Influence of vegetable purees on quality attributes of pastas made from bread wheat (T. aestivum)

Abstract

Various vegetable puree-incorporated quick cooking pastas (VPP) from non-durum wheat T. aestivum were developed and their quality attributes were evaluated. The results indicated that maximum incorporation of puree was used in carrot pasta (420 g/kg) and minimum amount was incorporated in beetroot pasta (150 g/kg). High yellowness was observed in carrot pasta (20.33) and low in the case of beetroot pasta (8.73). All VPP had lower cooking loss, swelling index and texture values than the control. Overall sensory scores of all the VPP was low as compared to the control except in the case of carrot pasta (6.1) which had a score comparable with the control (6.2). The pigment and crude fiber content were found to be higher in VPP. The scanning electron microscopy (SEM) analysis of the cooked pastas revealed that addition of purees have altered microstructure of pasta comprising starch granules and protein matrix network which contributed to the difference in the cooking loss.

Se desarrollaron distintas variedades de pasta de cocción rápida que incorporan puré vegetal (VPP por sus siglas en inglés) de trigo no duro T. aestivum, evaluándose sus atributos cualitativos. Los resultados indican que en la pasta con zanahoria se utilizó la cantidad máxima de puré (420 g/kg), en tanto que en la pasta con remolacha se empleó la cantidad mínima (150 g/kg). Se observó un alto nivel de color amarillento en la pasta con zanahoria (20,33) y un nivel escaso de este color en el caso de la pasta con remolacha (8,73). En comparación con el grupo de control, todas las VPP experimentaron bajos niveles de pérdida en el índice de hinchamiento y de textura durante la cocción. Asimismo, comparando con el grupo de control, en términos sensoriales la puntuación general de todas las VPP fue reducida, excepto en el caso de la pasta con zanahoria (6,1), cuya puntuación fue equivalente a la del grupo de control (6,2). Se constata que tanto el pigmento como el contenido de fibra cruda son superiores en las VPP. El análisis SEM de las pastas cocidas indica que la incorporación de purés alteró la microestructura de la pasta, formada de gránulos de almidón y un tejido de matriz de proteínas, lo cual repercutió en la pérdida durante la cocción.

Keywords:

• vegetable puree
• pasta
• microstructure
• amylograph

Palabras clave:

• puré vegetal
• pasta
• microestructura
• amilógrafo

Introduction

Pasta is one of the most ancient, nourishing and versatile dishes both from nutritive and gastronomic points of view (Antognelli, 1980). Pasta is a popular traditional food with origins from first century BC (Agnesi, 1996) and continues to be popular to this day owing to its ease of preparation, low cost, storage stability and nutritional qualities around the world. The consumption of pasta products is steadily increasing due to demand for new foods, new tastes and better buying power. People are also more aware of nutrition and health.

The best pasta products are traditionally manufactured with only durum wheat because of excellent rheological properties of the dough and the superior color, cooking quality and consumer acceptance of the product (Dexter & Matson, 1979). Specially blended pasta products with non-durum wheat ingredients such as inulin, guar gum, pea fiber, locust bean gum, xanthan gum, bamboo fiber, β-glucan (Brennan & Tudorica, 2007; Brennan, Victor, & Tudorica, 2004) and whey protein concentrate (Prabhasankar, Jyotsna, Indrani, & Venkateswara Rao, 2007) that enhance the nutritional properties of the resulting pasta are also known. The legumes like “urad” and mung bean can be utilized to improve nutritional quality of pasta (Galvez, Resurreccion, & Ware, 1995; Sarabhai, 1992). Replacement of “mung” bean starch by modified potato and sweet potato starch in oriental noodles made with T. durum wheat has been attempted (Chiu & Chua, 1989). Pasta flour supplemented with Cowpea (Vigna unguiculato L. Walp) meal indicated that high temperature drying and addition of cowpea meal could overcome some of the constraints of using soft wheat flour in pasta production (Bergman, Gilberto, & Weber, 1994). Wheat flour substituted with fenugreek flour (raw, soaked, or germinated) at 50–200 g/kg levels increased the protein, fat, lysine, minerals and dietary fiber contents proportionately. 200 g/kg substitution was found to be acceptable in terms of sensory properties in noodles and macaroni preparations (Hood and Jood, 2004). Addition of amaranth leaves or grain amaranth in the form of flour at 30 g/kg and 100 g/kg level respectively to the T. durum flour was possible (Schneider & Petrova, 2002). Addition of amaranth increased protein contents of the dough over that of control.

