Effect of Microwave–Vacuum Drying and Pea Protein Fortification on Pasta Characteristics

Abstract

The widespread popularity of pasta has driven innovations in formulations and production technologies to enhance its versatility. Techniques such as alternative drying methods and fortification of wheat pasta seek to improve the nutritional value and functional properties of pasta products, thereby increasing their attractiveness to consumers. This study aimed to evaluate the effects of microwave–vacuum drying versus conventional drying on the characteristics of durum wheat semolina pasta, including moisture content, water activity, microstructure, colour, texture, weight gain factor, and cooking loss. Three types of pea protein concentrates (80, 84, and 88% dry matter) were used at levels of 3, 6, and 9% (g/100 g flour). Results indicated that microwave–vacuum drying had a significant impact on the physical properties and cooking quality of pasta. Microwave–vacuum drying caused material puffing, resulting in microstructure with high open porosity (64.1%) and minimal closed porosity (0.1%). This has likely contributed to the short rehydration time (2 min in boiling water) of produced pasta, effectively transforming it into an instant food product. All pasta samples had low water content (<9%) and water activity (<0.4), which ensure food safety. The microwave–vacuum-dried pasta weight gain factor (2.2) was lower than in the conventionally dried pasta (2.8). The firmness of microwave–vacuum-dried pasta was significantly higher (135 g) than that of conventional pasta (16 g). Fortification with pea protein enhanced porosity but did not affect pasta’s culinary parameters, such as weight gain or cooking loss, although it resulted in darker pasta (p = 0.001), especially notable with a 9% pea protein addition.

1. Introduction

Durum wheat flour (semolina) is considered the best raw material for pasta production. It is a good source of low-glycaemic-index carbohydrates with low fat and sodium contents [1,2,3]. However, most pasta is produced from refined flour, which is rich in easily digestible carbohydrates. These products have a low fibre content and other biologically active compounds, such as phenolic acids, flavonoids, and vitamins [1,2,3,4,5,6]. Moreover, a great limitation of pasta lies in the deficiency of lysine and threonine, leading to an insufficient biological value of the protein content [4,5,6,7].

There is a growing demand among consumers for high-protein products. The food industry, with this in mind and the state of the natural environment, is proposing the usage of plant proteins instead of animal proteins. The literature data prove that enriching pasta with alternative additives increases its nutritional value [5,6,7,8,9]. Alternative additives that are rich in protein or deficient amino acids may include ingredients derived from pseudo cereals, legumes, wheat germ, spinach, egg white, banana, potato juice, and mushroom powder [3,4,5,6,7,8,9,10,11,12,13,14,15]. Legume proteins are rich in lysine but have a relatively low content of sulphur-containing amino acids (methionine, cysteine, and tryptophan) [16]. Consequently, legumes and grains complement each other nutritionally, forming a comprehensive balance of essential amino acids [6,11,12,13,14]. Enriching pasta with additives made from legumes such as flour, concentrate, or isolate increases its nutritional value. Research has demonstrated a significant increase in protein and mineral content in pasta with the addition of legume products [7,8,12,14,15]. The use of pea protein deserves particular attention. Depending on the variety, 100 g of dry matter of peas may contain 25–35 g of protein, 1–3.9 g of fat, 33–47 g of starch, 26 g of dietary fibre, and 3–4 g of mineral compounds in the form of ash [16]. In addition, peas are a source of biologically active compounds such as thiamine, pantothenic acid, folic acid, and ascorbic acid. Unlike other legumes, beans, and soybeans, peas do not contain antinutritional substances, and the production of preparations in the form of a concentrate or isolate leads to improved functional properties of pea protein. The biological value of pea protein is 48–69%, and the limiting amino acid is tryptophan [17]. Therefore, the easiest way to increase the biological value of protein is to include it in cereal products. Pea protein concentrates and isolates with different protein content and functional properties are available on the market. This necessitates testing and checking the possibility of using commercial pea protein in pasta. Studies of commercial pea protein (concentrates and isolates) showed that one of the basic flavours was cereal/grain [18]. It can be assumed that commercial preparations of pea protein can be used in pasta without changing its flavours. However, modification of the basic pasta recipe by adding alternative raw materials to wheat flour disrupts the structure of gluten proteins. This affects the deterioration of the physical properties of pasta [10,14,15,19,20,21]. The structure and texture change, hardness, and plasticity are reduced; stickiness increases; and the loss of dry substances during cooking increases [12,13,18,20,21].

