Studies on the Functional Characteristics of Flour/Starch from Wrinkled Peas (Pisum Sativum)

Abstract

Flour and starch from mechanically and field dried peas of two cultivars were evaluated for physico-chemical and functional properties. The noodle making properties of pea starch were also compared with potato starch. Field dried pea flour from both the cultivars showed higher starch content than mechanically dried peas. The field dried pea starch, showed lower water binding capacity, swelling power, and solubility as compared to those from mechanically dried pea starch. The mechanically dried pea starches showed lower retrogradation and higher freeze thaw stabilities compared to field dried pea starches. Pea starch noodles showed significantly lower cooking weight and cooking loss than potato starch noodles. Overall acceptability scores for pea and potato starch noodles did not differ significantly.

Keywords:

• Wet fractionation
• Starch
• Flour
• Retrogradation
• Solubility
• Swelling power
• Water binding capacity
• Freeze-thaw stability

Introduction

There is a large variation in composition and nutritional value of smooth and wrinkled peas as affected by both genetic and environmental factors.1–3 Pea starch, which constitutes 35–60% dry weight, has been recognized as a potential food ingredient.[4] Starch concentration is higher in smooth peas than in wrinkled ones. Pea starches are of interest since their amylose spectrum covers a wide range from 30% in smooth pea starch to over 90% in the starch of wrinkled cultivars.[5] [6] Pea starch, which contains a greater percentage of amylose than do other starches, is characterized by a high gelatinization temperature, resistance to shear thinning, fast retrogradation, and high elasticity of gel. Fast retrogradation and high elasticity of gel are necessary for food products like sausages, other meat products, and gluten free noodles. Resistance of starch paste to shear thinning at high temperature is important for canned foods and extruded snacks.7–9

Only the starch from smooth peas with plain, round to oval granules is produced on a commercial scale. Many problems related to kernel shape, size, and granule structure are encountered during isolation of starch from wrinkled peas.[10] Moreover, difficulties in seed dehulling make effective extraction of starch or protein from wrinkled peas complex.

Laboratory and pilot-scale facilities have been developed for the production of protein and starch concentrates from peas. A difficult fractionation process has been a problem in the utilization of pea starch. Dry method of fractionation using pin milling and air classification for starch separation and protein has been developed.[5] The starchy concentrates are obtained in 50–55% yield by air classification of pea flour and these concentrates can be further refined to give pure starch in 75–80% yield. These processes typically result in high starch damage and low purity of the final starch product.[10] The wet method used water solubilization of protein and removal of by-products by centrifugation. Compared to dry methods, wet methods of legume starch isolation are lengthy, laborious, and costly. Difficulties in the separation of pure starch from peas include a highly hydratable fine fiber and the strong adherence of large amount of insoluble proteins to the starch granules.[11] A method developed by Czuchajowska and Pomeranz[12] for isolation of pure starches and protein concentrate combines elements of both dry and wet fractionation process. This method involves an initial selection of milled legume flour, followed by a simple and fast wet fractionation process.

Pea starch is an excellent raw material used to modify food texture and consistency. Therefore, information on starch properties in the starch water system, such as thermal behavior, rheological properties of paste, and thickening and gelling properties are important to improve the texture of food products containing starch. Textural characteristics of food products vary with the type of starch. Once the characteristics of starch are defined, it is easy to find a suitable application for the starch in food products. The present work was carried out to study various functional properties of starch.

Materials and Methods

Materials

Garden peas of two cultivars (Pb-87 and Pb-88) were procured from the farm of a progressive pea grower of dist. Ludhiana, India. Pea pods of both cultivars were harvested in the month of March, 2001 (125 days after sowing). Pods were shelled manually; grains were blanched in 0.5% KMS (Pot. metabisulfite) solution at 90°C for 5 min and dehydrated at 65°C to final moisture content of less than 10% in a hot air cabinet drier. Other lots of peas of both the varieties were allowed to mature on the plant till the plant foliage dried up. Harvested pods were dried in shade for few days and shelled manually, and grains were further dried in shade to a moisture content of less than 10%. Pea samples were packed in polythene bags and stored in airtight containers for further use.

