Effect of oat β-glucan fiber powder and vacuum-drying on cooking quality and physical properties of pasta

Abstract

Oat β-glucan fiber powder was added to pasta dough at levels of 40, 80, 120, 160, and 200 g/kg. Pasta was dried at very high temperature and in a vacuum dryer. The cooking quality was evaluated based on the swelling index, water uptake, and cooking loss measurement. Further tests were carried out to determine the color, hardness, adhesiveness, total dietary fiber (TDF), and β-glucan content in pasta. The results showed that vacuum-drying had a significant impact on the cooking quality and physical properties of pasta. Water uptake and swelling index were higher and the cooking loss was lower in vacuum-dried pasta than in pasta dried using very high temperature (VHT) technology. The swelling index, water uptake, and cooking loss were significantly higher in samples with oat β-glucan fiber powder compared to control. Pasta with oat powder was darker, softer, and less sticky than semolina pasta. Lightness of vacuum-dried samples was higher while redness was lower than in conventionally dried samples.

Se añadió fibra de avena β-glucano en polvo a la masa de pasta a niveles 40, 80, 120, 160 y 200 g/kg. La pasta se secó a altas temperaturas en un secador al vacío. Se evaluó la calidad de cocinado en base al cálculo del índice de hinchazón, la absorción de agua y la pérdida de volumen en el cocinado. Se realizaron otras pruebas para determinar el color, la dureza, la adhesión, el total de fibra alimentaria y el contenido de β-glucano en la pasta. Los resultados mostraron que el secado al vacío tuvo un impacto significativo en la calidad del cocinado y las propiedades físicas de la pasta. La absorción de agua y el índice de hinchazón fueron mayores, aunque la pérdida de volumen en el cocinado fue menor en la pasta secada al vacío que con aquella secada con tecnología VHT. El índice de hinchazón, la absorción de agua y la pérdida de volumen en el cocinado fueron significativamente elevados en muestras con fibra de avena β-glucano en polvo en comparación con las muestras control. La pasta con avena en polvo resultó ser más oscura, suave y menos pegajosa que la pasta con semolina. La ligereza de las muestras secadas al vacío fue mayor, mientras que el color rojizo fue menor que en las muestras secadas de manera convencional.

Keywords:

• vacuum-drying
• β-glucan
• dietary fiber
• pasta

Palabras clave:

• secado al vacío
• β-glucano
• fibra alimentaria
• pasta

1. Introduction

Pasta is manufactured from durum wheat semolina and is a good source of low glycemic index carbohydrates (Björk, Liljeberg, & Ostman, 2000; Brennan, 2008). As pasta is considered to be a good vehicle for nutrient addition, several studies have aimed to develop pasta with an enhanced nutritional value (Bustos, Perez, & León, 2011; Chillo, Laverse, Falcone, & Del Nobile, 2008). In the context of the recent trend toward diets high in fiber it may be desirable to incorporate dietary fiber into pasta recipes (Aravind, Sissons, Egan, & Fellows, 2012; Bustos et al., 2011; Chillo et al., 2008). Addition of dietary fiber would increase the nutritional value and lower the glycemic index and caloric content of pasta. Dietary fiber has important physiological and metabolic functions in the human body including reduction of cardiovascular disease and colorectal cancer risk, prevention of constipation, and production of short-chain fatty acids (Bazzano, He, Ogden, Loria, & Whelton, 2003; Karppinen, Liukkonen, Aura, Forssell, & Poutanen, 2000; Sabanis, Lebesi, & Tzia, 2009). Dietary fiber functions in the human body vary depending on their source, components, and the chemical structure. Among cereals, oats and barley have been reported to have the highest content of β-glucans (30–80 g/kg and 20–200 g/kg, respectively) (El Khoury, Cuda, Luhovyy, & Anderson, 2012). According to Commission Regulation (EU) No 1160/2011, 3 g of β-glucans per day can lower the serum total and low-density lipoprotein (LDL) cholesterol levels and reduce the risk of coronary heart disease. β-Glucan has been shown to have an impact on glycemic control, insulin responses, reduction of plasma total and LDL cholesterol levels (El Khoury et al., 2012). Pasta enrichment with dietary fiber rich in β-glucan would contribute to an increase in fiber intake and reduce the glycemic index and caloric value of the pasta product.