In pasta production, drying plays a critical role. During drying, due to the simultaneous heat and mass transfer, dehydration occurs and the water activity of the material decreases. These transport phenomena strongly influence the physical properties of the material, such as moisture content, structure, density, and porosity, which determines the qualities of the final product [22]. Pasta is most often dried by convection at 70–90 °C to obtain a moisture content of 11–13% [1]. However, slow heat transfer, long drying time, high energy consumption, costs and the poor rehydration characteristics of the convection-dried products are disadvantageous [23]. These problems have promoted research into alternative drying methods [23,24]. During microwave–vacuum (MV) drying, the material is heated using microwaves in a low-pressure environment [24,25]. The rapid process of water evaporation under reduced pressure produces material with a porous structure—a phenomenon commonly referred to as puffing [24]. Microwave–vacuum drying is characterised by facilitated mass transfer from the material’s centre to its outer layers, lower drying temperatures, and a low oxygen concentration in the drying chamber compared to convective drying [25,26]. This facilitates the preservation of the product’s taste, aroma, colour, and nutritional properties. The loss of thermolabile compounds such as vitamins and colourants in materials subjected to MV drying is significantly minimised [26]. Properly selected low pressure during MV drying protects the material from overheating and increases the intensity of water evaporation [24,25,26,27,28]. According to Carvalho et al. [28], the use of a vacuum causes the lower product temperature and shorter drying time. The consequence of this limited oxidation is maintaining the colour and the taste of the primary product. Research conducted by Marzec and Ambroziak [27] showed that the microwave–vacuum technique can be used to successfully dry pasta made from semolina and common wheat flour with the addition of cocoa.

The drying parameters used, microwave power: 400 W; pressure: 35, 45, and 55 hPa; and drying time: 100 s, allowed for obtaining high-quality products. The pasta was characterised by a very short hydration time; so, it can be an alternative to instant pasta. The drying parameters used resulted in obtaining pasta with a water content of up to 10% and water activity lower than 0.4. Microwave–vacuum drying was successfully used to produce dried snacks from quince [29] and carrot [30]. It was proven that this method can be an alternative to freeze-drying. Using the microwave–vacuum method, the drying speed increases significantly, and the time is shortened by 70–90% compared to convective drying [22]. Microwave–vacuum drying of barley grain resulted in lower product temperatures and a 35.9% reduction in drying time compared to microwave drying alone [28]. Combining vacuum and microwaves makes drying fast and energy-efficient [22,31]. Due to lower energy consumption, costs may be lower than traditional drying [32].

The search for innovative solutions continues to aim at refining the drying process and enhancing the nutritional value, as well as the qualitative and culinary characteristics, of the resulting pasta. Therefore, the objectives of this research were the following: (i) to evaluate and compare the effects of conventional drying and microwave–vacuum drying on pasta quality and (ii) to examine the changes prompted by pea protein addition on the microwave–vacuum-dried pasta. These findings may promote the new thermal processing method to produce enriched pasta using a highly efficient drying process.

2. Materials and Methods

2.1. Materials

The investigated material consisted of conventionally dried and microwave–vacuum-dried pasta made from semolina (Polskie Młyny, Teresin, Poland) and water. In addition, pasta with commercial pea protein concentrate (H and N), protein isolate (P), and microwave–vacuum-dried pasta. The following types of pasta were produced: semolina pasta—conventionally dried (C) semolina pasta (control sample); microwave–vacuum (MV)-dried semolina pasta with the addition of 3%, 6%, and 9% (g/100 g flour) high amounts of pea protein concentrate with a protein content of 80 (% dry matter) (H3, H6, H9); pea protein concentrate with a protein content of 84 (% dry matter) (N3, N6, N9); and protein isolate with a protein content of 88 (% dry matter) (P3, P6, P9).

The pasta was produced under laboratory conditions at a room temperature of 22 °C. Semolina, water, and plant protein preparations were weighed using an analytical balance type PS 600/C/2 (Radwag, Radom, Poland). The water content was adjusted to ensure a moisture level of approximately 35 ± 2% (g H₂O/100 g dough) in the dough. Subsequently, the ingredients were mixed in a Thermomix TM31-1 (Vorwerk & Co., Wuppertal, Germany) for 8 min in dough-kneading mode. Rolling was performed using a kitchen robot (KitchenAid, Benton Harbor, USA). The dough was rolled into sheets until a 1 mm thickness was achieved. The final step involved shaping the dough into strands using a kitchen robot equipped with a spaghetti cutter, followed by cutting the strands into 40 mm lengths.

2.2. Drying Procedure

Conventional drying was carried out in a chamber dryer Sup-65WG (WAMED Medical Equipment Factory, Warsaw, Poland) under constant parameters: drying temperature, pressure, and drying time (70 °C, 101 hPa, 10 h). Microwave–vacuum drying was conducted in a microwave–vacuum dryer (Promis-Tech, Wrocław, Poland) under constant parameters: constant drying temperature, microwave power, pressure, drying time, and sample stabilisation time (40 °C, 400 W, 40 hPa, 500 s, stabilisation time 100 s). Drying parameters were selected based on previous experience [27] and preliminary investigations performed on strand-shaped pasta. Each type of material was dried in two replicates. Research samples were cooled to room temperature and stored for further analysis in bags made of polypropylene film (Pakmar, Warsaw, Poland) at room temperature and relative air humidity of 65–70%. The dry pasta samples are shown in Figure 1.