Addition of vegetables and fruits to pasta can contribute to a natural attractive look, new tastes, and a sense of a complete meal with all the goodness of the vegetables and fruits that have been incorporated. Conventional vegetable pastas, such as spinach and tomato-containing pastas, consist mainly of wheat flour with about 3 to 3.5 percent by weight or less vegetable solids, and tend to change in color and flavor during processing, storage and upon cooking (Villota & Maksimoski, 1996).

Pasta is normally made from T. durum semolina. 950 g/kg of the wheat produced in India is of medium hard bread wheat T. aestivum variety and only 40 g/kg durum wheat. With the objective of using surplus bread wheat available, this study was undertaken to see the possibility of making nutritious pasta by using various vegetable purees in fresh form to a maximum possible level in the semolina from T. aestivum. Fresh purees are used in the study and not dried powders as other researchers used elsewhere. The color intensity and distribution of pigments are therefore better in the dough thus improving the quality of the pasta. This avoids drying of vegetable purees prior to their addition to the flour. The quality of the pastas was examined for cooking properties like cooking time, water absorption, texture, taste and aroma of the cooked products and sensory assessment was conducted. Effect of addition of vegetable purees on the micro structural characteristics of the prepared pastas was also studied.

Materials and methods

Materials

A commercial sample of semolina from T. aestivum wheat was analyzed for moisture, ash, gluten, protein and β-carotene content according to the AACC methods (2005). Vegetable purees were also analyzed for crude fiber and pigments such as total carotenes, lycopenes, chlorophyll (Ranganna, 2005) and betalains (Nilsson, 1970).

Preparation of vegetable pasta

Vegetables such as carrot, spinach, and beetroot were procured from the local market, washed, sorted, peeled and sliced. Canned tomato puree (Guruji Brand) was procured from the local market for the present work. Each of the other purees were prepared by blanching the slices followed by milling. The homogenized puree was mixed with the dry semolina in required quantities as described in a patent (Rekha, Chauhan, Prabhasankar, Ramteke, Venkateswara Rao, 2008). The quantity of vegetable purees added was based on the final moisture content of the pasta dough which was between 280 and 300 g/kg. The dough was kneaded for 10 min, and extruded using a lab scale (14.71 N Capacity) single screw extruder (la Monferrina, Asti, Italy) fitted with a die for spiral shaped pasta with rotating blades to cut the pasta to a length of 2.5 cm. The spiral shaped samples were dried at 60°C for 3 h in a hot air drier (Magums, Mumbai, India). The moisture content of the pastas used for the study is 70 g/kg which was measured using hot air oven. Pasta prepared without addition of any vegetable puree was taken as control.

Experimental procedures

Moisture determination

Moisture content of pasta samples was measured as per the method of the AACC (2005).

Analysis of pigments

Total carotenes, lycopene and total chlorophyll of the samples were analyzed as per the standard methods described by Ranganna (2005) whereas Nilsson's (1970) method was adopted for the determination of betalains.

Total carotenes determination

The method involves the extraction of carotenes using acetone followed by petroleum ether. Optical density (OD) measurement of petroleum ether extract at wavelength of 452 nm has been made use to estimate the total carotenes. It is calculated by substituting the readings in the following equation.

Lycopene determination

The red color of tomato is predominantly due the pigment lycopene. Lycopene has absorption maxima at 503 and the molecular extinction coefficient at 503 nm is 17.2 × 10⁴. A rapid method for the estimation of lycopene in tomato products is based on the measurement of absorption of the petroleum ether extract at 503 nm.

Total chlorophyll determination

The method involves the extraction of chlorophyll using acetone followed by ether. Optical density (OD) measurement of an ether extract of chlorophyll at wavelengths 660 and 642.5 nm (for chlorophyll a and chlorophyll b respectively) has been used to estimate the total chlorophyll. Total chlorophyll is calculated by substituting the readings for a and b in the following equation.