The cooking quality of pasta and the consumer perception of the product are largely affected by drying conditions. Unless pasta is to be sold as a fresh product with a short shelf-life it must be further processed to ensure biochemical and microbiological stability (Johnston, 2001). At the industrial scale, pasta is dried to a moisture content of 120 g/kg, however, the Federal Code of Regulations allows pasta moisture to be as high as 130 g/kg (Stuknytė et al., 2014; Food and Drug Administration, 2014). Currently, pasta is mostly manufactured with the use of high and very high temperature drying technologies that have been shown to shorten drying time when compared to low temperature drying and reduce the number of microorganism’s (Güler, Köksel, & Ng, 2002). High temperatures during drying may also have an impact on pasta color, as excessive temperatures may result in brown discoloration due to Maillard reactions (Anese, Nicoli, Massini & Lerici, 1999). Furthermore, the dehydration process must be managed carefully to prevent cracking of the product due to an excessive moisture gradient between the surface and the core of the pasta (Johnston, 2001; Marchylo & Dexter, 2001). During vacuum-drying, reduced pressure intensifies the mass transfer due to an increased pressure gradient between the core and the surface of the pasta (Alibas, 2007; Péré & Rodier, 2002). The rate of moisture transfer from the core to the surface is higher compared to atmospheric pressure drying (Gunasekaran, 1999). Moreover, the vacuum reduces the boiling point of the solvent allowing a decrease of drying temperature. Compared with conventional air drying, reduced pressure drying has a higher drying rate, lower drying temperature, and oxygen deficient processing environment (Wu, Orikasa, Ogawa, & Tagawa, 2007). Due to the absence of oxygen during vacuum-drying, oxidative degradation reactions are minimized (Jena & Das, 2007). Although many studies have investigated the use of vacuum-drying during food production, to our knowledge no such study has been focusing on pasta products (Arévalo-Pinedo & Murr, 2007; Cui, Xu, & Sun, 2004; Giri & Prasad, 2007). As pasta is difficult to dry due to slow water migration from the core to the surface it may be feasible to introduce vacuum-drying to pasta technology to achieve a higher quality final product.

The aim of the present study was to determine the impact of oat β-glucan fiber powder addition and the drying method on the cooking quality and physical properties of durum wheat semolina pasta.

2. Materials and methods

2.1. Raw materials

Durum wheat fusilli was made using commercial semolina obtained from Assmannmühlen GmbH (Guntramsdorf, Austria). Oat β-glucan fiber powder was obtained from Microstructure Sp. z o.o. (Warsaw, Poland). The powder contained 440 g/kg of oat fiber (230 g/kg insoluble fractions and 210 g/kg soluble fractions, including 160 g/kg of β-glucan).

2.2. Pasta preparation

Durum wheat semolina was substituted with oat β-glucan fiber powder in five proportions: 40, 80, 120, 160, and 200 g/kg. Pasta prepared from semolina without powder addition was referred to as the control sample. Semolina and oat powder blends were mixed and hydrated with tap water (water temperature = 35°C) to 320 g/kg moisture in a pasta machine (P3, La Monferrina, Italy). After mixing, pasta was extruded at 50 rpm through a fusilli forming a die and dried using one of the two technologies. Very high temperature (VHT) drying was performed in a convection oven (Convect-Air Professional CPE 110, Küppersbusch, Germany) for 10 min at 80°C, then for 40 min at 94°C and 37% relative humidity (RH) and subsequently for 180 min at 80°C and 69% RH. Vacuum-drying was conducted at 80°C, 15 kPa for 180 min in a vacuum oven (VO500, Mammert, Germany) equipped with a vacuum pump (range 1 to 110 kPa).