2.3. Moisture Content and Water Activity

The moisture content in the dried pasta was determined according to the literature [27] by drying the test material in a laboratory dryer Sup-65WG (WAMED Medical Equipment Factory, Warsaw, Poland). The samples were dried at 105 °C for 3 h. Water activity was measured using the AquaLab Series 3 water activity metre (Decagon Devices, Inc., Pullman, WA, USA) at a temperature of 22 ± 1 °C. The measurement was conducted in two replicates.

2.4. Microstructure

The microstructure of dried pasta was examined using a Phenom XL scanning electron microscope (Phenom World B.V., Eindhoven, The Netherlands). Samples of approximately 10 mm in length were affixed to a stage and sputter-coated with gold using a low-vacuum sputter coater Leica EM ACE200 (Leica Microsystems, Wetzlar, Germany). The coating thickness was 5 nm. Observations were made in ten replicates at 1000× magnification, capturing images at random locations.

The 3D structure of the dried pasta was investigated using X-ray microtomography with Skyscan 1272 v.1.1.7 (Bruker microCT, Kontich, Belgium). Scanning was performed in two replicates, with a scanning time of 45 min for each sample, using radiation source parameters of 40 kV and 193 μA without a filter. During the scan, two-frame averaging and rotation steps of 0.4° over a total of 360° were used to reduce noise. Images with a resolution of 1344 × 2016 pixels were obtained, and the pixel size of the image was 12.5 μm. Specialized Bruker software (Bruker microCT, Kontich, Belgium) was used for image analysis. Image reconstruction was carried out using NRecon 1.6.9.8 software. For all pasta samples, the same grey scale reconstructions were set. A grey scale threshold range of 90–250 was used. The low grey value referred to pores (air). A CTAn 1.9.3.3 software was used for image analysis. The data-stack margins were clipped to a circle with a diameter of 40 pixels (1 pixel = 12.5 µm). A series of two-dimensional (2D) 597 slices were reconstructed into a 3D image. Then, 3D objects with a VOI size of 9.02 mm³ were measured. The 3D parameters were calculated (Skyscan 2008). A CTvol 3.3.0 software was used to obtain a realistic visualisation of the reconstructed pasta microstructure. Analysis of the obtained images and investigation of 3D structure parameters were conducted using CT Analyser 1.13.11.0+ software.

2.5. Colour

Colour analysis was carried out on the dried pasta (prior to the rehydration process) and on the rehydrated pasta (immediately after rehydration). The analysis was conducted using a Minolta CR-310 instrument (Konica Minolta, Tokyo, Japan) with a reflective method in the CIE L*a*b* colour space. L* represents lightness (white at 100 and black at 0), a* corresponds to red (positive values) and green (negative values), and b* corresponds to yellow (positive values) and blue (negative values). The measurement was performed in five measuring points for each sample. Based on the parameters a* and b*, the colour saturation (C*) was calculated according to the following formulas $C*=\sqrt{\left(\right[{a*]}^2+{\left[b*\right]}^2})$ [29].

2.6. Culinary Parameters

The culinary parameters of cooking loss and weight gain factor were determined during the rehydration of the dried pasta [33]. Five grammes of the test material were weighed on an analytical balance type PS 600/C/2 (Radwag, Poland). The conventionally dried pasta was rehydrated by cooking in 50 cm³ of boiling water for 4 min, occasionally stirring. The microwave–vacuum-dried pasta was rehydrated in 50 cm³ of boiling water for 2 min, occasionally stirring. Rehydrated pasta samples are shown in Supplementary Figure S1.

2.7. Textural Propoerties

The texture analysis was conducted on a texture analyser TA.HD Plus (Stable Micro Systems, Surrey, UK) interfaced with the computer Texture Exponent 32 software (Stable Micro Systems, Surrey, UK). A cylinder dish, which was 40 mm in diameter and 10 mm in height, was filled with cooked pasta (5 g). The compression test was conducted at a velocity of 1 mm/s until a deformation of 6 mm was achieved. The maximum force (firmness) and adhesiveness were determined from the compression curve.

2.8. Statistical Analysis

The obtained results underwent statistical analysis using Statistica 13.3 software (StatSoft, Poland). A one-factor analysis of variance (ANOVA) was performed to assess the influence of the drying method and the pea proteins used. The results were reported as mean ± SD. Tukey’s test was used to detect differences between the mean values of the measured parameters, with a significance level of α ≤ 0.05. The letters indicate homogeneous groups regarding the effect of the type of protein and the amount of added protein in lower- and upper-case letters, respectively.

