The quality of functional whole-meal durum wheat spaghetti as affected by inulin polymerization degree

Carbohydrate Polymers 173 (2017) 84–90

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The quality of functional whole-meal durum wheat spaghetti as affected by inulin polymerization degree Lucia Padalino a , Cristina Costa a , Amalia Conte a , Maria Grazia Melilli b , Carla Sillitti a,b , Rosaria Bognanni b , Salvatore Antonino Raccuia b , Matteo Alessandro Del Nobile a,∗ a b

University of Foggia, Department of Agricultural Sciences, Food and Environment, Via Napoli 25, 71122 Foggia, Italy National Council of Research, Institute for Agricultural and Forest Systems in the Mediterranean – Catania, Via Empedocle 58, Catania, Italy

a r t i c l e

i n f o

Article history: Received 2 April 2017 Received in revised form 18 May 2017 Accepted 24 May 2017 Available online 30 May 2017 Keywords: Whole-meal flour Inulin Polymerization degree Pasta quality Functional pasta

a b s t r a c t The use of inulin in pasta improves the nutritional value decreasing the glycemic index in the blood after pasta ingestion but it compromises the sensory characteristics in terms of elasticity, firmness, bulkiness and adhesiveness. Thus, in this work, the impact of substituting whole-meal durum wheat flour with inulin on cooking quality, sensory and textural properties, digested starch and chemical composition of spaghetti was investigated. Two types of inulin at two different concentrations (2% and 4%) were adopted: inulin extracted from cardoon roots (CRI) (high polymerization degree) and commercial inulin (CHI) (low polymerization degree) produced from chicory. From the chemical point of view, the sample with 4% CRI showed the greatest total dietary fibres content and the lowest available carbohydrates content. A global acceptable quality was also recorded in all the other technological and sensory properties of enriched pasta with both types and both concentrations of inulin. The most feature of the work is that when CRI was added to the dough, better results were recorded, thus suggesting that for pasta enrichment, the selection of inulin with proper polymerization degree is a strategic factor for final product acceptance. © 2017 Published by Elsevier Ltd.

1. Introduction Functional food can be any food consumed as part of an accustomed diet which, beyond basic nutritional functions, is demonstrated to have physiological benefits and/or reduces the risk of some diseases (e.g. cholesterol-lowering products), improves the general conditions of the body (e.g. pre- and probiotics) and can also be used for curing some illnesses (Menrad, 2003; MarkHerbert, 2004; Siro, Kapolna, Kapolna, & Lugasi, 2008). Functional food can be either an unmodified ‘natural food’ or a food developed by adding, modifying or removing a component from the food (Rakhesh et al., 2015Rakhesh, Fellows, & Sissons, 2015). Pasta is a staple food eaten daily or weekly in quantities constituting a dominant moiety of the diet in many countries, it is regularly eaten in such quantities that constitutes a dominant portion of

∗ Corresponding author. E-mail addresses: [email protected] (L. Padalino), [email protected] (C. Costa), [email protected] (A. Conte), [email protected] (M.G. Melilli), [email protected] (C. Sillitti), [email protected] (R. Bognanni), [email protected] (S.A. Raccuia), [email protected] (M.A. Del Nobile). http://dx.doi.org/10.1016/j.carbpol.2017.05.081 0144-8617/© 2017 Published by Elsevier Ltd.

the diet worldwide (International Pasta Organization, 2014). Pasta is favored by consumers for its versatility, ease of transportation, handling, cooking and storage properties, availability in numerous shapes and sizes, high digestibility, good nutritional qualities and relatively low cost. Therefore, pasta can be used as carrier of specific compounds. It is traditionally manufactured from durum wheat semolina (Rakhesh et al., 2015). Recently, the development of enriched pasta with a high dietary fibre content would be a good way to increase the fibre intake and reduce the glycemic index (Padalino et al., 2015). Dietary fibre is rich in fruits, vegetables and whole grains, and consists of portions of plant foods that are edible and non-digestible by humans (Jones, Lineback, & Levine, 2004). The fibers can be soluble and insoluble. Among the soluble fibers, inulin plays an outstanding role. Inulin is an indigestible fructo-oligosaccharide which naturally occurring plant carbohydrates stored in various amounts in tubers, bulbs and tuberous roots of several edible fruits and vegetables and in particular large amounts in the tubers of Helianthus tuberosus (Jerusalem artichoke) and Cichorium intybus (chicory) (Apolinário et al., 2014; ´ ´ Drabinska, Zielinski, & Krupa-Kozak, 2016). Depending on species and age of the plants, inulin presents different degree of polymerization, from low fructose unit numbers (e.g. chicory with 20 units