2.3. Pasta cooking quality

2.3.1. Optimal cooking time

The optimal cooking time (OCT) was determined according to the approved method of the American Association of Cereal Chemists (approved method 66-50, AACC 2000) on 10 g samples of dried pasta. OCT was indicated when the inner white core of the pasta disappeared when squeezed between two glass plates. Measurements were performed in triplicate.

2.3.2. Water uptake

The water uptake was evaluated as described by Petitot, Boyer, Minier, and Micard (2010). A 10 g dry pasta sample was weighed before and after cooking for the OCT. Measurements were repeated three times. Water uptake was calculated using Equation (1):

(1)

2.3.3. Swelling index

The swelling index (SI) was determined according to the method described by Cleary and Brennan (2006). A 10 g sample of pasta was cooked at its OCT, weighted, and dried at 105°C for 16 h. Measurements were repeated three times. The swelling index value was calculated using Equation (2):

(2)

2.3.4. Cooking loss

The cooking loss was determined as described by Chillo et al. (2008). A 10 g sample was cooked in 300 ml of boiling distilled water. Cooking water was collected, dried in an air oven at 105°C for 16 h, and the residue was weighted. Measurements were performed in triplicate. The cooking loss was expressed as a percentage of the starting material.

2.4. Color

The color of dried and cooked pasta was determined instrumentally using a Minolta CR-400 Chroma Meter (Model CR-400, Konica Minolta Inc., Tokyo, Japan) with the L*a*b* measuring system (illuminant D65, 2° standard observers, measurement area: ⊘ 8 mm). Values of L* (lightness), a* (–greenness; +redness), and b* (–blueness; +yellowness) were determined. White calibration was performed with a reference standard (L* = 98.45, a* = −0.10, b* = −0.13) in order to achieve accurate measurements. Measurements were performed at 10 measuring points of each sample.

2.5. Textural properties

The texture of cooked pasta was determined using a universal testing machine (model 5965, Instron, MA, USA) equipped with a 35 mm cylindrical probe. Samples were subjected to double compression at a constant rate of deformation (2 mm/s) to 70% of the initial pasta thickness. From the texture profile analysis curve, textural parameters of hardness and adhesiveness were determined. Measurements were repeated five times.

2.6. Total dietary fiber (TDF) content and β-glucan content

Measurement of TDF was carried out according to the AOAC 2009.01 method using the FOSS Fibertec E 1023 system (Hillerød, Denmark). β-Glucan content was determined by the AOAC Official Method 995.16 with the use of the Megazyme mixed-linkage β-glucan assay kit (Megazyme International Ltd., Ireland).

2.7. Statistical analysis

The data were statistically analyzed by one-way analysis of variance (ANOVA). A value of P ≤ 0.05 was used to indicate a significant difference. Statistica 10 for Windows (StatSoft Inc., Tulsa, OK, USA) was used for all statistical analyses.

3. Results and discussion

3.1. Pasta cooking quality

One of the most important qualitative factors influencing the overall quality of pasta is cooking performance. Good quality pasta should maintain form during cooking and increase in volume with minimal material losses (Cleary & Brennan, 2006).

