2.4.1. FTIR Analysis of Flours

FTIR analysis allowed the identification of changes in bonding and possible interactions between composite flour components, underlying the impact of GP addition to WWF. The representative spectra of OGP and control samples is presented in Figure 1 and shows the peaks of the functional groups and the vibration ways of the compounds. Several peaks were identified in the analyzed spectra (650–4000 cm–1) and were attributed to the molecular linkages of some chemical components such as starch, proteins and polyphenols.

The deconvoluted spectra in the range of 800–1300 cm−<sup>1</sup> (Figure 1b1) showed the characteristics of starch grains. The amount of hydrated starch structures was identified at 995 cm−<sup>1</sup> , the amorphous starch at 1022 cm−<sup>1</sup> and the short-ordered starch structures at 1047 cm−<sup>1</sup> [30]. No significant changes (*p* > 0.05) were observed in starch structure between OGP and control samples (Table 3). The intermolecular associations were identified at 1613–1620 cm−<sup>1</sup> , the intramolecular associations at 1627–1635 cm−<sup>1</sup> , β-sheets structures at 1620–1644 cm−<sup>1</sup> , α-helix at 1650–1660 cm−<sup>1</sup> and β-turn at 1660–1680 cm−<sup>1</sup> [31,32]. The OGP sample presented higher inter- and intra-molecular associations compared to the control, which lacked absorbance for intramolecular associations. Significant lower (*p* < 0.01) α-helix conformations were identified for OGP compared to the control, while β-turn and

antiparallel β-sheets structures were higher (Table 3). The presence of fibers could be observed from the peaks at 1149 and 1077 cm−<sup>1</sup> [30], while the phenolic compounds could be identified at 1609–1608 and 1519–1516 cm−<sup>1</sup> [33] (Figure 1b2) and 1747 cm−<sup>1</sup> . the peaks at 1149 and 1077 cm−1 [30], while the phenolic compounds could be identified at 1609–1608 and 1519–1516 cm−1 [33] (Figure 1b2) and 1747 cm−1.

*Plants* **2021**, *10*, 926 6 of 17

**Figure 1.** (**a**) Average spectra of optimal wheat-grape peels (OGP) and control samples in mid-infrared region; (**b1**) starch components' deconvoluted spectra; (**b2**) protein and polyphenol components' deconvoluted spectra. **Figure 1.** (**a**) Average spectra of optimal wheat-grape peels (OGP) and control samples in mid-infrared region; (**b1**) starch components' deconvoluted spectra; (**b2**) protein and polyphenol components' deconvoluted spectra.

2.4.2. Pasta Chemical Properties **Table 3.** Optimal and control product properties.


Radical scavenging activity (%) 38.74 ± 1.14 a 20.15 ± 0.26 b RDS (% dm) 54.38 ± 0.24 a 69.78 ± 0.69 b OGP—optimal formulation of wheat flour with grape peels, RDS—rapid digestible starch, SDS—slowly digestible starch, dm—dry matter, a–b means in the same row followed by different letters are significantly different (*p* < 0.05).

OGP—optimal formulation of wheat flour with grape peels, RDS—rapid digestible starch, SDS slowly digestible starch, dm—dry matter, a–b means in the same row followed by different letters

SDS (% dm) 19.61 ± 0.95 a 17.35 ± 0.20 b

#### 2.4.2. Pasta Chemical Properties *Plants* **2021**, *10*, 926 7 of 17 *Plants* **2021**, *10*, 926 7 of 17

The chemical compositions of the OGP and control sample are presented in Table 3. GP addition to wheat flour caused a significant (*p* < 0.01) increase of the protein, lipid, ash and carbohydrate contents (Table 3) of pasta. The OGP sample presented higher radical scavenging activity (38.74%) compared to the control (20.15%). On the other hand, cooked pasta RDS significantly decreased (*p* < 0.01) when GP was added, while SDS increased compared to the control. GP addition to wheat flour caused a significant (*p* < 0.01) increase of the protein, lipid, ash and carbohydrate contents (Table 3) of pasta. The OGP sample presented higher radical scavenging activity (38.74%) compared to the control (20.15%). On the other hand, cooked pasta RDS significantly decreased (*p* < 0.01) when GP was added, while SDS increased compared to the control. GP addition to wheat flour caused a significant (*p* < 0.01) increase of the protein, lipid, ash and carbohydrate contents (Table 3) of pasta. The OGP sample presented higher radical scavenging activity (38.74%) compared to the control (20.15%). On the other hand, cooked pasta RDS significantly decreased (*p* < 0.01) when GP was added, while SDS in-

#### 2.4.3. Microstructure Analysis 2.4.3. Microstructure Analysis

creased compared to the control.

Dry pasta microstructure analysis revealed a well-developed matrix comprised of a gluten network, which encompassed starch grains and fiber fractions (Figure 2). In both the control and OGP samples round and lenticular starch shapes with smooth surfaces were observed. The addition of GP resulted in a compact dough structure in which the proteins embedded the fine particles of fibers and starch grains. Dry pasta microstructure analysis revealed a well-developed matrix comprised of a gluten network, which encompassed starch grains and fiber fractions (Figure 2). In both the control and OGP samples round and lenticular starch shapes with smooth surfaces were observed. The addition of GP resulted in a compact dough structure in which the proteins embedded the fine particles of fibers and starch grains. 2.4.3. Microstructure Analysis Dry pasta microstructure analysis revealed a well-developed matrix comprised of a gluten network, which encompassed starch grains and fiber fractions (Figure 2). In both the control and OGP samples round and lenticular starch shapes with smooth surfaces were observed. The addition of GP resulted in a compact dough structure in which the

(**a**) (**b**) (**a**) (**b**)

**Figure 2.** Dry pasta microstructure of (**a**) control and (**b**) optimal sample with grape peels (OGP): SG—starch grain; P protein matrix; F—fiber. **Figure 2.** Dry pasta microstructure of (**a**) control and (**b**) optimal sample with grape peels (OGP): SG—starch grain; P—protein matrix; F—fiber. **Figure 2.** Dry pasta microstructure of (**a**) control and (**b**) optimal sample with grape peels (OGP): SG—starch grain; P protein matrix; F—fiber.

proteins embedded the fine particles of fibers and starch grains.

Dough ingredients influenced the pasta extrusion process, which resulted in surface structure changes. The addition of GP caused a slight increase of pasta surface roughness, as can be seen in Figure 3. OGP pasta presented an uneven surface compared to the control. The alternation of high and low regions was given by the use of the *rigatoni* mold. Dough ingredients influenced the pasta extrusion process, which resulted in surface structure changes. The addition of GP caused a slight increase of pasta surface roughness, as can be seen in Figure 3. OGP pasta presented an uneven surface compared to the control. The alternation of high and low regions was given by the use of the *rigatoni* mold. Dough ingredients influenced the pasta extrusion process, which resulted in surface structure changes. The addition of GP caused a slight increase of pasta surface roughness, as can be seen in Figure 3. OGP pasta presented an uneven surface compared to the control. The alternation of high and low regions was given by the use of the *rigatoni* mold.

**Figure 3.** Three-dimensional dry pasta surface of (**a**) control and (**b**) optimal sample with grape peels (OGP). **Figure 3. Figure 3.**  Three-dimensional dry pasta surface of ( Three-dimensional dry pasta surface of (**aa**) control and (**b**) optimal sample with grape peels (OGP). ) control and (**b**) optimal sample with grape peels (OGP).