Total chlorophyll (mg/liter) = (7.12 × OD at 660 nm)+ (16.8 × OD at 642.5 nm)

Total betalains

The red beetroot is a good source of red and yellow pigments known as betalains. The spectrophotometric method (Nilsson, 1970) directly determines the betacyanine – βc (red–blue pigments) and betaxanthine- βx, (yellow) pigments in beet root without initial separation. The extinction values (E^1cm _1%) betanine and vulgaxanthine-I are 1120 and 750 at their respective absorption maxima (Abeysekere, Sampathu, & Shankaranarayana, 1990) were considered for calculating the total betalains. For estimation of pigments in beet-based pastas, representative sample was blended with extracting solvent (water) and made up to 100 ml. The absorbance of the clear extract was measured at 540 and 480 nm in one cm cell using water as blank. The total betalains were calculated by the following equation.

Color measurement

The values of surface color of raw pasta in terms of lightness (L) and color (+a: red; −a: green; +b: yellow; −b: blue) were measured according to the method of Jyotsna, Prabhasankar, Indrani, and Venkateswara Rao (2004) using Hunter lab color measuring system (Color measuring Labscan XE system, USA). A standard white tile of barium sulfate (100% reflectance) was used as a perfectly white object for calibration of the instrument with the illuminant. Pasta samples were placed in the sample holder and the reflectance was auto-recorded for the wavelength ranging from 360–800 nm.

Cooking time

Cooking time of pasta samples was estimated as per AACC method 66-50 (AACC, 2005).

Cooking quality of pasta

To evaluate the cooking quality, 25 g of pasta was added to 250 ml of boiling water. The pasta samples were cooked for 3 min and drained for 5 min. Cooked weight was determined by weighing the drained pasta and was reported in grams. At the end of 3 min, the volume of gruel was measured. The gruel was stirred well and 20 ml of the gruel was pipetted to a Petri plate and evaporated into dryness over a water bath. Then the Petri plate was transferred to a hot air oven maintained at 105 ± 2°C and dried to no further change in the mass (ISI, 1993).

Swelling Index

Swelling Index of cooked pasta (SI: grams of water per gram of dry pasta) was evaluated by drying pasta samples to constant weight (Fardet, 1999) at 105°C, expressed as [weight of cooked product − weight after drying]/weight after drying (Tudorica, Kuri, & Brennan, 2002).

Water absorption

Water absorption of drained pasta was determined as [weight of cooked pasta − weight of raw pasta]/weight of raw pasta] × 100.

Pasta firmness

The firmness was measured as described by Prabhasankar et al. (2009). The firmness of cooked pasta samples was measured by using a Texture Analyser model Tahdi (Stable Microsystems, Surrey, UK). Three-cooked pasta pieces (spaghetti shape equivalent to the length of spirals 3 cm) were sheared at a 90° angle. The shear (Newton “N”) was performed using a probe (30 mm diameter) at a crosshead speed of 50 mm/min and load cell of 49.03 N. The force required to shear the pasta was measured. The results reported are the averaged of four readings.

Amylograph characteristics

The effect of addition of carrot, tomato, spinach and beetroot pulps on the amylograph characteristics of semolina was studied using a Micro-Visco Amylograph (Model 803201, Brabender, Germany) according to AACC methods (2005).

Sensory evaluation

Panels of 15 judges, who are familiar with the quality characteristics of pasta, were recruited to perform the sensory evaluation of cooked pasta using a 9-point hedonic scale (Amerine, Panagbrone, & Roester, 1965). Attributes, which are indicative of major quality differences in cooked pasta, were selected, i.e. appearance, strand quality, mouth feel, flavor and overall quality. The sensory attributes along with their description is presented in Table 1.

Table 1. Sensory parameters and their description for quality of pastas.
Tabla 1. Parámetros sensoriales y su descripción en términos de la calidad de las pastas.

