This study optimizes the pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil to produce a yellow pyrodextrin with the lowest enzymatically available starch (AS) content and color difference (ΔE) index.
Carbohydrate Polymers 242 (2020) 116382 Contents lists available at ScienceDirect Carbohydrate Polymers journal homepage: www.elsevier.com/locate/carbpol Pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil and physicochemical characterization of yellow pyrodextrins T Mighay Lovera (Dr.)a,b,1,*, George Meredite Cunha de Castro (M.S.)a, Natalia da Rocha Pires (Dr.)c, Maria Socorro Rocha Bastos (Dr.)d, Márjory Lima Holanda-Araújo (Dr.)a, Alexander Laurentin (Ph.D.)e, Renato de Azevedo Moreira (Dr.)b, Hermógenes David de Oliveira (Dr.)a a Department of Biochemistry and Molecular Biology, Federal University of Ceará, CEP 60440-900, Fortaleza, Ceará, Brazil University of Fortaleza, Health Sciences Center, Av Washington Soares, 1321 Edson Queiroz, CEP 60811-905, Fortaleza, Ceará, Brazil Department of Organic and Inorganic Chemistry, Federal University of Ceará, CEP 60440-554, Fortaleza, Ceará, Brazil d Food Packaging Technology Laboratory, Embrapa Agroindústria Tropical, St Dr Sara Mesquita, 2270-Pici, CEP 60511-110, Fortaleza, Ceará, Brazil e Instituto de Biología Experimental, Facultad de Ciencias, Universidad Central de Venezuela, Apartado postal 47114, Caracas, 1041-A, Venezuela b c A R T I C LE I N FO A B S T R A C T Keywords: Pyroconversion Response surface methodology Digestibility Available starch Dietary fiber Physicochemical properties This study optimizes the pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil to produce a yellow pyrodextrin with the lowest enzymatically available starch (AS) content and color difference (ΔE) index At 140 °C (fixed heating temperature), the effects of acid concentration (0.65 − 2.99 g of HCl/kg of starch) and incubation time (53 − 307 min) on the response variables were evaluated using a response surface methodology Some physicochemical characteristics were also determined on pyrodextrins Both factors negatively affected the AS content, although positively influenced the ΔE (P < 0.05) The yellow pyrodextrin produced with 1.82 g/kg and heating for 307 min, presented physicochemical properties similar to the commercial pyrodextrins from potato starch, with 46.6 % of AS, 24.5 of ΔE, high solubility and very low viscosity The pyrodextrinization caused a decrease of 30 − 54 % in AS content (P < 0.05), making these yam pyrodextrins a promising material for water-soluble and very low viscous dietary fiber Introduction The dietary changes towards an increase in fiber intake have been associated with a reduction in the risk of developing chronic diseases such as type-2 diabetes, cardiovascular disease and colorectal cancer (Lockyer, Spiro, & Stanner, 2016) To fulfill the consumers' demand for healthy processed foods, there is a growing interest in the food industry in fortifying their products with dietary fiber and/or the physiological analogs (Kapuśniak & Nebesny, 2017) One of the analogous carbohydrates to dietary fiber is pyrodextrin Yellow pyrodextrins are heat-treated starches prepared under low moisture content in an acidic environment (Laurentin, 2004) The formation of indigestible fractions during the process requires the inclusion of mineral acid as catalyst when the pyrolysis is carried out at temperatures below 200 °C and for relatively short periods (minutes to several hours) (Kroh, Jalyschko, & Häseler, 1996; Laurentin, Cárdenas, Ruales, Pérez, & Tovar, 2003; Wurzburg, 1986) The acidification is commonly performed by spraying a diluted acid solution onto the dry starch powder (Campechano-Carrera, Corona-Cruz, Chel-Guerrero, & Betancur-Ancona, 2007; Laurentin et al., 2003; Luo et al., 2019), or by adjusting pH of the starch slurry with a diluted acid solution, followed by dehydration and pulverization before pyroconversion (Bai & Shi, 2016), or by distributing the acid in the form of gas (Lin, Lin, Zeng, Wu, & Chang, 2018) A homogeneous distribution is of importance for Abbreviations: ΔE, color difference; Adj-R2, adjusted R2; AS, available starch; CCRD, central