Milling

Pea grains were graded based on size (diameter) into three grades, i.e., grade I (>8 mm), grade II (8–6.5 mm), and grade III (<6.5 mm) using a grader having sieves with openings of different diameters. Calculated amounts of water were added to weighed pea samples to obtain the final moisture content of 10%. The pea samples were kept in airtight containers overnight, and 1% additional water was added just before milling. Grains of different grades were milled separately by properly adjusting the gap using mini dhal mill developed by C.F.T.R.I. Mysore. Dhal and brokens obtained from all the three grades were mixed and milled to flour using a Buhler experimental roller mill.

Starch Isolation

Six flour fractions obtained during milling were mixed and used for fractionation into starch and water solubles according to the patented wet fractionation process.[12] The sample (200 g) was blended with 500 mL of water for 3 min using a blender. The slurry was then centrifuged at 5000 rpm for 10 min. The supernatant was then decanted, and remaining solid layers were blended in 500 mL of water and centrifuged again. The same procedure was repeated once more. The supernatant was decanted and the precipitate was resuspended in excess of 0.2% sodium hydroxide. After centrifugation, the starch was washed two times with water (neutralized to pH = 7). The supernatant was discarded after each washing. The starch was dried at room temperature and passed through 100-mesh sieve. Yield was expressed as follows:

Physico-chemical Analysis

Samples of pea flour/starch were analyzed for moisture content, crude protein content, sugars, ash content,[13] starch content,[14] crude fiber,[15] amylose content,[16] and water binding capacity.[17]

Swelling Power and Solubility

Determinations of swelling power and solubility were run at temperature interval of 10°C over the range from 55 to 95°C according to the method of Leach et al.[18] The sample (2 g) was suspended in 15 mL of distilled water. The suspension was stirred at a rate sufficient to keep the starch completely suspended. It was placed into a thermostatically controlled water bath maintained at the desired temperature (±0.1°C) and held for 30 min, with continued slow stirring during this period. The sample was then rinsed out into the weighed bottle with sufficient distilled water to bring the total weight of water present to 20 g (including the moisture in the original starch). The bottle was stoppered, mixed by gently shaking, and then centrifuged for 15 min at 2200 rpm. The clear supernatant was carefully drawn off by suction to within ¼ in. of the precipitated paste. An aliquot of the suspension was evaporated to dryness on the steam bath and then dried for 4 h in a hot air oven at 120°C. The percentage of soluble components extracted from the starch was calculated on a dry basis. The remaining aqueous layer above the sedimented starch paste was then siphoned off as quantitatively as possible. The bottle and paste was reweighed, and the swelling power calculated as the weight of sedimented paste per gram of dry-basis starch. The value was corrected for solubles to provide a measurement of swell of the undissolved portion of starch.

Determination of Free Water in Flour/Starch Paste

Free water was determined for flour/starch paste of different concentrations (10–20% db) using the method of Zheng and Sosulski.[19] “Free water” was the water separated by centrifugation from a freshly prepared paste. Free water was determined in 5-cc syringes. A single piece of Whatman #114 filter paper (11 mm dia.) was placed on the bottom of the syringe; 0.2 g Celite (diatomaceous silica, Sigma Chemical Co.) was then added on the top of the filter paper. Water was added to the syringe to moisten the Celite, and then the Celite layer was pounded with a glass rod to ensure a complete seal at the bottom of the syringe. The syringe was placed in a 14 × 95 mm centrifuge tube, and then centrifuged at 5000 rpm for 10 min to remove surplus water from the Celite, after which the syringes were weighed (wt₀). Two to 2.5 g sample was added to each syringe, and the syringe was weighed (wt₁) again. The syringe was then centrifuged at 5000 rpm for 10 min before final weighing (wt₂). Percent free water was calculated as:

Refrigeration and Freeze-thaw Stability

The procedure developed by Zheng and Sosulski[19] for determination of water separation from cooked flour and starch pastes after refrigeration and freeze-thaw was followed.

Paste preparation

The paste (150 g), 20% d.b. (w/w), was contained in 400 mL stainless steel chamber equipped with a mixing blade and heated in boiling water bath for 10 min with a mixing speed of 1000 rpm using a mixer. Sodium benzoate (0.15 g) was added to the 150 g paste sample after cooking to prevent microbial activity during repeated refrigeration or freeze-thaw treatments. The paste was cooled to room temperature (25°C) before free water in fresh paste was determined. Each paste was divided into two 60 g samples contained in 70 mL bottles, which were sealed with screw lid, and stored at either 4°C (refrigeration) or −18°C (freezer).