Sensory parameters	Description
Appearance	Typical commercial pasta appearance
Strand quality	Judged based on the lack of surface cracks/damages, surface stickiness and intactness, which, indicates the strength to withstand the severity of cooking.
Mouth feel	Typical cooked commercial pasta mouth feel
Flavor	Typical cooked pasta flavor with respect to carrot/spinach/tomato/beetroot

Statistical analysis

The means of all the parameters were examined for significant difference by analysis of variance (ANOVA) in MS Excel 2007 and mean separation was accomplished by Duncan's multiple range test.

Scanning electron microscopy

The cooked pasta samples were kept at −20°C overnight and then freeze dried (Heto Drywinner DW3) for 5–6 h. Samples were cut transversally with a sharp blade without damaging the structure and subjected to scanning microscopy. They were then attached to the specimen stubs with silver conducting paint. The mounted specimens were coated with a layer of gold, about 2 to 25 nm thick in a Philips vacuum evaporator. Scanning electron microscope studies were performed using a low temperature of −25°C in the LEO 435 VP scanning electron microscope (Leo Electron Microscopy Ltd., Cambridge, UK) at a pressure 1–1.5 torr and an accelerating voltage of 20 kV.

Results and discussion

Quality characteristics of semolina and vegetable purees

The semolina used for the pasta preparation was analyzed for moisture (106.2 g/kg), ash (7.0 g/kg), gluten (80.5 g/kg), β-carotene (2 mg/kg) and protein (80 g/kg) on dry weight basis. The pigments like total carotenes (18 mg/kg), lycopenes (67 mg/kg), betalains (91 mg/kg) and total chlorophyll (11 mg/kg) were found in vegetable purees of carrot, tomato, beetroot and spinach, respectively. The crude fiber found in vegetable purees of carrot puree, tomato, beetroot and spinach was 5.1 g/kg, 11 g/kg, 25 g/kg, and 18 g/kg, respectively.

Color measurement

Color values were measured for the cooked and the uncooked pasta samples. Plain pasta was used as control. The control had the highest value for lightness “L” followed by carrot, beetroot, spinach and tomato-incorporated pasta in uncooked form (Table 2). After cooking, the samples showed corresponding increases in “L” values which indicate some loss of color during cooking. Value for redness, “+ a” in the uncooked pasta samples was highest for carrot followed by beetroot. The overall color of carrot pasta was orange due to higher “+ b” values indicating yellowness while beetroot appears red due to lesser “+ b” values in the samples. Tomato pasta also has orange appearance due to equal “+ a” and “+ b” values. Uncooked spinach pasta has good green color as seen by negative “a” value that indicates green shade. It also has some yellowness as indicated by its “b” value. These values indicated that the dried pastas had colors closer to the respective vegetable used (Figure 1). The color of the cooked samples was slightly lesser as seen in Table 2. Leaching of colors during cooking was negligible in all cases other than beetroot. This could be due to the more water-soluble nature of “betalins,” than carotenes and chlorophylls. Reduction in color intensity of cooked pastas could be due to swelling of the pastas and conversion of pigments resulting in increase in yellowness or “+ b” values during cooking. But all the pastas had good attractive color after cooking.

Figure 1. (A) Beetroot pasta; (B) Carrot pasta; (C) Control pasta; (D) Spinach pasta; and (E) Tomato pasta.

Figura 1. (A) Pasta de remolacha; (B) Pasta de zanahoria; (C) Pasta de control; (D) Pasta de espinaca y (E) Pasta de tomate.

Table 2. Color values of raw and cooked vegetable based pastas.
Tabla 2. Valor de color de las pastas vegetales crudas y cocidas.

	L		a		b
Sample	Raw	Cooked	Raw	Cooked	Raw	Cooked
Control	40.21 ± 1.04^a	50.22 ± 1.04^a	0.02 ± 0.003^d	–2.61 ± 0.02^d	13.17 ± 0.43^b	8.19 ± 0.10^c
Carrot	34.54 ± 0.75^b	39.17 ± 1.04^b	16.27 ± 0.35^a	8.76 ± 0.03^b	17.88 ± 0.38^a	20.33 ± 0.29^a
Spinach	28.33 ± 0.64^c	32.17 ± 0.61^e	− 7.10 ± 0.12^e	− 8.70 ± 0.03^e	11.78 ± 0.09^c	14.30 ± 0.23^b
Tomato	25.06 ± 1.03^d	34.20 ± 0.74^d	9.84 ± 0.25^c	10.62 ± 0.05^a	9.85 ± 0.09^d	14.43 ± 0.88^b
Beetroot	28.58 ± 0.47^c	35.69 ± 0.76^c	14.64 ± 0.86^b	6.41 ± 0.02^c	5.62 ± 0.06^e	8.73 ± 0.08^c
Note: Means of the triplicates ± standard error. a,b.c.d.e: columnwise values with different superscripts are significantly different (p < 0.05).
Nota: Medias de los triplicados ± desviación estándar. a,b,c,d: Valores de columna con diferentes superíndices son significativamente diferentes (p < 0,05).