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of fructose) until 100 units of some Asteracean plants (Cynara, Echinops, topinambur, etc.) (Raccuia & Melilli, 2004, 2010). In food, oligofructose is more commonly used as sweet-replacer and longer chain inulin is used mostly as fat replacer and texture modifier (Kelly, 2008). Both inulin and oligofructose are used as dietary fiber and prebiotics in functional foods. Its longer chain length makes inulin more useful for pharmaceutical purposes than oligofructose (Maartens et al., 2015). The addition of inulin could compromise sensory, technological and nutritional aspects of pasta and could not be accepted by consumers. Aravind, Sissons, Egan, and Fellows (2012) studied that two inulin types with different degrees of polymerisation and crystallinity have different levels of integration with the starch–gluten matrix during pasta preparation. Recently, Liu et al. (2016) investigated by scanning electron microscopy the effects of three types of inulin with different degrees of polymerization on the structure of protein component of wheat dough (gluten, gliadin and glutenin). Besides, Luo et al. (2017) observed that the gelatinization and retrogradation properties of wheat starch were largely dependent on degree of polymerization and inulin content. The aim of this work was to evaluate the effects of the addition of inulin with different polymerization degrees on the chemical and sensory properties of spaghetti based on whole-meal durum wheat flour. Specifically, inulin extracted from cardoon roots and commercial inulin produced from chicory at two concentrations (2% and 4%) were used. 2. Materials and methods 2.1. Raw material The whole-meal flour (cv Senatore Cappelli) was bought from Molino Riggi (Caltanisetta, Italy). 2.2. Location of the trial, plant material and crop management Cynara cardunculus L. var. altilis DC, line CDL, was cropped in the experimental field of Assoro (EN. 37◦ 30 54 N; 14◦ 16 26 E, 279 m. a.s.l.) located in the internal hilly area of Sicily. Soil characteristics are 64% sand, 24% silt, 13% clay%, 1.5%, organic matter, 1.0‰ total nitrogen, 35 ␮g/g P2 O5 and 403 ␮g/g K2 O. Cultivated cardoon plants were sown on September 2012, using a density of 6 plant m−2 . During the two years of the experiment, the energy inputs for crop management were minimized. Crop water requirements were satisfied by rain and one irrigation per year in May (flowering) with 50 mm of water. In the first year, another irrigation (50 mm of water) was carried during the establishment of the crop. Each year, plants were fertilized with N at 50 Kg ha−1 (October) and two manual weedings were carried out in October and December. In the second year, the crop regrowth was naturally carried out by rainfall. Roots were collected (up to a depth of 40 cm) in May 2014 at Assoro before plant flowering. The crop was two years old. The harvest time was chosen on the basis of inulin metabolism (synthesis and breakdown of the polymer) in cardoon, because in previous studies it was demonstrated plants maximize yields in long polimerisation degree (DP) inulin before flowering, after that inulin breakdown follows to supply energy for heads development and achenes ripening (Melilli et al., 2014; Raccuia & Melilli, 2010). 2.3. Inulin extraction and purification In the laboratory, the moisture content of a representative sample of roots was measured after drying the plant material to a constant weight in a thermo-ventilated drying oven at 105 ◦ C. Fresh roots (consisting of both primary and secondary roots) was washed in cold tap water, scraped and ground to a fine powder.

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100 g of the original homogenate was diluted tenfold with water and put in a boiling water bath for 30 min. After cooling to room temperature the extract was filtered and centrifuged at 3000g for 5 min. The inulin extracted was precipitated at 0 ◦ C overnight. The supernatants was removed and inulin was washed with distilled water and precipitated at 0 ◦ C overnight. The washing process was repeated until inulin was white. The colour was determinate by colorimeter Minolta CR 400. Values of L* upper than 85 has been accepted for purification. Inulin was lyophilized in petri dishes and used for pasta production (called CRI, high DP). On lyophilized inulin the moisture content was determined in a thermo-ventilated oven at 105 ◦ C. The moisture content resulted less than 0.5 g 100 g−1 of fresh weight. To test the effect of the degree of polymerization during the pasta production, commercial inulin from Chicory intibus was pur® chased by Orafti . The mean degree of polymerization was 20–25 fructose units (called CHI, low DP).