OCT did not differ between the samples dried under various conditions and with different levels of oat β-glucan fiber powder addition (Table 1). The swelling index values of pasta samples dried by the conventional and vacuum-drying method are shown in Table 1. The swelling index values for conventionally dried pasta with up to 80 g/kg of oat β-glucan fiber powder were not different from the control sample. Higher semolina flour substitution caused a significant (P ≤ 0.05) increase of the swelling index. The highest value for conventionally dried pasta was observed in the sample with 200 g/kg of oat β-glucan fiber powder addition. In vacuum-dried pasta, a significant increase of the swelling index was observed in all samples with oat β-glucan fiber powder addition. The swelling index value increased with an increase of oat β-glucan fiber powder addition up to 120 g/kg, however this value did not differ significantly between samples with 120, 160, and 200 g/kg of non-gluten additive. An increased swelling index with β-glucan addition was also observed by Chillo, Ranawana, and Henry (2011) who studied the effect of barley β-glucan concentrates on the cooking quality of spaghetti. Our data are in line with the findings of Cleary and Brennan (2006), who reported an increase of the swelling index in pasta samples fortified with β-glucan fiber. Similar results were also obtained by Tudorica, Kuri, and Brennan (2002) for pasta with addition of guar gum. According to Cleary and Brennan (2006), increased swelling index values might be related to greater water absorption during cooking due to the high water-binding capacity of fiber.

Table 1. Cooking quality of pasta samples with oat β-glucan fiber powder addition dried in a conventional and vacuum dryer.

Tabla 1. Calidad de cocinado de las muestras de pasta con adición de fibra de avena β-glucano en polvo secada de forma convencional y con secador al vacío.

Oat β-glucan fiber powder addition [g/kg]	Optimal cooking time [min]		Swelling index [g of water/g of dry pasta]		Water uptake [g/100 g of raw pasta]		Cooking loss [g/100 g of raw pasta]
	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying
0	6.5	6.5	1.36^Aa ± 0.042	1.42^Aa ± 0.026	112.44^Aa ± 2.734	120.64^Ba ± 3.061	4.26^Aa ± 0.113	4.17^Aa ± 0.072
40	6.5	6.5	1.39^Aab ± 0.021	1.68^Bb ± 0.023	113.96^Aab ± 2.001	126.94^Bb ± 2.281	5.63^Bbc ± 0.172	4.80^Ab ± 0.133
80	6.5	6.5	1.42^Aabc ± 0.041	1.71^Bb ± 0.035	117.66^Abc ± 3.141	125.80^Bb ± 2.986	5.81^Bc ± 0.183	5.19^Ac ± 0.019
120	6.5	6.5	1.43^Abc ± 0.030	1.83^Bc ± 0.021	123.75^Ade ± 3.172	126.05^Ab ± 2.809	5.93^Bb ± 0.044	5.17^Ac ± 0.030
160	6.5	6.5	1.48^Acd ± 0.020	1.86^Bc ± 0.025	120.31^Acd ± 2.122	126.04^Ab ± 3.284	6.57^Bd ± 0.141	5.47^Ac ± 0.165
200	6.5	6.5	1.53^Ad ± 0.038	1.86^Bc ± 0.036	126.81 ^Ae ± 1.784	132.90^Bc ± 2.497	6.75 ^Bd ± 0.209	5.93^Ad ± 0.077

Note: Means ± standard deviations (n = 3). ^(a-e) Means within a column with different superscripts are significantly different (P ≤ 0.05). ^(A-B)Means within a row with different superscripts are significantly different (P ≤ 0.05).

Nota: Promedios ± desviaciones estándar (n = 3). ^(a-e) Los promedios en una misma columna con distinto superíndice son significativamente diferentes (P ≤ 0,05). ^(A-B)Los promedios en una misma fila con distinto superíndice son significativamente diferentes (P ≤ 0,05).

Samples dried under reduced pressure had a significantly higher swelling index than samples dehydrated using VHT technology. The differences in the swelling index might be related to the drying process mechanism. The moisture gradient inside the pasta products during drying causes different shrinkage rates between the surface and the core which may result in internal stress within the product. If the surface moisture evaporates too quickly, a barrier may be formed in the outer layer, which may lead to cracks and fractures inside the pasta (Zweifel, 2001). The decreased pressure used in vacuum-drying enhances the mass and moisture transfer due to an increased pressure gradient between the core and the surface of pasta (Alibas, 2007; Gunasekaran, 1999; Péré & Rodier, 2002). Increased moisture transfer prevents surface barrier formation and decreases the internal stress within the pasta, which may contribute to the structure of the dried product, resulting in higher cooking quality.