Cooking quality

As observed in Table 3, addition of vegetable purees to soft wheat pasta did not result in any significant change in the cooked weights. Lesser cooking time (3–4 min) can be explained due to faster reconstitution of fine vegetable matter distributed in the pasta matrix. Cooking losses were found to be high in the case of T. aestivum (12 g/kg) and decreased with addition of vegetable purees (less than 10 g/kg). This could be due to better binding of starch granules and vegetable matter in gluten network as observed by the scanning electron microscopy (SEM) observations. The present study observation is in line with report made by Prabhasankar et al (2009).

Table 3. Effect of vegetable purees on the cooking quality and sensory scores of pastas.
Tabla 3. Efecto de los purés vegetales en la calidad de cocción y en la puntuación sensorial de las pastas.

Pasta samples	Appearance^#	Strand quality^#	Mouth feel^#	Flavor^#	Overall quality^#	Vegetable purees (g/kg fwb*)	Cooked weight (g/kg)	Water absorption of drained pasta (g/kg)	Swelling Index (ml/g dry matter)	Cooking loss (g/kg)	Firmness (Shear) (N)
Control	5.4 ± 0.32^a	7.1 ± 0.34^c	6.8 ± 0.45^d	5.7 ± 0.40^b	6.2 ± 0.35^c	–	2440 ± 1^a	1208 ± 0.1^c	1.64 ± 0.12^e	12.0 ± 0.05^d	4.12 ± 0.17^d
Carrot-pasta	6.6 ± 0.24^d	6.3 ± 0.33^b	6.2 ± 0.30^c	5.7 ± 0.33^b	6.1 ± 0.26^c	420	2400 ± 1.5^a	1165 ± 0.2^b	1.44 ± 0.10^c	7.1 ± 0.14^a	2.75 ± 0.13^a
Spinach-pasta	5.7 ± 0.31^b	5.6 ± 0.28^a	5.2 ± 0.33^a	5.0 ± 0.36^a	5.4 ± 0.30^a	200	2480 ± 0.58^b	1163 ± 0.1^b	1.32 ± 0.09^b	7.1 ± 0.12^a	3.43 ± 0.18^b
Tomato-pasta	5.9 ± 0.29^b	5.5 ± 0.34^a	5.6 ± 0.40^b	5.4 ± 0.34^a	5.5 ± 0.22^a	400	2484 ± 1.16^b	1058 ± 0.1^a	1.24 ± 0.11^a	8.4 ± 0.15^b	3.73 ± 0.14^c
Beetroot-pasta	6.0 ± 0.35^c	6.2 ± 0.35^b	5.5 ± 0.35^b	5.2 ± 0.39^a	5.7 ± 0.28^b	150	2480 ± 0.77^b	1188 ± 0.1^b	1.53 ± 0.14^d	7.4 ± 0.12^c	3.14 ± 0.08^b
Note: #Mean scores ± S.D. of three replications. *Flour weight basis. a,b.c.d.e: columnwise values with different superscripts are significantly different (p < 0.05).
Nota: Valores medios ± desviación estándar de tres replicas. *En base a peso de harina. a,b,c,d: Valores de columna con diferentes superíndices son significativamente diferentes (p < 0,05).