Refrigeration treatment

The bottles containing flour or starch pastes were stored in a refrigerator at 4°C for 1 wk and then held at room temperature for 6 h before measurement of absorbed water were made. This single refrigerated storage cycle was repeated four times for all samples.

Freeze-thaw treatment

Freeze-thaw treatments were performed by storing the paste in the freezer for 16 h, then thawing at 40°C for 2 h. After determination of absorbed water, the gel was refrozen and thawed to repeat the cycle. All samples were treated with four freeze-thaw cycles.

Determination of absorbed water released

“Absorbed water” was the water removed by centrifugation after refrigeration or freeze-thaw cycle. After each cycle, the gels were sampled for measurement of absorbed water. The 2.0–2.5 g samples were placed in the 5-cc syringes as described for measuring free water. However, the Celite layer was replaced by 0.02–0.03 g of cotton that was packed tightly in the bottom of the syringe with a glass rod. After weighing and centrifuging the sample at 5000 rpm for 10 min and reweighing the sample and syringe, the absorbed water in the gels was calculated by the same formula as for free water.

Net syneresis

Net syneresis was calculated by subtracting free water from absorbed water released after each refrigeration and freeze-thaw treatment.

Starch Noodles

The procedure described earlier[20] was adopted for starch noodle preparation and quality evaluation. Dry starch (95 parts) was mixed with 5 parts of cooked starch (db). A dry starch/water ratio of 1:7 (w/v) was used to prepare cooked starch. The mixture of cooked and dry starch was mixed in a single speed pin head mixer (National Manufacturing Co., Lincoln, NE, USA) for 3 min. It was extruded with a cylindrical hand extruder (1.6 mm diameter openings) to prepare noodles. The noodles were immersed in boiling water for 30 s, cooled in running water for 3 min, and drained. The noodles were dried on a polyethylene sheet at room temperature. The dried noodles were stored in airtight containers. For determination of cooked weight and cooking loss of noodles made from different starches, noodle strands were cut into 5 cm long pieces (10 g) and soaked in distilled water (500 mL) for 5 min. The noodle strands were drained and cooked in boiling water (300 mL) for 5 min. Aluminium foil was used to cover the beaker during cooking to avoid evaporation losses. The noodles were drained, rinsed with distilled water (100 mL), and redrained for 3 min. The wet noodles were weighed for the determination of cooked weight. The rinse water was collected in a preweighed beaker and placed in an air oven at 110°C for 24 h. The residue was weighed and reported as cooking loss (percentage of weight of dry starch noodles before cooking). The cooked noodles were evaluated for sensory quality by a semi-trained panel of six judges using a nine point hedonic scale.

Results and Discussion

Physico-chemical Characteristics of Flour

The protein, ash, starch, fiber, sugars, and WBC (water binding capacity) of flours obtained from different pea cultivars is presented in Table 1. Protein content of pea flours varied between 31.24 and 32.64%. Pb-88 pea flour showed significantly higher protein content than Pb-87 pea flour. Flours obtained from mechanically dried peas from both the cultivars showed significantly higher protein content than those from field dried peas. Kosson et al.[2] documented that the protein content of whole wrinkled peas ranged between 24.69 and 26.32% for different pea cultivars. Daveby et al.[21] reported higher crude protein content at a very early stage of maturity, which later decreased to relatively stable levels. Das et al.[22] analyzed peas after 110 and 120 days of harvesting and reported an increase in crude protein content from the early to late maturity. Pb-88 pea flour showed significantly higher ash content than Pb-87 flour. The flour from mechanically dried peas showed higher ash content than their counterpart from field dried peas; however, the difference was not statistically significant. A decrease in ash content during the development of seeds had been reported earlier.[22]

Table 1 Mean values showing the effect of cultivar and processing treatment on the physico-chemical characteristics of pea flour

