**1. Introduction**

Wheat flour is the basic ingredient for many staple foods, such as bread, pasta, muffins, biscuits, etc., consumed worldwide. Food industry evolution implies the development of novel products with high nutritional value that could capture consumers' attention. In countries such as Romania, where the cultivated area of durum wheat (*Triticum durum*) is small, only 1% of the total wheat cultivated area [1], pasta producers usually use common (*Triticum aestivum*) wheat flour for short pasta manufacturing, trying to achieve the quality of durum wheat pasta by employing special processing technologies such as vacuum dough mixing and extrusion.

The nutritional and technological behavior of wheat flour can be changed by applying various physical treatments, one of them being heat-moisture treatment (HMT) which implies flour heating at higher level than the gelatinization temperature and under water restriction (<35%) [2]. HMT is an easy to control process and it is eco-friendly compared to chemical modifications of starch-based matrices. The intensities of component change in wheat flour during treatment depends on the regime applied (temperature, time, and moisture level), but also on the interactions between molecules, especially starch-protein and starch-lipids [3]. The main effects of HMT consist of starch crystalline area disruption, double helices destruction, and a reorganization of the crystallites and interactions between wheat polymer chains [4]. These molecular changes lead to nutritional value enhancement, but also to different technological properties of the final product. Some studies have revealed positive effects of HMT, including improving starch digestibility, increasing resistant and slowly digestible starch, and lowering rapid digestible starch values [4,5]. Dough rheological properties and final product texture are affected by flour treatment,

**Citation:** Iuga, M.; Batariuc, A.; Mironeasa, S. Synergistic Effects of Heat-Moisture Treatment Regime and Grape Peels Addition on Wheat Dough and Pasta Features. *Appl. Sci.* **2021**, *11*, 5403. https://doi.org/ 10.3390/app11125403

Academic Editor: Francisco Artés-Hernández

Received: 10 May 2021 Accepted: 7 June 2021 Published: 10 June 2021

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**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

depending on the amylose content, starch shape deformation that may occur, starch swelling and interactions between continuous and dispersed phases [3,6]. Liao et al. [7] reported higher elastic and viscous moduli of vermicelli pasta dough from HMT potato starch as the moisture content applied was higher, with the textural parameters in terms of hardness, springiness and chewiness also increasing with treatment moisture increase.

The wine industry generates high amounts of valuable by-products that can be successfully incorporated in food formulations as functional ingredients due to their raised quantity of dietary fibers and bioactive compounds with antioxidant properties [8,9]. Grape peels are rich in dietary fibers, 98.5% being represented by insoluble fractions, the chemical composition depending on the variety and vinification process [10]. The potential of grape peels to inhibit oxidative processes is given by their high contents of polyphenols such as anthocyanins, hydroxycinnamic acids, catechins, and flavonols [10,11]. Therefore, grape peels can be used to increase the nutritional and functional value of foods. Gaita et al. [12] reported higher polyphenolics and antioxidant activities of pasta enriched with grape peels. According to the data presented by Savla and Yardi [13], the addition of 5% grape pomace to gluten free pasta caused the increase of fiber content 13.50 times compared to the control. Tolve et al. [14] obtained increases of total polyphenolics content of pasta with grape pomace of 200–500% compared to the control. Gaceu et al. [15] stated that wheat flour supplemented by 15% grape peels presented 90% more fiber than flour without addition, while the calcium and potassium contents were improved by more than 150%. Sant'Anna et al. [16] reported higher cooking loss (5.38–6.35%) of fettuccini pasta with 25–75 g/kg grape marc incorporated, compared to the control (5.45%).

The rheological tests can give valuable information about the interactions between grape peels and wheat flour components and gluten matrices, and could differentiate the rheological behavior of supplemented flour dough during mixing, modelling and drying [17]. Frequency sweep tests can provide information about the differences of dough structures between samples with different ingredients added [18]. For this purpose, the deformation frequency is increased progressively at a constant amplitude of the strain. The results obtained at low frequencies led to the behavior of dough at slow changes of stress, while at high frequencies information of dough response to fast load is given [18]. Dough rheology and final product texture could be negatively affected by the addition of fiber-rich ingredients, depending on the amount and particle size. In order to minimize the negative effects of grape peels addition on dough rheological and pasta texture properties due to the gluten dilution, a small particle size could be used since a smaller impact was observed in previous studies [19]. According to the literature, wheat dough with grape peels added presented higher hardness compared to the control [20], with the elastic and viscous moduli being higher compared to the control [17]. The data presented by Tolve et al. [14] showed an increase in durum wheat pasta firmness of 30% and an increase in adhesiveness caused by the addition of grape pomace, while uncooked pasta luminosity decreased from 65.95 to 43.55 [14].