Firmness studies

Firmness analysis of the samples as shown in Table 3 indicated that although there was no significant difference in the shear (N) values for spinach, tomato and beetroot pastas, they were lower than those of control samples. Carrot pasta was slightly softer as compared to others. Incorporation of vegetable matter rendered a softer texture, which could be due to non-starchy nature of vegetables in the starch matrix. Carrot-incorporated pastas had lesser shear values which could be due to higher content of vegetable matter (420 g/kg) in these formulations. Beetroot, spinach and tomato followed next in that order.

Sensory evaluation

Sensory evaluation report indicated that carrot pasta scored better appearance score (6.6) followed by beetroot pasta (6.0) than control (5.4) and other pasta samples. In the case of strand quality, control was rated best (7.1) followed by carrot (6.3) and beetroot (6.2). In the case of mouth feel, carrot pasta (6.2) was judged as better than other vegetable-based pasta samples. The overall quality score indicated that carrot pasta (6.1) is best among the vegetable pastas and also very close to control pasta (6.2) (Table 3). The sensory study clearly indicated that the incorporation of carrot puree improved the appearance, mouth feel, flavor, and overall quality of the developed pasta.

Pasting characteristics of vegetable puree pasta

Amylographic studies of vegetable puree-incorporated pasta samples indicated that peak viscosity was slightly affected when compared to control pasta sample. This was more pronounced in the case of spinach- and tomato puree-incorporated pastas (Figure 2). However, beetroot- and carrot puree-incorporated pastas were not much affected with respect to peak viscosity values and their values are comparable with that of control pasta. Pasting temperature (PT) values of vegetable puree-incorporated pasta samples have inverse relationship with peak viscosity values. Spinach and tomato pasta samples have lowest PT values and beetroot has high PT. There is not much variation in setback values, which could be one of the reasons for less cooking loss in the case of vegetable pasta samples.

Figure 2. Pasting characteristics of vegetable pasta; (a) Amylograph of vegetable pastas; (b) Comparison of various pasting parameters of vegetable pasta; CPV – Cold Paste Viscosity; PV – Peak Viscosity; BD – Break Down; PT – Pasting Temperature.

Figura 2. Características de pegado de pasta vegetal: (a) Amilógrafo de pastas vegetales; (b) Comparación de varios parámetros de pegado de pasta vegetal; VPF- Viscosidad de pasta fría; VM- Viscosidad máxima; D- Descomposición; TP- Temperatura de pegado.

Influence of vegetable puree on the microstructure of the pasta

Variation in the network of starch granules and protein matrix were observed in the micrographs of cooked pasta samples (Figure 3). The formation of gluten matrix is evident in case cross-section micrographs of pasta samples containing vegetable purees. The microstructure of pasta was altered with addition of vegetable purees. This could be due to protein matrix–starch granule network which was affected by fibers present in the vegetable purees. In the case of control, starch granules were covered by film of protein matrix which is more evident in the higher magnification scanning electron micrograph of cross section of pasta sample (Figure 3f). In the case of beetroot pasta samples, the network was further strengthened (Figure 3g); however, holes were observed in its surface micrograph (Figure 3l). With respect to carrot pasta, similar pattern like beetroot was observed except the gelatinized starch granules formed network with protein granules and purees (Figure 3h). In the case of tomato and spinach pasta, similar kind of surface micrographs (Figure 3n and 3o) were observed. There were no holes observed in the case of tomato and spinach pasta which was similar to that of “control” surface micrograph (Figure 3k). In the case of spinach pasta, some intact starch granules were observed apart from the network of starch, puree and protein whereas in the case of tomato pasta, very few intact starch granules were found (Figure 3i and 3j). The variations in the vegetable pasta micrograph observations could be due to the differing network/binding capacities of the purees with protein and starch granules of wheat. It has been reported that alginate forms a stable complex with starch, which in turn inhibits rupture on gelatinization, and reduced starch loss on subsequent cooking (Chawan, Merritt, & Matuszak, 1995). For good quality pastas, the thin film of protein network has to be formed and enveloping the entire gelatinized starch granules is crucial in determining the cooking quality of pasta products (Jyotsna et al., 2004).

Figure 3. Microstructure of cooked vegetable puree-incorporated pastas; a, b, c, d, e – 100X (Cross section); f, g, h, i, j – 2000X (Cross section); k, l, m, n, o – 2000X (Surface).

