96 hrs	120 hrs
PBW-343	0.349^a	0.354^a	0.356^a	0.358^a	0.361^a	0.364^a
PBW-373	0.353^a	0.357^a	0.359^a	0.360^a	0.364^a	0.368^a
PBW-154	0.352^a	0.356^a	0.358^a	0.361^a	0.362^a	0.365^a
PDW-233	0.350^a	0.354^a	0.357^a	0.360^a	0.362^a	0.362^a

Note: Values with similar superscripts in column do not differ significantly (p<0.05).

Figure 3. Differential scanning calorimetry endotherms of starches separated from different wheat cultivars (A) PBW-373, (B) PBW-343, (C) PDW-233, (D) PBW-154.

Retrogradation Properties

The retrogradation enthalpy (ΔH _ret) was lower than gelatinized enthalpy for all wheat cultivars (Fig. 4, Table 5). The ΔH _ret was highest for PBW-343 starch (2.94 J g⁻¹) and lowest for PBW-373 starch (2.27 J g⁻¹). The recrystallization of starch molecules occurred during storage and reheating of aged starch gel in a DSC produced an endothermic transition, which was observed to be absent in freshly gelatinized samples as observed earlier.16 The ΔH _ret values were also observed at lower temperature ranges than for gelatinization as observed earlier by Russel.37 However, the transition temperature of starch did not differ significantly. During storage, the amylopectin fraction progressively re-orders and recrystallization of amylopectin branch chains has been observed to occur in less ordered manner in stored starch gels than in native starches as observed by Ward et al.38 The retrogradation (%) measured as ratio of Δ_ret/Δ_gel showed highest tendency of PDW-233 starch towards retrogradation. The retrogradation (%) of PBW-343 and PBW-373 starch did not differ significantly. The variation in the thermal properties among starches from different wheat cultivars may be attributed to the variation in size, shape of granules, and amylose/amylopectin ratio of starches. Whsitler and Bemiller39 observed that a greater amount of amylose has traditionally been linked to a greater retrogradation tendency in starches, however, in the present study, amylose content varied significantly among wheat cultivars. Therefore, the role of amylopectin, intermediary materials, phospholipids during refrigerated storage can not be ruled out.35 The intermediate materials with longer chains than amylopectin may also form longer double helices during reassociation under refrigerated storage conditions.

Table 5 Thermal properties of starches from different wheat cultivars

Cultivar	T o (°C)	T p (°C)	T c (°C)	ΔH gel (J g^−1)	PHI	R	(%)R
PBW-343	61.4^c	65.3^c	70.2^c	6.6^b	1.67^b	8.8^bc	22.6^a
PBW-373	59.2^b	62.7^a	66.7^a	5.2^a	1.46^a	7.5^a	22.9^a
PBW-154	58.8^ab	63.1^a	67.7^ab	6.8^b	1.57^ab	8.9^bc	25.0^b
PDW-233	58.0^a	62.1^a	67.6^b	6.6^b	1.61^b	9.6^c	27.8^c

Note: T _o, onset temperature; T _p, peak temperature; R, gelatinization range (T _c−T _o); ΔH _gel, enthalpy of gelatinization (dwb, based on starch weight); PHI, peak height index, ΔH _gel/(T _p−T _o); ΔH _ret, enthalpy of retrogradation; (%)R, percentage of retrogradation (ratio of enthalpy of retrogradation to enthalpy of gelatinization). Values with similar superscripts in column do not differ significantly (p<0.05).

Table 6 Thermal properties of starches separated from different wheat cultivars after 7 days storage period at 4°C

Cultivar	T o (°C)	T p (°C)	T c (°C)	ΔH ret (J g^−1)
PBW-343	37^a	48.9^a	58.6^b	2.94^b
PBW-373	36.7^a	47.3^a	58.4^b	2.27^a
PBW-154	37.8^a	48.3^a	56.4^a	2.38^ab
PDW-233	37.8^a	48.8^a	57.4^ab	2.64^ab

Note: T _o, onset temperature; T _p, peak temperature; R, gelatinization range (T _c−T _o); ΔH _gel, enthalpy of gelatinization (dwb, based on starch weight); PHI, peak height index, ΔH _gel/(T _p−T _o); ΔH _ret, enthalpy of retrogradation; (%)R, percentage of retrogradation (ratio of enthalpy of retrogradation to enthalpy of gelatinization). Values with similar superscripts in column do not differ significantly (p<0.05).

Figure 4. Retrogradation enthalpy (ΔH _ret) is lower than gelatinized enthalpy for all wheat cultivars.

Conclusion

The results suggest that the granule size and ratio of small/large granules seems to be main factor responsible for the differences in grain hardness between wheat cultivars. The granule crystallinity, amylopectin structure, protein content, and phospholipids content effect on the various properties of starch may not be ruled out. The swelling power of flour and starch granules was observed to be associated with noodle textural properties. The PBW-154 cultivar showed highest amylose content and highest oil uptake by noodles. The flour showing lower swelling power and small starch granules resulted into noodles having higher hardness, chewiness, cohesiveness, and packability. The relationship between these constituents and starches properties is in progress in our laboratory and will be observed in our future publications. Further work could include DSC on the lipid–amylose complex endotherm, sensory testing of noodle quality, and the question of oil uptake vs. starch/flour properties.