In Europe, pasta is usually made from durum semolina, while for Asian noodle manufacturing soft wheat flour is used [21]. Soft wheat pasta is usually processed by sheeting and cutting, while pasta from durum wheat is cold-extruded. Thus, compared to durum wheat pasta, soft wheat pasta has a softer and more elastic structure, with a color that ranges from "white to creamy white to moderately yellow". Durum wheat products are characterized as having a harder structure, intense yellow nuance, nutty flavor, stability to overcooking, and a particular eating quality [22]. The intrinsic properties of wheat flour and the processing conditions are the most important factors that influence pasta cooking quality [23].

There are a few researches presenting the impact of HMT applied to wheat. Furthermore, even if there are some papers that showed the influence of grape peels on dough and final product properties, to our knowledge, no studies have been published regarding the combined effect of HMT and grape peels addition on common wheat dough and pasta quality. Thus, the aim of this investigation was to evaluate the synergistic effects of HMT

regime in terms of temperature, time, and moisture content and grape peels addition level on dough rheology and texture and on pasta's functional, physical, and textural properties in order to optimize the production process.

#### **2. Materials and Methods**

#### *2.1. Materials and Treatment Regime*

The wheat flour used for investigation belonged to the *Triticum aestivum* species and was produced in 2019 by Dizing S.R.L. (Brusturi, Neamt, Romania). Grape peels flour (GPF) of the Feteasca Regala variety coming from Iasi Research and Development Center for Viticulture and Vinification (Iasi, Romania) was obtained from grinding in a Kitchen Aid mill (Whirlpool Corporation, Benton Harbor, MI, USA), after manual separation from dried pomace. The particle size of <180 μm was achieved by sieving the resultant flour on a Retsch Vibratory Sieve Shaker AS 200 basic (Retsch GmbH, Haan, Germany). The magnitude of changes caused by heat moisture treatment (HMT) depend on wheat botanical origin, amylose and amylopectin contents, and treatment conditions such as temperature, moisture, and time [6]. The conditions of HMT should be selected in function of cereal type, since native starches present different properties, especially different amylose-amylopectin ratio, and have different processing requirements [24].

HMT of wheat flour was done according to a process outlined in a previous study [25]. The desired moisture was achieved by calculating the appropriate amount of water, according to the native flour moisture previously determined (Figure 1). Water was incorporated in small portions into wheat flour samples by continuous mixing in a sealed system of a Kitchen Aid mixer (Whirlpool Corporation, Benton Harbor, MI, USA), and the mix was placed in hermetically sealed glass containers in 2 cm layers (about 200 g). After 24 h of resting at 20 ◦C for moisture equilibration, the samples were placed in a convection oven for the given time in agreement with the experimental matrix, which was calculated after 30 min of sample thermalization. After 30 min of cooling, the treated flour was dried at 40 ◦C for 12 h, ground, and sieved to obtain a particle size of <300 μm.

**Figure 1.** Heat moisture treatment (HMT) graphical representation.

#### *2.2. Dough and Pasta Manufacturing*

Composite flours from treated wheat flour and grape peels were obtained by 15 min mixing the appropriate amounts of ingredients in a Yucebas Y21 machine (Izmir, Turkey).

Pasta dough with a moisture of 40% was produced by adding the corresponding water to the flour (according to the moisture previously established) and mixing for 5 min in a

Kitchen Aid mixer (Whirlpool Corporation, Benton Harbor, MI, USA). Moisture contents were checked with a Kern DBS thermobalance with infrared emission quartz heaters (Kern, Balingen, Germany). The dough was put for at least 15 min in sealed containers for moisture equilibration, then the pasta was modeled using a rigatoni mold accessory of the Kitchen Aid mixer. Pieces of dough were subjected to rheological and texture analysis before pasta modelling. Samples were dried first for 30 min at 20 ◦C, then 60 min at 40 ◦C, 120 min at 80 ◦C, and 120 min at 40 ◦C [26]. After cooling, pasta was packed in polyethylene bags and kept in a dry place until analysis.

#### *2.3. Synergistic Effects of HMT and GPF on Dough Properties*

#### 2.3.1. Dough Rheological Behavior

Dynamic rheological testing was carried out by means of frequency sweep analysis on a Thermo-HAAKE, MARS 40 (Karlsruhe, Germany) device. Laminated dough samples rested for at least 15 min [27] were placed between the parallel plates at a gap of 3 mm, and the edges were sealed with Vaseline to avoid water evaporation. The elastic (G') and viscous (G") moduli variation with frequency were registered at 20 ◦C in triplicate by increasing the range from 0.1 to 20 Hz, at a strain of 15 Pa, in the linear viscoelastic region previously established. For further optimization, the values of G' and G" at 1 Hz frequency were considered.

#### 2.3.2. Dough Texture

Texture profile analysis (TPA) was used to evaluate dough firmness in triplicate by double cycle compression on a Perten TVT-6700 texturometer (Perten Instruments, Hägersten, Sweden). For this purpose, a spheric piece of dough of 50 g was subjected to analysis at a testing speed of 5.0 mm/s and a trigger force of 20 g [28], with a 35 mm cylindrical probe. The measurements were performed the same day as pasta manufacturing, at 20 ◦C.