Figura 3. Microestructura de pastas de puré vegetal incorporado cocidas; a,b,c,d,e, – 100X (Sección transversal); f, g, h, i, j – 2000X (Seccioón transversal); k,l,m,n,o – 200X (Superficie).

In the present study, it is more evident from the surface micrographs of pastas that the incorporation of vegetable purees enhances this network formation. Micrographs of vegetable pastas have shown high entrapment of starch granules within a protein network. This was also supported by cross-section micrographs of cooked pasta samples. The honeycomb like structure in which gelatinized starch granules are entrapped in the gluten matrix was observed in the case of control. This network strength was enhanced in the case of pasta with vegetable purees. Jyotsna et al. (2004) studied the effect of additives on the microstructure of vermicelli. They found the honeycomb network formed between protein and starch granules of cooked vermicelli has been affected by addition of additives such as GMS (Glycerol Monostearate), SSL (Sodium stearoyl-2-lactylate) and enzyme glucose oxidase. Similarly Prabhasankar et al. (2007) studied the effect of combination of animal protein, ascorbic acid, and vital gluten on the microstructure of vermicelli. They found the gluten network (honeycomb structure) has been affected by addition of whey protein concentrate (WPC). However, the microstructure of WPC-incorporated vermicelli has been improved by addition of additives. The present SEM study indicates that addition of vegetable purees enhanced the interaction between starch granules and protein matrix, which resulted in improved quality pasta. This could also be due to greater water holding capacity of puree resulting in a better network formation between starch and protein matrix.

Effect of incorporation of vegetable purees in pasta quality characteristics

Maximum levels of fresh vegetable purees that could be mixed to the fixed amount of dry semolina were standardized based on the final moisture content of the dough. Effect of incorporation of carrot 420 g/kg on fresh weight basis (fwb), spinach (200 g/kg), tomato puree (400 g/kg) and beetroot (150 g/kg) into the pasta dough changed the quality parameters of the finished and cooked product. Results showed that the use of vegetable purees with soft wheat semolina produced significant change in the cooked weight, decreased cooking loss and color values as shown in Tables 2 and 3. The vegetable puree-incorporated pastas when analyzed for the carotene, lycopene, betalain contents indicated that they retained considerable levels of each of these nutrient pigments (Table 4) known for their health beneficial properties. Protein content and crude fiber content did not improve with the addition of vegetable puree.

Table 4. Nutritional composition of dried vegetable pastas.
Tabla 4. Composición nutricional de las pastas vegetales secas.

Pasta samples	Nutritional pigments (mg/kg)		Crude fiber (g/kg)	Protein (g/kg)
Control	Carotenes	Traces	2.7 ± 0.01	88.0 ± 0.09
Carrot	Total carotenes	23.0 ± 0.03	2.9 ± 0.01	86.0 ± 0.08
Spinach	Total chlorophyll	15.0 ± 0.02	3.3 ± 0.02	86.0 ± 0.09
Tomato	Carotenes	1.5 ± 0.02	2.9 ± 0.01	85.0 ± 0.08
	Lycopenes	10.8 ± 0.01
Beetroot	Betalains	7.0 ± 0.01	2.7 ± 0.01	86.0 ± 0.07
Note: Means of the triplicates ± standard deviation.
Nota: Valores medios ± desviación estándar.

Conclusion

Vegetable purees, like beetroot, carrot, spinach, and tomato, were incorporated to prepare pasta and their quality attributes were studied. It was observed that incorporation of vegetable puree moderately affected the overall quality of the developed vegetable pasta. It was observed that addition of vegetable purees improved cooking quality of all the pastas with less cooking losses. Thus, it may be concluded that the incorporation of vegetable purees affects the pasta quality attributes and it imparts natural attractive color to the pasta. The quality changes in the developed pasta were supported by SEM micrographs where the interaction between starch granules and protein matrix was altered by the addition of vegetable purees. So, this study could successfully explore the addition of vegetable purees in the preparation of quick cooking, shelf stable and naturally colored pastas. More studies will be needed to improve the quality attributes of vegetable purees-based pasta.

Acknowledgment

The authors thank Dr. S. Rajarathnam, Head, FVT Department, for constant support and encouragement.