composite rotational design; db, dry mass basis; DE, dextrose equivalent; MW, molecular weight; Pyr, pyrodextrin; RSM, response surface methodology ⁎ Corresponding author E-mail addresses: mighay.lovera@ciens.ucv.ve (M Lovera), georgemeredite@gmail.com (G.M.C.d Castro), npires@ymail.com (N.d.R Pires), socorro.bastos@embrapa.br (M.d.S.R Bastos), marjory.holanda@ufc.br (M.L Holanda-Araújo), alexander.laurentin@ciens.ucv.ve (A Laurentin), rmoreira@unifor.br (R.d.A Moreira), hermogenes@ufc.br (H.D.d Oliveira) Permanet address: Instituto de Biología Experimental, Facultad de Ciencias, Universidad Central de Venezuela, Apartado postal 47114, Caracas 1041-A, Venezuela https://doi.org/10.1016/j.carbpol.2020.116382 Received 29 October 2019; Received in revised form 24 April 2020; Accepted 26 April 2020 Available online 11 May 2020 0144-8617/ © 2020 Elsevier Ltd All rights reserved Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al nutritional characteristics, if sufficiently exploited, could generate interesting applications in both food and non-food industry (Amani, Kamenan, Rolland-Sabaté, & Colonna, 2005; Otegbayo, Oguniyan, & Akinwumi, 2014) Response surface methodology (RSM) is a statistical method, used to design experiments, build models, evaluate the effects of factors and search optimum conditions of factors for desirable responses (Myers & Montgomery, 1995) In RSM, a central composite rotational design (CCRD) is useful to build a second-order polynomial model for the response variable without needing to use a complete three-level factorial experiment, limiting the number of assays When the experimental space is unknown and non-preliminary experiment is performed, a novel starch source could be tested using a CCRD, bringing additional information about the relationship between the variables (dependent and independent) selected Pyrodextrins from Dioscorea spp have been studied only to a limited extent, as well as the use of RSM to evaluate the effect of pyroconversion conditions on digestibility and physicochemical characteristics Therefore, this study aimed to optimize the pyroconversion of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil to produce a yellow pyrodextrin with the lowest enzymatically available starch (AS) content and color difference (ΔE) index, and dextrose equivalent (DE) values < 10; and to evaluate the acid concentration and incubation time effects on digestibility and some physicochemical properties of pyrodextrins This research provides a set of conditions for pyroconversion of yam starch and prepares yellow pyrodextrins with different in vitro digestibility and physicochemical properties, with potential applications in both food and non-food industry minimizes the undesired charring resulting from uneven catalysis during the course of pyroconversion (Wurzburg, 1986) The chemical reactions that occur during pyrodextrinization of starch are complex and involve hydrolysis, transglucosydation, repolymerization, and oxidation (Bai & Shi, 2016; Wurzburg, 1986) Transglucosydation reactions predominate in the formation of yellow pyrodextrins and structural analyses have revealed the formation of new glycosidic bonds, such as 1→2, 1→3 and 1→6 (Bai & Shi, 2016; Laurentin, 2004; Luo et al., 2019; Okuma & Matsuda, 2002) in either αor β-anomers, with a simultaneous reduction of 1→4 linkages occurrence (Le Thanh-Blicharz, Blaszczak, Szwengiel, Paukszta, & Lewandowicz, 2016) Also, an extensively branched structure but with lower molecular size than starch molecule has been previously reported (Bai & Shi, 2016; Han, Kang, Bai, Xue, & Shi, 2018) The result of pyrodextrinization is a cold-water-soluble product, with low or nil viscosity in solution, partially resistant to digestion or indigestible, highly fermented in the colon and capable of affecting the growth of probiotic bacteria, such as Lactobacillus and Bifidobacterium strains, acting as prebiotics (Barczyńska, Śliżewska, Libudzisz, Kapuśniak, & Kapuśniak, 2015; Laurentin & Edwards, 2004; Le ThanhBlicharz, Sip, Malcher, Prochaska, & Lewandowicz, 2015) In modified starches by dextrinization, the pyroconversion has the advantage