3. Results

3.1. Moisture Content and Water Activity

To ensure food safety, it is desirable to decrease the moisture content in food products to a minimal water activity level. Drying prolongs shelf life by reducing the moisture content for undesirable chemical reactions and microbial proliferation. The moisture content of pasta samples adheres to stringent standards, not surpassing 10%, a benchmark denoting good quality according to the Codex Alimentarius for this product category. Notably, the moisture content in pasta samples exhibits a range from 5.07% to 8.13% (

Table 1. Moisture content, water activity, and 3D microstructure parameters of conventionally dried (C) and microwave–vacuum-dried (MV) pasta and with the addition different levels of pea protein: 3, 6, 9% (g/100 g flour); type of pea protein: H (80% dry matter), N (84% dry matter), and P (88% dry matter).

Sample Code	Moisture Content (g/100 g)	Water Activity	Percent Object Volume	Object Surface	Object Surface/Volume Ratio	Closed Porosity (Percent)	Open Porosity (Percent)	Structure Model Index
C	6.35 ± 0.91	0.383 ± 0.002	96.65 ± 0.17	48.60 ± 1.62	10.78 ± 0.38	2.40 ± 0.38	0.97 ± 0.21	−17.77 ± 0.52
MV	6.55 ± 0.12	0.343 ± 0.003 bc	35.88 ± 1.24 abc	191.20 ± 11.15	59.00 ± 1.40 a	0.09 ± 0.00	64.08 ± 1.24 abc	0.25 ± 0.10 a
p-value	0.781	0.004 *	<0.001 *	0.003 *	<0.001 *	0.013 *	<0.001 *	<0.001 *
H3	7.47 ± 0.82	0.338 ± 0.000 bcB	33.45 ± 3.16 abc	217.69 ± 18.13	72.13 ± 0.81 bc	0.02 ± 0.01	66.54 ± 3.16 abc	0.71 ± 0.24 ab
H6	8.13 ± 0.55	0.351 ± 0.002 cB	37.67 ± 4.69 bc	224.88 ± 23.51	66.21 ± 1.32 ab	0.07 ± 0.02	62.30 ± 4.70 ab	0.37 ± 0.26 ab
H9	7.79 ± 0.20	0.344 ± 0.003 bcB	28.69 ± 0.15 a	225.98 ± 3.19	87.27 ± 1.70 d	0.02 ± 0.01	71.31 ± 0.16 c	1.15 ± 0.05 b
N3	7.06 ± 0.43	0.331 ± 0.007 abA	38.80 ± 0.07 bc	229.11 ± 27.40	65.41 ± 7.70 ab	0.08 ± 0.06	61.17 ± 0.04 ab	0.42 ± 0.11 a
N6	6.15 ± 0.76	0.316 ± 0.005 aA	37.25 ± 1.34 abc	252.34 ± 9.80	75.14 ± 5.62 bcd	0.01 ± 0.01	62.74 ± 1.35 abc	0.52 ± 0.27 ab
N9	7.93 ± 0.47	0.319 ± 0.001 aA	35.76 ± 0.31 abc	237.97 ± 10.39	73.71 ± 2.58 bc	0.02 ± 0.00	64.23 ± 0.31 abc	0.60 ± 0.06 ab
P3	5.07 ± 2.30	0.337 ± 0.009 bcB	31.26 ± 3.72 ab	223.59 ± 26.41	79.23 ± 0.07 cd	0.01 ± 0.00	68.74 ± 3.72 bc	0.78 ± 0.01 ab
P6	6.99 ± 0.09	0.343 ± 0.001 bcB	40.65 ± 0.65 c	266.00 ± 4.23	72.49 ± 0.01 bc	0.03 ± 0.01	59.34 ± 0.65 a	0.49 ± 0.01 ab
P9	6.99 ± 0.86	0.332 ± 0.000 abB	37.50 ± 0.92 abc	244.71 ± 10.90	72.26 ± 1.46 a	0.02 ± 0.01	62.49 ± 0.91 abc	0.56 ± 0.04 ab
One-way analysis of variance (ANOVA)
Factors	p-value
Protein addition	0.130	<0.001 *	0.008 *	0.051	<0.001 *	0.054	0.008 *	0.005 *
Type of protein	0.089	0.003 *	0.207	0.209	0.615	0.577	0.208	0.268

*—means significant differences at a confidence level of 0.05; the same letters mean no statistically significant differences between the analysed value of parameters; homogeneous groups: a, b, c, d—pea protein addition; A, B—type of protein.

).

The water activity values of all pasta samples were low, varying from 0.316 to 0.351 (Table 1). Across all samples, the water activity consistently remained below 0.6, the minimum water activity threshold required for microbial growth, where physiological activities essential for cell division were inhibited [34]. Maintaining a water activity this low makes the pasta’s shelf life stable and significantly enhances its longevity, ensuring that the product retains its quality throughout its storage [35]. This stability benefits manufacturers as well as provides consumers with the convenience of having a reliable, long-lasting pantry-staple product that requires minimal storage requirements. This underscores the efficacy of the microwave–vacuum-drying method in achieving superior water activity control in the pasta, which contributes to enhanced stability.