2.4. Inulin characterization A representative sample of fresh roots was washed in cold tap water, scraped and ground to a fine powder with a mortar and pestle under liquid nitrogen. One gram of the original homogenate was diluted fivefold with water and put in a boiling water bath for 30 min. After cooling to room temperature the extract was centrifuged at 3000g for 5 min. A part of this fraction was diluted 10-fold with distilled water to analyse free sugars (glucose, fructose, and sucrose) and another fraction (500 ␮L) was hydrolysed at 70 ◦ C for 2 h using 5 ␮L of 3 N HCl to analyse total fructose. Both the fractions were analysed using high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC PAD) (Thermofisher 3000), consisting of a metal-free isocratic pump, a pulsed amperometric detector, a metal-free injection valve with a 20 ␮L injection loop, and a CarboPac PA10 column (4 × 250 mm) with the guard column. The detection cell contained a gold working electrode (1.0 mm in diameter) and an Ag/AgCl reference electrode; the counter electrode was a titanium cell body across the 25 mm thin-layer channel from the working electrode. The column was regenerated with 1 M NaOH for 10 min and equilibrated for 20 min after every run. Pulsed amperometric detection was carried out with the following waveform: t = 0.00 s (E = +0.05 V), t = 0.49 s (E = +0.60 V), and t = 0.62 s (E = −0.60 V). The integration was at 0.28 s (beginning) and 0.48 s (end). The response time was 1 s, and the electric signal was integrated in nanocoulomb (nC). All experiments were carried out at 30 ◦ C under the following elution conditions: 90 mM NaOH with 50 mM Na-acetate for 1 min followed by a linear gradient from 50 to 500 mM Na acetate in 90 mM NaOH over a 60-min period with a flow-rate of 1 mL/min. Quantification was performed on the peak areas with the external standards methods for ␣-glucose, fructose, and sucrose (SIGMA, Steinhem, Germany). The carbohydrate standard solutions to be injected were prepared fresh daily. The maximum DP was recorded counting the peaks over a threshold of 10 nC of the chromatograms obtained in runs of 120 min under the following elution conditions: 90 mM NaOH with 50 mM Na-acetate for 1 min followed by a linear gradient from 50 to 500 mM Na acetate in 90 mM NaOH over a 120-min period with a flow-rate of 0.8 mL/min. Inulin content (I) and the average chain length (mean DP) were calculated as suggested by Baert (1997): I = (F + G) − (f + g + s), mean DP: (F − f − 0.525s)/(G − g − 0.525s) where F and G are total fructose and glucose after acid-hydrolysis and f, g, and s the reducing free sugars fructose, glucose, and sucrose before acid-hydrolysis. All the analyses were performed in duplicate and are reported on a dry matter (DM) basis. Inulin is reported in g kg−1 DM.

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2.5. Spaghetti preparation Spaghetti was produced with commercial whole-meal durum wheat flour cv Senatore Cappelli by using the following operating conditions: whole-meal flour was mixed with water with a rotary shaft mixer (Namad, Rome, Italy) at 25 ◦ C for 20 min so as to obtain a dough with 30% moisture content. Then, the different types of inulin were added to flour at two levels, 2% and 4% (w/w): inulin extracted from cardoon roots (CRI, high DP) and commercial inulin ® produced from chicory (CHI, low DP) (Orafti ). In order to ensure the solubility of the inulin powder, they were previously dissolved in water. Pasta without inulin was produced and used as control (CTRL). The dough was extruded with a 60VR extruder (Namad). The extrusion pressure was about 4 MPa, whereas the temperature of the spaghetti after the extrusion was about 27–28 ◦ C. The extruder was equipped with a screw (30 cm in length, 5.5 cm in diameter), which ended with a bronze die (diameter hole of 1.70 mm). The screw speed was 50 rpm. Subsequently, the pasta was dried in a dryer (SG600; Namad). The process conditions applied were the following: 1st step, time 20 min at 60 ◦ C and 65% moisture (named as external drying); 2nd step, time 130 min at 90 ◦ C and 79% moisture (named as wrapping); 3rd step, time 150 min at 75 ◦ C and 78% moisture (named as drying); 4th step, time 160 min at 45 ◦ C and 63% moisture; 5th step, time 1040 min at 50 ◦ C and 50% moisture. The 4th and 5th steps are used for the cooling phases of spaghetti. 2.6. Sensory analysis Dry spaghetti samples were submitted to a panel of fifteen trained tasters (six men and nine women, aged between 28 and 45) in order to evaluate the sensory attributes. The panelists were selected on the basis of their sensory skills (ability to accurately determine and communicate the sensory attributes such as appearance, odor, taste and texture of a product). The panelists were also trained in sensory vocabulary and identification of particular attributes by evaluating durum wheat commercial spaghetti (ISO 11036, 7304). They were asked to indicate color and resistance to break of uncooked spaghetti. Elasticity, firmness, bulkiness, adhesiveness, fibrous nature, color, odor and taste were evaluated for cooked spaghetti (Padalino et al., 2013). To this aim, a nine-point scale, where 1 corresponded to extremely unpleasant, 9 to extremely pleasant and 5 to the threshold acceptability, was used to quantify each attribute (Petitot, Boyer, Minier, & Micard, 2010). On the basis of the above-mentioned attributes, panelists were also asked to score the overall quality of the product using the same scale.