that produces indigestible materials and fully soluble preparations that satisfy the condition to be a resistant starch, with the technological disadvantage that under pyrodextrinization a darker color is develop compare to enzymatically-hydrolyzed and acid-modified starches (maltodextrins and acidic hydrolysates, respectively), which requires later processing of the final products Pyrodextrins are classified as a food additive [INS No 1400] (FAO, 2001) and a food ingredient (EU Commission Directive, 2000) Products based on pyrodextrins are found commercially, and they are industrially produced from corn, potato and wheat starches (LefrancMillot, 2008; Ohkuma, Hanno, Inada, Matsuda, & Katta, 1997) Because their physicochemical, functional and nutritional properties, nonconventional starch sources such as lentil, sorghum, cocoyam, sagu, cassava, and beans were also appropriated for preparing pyrodextrins with high solubility, low viscosity and different ranges of indigestibility (Campechano-Carrera et al., 2007; Laurentin et al., 2003), depending on the pyroconversion condition and the origin of starch used Yam (Dioscorea spp.) starch is an excellent source of resistant starch based on the low digestibility found in some species (Lovera, Pérez, & Laurentin, 2017; Riley, Bahado-Singh, Wheatley, & Asemota, 2014) and could be used as an alternative to other tuber and root starches, such as potato or cassava, to produce pyrodextrins and potentials carbohydrates prebiotic Recently, Luo et al (2019) prepared pyrodextrins by spraying the Chinese yam (Dioscorea opposita Thunb.) starch with a HCl solution (0.01 M) in a final acid concentration of 0.07 ∼ 0.23 % (w/w) on a dry starch basis, heating temperatures between 130 ∼ 170 °C, and treatment times of 30 ∼ 120 These pyrodextrins presented an enzyme-resistant fraction content in the range of 11.8 − 71.3 %, a whiteness index of 80.7 − 34.5 % and a water-solubility between 14.3 − 98.4 % These authors also obtained an enzyme-resistant dextrin produced by simultaneous pyroconversion and chemical modification of Chinese yam starch in the presence of an organic acid (citric acid) as a modifying factor, which presented characteristics that make it suitable for use in the soft drink industry as the soluble dietary fiber and prebiotic in the beverages The yellow yam (D cayennensis Lam cultivar “inhame-da-Costa”) together with the water yam (D alata L cultivar “inhame São Tomé”) are the most widely cultivated species in the Northeast of Brazil Despite the wide distribution and its importance as a pharmacological and food source, yams are referred to as an underutilized species (Siqueira, 2011) Research in this field would further help the development of yams as a sustainable crop, as well as the processing of the added value of their starches (Zhu, 2015) Dioscorea genus is a source of native starches whose functional, physicochemical properties and Materials and methods 2.1 Raw material and chemicals Yam tubers (Dioscorea sp.) were purchased from the local market in Fortaleza, Ceará State, grown in the Northeast of Brazil Analytical grade reagents and enzymes (EC: 3.2.1.1 and EC: 3.2.1.3) were purchased from Sigma-Aldrich Co (St Louis, MO, USA) 2.2 Starch extraction and chemical characterization The starch from yam tubers was extracted according to Pérez et al (2011) with minor variations Briefly, one portion of the edible tuber was blended in a Skymsen industrial blender (LAR-06MB, Santa Catarina, Brazil) for with twice their volume of distilled water and sieving the collected homogenate with a nylon cloth The grinding and screening operation was repeated three more times The resulting slurry was centrifuged (Hitachi Koki, Himac CR-22 G III, Tokyo, Japan) at 276 x g for 15 min, for easy separation of starch from the viscous mucilage The sediment was washed two times by suspension in distilled water and centrifugation, then was dried in a stove at 45 °C for 48 h The starch was ground in a mini chopper (Philips Walita, Brazil), screened through an 80-mesh sieve, and stored in a sealed plastic bag inside a desiccator Native starch was analyzed for crude protein (N × 6.25 %), ash