3.2. Two-Dimensional Microstructure

Adding alternative flours leads to biochemical changes in protein, starch, or fibre compositions, which affects the pasta structure and thus its quality [3]. In pasta’s microstructure analysis, starch particles exhibit a consistent morphology, primarily manifesting as circular or ellipsoidal shapes, with a noticeable variability in size (Figure 2). In contrast, proteins present irregular shapes within the matrix. Larger starch clusters are visibly dispersed within the protein matrix. The formation of starch agglomerates in the protein matrix is attributed to a combination of partial starch gelatinisation and protein denaturation processes. Notably, there is evidence of damage to certain starch granules (Supplementary Figure S2).

The apparent dark regions observed in the microstructure represent void spaces. In Figure 2, the arrows indicate the voids. The SEM image of conventionally dried pasta shows a more compact product surface and smaller voids. These are due to hot air drying associated with a slow heat transfer by convection and conduction. The increased frequency of voids in microwave–vacuum-dried samples suggests the presence of microcracks in the pasta structure. Structural damage was observed visually. The combination of reduced pressure and microwave heating causes rapid evaporation of water and puffing of the material [22,23,24,26,27,28,29,30,31]. Structural discontinuities contribute to a reduction in overall compactness. The observed cracks play a significant role in pasta properties by facilitating enhanced water penetration during the rehydration process. This phenomenon can be attributed to the improved accessibility of water pathways within the damaged structure, potentially influencing the overall rehydration kinetics [24,36].

3.3. Three-Dimensional Microstructure

Figure 3 shows the 3D microstructure. Conventionally dried pasta retained the shape of threads and microwave–vacuum-dried pasta obtained the shape of tubes. The microwave–vacuum-dried samples had the shape of a tube with a circular cross-section and was filled with pores. According to Ressing et al. [24], puffing is caused by two mechanisms: (i) the application of external vacuum and thus an internal overpressure of the trapped air; (ii) the generation of vapour due to the temperature rise in the dough. Conventionally dried pasta exhibited a lower number of pores, porosity coefficient, and pore volume compared to microwave–vacuum-dried pasta (Figure 3). In traditional pasta, sporadic pores were observed, mainly closed pores, in contrast to the highly porous structure of microwave–vacuum-dried pasta characterised by a substantial proportion of open pores. The structure of conventionally dried pasta shows evidence of tissue shrinkage and collapse, whereas the microwave–vacuum-dried samples exhibited no shrinkage. This difference can be attributed to a lower drying temperature, shorter drying time, and some tissue expansion (puffing) caused by internal water vapour characteristic of microwave–vacuum drying (Figure 3) [27,37]. The conducted research indicates that the pasta-drying method significantly influenced the porosity of the final product (p = 0.008) (Table 1).

A structure model index (SMI) determines the openness and shape of pores composing the 3D structure. Negative SMI values indicate a prevalence of closed pores, while positive values suggest a predominance of open pores. When SMI values are close to 0, pores take on a plate-like shape; a value close to 3 indicates a cylindrical shape, and values close to 4 correspond to a spherical shape [38]. Negative SMI values in conventionally dried pasta suggest a dense structure with closed pores, which leads to a longer cooking time and may provide a springier texture in the rehydrated product. In contrast, SMI values close to 0 for microwave–vacuum-dried pasta indicate a more open, plate-like structure, enhancing rehydration efficiency, resulting in a more convenient method and shorter time for rehydration, thereby improving consumers convenience.

From a technological point of view, adding pea protein may weaken the structure of the pasta [18]. The greatest puffing occurred in pasta with H pea protein concentrate. Three-dimensional projections showed that the use of H pea protein concentrate did not affect the shape of the pasta compared to the microwave–vacuum-dried control sample. The obtained samples had a circular cross-section similar to the control sample (Figure 3). Pasta with N and P pea protein concentrates were characterised by lower puffing, flattening, and did not have as regular of a shape as H. The use of the P pea protein isolate at a level of 9% (g/100 g flour) caused a significant change in the surface structure of the pasta. The surface was irregular and quite porous. According to Mercier et al. [20], the level of pasta fortification with pea protein concentrate had little effect on the properties of dried pasta (water content, density, porosity). Significant differences were caused by the temperature of the conventional drying process (40 and 80 °C).