Table 1 presents the water uptake of conventionally and vacuum-dried samples with increasing oat β-glucan fiber powder addition. Pasta dried using VHT technology with flour substitution above 40 g/kg and vacuum-dried samples fortified with oat β-glucan fiber powder showed significantly higher water uptake compared to control. These data are in line with the findings of Song, Zhu, Pei, Ai, and Chen (2013) who reported higher water uptake for noodles with wheat bran addition. Increased water absorption might be related to the higher amount of hydroxyl groups in fiber than in semolina, resulting in more interactions with water through hydrogen bonds.

The drying method had a significant impact on the water uptake. Vacuum-dried pasta showed higher values of this parameter, indicating better cooking performance compared to conventionally dried samples. As for the swelling index, the differences in water uptake values may be related to the drying mechanism. Prevention of structure deterioration due to minimalized internal stress within the pasta during vacuum-drying may contribute to the improvement of water absorption.

The cooking loss of pasta samples dried by the conventional and vacuum-drying methods is shown in Table 1. The cooking loss increased significantly with increasing oat β-glucan fiber powder addition from 4.26 g/100 g of raw pasta for the conventionally dried sample without flour substitution to 6.75 g/100 g of raw pasta in the sample with 200 g/kg of oat fiber powder and from 4.17 g/100 g of raw pasta in vacuum-dried samples without flour substitution to 5.93 g/100 g of raw pasta in vacuum-dried samples with 200 g/kg of oat β-glucan fiber powder. These findings are in accordance with Chillo et al. (2011) who reported an increase of cooking loss in pasta samples with addition of two barley β-glucan concentrates. During cooking, the protein matrix gradually disintegrates, allowing greater amounts of gelatinized starch to leach from the pasta (Cleary & Brennan, 2006). The addition of non-gluten material may weaken the overall structure of pasta and dilute the gluten strength resulting in increased mass loss into the cooking water (Rayas-Duarte, Mock, & Satterlee, 1996). Increased cooking loss might also be related to the dissolution of soluble fiber fractions into the cooking water.

The drying method had a significant impact on the cooking loss of pasta with oat β-glucan fiber powder. Vacuum-drying resulted in lower cooking losses than convection-dried samples. Control samples dried by various drying methods did not differ significantly (P ≤ 0.05).

3.2. Pasta color

Table 2 shows the results of color measurement of conventionally and vacuum-dried pasta samples with and without the addition of oat β-glucan fiber powder before cooking. Conventionally dried pasta with 40 g/kg of oat fiber powder did not differ from the control, however samples with higher semolina substitution showed a significant (P ≤ 0.05) decrease in lightness compared to pasta without oat fiber powder. In vacuum-dried pasta, the non-gluten additive significantly decreased the brightness compared to the control sample. The drying method did not have a significant impact on pasta lightness. Moreover, a significant increase of redness and a decrease of yellowness were observed for samples with oat β-glucan fiber powder for both drying methods. Vacuum-dried samples with 40, 80, and 200 g/kg of oat β-glucan fiber powder showed significantly (P ≤ 0.05) lower redness compared to convection-air dried pasta, while the rest of the samples did not differ significantly. The yellowness of pasta dried by VHT technology was higher than for vacuum-dried samples, with the exception of samples with 120 and 160 g/kg of oat β-glucan powder.

Table 2. Color measurements for dry pasta samples with oat β-glucan fiber powder.

Tabla 2. Mediciones de color para el secado de las muestras de pasta con fibra de avena β-glucano en polvo.