sel with 50 mL of distilled water and 5 mL maleate buffer (0.2 M pH 6.0, containing 0.15 g CaCl2 and 0.1 g sodium azide per liter) and allowed to equilibrate in a block at 37 ◦ C (GFL 1092; GFL Gesellschaft für Labortechnik, Burgwedel, Germany) for 15 min. Digestion was started by adding 0.1 mL amyloglucosidase (A 7095; Sigma Aldrich, Milan, Italy) and 1 mL of 2 g per 100 g pancreatin (P7545; Sigma Aldrich) in quick succession and the vessels were stirred at 130 rpm. An amount (0.5 mL) of the digested samples was taken at 0, 20, 60 and 120 min for the released glucose analysis. The sample digested to 120 min was homogenized through an Ultra Turrax (Ika Werke, Staufen, Germany). The digested samples were mixed with 2.0 mL of ethanol. After 1 h, the samples were centrifuged (2000g, 2 min) (Biofuge fresco; Heraeus, Hanau, Germany). Finally, the reducing sugar concentration was measured colorimetrically (␭ = 530 nm) using a Shimadzu UV–vis spectrophotometer (model 1700; Shimadzu corporation, Kyoto, Japan). Glucose standards of 10 mg/mL were used. Amyloglucosidase (0.25 mL) (EAMGDF, 1 mL per 100 mL in sodium acetate buffer 0.1 M, pH 5.2; Megazyme International 205 Ireland Ltd., Wicklow, Ireland) was added to 0.05 mL of the supernatant and incubated at 20 ◦ C for 10 min. Afterwards, 0.75 mL DNS solution (10% 3,5-dinitrosalicylic acid, 16% NaOH and 30% Na-K tartrate – Sigma Aldrich) was added to the above solution, heated to 100 ◦ C for 15 min and then cooled at 15 ◦ C for 1 h. Subsequently, 4 mL of distilled water (15 ◦ C) were added to the solution. The results were plotted as glucose release (mg) per g of sample vs. time. The starch digestibility was calculated as the area under the curve (0–120 min) for the tested products, and expressed as the percentage of the corresponding area for white bread (Padalino et al., 2013). 2.9. Spaghetti cooking quality The optimal cooking time (OCT) was evaluated according to the AACC-approved method 66-50 (2000). The cooking loss and the amount of solid substance lost into the cooking water were determined according to the AACC-approved method 66-50 (2000). The swelling index of cooked pasta was determined according to the procedure described by Cleary and Brennan (2006). The swelling index was expressed as following: (weight of cooked spaghetti) − (weight of spaghetti after drying)/(weight of spaghetti after drying). The water absorption of drained pasta was also determined as following: (weight of cooked spaghetti) − (weight of raw pasta)/ (weight of raw pasta)

2.7. Chemical analyses Dry spaghetti samples were ground to fine flour on a Tecator Cyclotec 1093 (International PBI, Hoganas, Sweden) laboratory mill (1-mm screen – 60 mesh). Protein content (% Nx5.7) was analyzed using the micro-Kjeldahl method according to AACC method 46-13 (2000). Total dietary fiber (TDF), soluble water dietary fiber (SDF) and insoluble water dietary fiber (IDF) contents were determined by means of the total dietary fiber kit (Megazyme International Ireland Ltd., Wicklow, Ireland) based on the method of Lee, Prosky, and DeVries (1992). The available carbohydrates (ACH) were determined according to the method of McCleary and Rossiter (2006) as described in the ACH assay kit (Megazyme). 2.8. In vitro digestion and analysis of digested starch The digestion was carried out as described by Padalino et al. (2013). Dry spaghetti samples (5 g) were cooked (5.0 × 1.0 cm lengths) in 50 mL of boiling water to the optimal cooking time (OCT). The cooked spaghetti were tipped into a digestion ves-