Factors	Crude protein (%)	Ash (%)	Starch (%)	Crude fibre (%)	Reducing sugars (%)	Non reducing sugars (%)	Total sugars (%)	WBC (g/g)
Cultivar	Pb-87	31.35	3.08	44.11	5.68	1.29	3.93	5.22	3.26
Pb-88	32.35	3.60	46.70	5.71	1.09	4.19	5.27	3.38
Treatment	Mech. dried	32.05	3.38	44.96	5.13	1.31	4.01	5.32	4.15
Field dried	31.65	3.29	45.86	6.26	1.07	4.11	5.17	2.49
CD (5%)	Cultivar (C)	0.39	0.10	0.47	NS	0.09	0.11	NS	NS
Treatment (Tr)	0.39	NS	0.47	0.16	0.09	NS	0.09	0.13
C × Tr	NS	NS	0.66	NS	NS	NS	NS	NS

Pb-88 flour showed significantly higher starch content than Pb-87 flour. The mechanically dried pea flour from both the cultivars showed significantly lower starch content than field dried pea flours. Kosson et al.[2] found that starch content of whole wrinkled peas ranged between 25.2 and 27.6% for different American pea cultivars. Starch was found to be the main constituent in the dehulled seeds at all stages of harvest, with a rapid increase from very early stages to peak values. After that, the starch content declined slowly.[21] Das et al.[22] did not observe any change in starch content in the peas harvested after 110 and 120 days of sowing. Flours obtained from field dried peas showed significantly higher fiber content than mechanically dried pea flours. The differences may be attributed to the differences in maturity or bran contamination during milling. Fiber content has been reported to increase with seed development.[21] [22]

Pb-87 pea flour showed significantly higher reducing sugar content than Pb-88 pea flours. The mechanically dried pea flour from both the cultivars showed significantly higher reducing sugar content than their counterpart from field dried pea flour. Glucose content has been reported to range between 0.14 and 0.24% in seeds of various cultivars of wrinkled peas.[2] Glucose + fructose content in the dehulled seeds is reported to decrease rapidly from the very early stage of maturity and, thereafter, remained at low level.[21] Pb-88 pea flour showed significantly higher nonreducing sugars than Pb-87 pea flour. The total sugar content of flour obtained from mechanically dried peas was found to be significantly higher compared to field dried pea flour. It has been reported that sucrose content ranged between 1.78 and 2.57% in seeds of various varieties of wrinkled peas.[2] The sucrose content decreased dramatically during early seed development and then stabilized at a low level.[21] WBC of flour obtained from mechanically dried peas was found to be significantly higher than flour from field dried peas. Differences in WBC of flour may be attributed to the differences in starch, protein, and fiber content of different samples.[23]

Physico-chemical Characteristics of Starch

Pb-88 flour showed a significantly higher mass yield of starch than Pb-87 pea flour (Table 2). The field dried peas from both the cultivars showed higher mass yield than mechanically dried pea flours. Pb-88 pea flour showed significantly higher starch yield than Pb-87 pea flour. The mechanically dried peas showed significantly lower starch yield than field dried peas. Meuser et al.[24] reported a starch yield of 89% at laboratory scale and 63–78% at pilot scale process for peas. Pb-88 flours showed significantly higher starch content in the isolated samples than Pb-87 flours. Field dried peas showed significantly higher starch content in the isolated samples than mechanically dried peas. Differences in purity of starch correspond to the starch content of flour samples used for isolation. Czuchajowska et al.[25] reported a purity of 97.5% in starch isolated from wrinkled peas using a wet fractionation process. The starch isolated from mechanically dried pea flours showed significantly higher protein content than starch from field dried pea flours. Higher residual protein content in the isolated starch could be explained by the difficulty in the fractionation process of wrinkled peas due to their high fiber content and composite starch granules.[26]

Table 2 Mean values showing the effect of cultivar and processing treatment on the physico-chemical characteristics of pea starch

Factors	Mass yield (%)	Starch yield (%)	Crude protein (%)	Ash (%)	Starch (%)	Amylose (% of starch)	WBC (g/g)
Cultivar	Pb-87	33.59	72.23	0.88	0.53	94.86	81.22	5.96
Pb-88	35.56	73.67	0.96	0.64	96.75	75.20	5.92
Treatment	Mech. dried	33.80	71.84	1.26	0.62	95.56	78.23	6.47
Field dried	35.36	74.07	0.58	0.54	96.05	78.19	5.41
CD (5%)	Cultivar (C)	0.77	0.96	NS	0.10	0.58	0.76	NS
Treatment (Tr)	0.77	0.96	0.17	NS	NS	NS	0.16
C × Tr	NS	NS	0.24	0.14	NS	1.07	NS