Oat β-glucan fiber powder addition [g/kg]	L*		a*		b*
	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying
0	67.57^Ab ± 1.652	68.56^Ad ± 2.389	0.28 ^Aa ± 0.355	0.08^Aa ± 0.401	25.83^Be ± 1.557	23.86^Ae ± 1.696
40	66.07^Ab ± 2.465	65.78^Ac ± 1.286	0.90 ^Bb ± 0.130	0.60^Ab ± 0.185	24.58^Bd ± 1.533	21.32^Ad ± 1.083
80	60.45^Aa ± 6.067	65.45^Bc ± 3.732	1.47 ^Bc ± 0.255	0.88^Ab ± 0.360	21.78^Bc ± 1.305	20.65^Acd ± 1.000
120	60.90^Aa ± 3.666	62.32^Ab ± 3.829	1.90 ^Ad ± 0.358	1.68^Ac ± 0.371	19.43^Ab ± 0.987	19.53^Abc ± 1.419
160	59.34^Aa ± 2.511	60.75^Ab ± 1.951	1.99 ^Ad ± 0.279	1.76^Ac ± 0.249	18.55^Aab ± 1.161	18.55^Ab ± 1.232
200	57.99^Aa ± 3.627	58.83^Aa ± 3.436	2.46 ^Be ± 0.224	1.86^Ac ± 0.417	17.78^Ba ± 1.209	16.56^Aa ± 0.997

Note: Means ± standard deviations (n = 10). ^(a-e) Means within a column with different superscripts are significantly different (P ≤ 0.05). ^(A-B) Means within a row with different superscripts are significantly different (P ≤ 0.05).

Nota: Promedios ± desviaciones estándar (n = 10). ^(a-e) Los promedios en una misma columna con distinto superíndice son significativamente diferentes (P ≤ 0,05). ^(A-B) Los promedios en una misma fila con distinto superíndice son significativamente diferentes (P ≤ 0,05).

Color measurement of pasta samples after cooking is shown in Table 3. It can be observed that the L* value for cooked pasta was lower than that for dry pasta samples. Conventionally, dried samples did not differ significantly depending on the level of flour substitution up to 160 g/kg of oat β-glucan fiber powder. Pasta with 200 g/kg of oat fiber powder differed significantly from the control and had the lowest value of L* (49.13 ± 7.378). Vacuum-dried pasta samples did not show a difference in lightness up to 80 g/kg of oat β-glucan fiber powder. In samples with higher flour substitution, a significant decrease of the L* value was observed. The redness of cooked pasta dried by both methods increased with increasing semolina substitution level (with the exception of vacuum-dried pasta with 40 g/kg of oat β-glucan fiber powder). Vacuum-dried pasta with 40, 120, and 200 g/kg showed significantly (P ≤ 0.05) lower redness compared to convection-air dried pasta, while the rest of the samples did not differ significantly. The yellowness was unaffected by the drying method and by oat β-glucan fiber powder addition up to 120 g/kg. In samples with higher semolina substitution, a decrease of the b* value compared to control was observed.

Table 3. Color measurements for cooked pasta samples with oat β-glucan fiber powder.

Tabla 3. Mediciones de color para las muestras de pasta cocinada con fibra de avena β-glucano en polvo.

Oat β-glucan fiber powder addition [g/kg]	L*		a*		b*
	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying	Convection-air drying	Vacuum-drying
0	57.26^Ab ± 8.256	65.70^Bb ± 7.474	−2.28^Ad ± 0.534	−2.47^Ad ± 0.240	18.45^Ac ± 2.830	18.20^Ab ± 1.554
40	57.20^Ab ± 6.015	59.19^Aab ± 2.229	−1.80^Bc ± 0.608	−2.93^Ad ± 0.429	17.94^Ac ± 1.611	17.04^Aab ± 1.732
80	55.20^Aab ± 8.593	60.17^Aab ± 9.078	−1.38^Ac ± 0.513	−1.60^Ac ± 0.594	17.69^Ac ± 2.003	16.93^Aab ± 1.305
120	54.94^Aab± 7.444	55.32^Aa ± 5.337	−0.47^Bb ± 0.521	−1.02^Ab ± 0.489	17.13^Abc ± 1.343	16.40^Aab ± 2.359
160	52.32^Aab ± 7.713	56.24^Aa ± 13.318	−0.11^Ab ± 0.239	−0.07^Aa ± 1.088	15.77^Aab ± 1.262	15.97^Aa ± 1.875
200	49.13^Aa ± 7.378	54.01^Ba ± 6.850	0.56^Ba ± 0.474	0.01^Aa ± 0.385	15.04^Aa ± 1.420	15.25^Aa ± 4.578