Three measurements were performed for each analysis, and the mean values were calculated. 2.10. Spaghetti hardness and adhesiveness For each test, three spaghetti strands (40 mm length) were cooked at the OCT. After cooking, the spaghetti samples were gently blotted and submitted to hardness and adhesiveness analysis by means of a Zwick/Roell model Z010 Texture Analyzer (Zwick Roell Italia S.r.l., Genova, Italia) equipped with a stainless steel cylinder probe (2 cm diameter). The three samples were put side by side on the lower plate, and the superior plate was moved down onto the spaghetti surface. The hardness (mean maximum force, N) and the adhesiveness (mean negative area, Nm) were properly measured. Six measurements for each spaghetti sample were performed. Trial specifications were as follows: preload of 0.3N; load cell of 1 kN; percentage deformation of 25%; crosshead speed constant of 0.25 mm s −1 (Padalino et al., 2013).

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Fig. 1. Free sugars in cardoon inulin (CRI) extract. Extracts have been 10 fold diluted before injection in HPAEC.

2.11. Cooking loss of inulin

3.2. Pasta quality

On 1 ml of residual water of the cooking test, the amounts of inulin eventually released by pasta was determined in HPAEC PAD, using the same method described for inulin extracted from roots. Only the content of fructose was considered for the calculation, because of the glucose released by starch during acid hydrolysis could interfere with the free glucose of the long inulin chain.

The addition of inulin to pasta is expected to influence the structure of pasta, altering the continuity of the protein network, as well as the protein–starch interactions, and consequently the organoleptic characteristics. Recently, Nawrocka, SzymaskaChargot, Mìs, Wilczewska, and Markiewicz (2017) also observed from SEM that the addition of polysaccharides such as inulin caused changes in the structure of gluten proteins mainly due to considerable changes in the conformation of disulphide bridges. Sensory attributes of dry spaghetti samples investigated in this work are listed in Table 1, for both cooked and uncooked samples. Regarding the uncooked spaghetti, all samples recorded a positive score of overall quality, with exception of the 4-CHI sample (pasta enriched with CHI at 4%), mainly due to its low break to resistance value. These results are in accordance with Mastromatteo, Iannetti, Civica, Sepielli, and Del Nobile (2012), who found that the increase of inulin content caused an increase in the brittleness of maize-based spaghetti. The colour of final uncooked enriched pasta was not significantly affected by the inulin addition. Concerning the sensory quality of cooked samples, the increase in inulin amount determined a decline of overall quality (OQS), as compared to the CTRL sample, mainly due to an increase in adhesiveness and bulkiness. These results are consistent with the hypothesis that upon inulin addition a weaker gluten network is formed. The hypothesis was confirmed by Nawrocka, Szymaska-Chargot, Mìs, Wilczewska, and Markiewicz (2017) who observed from FT-Raman spectroscopy the effects of the addition of dietary fibre polysaccharides on the dough. Moreover, on cooking, the starch may not be properly encapsulated within the protein matrix. Therefore, amylose may be free to diffuse toward the spaghetti surface, where it can form a “starchy” layer, resulting in higher levels of stickiness and adhesiveness. Moreover, the samples enriched with inulin showed a slight less elasticity, although there are not significant differences with respect to the CTRL sample. The reduction of pasta elasticity with fibre addition is also consequence of the weak gluten matrix which can be explained by three concomitant factors: the physicochemical nature of inulin fiber, the discontinuity in the protein network caused by inulin addition, and the disruptive behaviour of inulin fibres on the protein-starch binding during pasta formation. In fact, inulin is hygroscopic and competes with starch and proteins for water upon semolina hydration. This may lead to an incomplete gluten hydration, which in turn may determine the formation of a weak gluten network (Nawrocka et al., 2016a,b). In fact, the optimal amount of water is a crucial parameter for the formation of a strong gluten network (Yalla & Manthey, 2006). Concerning the influence of the inulin polymerization degree, data listed in Table 1 suggest that the OQS increased as the inulin

2.12. Data analysis Experimental data were compared by one-way analysis of variance (ANOVA). A Duncan’s multiple range test, with the option of homogeneous groups (P < 0.05), was carried out to determine significant differences between spaghetti samples. STATISTICA 7.1 for Windows (StatSoft, Inc, Tulsa, OK, USA) was used for this aim.