3.4. Colour Analysis

The colour of pasta plays a crucial role in influencing consumer acceptance, with a bright yellow hue being particularly preferred by consumers [11]. An important factor determining the colour of the pasta is the technology, especially the conditions of the drying process [3,14,39,40]. The conventionally dried and microwave–vacuum-dried pasta differed significantly in terms of lightness (L*) (p = 0.001) and redness (a*) (p = 0.003) (

Table 2. Colour parameters of conventionally dried (C) and microwave–vacuum (MV)-dried pasta and with the addition different levels of pea protein: 3, 6, 9% (g/100 g flour); type of pea protein: H (80% dry matter), N (84% dry matter), and P (88% dry matter).

Sample Code	Dried Pasta				Cooked Pasta
	L*	a*	b*	C*	L*	a*	b*	C*
C	62.79 ± 0.94	1.95 ± 0.35	19.63 ± 0.61	19.72 ± 0.63	67.85 ± 0.52	−0.80 ± 0.11	11.29 ± 0.45	11.32 ± 0.44
MV	74.45 ± 0.87 a	1.16 ± 0.68 a	20.69 ± 1.95 c	20.74 ± 1.89 c	74.45 ± 0.73 e	−0.19 ± 0.16 a	13.50 ± 0.36 ab	13.50 ± 0.36 abc
p-value	0.001 *	0.003 *	0.061	0.071	0.001 *	0.054	0.063	0.064
H3	71.49 ± 0.68 a	2.10 ± 0.11 cde	17.44 ± 0.76 ab	17.56 ± 0.76 ab	72.69 ± 0.55 bc	1.33 ± 0.07 deB	12.46 ± 0.12 aA	12.53 ± 0.11 aA
H6	74.87 ± 1.14 ab	2.11 ± 0.07 cde	19.66 ± 0.06 bc	19.77 ± 0.06 bc	72.29 ± 0.32 b	1.48 ± 0.12 eB	12.71 ± 0.31 abA	12.80 ± 0.32 aA
H9	71.74 ± 2.09 ab	2.88 ± 0.08 f	17.57 ± 0.25 ab	17.80 ± 0.24 ab	70.13 ± 0.66 a	2.15 ± 0.10 fB	12.89 ± 0.39 abA	13.07 ± 0.40 abA
N3	77.57 ± 0.59 b	1.65 ± 0.05 bc	19.93 ± 0.39 bc	19.99 ± 0.38 bc	73.88 ± 0.79 de	0.71 ± 0.27 cdA	13.49 ± 0.65 abcB	13.51 ± 0.66 abcB
N6	72.03 ± 4.32 ab	1.28 ± 0.06 bcd	16.14 ± 0.67 a	16.19 ± 0.67 a	72.03 ± 0.76 b	1.01 ± 0.12 cdeA	14.95 ± 0.21 cdB	14.99 ± 0.21 cdB
N9	74.16 ± 0.67 ab	2.59 ± 0.28 ef	21.08 ± 0.02 c	21.23 ± 0.01 c	72.55 ± 0.23 bc	1.11 ± 0.10 cdeA	14.48 ± 0.32 bcdB	14.52 ± 0.31 bcB
P3	77.04 ± 3.14 b	1.13 ± 0.13 ab	18.88 ± 1.66 abc	18.91 ± 1.67 abc	73.79 ± 0.44 de	0.16 ± 0.11 abA	13.13 ± 0.32 abB	13.18 ± 0.34 abAB
P6	74.03 ± 0.43 ab	2.58 ± 0.04 ef	19.51 ± 0.06 bc	19.67 ± 0.07 bc	73.33 ± 0.58 cd	0.50 ± 0.12 bcA	13.62 ± 0.14 abcB	13.63 ± 0.14 abcAB
P9	68.24 ± 1.06 a	2.42 ± 0.11 def	20.84 ± 0.90 c	20.97 ± 0.90 a	70.89 ± 0.71 a	1.15 ± 0.20 deA	15.36 ± 0.30 dB	16.35 ± 2.13 dAB
One-way analysis of variance (ANOVA)
Factors	p-value
Protein addition	0.039 *	<0.001 *	0.001 *	<0.001 *	<0.001 *	<0.001 *	<0.001 *	<0.001 *
Type of protein	0.683	0.458	0.299	0.324	0.245	0.001 *	0.007 *	0.013 *

*—means significant differences at a confidence level of 0.05; the same letters mean no statistically significant differences between the analysed value of parameters; homogeneous groups: a, b, c, d, e, f—pea protein addition; A, B—type of protein.

). The conventionally dried sample was darker than its microwave–vacuum dried counterpart.

Microwave drying removes moisture by converting it into water vapour, allowing drying to occur without causing surface overheating. Consequently, the microwave–vacuum-dried sample was well preserved, with minimal surface colour degradation [23,26]. A lower temperature and shorter drying duration reduced the impact of Maillard reactions, hence the lower values for a* (redness) [40]. Whereas, conventionally dried samples have been adversely affected by nonenzymatic browning due to the application of higher temperature and longer time, leading to melanoidins development [25,41]. No substantial influence of the drying method on the parameters b* and C* of the dried pasta was observed. It should be emphasised that after cooking the pasta, the L* values differed significantly (Table 2), indicating that the microwave–vacuum-dried sample was lighter than the conventionally dried sample after rehydration.