Note: Means ± standard deviations (n = 10). ^(a-d) Means within a column with different superscripts are significantly different (P ≤ 0.05). ^(A-B) Means within a row with different superscript are significantly different (P ≤ 0.05).

Nota: Promedios ± desviaciones estándar (n = 10). ^(a-d) Los promedios en una misma columna con distinto superíndice son significativamente diferentes (P ≤ 0,05). ^(A-B) Los promedios en una misma fila con distinto superíndice son significativamente diferentes (P ≤ 0,05).

Similar results were obtained by Chillo et al. (2008) who reported a decrease of lightness and yellowness in pasta fortified with bran and buckwheat flour. Knuckles, Hudson, Chiu, and Sayre (1997) also reported lower lightness and b* values in pasta supplemented with barley β-glucan. However, Chillo et al. (2011), who studied the effect of two barley β-glucan concentrates on pasta quality, did not observe significant differences in fortified pasta compared to control samples. The absence of differences in pasta color reported by Chillo et al. (2011) is likely due to the low percentages of barley fractions used (up to 100 g/kg).

The observed decrease of lightness and an increase of redness reported here may be a result of non-enzymatic browning. At very high temperatures, Maillard reactions may occur, which leads to the formation of melanoidins, brown-colored nitrogenous polymers and co-polymers (Anese et al. 1999). The presence of brown products originating from Maillard reactions causes an increase in brown pasta color and a decrease of lightness. Due to the reduction of the solvent’s boiling point in vacuum-drying technology, lower temperatures can be used during pasta processing, resulting in higher lightness and lower redness of the final product. However, lower temperatures used during vacuum-drying might have resulted in higher losses of yellow pigment during pasta processing. Higher yellowness of uncooked pasta samples dried by VHT technology might be due to the thermal inactivation of bleaching enzyme, lipoxygenase, which occurs at high temperature drying.

3.3. Textural properties

The textural properties of pasta, especially the ability to maintain form during cooking, are related to the cooking quality (Del Nobile, Baiano, Conte, & Mocci, 2005). The hardness (firmness) of pasta is determined as the peak force of compression during a simulation of the force required to penetrate pasta with teeth and represents the resistance to the first bite (Kruger, Matsuo, & Dick, 1996). Hardness measurements are presented in Figure 1. It can be observed that the firmness of cooked pasta decreases with increasing addition of oat β-glucan fiber powder for both drying methods. These data are in line with the findings of Cleary and Brennan (2006), who also reported a loss of hardness in pasta fortified with barley β-glucan fiber. Firmness decrease may be attributed to the higher moisture of cooked pasta with addition of fiber additives than in control samples due to higher water absorption (Tudorica et al., 2002). Additionally, loss of hardness can be a result of physical disruption of the protein matrix within the pasta due to the presence of non-gluten additives.

Figure 1. Hardness of pasta with oat β-glucan fiber powder dried in a convection-air and vacuum dryer (n = 5).

Figura 1. Dureza de la pasta con fibra de avena β-glucano en polvo por convección forzada y con secador al vacío (n = 5).

The drying method had a significant (P ≤ 0.05) impact on pasta hardness. Vacuum-dried samples showed lower hardness values than samples dried in a convection-air oven, which may be a result of higher water absorption of the pasta dried under reduced pressure. Moreover, pasta dried under reduced pressure showed a lower decrease of firmness in samples with increasing levels of β-glucan powder addition.