3. Results and discussion 3.1. Inulin characterization ®

Inulin manufactured by ORAFTI (Tienen, Belgium) as Raftilose Synergy1 is an oligofructose enriched-inulin. This is a 1/1 mixture of long chain and short chain fractions of inulin extracted from chicory roots (CHI, low DP) (Cichorium intybus). Inulin is made by a set of linear chains of fructose molecules, with DP ranging between 3 and 65. It can be fractionated into a slowly fermentable long-chain fraction (DP ranging from 10 to 65, average 25) or in a rapidly fermentable fraction made of oligofructose (DP ranging from 3 to 8, average 4). Synergy1 is a mixture of both fractions, and has a high amount of long chains relative to the native product. Inulin from cardoon (CRI, high DP) was extracted and purified in our laboratories. It was possible to extract from 1 kg of dry and peeled roots, a total sugar amount, as sum of glucose, fructose and sucrose of 959 g kg−1 of d.m. Inulin was 820 g kg−1 d.m. Free sugars were 4.0 (glucose), 91.4 (fructose) and 43.5 (sucrose) g kg−1 of d.m. Free sugars characterization is reported in Fig. 1. The maximum degree of polymerization recorded was, in this plant phenological phase, 80 fructose units, with a mean DP of 50 fructose units (Fig. 2). Data confirmed what reported for cardoon in previous works (Raccuia & Melilli, 2011), making cardoon a potentially crop for inulin production in Mediterranean environment. In Fig. 2 is reported an overlay of the chicory (commercial) and cardoon inulin chromatograms obtained in HPAEC-PAD.

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Fig. 2. Inulin profiles from cardoon roots (CRI) (up) and from commercial inulin (CHI) (down). Solutions of both inulin have been prepared dissolving 1 g in 100 ml of hot water. Solutions have been 10 fold diluted before injection in HPAEC. Mean DP = (F − f − 0.525S)/(G − g − 0.525S) where F, G, are the total fructose and glucose after acid-hydrolysis and f, g and s the reducing free sugars fructose, glucose and sucrose before the acid-hydrolysis, respectively.

Table 1 Sensory characteristics of uncooked and cooked spaghetti samples with and without inulin. CRI: Inulin extracted from cardoon roots (high polymerization degree); CHI: Commercial inulin produced from chicory (low polymerization degree). Uncooked Spaghetti

CTRL 2-CHI 2-CRI 4-CHI 4-CRI a–c

Cooked Spaghetti

Color

Break to Resistance

Overall Quality

Elasticity

Firmness

Bulkiness

Adhesiveness

Color

Taste

Overall Quality

7.03 ± 0.22a 7.05 ± 0.30a 7.14 ± 0.28a 7.20 ± 0.30a 7.30 ± 0.30a

6.28 ± 0.35a 6.09 ± 0.28a 6.18 ± 0.34a 5.85 ± 0.28a 6.22 ± 0.34a

6.30 ± 0.30a 6.05 ± 0.33a 6.35 ± 0.28a 5.95 ± 0.30a 6.36 ± 0.35a

6.50 ± 0.30a 6.08 ± 0.30a 6.45 ± 0.36a 5.91 ± 0.25a 6.02 ± 0.28a

6.77 ± 0.36a 6.00 ± 0.34b 6.25 ± 0.40a,b 6.20 ± 0.34a,b 6.25 ± 0.23a,b

6.27 ± 0.28a 5.92 ± 0.25a,b 6.05 ± 0.30a,b 5.62 ± 0.40b 6.00 ± 0.31a,b

6.05 ± 0.30a 5.78 ± 0.30a,b 5.95 ± 0.37a,b 5.30 ± 0.35b 5.73 ± 0.35a,b

7.00 ± 0.33a 7.00 ± 0.42a 7.02 ± 0.40a 7.20 ± 0.42a 7.05 ± 0.35a

7.24 ± 0.27a 7.24 ± 0.24a 7.26 ± 0.26a 7.25 ± 0.20a 7.21 ± 0.25a

6.45 ± 0.31a 5.78 ± 0.27b,c 6.20 ± 0.27a,b,c 5.60 ± 0.31c 6.02 ± 0.25a

Means in the same column followed by different superscript letters differ significantly (p < 0.05).