The colour parameters (L*, a*, b*, and C*) were statistically significant depending on the amount of added pea protein (Table 2). The progressively darker colour of the pasta resulting from the addition of legume flour can be attributed to the increased ash content [14]. Furthermore, commercial pea proteins possess a slight yellow hue, which likely contributes to the pronounced colour changes observed with a higher protein addition. These findings underscore the necessity of analysing the fundamental composition of ingredients.

There are no statistically significant differences in colour parameters (L*, a*, b*, and C*) based on the type of protein in the pasta. The b* values, reflecting the yellow–blue axis, showed a consistent yellow tone across all samples, with values ranging from 16.14 to 21.08 for dried pasta. After rehydration, the yellow hue remained prominent, though the b* values were generally lower, with values ranging from 12.46 to 15.36, suggesting a slight loss in yellowness upon rehydration. Following the cooking process of the pasta, the quantity of added protein caused a colour change with significant differences in L*, a*, and b* parameters. Rehydrating led to a statistically significant difference in the values of a*, b*, and C* for the used types of pea protein.

3.5. Weight Gain Factor and Cooking Loss

The culinary quality and consumer perception of pasta were affected by the drying-process conditions [39]. After rehydration, the microwave–vacuum-dried pasta had a lower water content compared to the conventionally dried pasta (p < 0.001) (

Table 3. The moisture content, culinary, and textural parameters of conventionally dried (C) and microwave–vacuum (MV)-dried pasta and with the addition different levels of pea protein: 3, 6, 9% (g/100 g flour); type of pea protein: H (80% dry matter), N (84% dry matter), and P (88% dry matter).

Sample Code	Moisture Content (g/100 g)	Weight Gain Factor	Cooking Loss (%)	Force (g)	Adhesiveness (g·s)
C	67.92 ± 0.30	2.8 ± 0.4	8.8 ± 1.5	16.25 ± 1.99	−1.17 ± 0.31
MV	56.97 ± 1.15	2.2 ± 0.2	7.7 ± 0.4 B	135.35 ± 14.48 e	−8.04 ± 1.64 b
p-value	<0.001 *	0.016 *	0.063	0.010 *	0.002 *
H3	57.78 ± 2.68	2.2 ± 0.3	6.8 ± 0.5 A	86.43 ± 16.27 cde	−4.91 ± 0.61 ab
H6	56.65 ± 2.40	2.1 ± 0.1	6.0 ± 0.8 A	63.64 ± 9.23 abc	−2.71 ± 1.59 b
H9	55.03 ± 1.62	2.1 ± 0.1	6.1 ± 0.2 A	54.19 ± 10.90 abc	−2.26 ± 1.01 b
N3	58.82 ± 2.36	2.3 ± 0.1	7.3 ± 0.2 AB	53.99 ± 7.46 acb	−3.88 ± 0.67 b
N6	54.59 ± 1.74	2.1 ± 0.1	6.8 ± 3.8 AB	45.59 ± 11.25 abc	−4.62 ± 1.64 ab
N9	61.08 ± 1.88	2.5 ± 0.2	6.7 ± 0.2 AB	91.76 ± 14.93 de	−5.21 ± 3.09 ab
P3	60.18 ± 2.48	2.5 ± 0.2	7.4 ± 0.5 B	38.09 ± 7.30 ab	−2.82 ± 0.50 b
P6	55.64 ± 0.20	2.2 ± 0.2	7.0 ± 0.1 B	45.67 ± 7.62 abc	−3.12 ± 0.32 b
P9	56.41 ± 1.81	2.1 ± 0.1	7.1 ± 1.3 B	32.97 ± 8.53 a	−1.79 ± 0.30 b
One-way analysis of variance (ANOVA)
Factors	p-value
Protein addition	0.057	0.191	0.308	0.001 *	0.001 *
Type of protein	0.399	0.534	0.011 *	0.212	0.276

*—means significant differences at a confidence level of 0.05; the same letters mean no statistically significant differences between the analysed value of parameters; homogeneous groups: a, b, c, d, e—pea protein addition; A, B—type of protein.

). The moisture content of the pasta with added protein after cooking was similar (p = 0.057). In pasta products with a lower moisture content, there are lesser interactions among denatured proteins. As a result, during rehydration, gluten formation and denaturation dominate the swelling and gelatinisation of starch, which can lead to better firmness, providing a better mouthfeel of the final product [42].