The results of adhesiveness measurements for convection-air and vacuum-dried pasta with oat β-glucan fiber powder are presented in Figure 2. Adhesiveness is a measure of the force needed to pull the probe away from a pasta sample and is related to the amount of amylose leaching from the gelatinized starch granules (Del Nobile et al., 2005; Sozer, Dalgıç, & Kaya, 2007). Generally, a decrease of adhesiveness with an increase of the oat β-glucan powder addition level for both drying methods was observed. The lowest value was achieved in the vacuum-dried sample with 200 g/kg of oat powder. A decrease of hardness and adhesiveness of pasta with an increase of oat β-glucan fiber powder addition resulted in a softer and less sticky final product. These results are in line with the findings of Cleary and Brennan (2006), who also observed lower stickiness of pasta fortified with barley β-glucan concentrates. However, contrasting results have been reported by Chillo et al. (2011), who observed a significant increase of adhesiveness in pasta samples with barley β-glucan concentrates. This higher adhesiveness proposed to be due to the gluten network being unable to entangle β-glucan and develop a strong structure.

Figure 2. Adhesiveness of pasta with oat β-glucan fiber powder dried in a convection-air and vacuum dryer (n = 5).

Figura 2. Adhesividad de la pasta con fibra de avena β-glucano en polvo secada por convección forzada y con secador al vacío (n = 5).

3.4. TDF and β-glucan content

The results of TDF measurements in convection-air and vacuum-dried pasta with oat β-glucan fiber powder addition are presented in Figure 3. TDF content increased with an increase of oat β-glucan fiber powder addition. The control sample, prepared from durum wheat semolina, contained 23 g/kg of TDF. Similarly, the total β-glucan content in pasta increased with an increase of oat β-glucan fiber powder addition, as presented in Figure 4. According to Regulation (EC) No 1924/2006, food products are permitted to be marked with the nutrition claim “high in fiber” if it contains at least 6 g of fiber per 100 g of product. This value was obtained for pasta with 80 g/kg of oat β-glucan fiber powder. Furthermore, pasta with 80 g/kg of semolina substitution contained over 12 g/kg of β-glucan. The drying method did not have a significant impact on either the TDF or β-glucan content.

Figure 3. TDF content in pasta with oat β-glucan fiber powder addition.

Figura 3. Contenido total de fibra alimentaria en pasta con adición de fibra de avena β-glucano en polvo.

Figure 4. Total β-glucan content in pasta with oat β-glucan fiber powder addition.

Figura 4. Contenido total de β-glucano en la pasta con adición de fibra de avena β-glucano en polvo.

4. Conclusions

The addition of oat β-glucan fiber powder and vacuum-drying had an impact on the cooking quality, textural properties, and color of durum wheat pasta. Incorporation of oat fiber powder into the recipe caused an increase in the swelling index, water uptake, and cooking loss values. Moreover, pasta with semolina substitution was darker, softer, and less sticky compared to control samples. Vacuum-drying achieved a higher cooking quality of pasta than in samples dried by VHT technology. Addition of 80 g/kg of oat β-glucan fiber powder increased the TDF content to a level that would permit using the nutrition claim “high in fiber” for pasta product (according to Regulation [EC] No 1924/2006). Pasta fortified with 80 g/kg showed preferable water absorption during cooking, similar color of cooked pasta, and adhesiveness and slightly lower hardness compared to control. Moreover, our data suggest that vacuum-drying results in a better quality of pasta with 80 g/kg of substitution compared to conventionally dried samples probably due to better prevention of deterioration of pasta structure. These results illustrate that addition of oat β-glucan fiber powder is a feasible approach for the production of a high fiber pasta product.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was realized within the project number [POIG.01.03.01-14-041/12] “Bioproducts”, innovative technologies of pro-health bakery products and pasta with reduced caloric value co-financed by the European Regional Development Fund under the Innovative Economy Operational Programme 2007–2013.