polymerization degree increased. This is true at both inulin concentrations tested in this work. A possible explanation is that as the inulin polymerization degree increased, the probability that entanglements are formed also increased (Brennan & Tudorica 2008). This should contribute to counteract the drawbacks related to the addition of inulin, improving the strength of the gluten network (Nawrocka et al., 2017b). No effects in terms of odour and taste were recorded after inulin addition. Also Aravind et al. (2012) reported that the odour and taste score were not changed upon inulin addition to durum wheat flour. The effects of both types of inulin on spaghetti technological properties are shown in Table 2. The optimal cooking time decreased with increasing level of inulin, due to the gluten dilution. It is conceivable that a physical disruption of the gluten matrix due to the presence of fibres and the reduction in gluten content as the amount of inulin increased may have facilitated the penetration of

water to the core of pasta (Chillo et al., 2008Chillo, Laverse, Falcone, Protopapa, & Del Nobile, 2008). In general, data listed in Table 2 highlight a rise of the cooking loss in spaghetti samples added with inulin when compared the CTRL sample. Again, this could be to due to a disruption of the protein-starch interactions and the uneven distribution of water within the pasta matrix, due to the competitive hydration tendency of the fiber, preventing optimal protein hydration during dough formation (Tudoricã, Kuri, & Brennan, 2002). Regarding the influence of the inulin polymerization degree, data listed in Table 2 shows that the cooking loss decreased as the inulin polymerization degree increased (CRI); whereas, no significant differences in water absorption and swelling index were observed. Most probably, the competition for water of inulin with semolina components (starch and protein) during dough formation, decreased as the inulin polymerization degree increased (CRI). In addition, data reported in Table 2 suggest that the adhesiveness increased in fortified samples as the inulin molecular weight

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Table 2 Cooking quality of spaghetti samples with and without inulin. CRI: Inulin extracted from cardoon roots (high polymerization degree); CHI: Commercial inulin produced from chicory (low polymerization degree). Sample

OCT (min)

Cooking Loss (%)

Swelling Index

Water Absorption (%)

Adhesiveness (Nmm)

Hardness (N)

CTRL 2-CHI 2-CRI 4-CHI 4-CRI

9.30 8.30 9.00 8.00 8.30

6.54 ± 0.20d 7.24 ± 0.33b 6.75 ± 0.08c,d 7.70 ± 0.16a 7.05 ± 0.27b,c

1.80 ± 0.04a,b 1.72 ± 0.04b,c 1.83 ± 0.05a 1.70 ± 0.02c 1.83 ± 0.06a

140 ± 1.84a,b 136 ± 2.04b,c 141 ± 5.51a,b 134 ± 1.73c 144 ± 1.54a

0.47 ± 0.00c 0.54 ± 0.04a,b 0.46 ± 0.05c 0.58 ± 0.03a 0.50 ± 0.02b,c

7.08 ± 0.62a 6.24 ± 0.22b 6.20 ± 0.35b 6.28 ± 0.25b 6.38 ± 0.28b

a–c

Means in the same column followed by different superscript letters differ significantly (p < 0.05).

Table 3 Chemical composition of spaghetti samples with and without inulin. CRI: Inulin extracted from cardoon roots (high polymerization degree); CHI: Commercial inulin produced from chicory (low polymerization degree). Sample

Protein (%)

CTRL 2-CHI 2-CRI 4-CHI 4-CRI

8.12 ± 0.29 7.80 ± 0.02b 8.19 ± 0.08a 8.02 ± 0.05a,b 7.85 ± 0.05b

a–c

IDF (%) a

SDF (%)

2.79 ± 0.09 3.31 ± 0.28b 3.46 ± 0.01b 3.83 ± 0.25a 4.13 ± 0.10a c

TDF (%)

2.59 ± 0.19 3.64 ± 0.05d 5.01 ± 0.02b 4.74 ± 0.05c 6.43 ± 0.24a e

Fat (%)

5.38 ± 0.21 6.96 ± 0.29c 8.47 ± 0.24b 8.57 ± 0.25b 10.54 ± 0.24a d

1.28 ± 0.12 1.32 ± 0.11a 1.57 ± 0.10a 1.21 ± 0.07a 1.43 ± 0.13a

b

ACH (g/100 g)

Starch digestibility

79 ± 1.00 74 ± 4.00b 72 ± 0.10b 72 ± 2.05b 65 ± 0.50c

61 ± 0.30a 60 ± 0.30b 56 ± 1.00d 58 ± 0.25c 50 ± 0.02e

a

Means in the same column followed by different superscript letters differ significantly (p < 0.05).

decreased. This is coherent with data on cooking loss. No losses of inulin were found in the processing water after cooking the spaghetti.