According to the literature data, the rehydration weight gain factor for pasta should fall within the range of 2 to 4 [27,33,39]. The weight gain factor after rehydration ranged from 2.6 to 3.5 for the pasta made of common wheat flour and semolina, which was microwave–vacuum-dried at different pressures (35, 45, and 55 hPa) with a microwave power of 400 W [27]. In our work, the rehydration weight gain factor of the pasta ranged from 2.1 to 2.9 (Table 3). The highest value was recorded for conventionally dried pasta, which had to be prepared traditionally, i.e., boiled, unlike the microwave–vacuum-dried pasta rehydrated in boiling water.

Cooking loss is the ability of the gluten–starch network to maintain the physical integrity of the pasta during the cooking process. This parameter should be less than 8% [43]. The cooking loss of conventionally dried pasta was outside the acceptable range of 8.8% (Table 3). In the microwave–vacuum-dried pasta, it was lower at 7.7%, but the difference was not significant (Table 3). This was caused by the compact and low porous microstructure of conventionally dried pasta.

Microwave drying resulted in a lower cooking loss value; however, the difference was not statistically significant compared to the conventionally dried sample. The cooking loss when pasta with pea protein was rehydrated with an optimal rehydration time of 2 min ranged from 6.0 to 7.4% (Table 3). Regardless of the added pea protein, H and P pastas had a cooking loss of less than 8%. The type of pea protein added resulted in a significant difference in cooking loss (p = 0.011), which can be attributed to the varying protein content in the formulations, particularly since P is a protein isolate with an 88% protein content (% dry matter). The substitution of wheat protein with pea protein can be linked to higher cooking losses resulting from structural changes in the protein network [44].

3.6. Textural Analysis

A significantly lower water content was found in cooked microwave–vacuum-dried pasta compared to convection-dried pasta (Table 3). Lower water content after cooking was beneficial because the pasta was firm (Table 3). Hardness is an important feature desired by consumers and is strongly inversely correlated with water content [27]. Previous studies have shown that microwave–vacuum-dried pasta had higher firmness than conventionally dried samples [39]. Microwave processing causes the formation of a compact structure of the starch-protein network and a lower swelling force of starch in the centre of the pasta during cooking [45,46]. Therefore, the penetration of water into microwave-dried pasta is delayed during cooking [47]. Adhesiveness is measured as the negative work after compression when the probe returns. As expected, the adhesiveness showed negative values. The higher adhesiveness of microwave–vacuum-dried pasta (Table 3) may be due to its porous microstructure and probably more even water distribution. The significantly higher porosity of microwave–vacuum-dried pasta could have increased the availability of starch during rehydration, which resulted in high adhesiveness. Studies showed that adhesiveness is closely related to the loss of soluble solids during cooking—the amylose leaching from the gelatinised starch granules [39]. However, no significant differences were observed in cooking-loss values between conventionally dried and microwave–vacuum-dried pasta (Table 3)

Furthermore, the addition of pea protein had a significant impact on the firmness (p < 0.001) and adhesiveness (p < 0.001) of microwave–vacuum-dried pasta. The addition of alternative raw materials such as legumes to semolina pasta often decreases its firmness compared to 100% durum wheat flour [3]. This can reduce consumer acceptance of pea-protein-enriched pasta, as consumers typically expect a firm texture, little stickiness, and a pleasant mouthfeel from pasta products [47].

4. Conclusions

The proposed microwave–vacuum-drying technique for semolina pasta enriched with commercial pea protein facilitates the production of high-quality instant products. The used drying parameters (temperature: 50 °C, pressure: 40 hPa, microwave power: 400 W) resulted in a porous microstructure within a short time frame of 500 s. As opposed to conventional drying, a puffing effect was observed. This significant difference in microstructure of microwave–vacuum-dried pasta contributed to a rapid rehydration time—2 min in boiling water. The pasta samples demonstrated low moisture content and water activity, thus providing microbiological stability and overall safety. Furthermore, the short drying time led to lighter-coloured samples with a reduced yellow hue. The weight gain factor and water content in the rehydrated microwave–vacuum-dried samples were lower, which led to an increased firmness of pasta. The incorporation of pea protein in microwave–vacuum-dried pasta resulted in an open, porous structure that positively influenced cooking loss and adhesiveness, although it decreased the firmness. Preliminary research on consumer acceptance suggests that pea-protein-enriched pasta may be satisfactory; however, given the importance of flavour, texture, and visual characteristics, further sensory analysis is needed. Notably, a 9% addition of pea protein resulted in a darker colour, likely due to the higher ash content associated with legume proteins. In this context, further analyses, particularly regarding the chemical composition of produced pasta, would be beneficial. Overall, the application of the microwave–vacuum-drying method for pasta presents a promising alternative for producing instant noodles without the need for additional processing. Despite the current high initial cost of the equipment, the benefits of reduced processing time and the unique qualities of the final product may yield financial benefits, especially if in the future there is progressive development and increasing popularity of this technology.