The starch obtained from different pea cultivars showed an ash content between 0.43 and 0.81%. Pb-88 starch showed significantly higher ash content than Pb-87 starch. Czuchajowska et al.[25] reported an ash content of 0.31% in the prime starch obtained from wrinkled peas using a wet fractionation process. The starches obtained from both the pea cultivars showed amylose content between 79 and 87%. Pb-87 starch had significantly higher amylose content than Pb-88 starch. A higher negative correlation between total pea starch content and starch amylose percentage was reported earlier.[2] An amylose content of 86% in the starch isolated from wrinkled peas had been documented earlier.[25] The mechanically dried peas starch showed significantly higher WBC than field dried pea starch. WBC has been reported to be affected by the association between amylose and amylopectin molecules in the starch.[27] The engagement of hydroxyl groups to form hydrogen and covalent bonds between starch chains lowers the WBC.[28]

Swelling Power and Solubility

A significant increase in swelling power with an increase in cooking temperature from 55 to 95°C was observed (Table 3). Pea flour from different cultivars did not differ significantly with respect to swelling power. The field dried pea flours showed significantly lower swelling power values as compared to mechanically dried pea flours. The swelling power of pea starches from different cultivars increased with an increase in cooking temperature. Pb-87 starches showed significantly higher swelling power than Pb-88 starches. The mechanically dried pea starches showed significantly higher swelling power than field dried pea starches. Leach et al.[18] reported a linear increase in swelling power with increase in cooking temperature from 50 to 95°C. Wrinkled pea starch showed a swelling power of 5.5 g/g at a cooking temperature of 95°C. A wide variation in swelling power of starches from different botanical sources has been reported. Schoch and Maywald[11] reported the lowest swelling power for wrinkled pea starch among various legume starches.

Table 3 Mean values showing the effect of cultivar, processing treatment, and temperature of cooking of pea flour/starch paste on the swelling power (g/g) and solubility (%)

Swelling power (g/g)		Solubility (%)
Factors	Flour	Starch	Flour	Starch
Cultivar	Pb-87	4.83	6.67	23.82	11.05
Pb-88	4.88	6.39	25.54	12.63
Treatment	Mech. dried	5.26	7.00	19.60	12.03
Field dried	4.46	6.06	29.76	11.66
Temperature	55	4.39	6.21	24.29	10.39
(°C)	65	4.52	6.31	24.42	11.26
75	4.74	6.44	24.34	11.50
85	5.02	6.71	25.30	12.40
95	5.62	6.98	25.05	13.26
CD (5%)	Cultivar (C)	NS	0.17	0.19	0.21
Treatment (Tr)	0.13	0.17	0.19	0.21
Temperature (Tm)	0.20	0.28	0.31	0.33
C × Tr	NS	0.25	0.27	0.29
C × Tm	NS	NS	0.43	0.47
Tr × Tm	NS	NS	0.43	0.47
C × Tr × Tm	NS	NS	0.61	0.66

Field dried pea flours showed slight increase in solubility with increases in temperature of cooking; however, mechanically dried pea flour did not show any significant change. The field dried pea flour showed mean solubility of 29.76% against 19.60% for mechanically dried pea flour. Pb-88 flours showed significantly higher water solubilities than Pb-87 flours. A significant decrease in water solubility with an increase in cooking temperature in the mechanically dried pea starches was observed, while field dried pea starches showed an increase in solubility with increase in temperature. Pb-87 starches showed significantly lower solubility than Pb-88 starches, which may be due to differences in amylose content. The mechanically dried peas starches showed significantly higher mean solubility value than field dried pea starches.