3.3. Chemical composition of pasta and starch digestibility In Table 3 the chemical composition of control sample and all samples supplemented with inulin are reported. Regardless the polymerization degree, one can observe that the percent of protein slightly declined as the concentration of inulin increased; on the contrary, the percentage of total dietary fibre increased, mainly due to the rise in soluble dietary fibre content (SDF). Specifically, 4-CRI sample showed the greatest TDF content with respect to the other investigated samples. This result is consistent with the fact that inulin is a non-digestible polysaccharide that is classified as dietary fibre (Mensink, Frijlink, van der Voort Maarschalk, & Hinrichs, 2015; Mensink, Frijlink, van der Voort Maarschalk, & Hinrichs, 2015). As regards to the fat content, Table 3 evidences that the samples enriched with inulin recorded a slightly decline, with exception of samples enriched with cardoon inulin. Accordingly, inulin has already been used successfully to replace fat in starch-rich products such as cakes, biscuits as well as pasta (Franck, 2002; López-Molina et al., 2015). In fact, the long chain length inulin has the ability to form inulin microcrystals that have a smooth creamy texture and provide a fat-like mouth sensation (Mittal & Usha Bajwa, 2012). The observed differences in this work could be associated to the inulin polymerization degree because it is responsible for the physico-chemical characteristics, as morphology (i.e., crystal morphology, crystal structure and structure in solution), solubility, rheology (i.e., viscosity, hydrodynamic shape and gelling), thermal characteristics and physical stability (i.e., glass transition temperature, vapour sorption and melting temperature) and chemical stability (Mensink et al., 2015a,b). As a consequence, the inulin microcrystals morphology or structure could to interfere with the extraction fat method, thus causing a rise in fat content for samples enriched with cardoon inulin. Data listed in Table 3 also show that the addition of inulin caused a decline in available carbohydrate. Specifically, the 4-CRI sample had a lower ACH content with respect to the other samples. In Table 3 is also reported the starch digestibility values of the samples. In general, the starch digestibility significant declined as the amount of the inulin increased. In line with the results

described by Aravind et al. (2012), it can be hypothesised that small amounts of inulin support formation of a well-developed protein–fibre matrix, subsequently acting as a physical barrier to starch-degrading enzymes, whereas larger amounts of inulin cause the gluten network to become more defective with a more open porous structure, which offers limited protection to starch granules during enzymatic attack. It is worth noting that samples supplemented with high polymerization degree inulin (CRI) showed a smaller starch digestibility values with respect to those with low polymerization degree inulin. Most probably, the low polymerization degree may have a greater disruptive effect on the starch-protein matrix that made it less likely to form a cohesive encapsulation layer (Aravind et al., 2012). It is also possible that either higher levels of inulin or higher degree polymerization inulin can inhibit starch swelling and reduce starch digestibility (Brennan & Tudorica, 2008).

4. Conclusions In this work the effects of both inulin extracted from cardoon roots (CRI, high DP) and commercial inulin (CHI, low DP) produced from chicory on quality and chemical composition of whole-meal durum wheat spaghetti were addressed. In general, the increase in inulin amount determined a decline of sensory quality even though the molecular weight of inulin played a key role on pasta acceptability. This effect may be directly ascribed to the probable entanglements created by high molecular weight inulin that generally improved pasta characteristics. Concerning the chemical composition, the sample enriched with 4% of cardoon inulin showed a greater TDF and lower available carbohydrate content with respect to the other samples. Besides, the starch digestibility significantly declined with the increase of inulin. Specifically, the samples supplemented with high DP inulin (CRI) showed a smaller starch digestibility than that of samples with low DP inulin (CHI). This result is ascribed to the fact that CHI inulin may have a greater disruptive effect on the starch–protein matrix, thus compromising its cohesive encapsulating layer. In conclusion, the DP of inulin significantly affected its interactions with gluten matrix during pasta formation and as consequence, inulin extracted from cardoon roots allowed realizing a final pasta very interesting from the nutritional point of view and also acceptable for sensory properties and cooking quality.

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