It is well documented that high amylose starches showed restricted swelling and solubilities.[11] [18] [29] Leach et al.[18] reported a solubility value of 82% for potato starch and 19.1% for wrinkled pea starch at 95°C. In an another study, swelling power values of 2.8–15.5% in the temperature range of 70–90°C were reported for wrinkled pea starches.[11] Mechanical drying of peas may have an annealing effect on starches. Jacobs and Delcour[30] reported that annealing and heat moisture treatments lowered amylose/carbohydrate leaching causing lower solubilities. Chung et al.[31] reported a decrease in solubility of mung bean starch with an increase in the temperature of annealing. These differences in solubility of mechanically dried and field dried starches may be attributed to differences in the morphological structure of starch granules.[32]

Free Water

Table 4 shows the data with respect to free water in fresh paste of pea flour/starch as affected by the cultivar and processing treatments at various concentrations. A drastic decrease in free water of the fresh flour paste was observed with an increase in concentration. Pb-87 flour paste resulted in a significantly higher free water value (30.90%) than Pb-88 flour paste (30.10%). The mechanically dried pea flour showed significantly higher free water as compared to field dried pea flour. A significant decrease in free water was observed with the increase in starch concentration from 10 to 20%. Pb-87 starch pastes showed significantly higher free water compared to Pb-88. Mechanically dried pea starch pastes showed higher free water content as compared to those from field dried peas. It has been reported that free water in freshly cooked paste of corn starch was >20% for 4–6% slurry, which decreased to 5–6% in 8–10% slurries. Wheat flour paste exhibited higher free water for 6 and 8% slurries than those from corn starch. Waxy corn starch paste showed <10% free water for 4–6% slurries.[19]

Table 4 Mean values of the effect of cultivar, processing treatment, and concentration of pea flour/starch paste on free water (%)

Free water (%)
Factors	Flour	Starch
Cultivar	Pb-87	30.90	23.36
Pb-88	30.10	19.17
Treatment	Mech. dried	32.82	27.31
Field dried	28.19	15.76
Concentration	10	61.87	39.67
(%)	12	48.22	32.11
14	32.89	24.19
16	22.17	15.30
18	11.05	10.76
20	6.83	7.18
CD (5%)	Cultivar (C)	0.59	0.45
Treatment (Tr)	0.59	0.45
Concentration (Cn)	1.02	0.78
C × Tr	0.83	0.64
C × Cn	NS	1.11
Tr × Cn	1.44	1.11
C × Tr × Cn	2.03	1.57

Absorbed Water Released and Net Syneresis

The mean value of absorbed water released from pea flour paste increased from 22.37 to 27.97% during refrigeration and 37.01 to 45.82% during freezing from 1st to 4th cycle, respectively (Tables 5 and 6). Pb-87 flours released significantly more absorbed water than Pb-88 in both refrigeration and freezing cycles. Among the processing treatments, mechanically dried pea flour resulted in significantly higher release of water in refrigeration as well as during freezing cycles. A significant increase in the release of water after repeated refrigeration and freezing cycles was observed. Among the cultivars, Pb-87 starches showed significantly lower mean values in both refrigeration and freezing treatments. Starch isolated from mechanically dried peas showed significantly higher values of released water compared to those from field dried peas in both refrigeration and freezing cycles. Zheng and Sosulski[19] used a 10% slurry of field pea starch (34% amylose) and reported that released absorbed water was up to 32.5 and 71.8% after the 4th refrigeration and freeze-thaw cycle, respectively.

Table 5 Mean values showing the effect of cultivar, processing treatment, and refrigeration cycles on absorbed water released (%) and net syneresis (%) from pea flour/starch paste

Absorbed water released (%)		Net syneresis (%)
Factors	Flour	Starch	Flour	Starch
Cultivar	Pb-87	26.39	24.14	19.31	16.49
Pb-88	24.01	25.22	17.40	18.55
Treatment	Mech. dried	27.06	26.04	18.05	16.40
Field dried	23.34	23.33	18.66	18.64
Refri. cycle	1	22.37	22.34	15.54	15.12
2	23.89	24.01	17.07	16.96
3	26.57	25.59	19.75	18.29
4	27.97	26.81	21.07	19.70
CD (5%)	Cultivar (C)	0.45	0.49	0.43	0.44
Treatment (Tr)	0.45	0.49	0.43	0.44
Refri cycle (R)	0.64	0.69	0.61	0.62
C × Tr	0.64	0.69	0.61	0.62
C × R	NS	NS	NS	NS
Tr × R	NS	NS	NS	NS
C × Tr × R	NS	NS	NS	NS

Table 6 Mean values of the effect of cultivar, processing treatment, and freezing cycles on absorbed water released (%) and net synersis (%) from pea flour/starch paste

Absorbed water released (%)		Net syneresis (%)
Factor	Flour	Starch	Flour	Starch
Cultivar	Pb-87	46.50	37.62	39.33	29.81
Pb-88	35.93	38.15	29.44	31.41
Treatment	Mech. dried	42.29	38.80	33.25	29.17
Field dried	40.14	36.97	35.32	32.06
Freezing	1	37.01	34.34	30.19	27.16
cycle	2	39.31	37.09	32.48	29.91
3	42.71	39.27	36.00	31.71
4	45.82	40.84	38.87	33.67
CD (5%)	Cultivar (C)	0.47	0.48	0.45	0.53
Treatment (Tr)	0.47	0.48	0.45	0.53
Freezing cycle (F)	0.67	0.68	0.63	0.75
C × Tr	0.67	NS	0.63	0.75
C × F	0.95	0.96	0.89	NS
Tr × F	NS	0.96	NS	NS
C × Tr × F	1.34	NS	1.26	NS

A significant increase in the net syneresis with increase in number of refrigeration and freezing cycles was observed. Pb-87 pea flour showed significantly higher net syneresis values in both refrigeration and freezing cycles. Mechanically dried pea flours from both pea cultivars exhibited significantly lower mean net syneresis as compared to their counterpart, field dried pea flours. Mean net syneresis values varied between 15.12 and 19.70% and 27.16 to 33.67% for refrigeration and freezing cycles, respectively. Contrary to flour, Pb-87 starch showed lower values of net syneresis in both refrigeration and freezing cycles. The mechanically dried pea starches from both the pea cultivars showed lower mean net syneresis in both refrigeration and freezing cycles than did field dried pea starches. Corn, arrowroot, and field pea starches have been reported to have the highest net syneresis values in both refrigeration and freezing treatments among 14 starches from different botanical sources studied.[19]

Starch Noodle Quality

Cooked weight and cooking loss of noodles made from different pea starches did not differ significantly (Table 7). Pea starch noodles showed significantly lower cooking weight and cooking loss than potato starch noodles. Overall acceptability scores for pea and potato starch noodles did not differ significantly. Lower cooked weight and cooking loss of pea starch noodles than potato starch noodles may be attributed to their lower swelling power and solubility compared to potato starch. It is well documented that high amylose starches showed restricted swelling and solubilities.[11] [18] [29] Schoch and Maywald[11] reported a lowest swelling power for wrinkled pea starch among various legume starches. Leach et al.[18] reported solubility value of 82% for potato starch and 19.1% for wrinkled pea starch at 95°C. It had been reported earlier that navy and pinto bean starches exhibited cooking quality similar to commercial mung bean starches noodles, but with respect to sensory quality, potato starches were more suitable than navy and pinto bean starches.[33]

Table 7 Noodle making quality of pea and potato starches

Starch source	Cultivar	Treatment	Cooked weight (g)	Cooking loss (%)	Overall acceptability score (out of 9.0)
Pea	Pb-87	Mech. dried	22.85	0.29	6.8
Field dried	19.97	0.30	6.8
Pb-88	Mech. dried	21.91	0.30	6.9
Field dried	20.51	0.33	7.1
Potato	44.52	0.61	7.0
CD (5%)	1.41	0.07	NS

Conclusion

Pb-88 cultivar was observed to be more suitable for starch processing because of a higher starch content. Field dried pea flour from both cultivars showed higher starch content than from mechanically dried peas. Wrinkled pea starches, which are exceptionally high in amylose content, showed unique functional properties. The field dried pea starch showed lower swelling power, WBC, and solubility than the mechanically dried pea starch. Pb-87 starch had better freeze-thaw stability than Pb-88. Mechanical dried pea starches resembled annealed starches and showed lower retrogradation and higher freeze thaw stabilities compared to field dried pea starch. Sensory quality of pea starch noodles was comparable to potato starch noodles. The results revealed that wrinkled pea starches are more suitable for the industries where thermo-stable paste without breakdown and with restricted swelling and solubility required.