and crude fat following methods described in AACC International (2003): 46–11A; 08–17 and 30–10, respectively Amylose content was determined colorimetrically according to ISO (6647)-1 (2007) method The moisture content was determined for native starch and pyrodextrins by drying g of a sample at 130 °C for h All analyses were performed in triplicate 2.3 Pyroconversion process A CCRD 22 was performed with Statistica 10.0 software (StatSoft, Inc.), using an α = ± 1.41 to generated levels and 11 total assays (4 factorial points, axial points and repetitions in the central point, C) Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al starch, and using the Eq (1): Table A CCRD 22 matrix for pyrodextrins production from yam starch.a Assays Pyr-1 Pyr-2 Pyr-3 Pyr-4 Pyr-5 Pyr-6 Pyr-7 Pyr-8 Pyr-9 (C) Pyr-10 (C) Pyr-11 (C) a ΔE = Independent variables real value (coded value) Acid concentration (X1) (g HCl/kg of starch, db) Incubation time (X2) (min) 0.99 (−1) 0.99 (−1) 2.65 (+1) 2.65 (+1) 0.65 (−α) 2.99 (+α) 1.82 (0) 1.82 (0) 1.82 (0) 1.82 (0) 1.82 (0) 90 (−1) 270 (+1) 90 (−1) 270 (+1) 180 (0) 180 (0) 53 (−α) 307 (+α) 180 (0) 180 (0) 180 (0) (ΔL*)2 + (Δa*)2 + (Δb*)2 (1) where ΔL*, Δa* and Δb* were the differences in the values of whiteness (L*), redness-to-greenness (a*) and yellowness-to-blueness (b*), respectively 2.4.3 Dextrose equivalent The number of reducing groups on native starch and pyrodextrins was determined as follows: 20 mL of such suspension (1 % w/v, db) was gelatinized in a boiling water bath for 20 After cooled, the solution was transferred into a 50 mL volumetric flask, made up to volume with distilled water and mixed The reducing sugars were measured according to the 3,5−dinitrosalisilic acid (DNS) method with mL of DNS reagent and an equal volume of gelatinized sample (Hostettler, Borel, & Deuel, 1951) The DE was expressed as a percentage of the reducing value of pure dextrose calculated on dry basis (Le ThanhBlicharz et al., 2016) C, central point; Pyr, pyrodextrins The central point was a priori selected from the pyrodextrinization standard condition tested by Laurentin et al (2003) with a fixed heating temperature of 140 °C, which reported a 52 % reduction (P < 0.05) in the enzymatically AS content compare to the native starch The RSM was used to evaluate the isolated and combined effects of acid concentration (X1) and incubation time (X2) on AS content, ΔE index, and DE value of the pyrodextrins produced from native starch (Table 1) The independent variables were expressed as a final acid starch ratio (g of HCl/kg of starch, dry mass basis, db) and minutes The pyroconversion was performed according to Laurentin et al (2003) with modifications Briefly, 22 g (db) of yam starch was placed in a mortar and a specific volume (ranged from 0.18 to 0.82 mL) of 2.2 M HCl solution was sprayed on starch to a final acid starch ratio, as showed in Table 1, mixed thoroughly and let sit overnight at room temperature Then, it was roasted in a stove at 140 °C for the corresponding time The pyrodextrin was cooled to room temperature for 30 min, ground, passed through 80-mesh sieve, and stored in a closed plastic container inside a desiccator until use The yield of pyrodextrinization was calculated as the mass ratio on dry basis of the obtained pyrodextrin to native starch used and expressed as percentage AS content, ΔE index, and DE value of the pyrodextrins were determined (in triplicate), and the optimum pyrodextrinization condition which produced the lowest AS content and ΔE index compared to the native starch, and DE values < 10, was selected 2.4.4 Water solubility The water solubility was assayed for triplicate according to Campechano-Carrera et al (2007) Briefly, 40 mL of a % (w/v, db) starch suspension was prepared in a 50 mL centrifuge tube and placed in a water bath at 25 °C for 30 with agitation every Then, the solution was centrifuged at 2120 x g for 15 min, and 10 mL of supernatant was removed, placed in a constant-weight crucible and dried in a stove at 120 °C for h to obtain the weight of dissolved starch The water solubility was calculated as follows (Eq (2)): Water solubility= dry weight of dissolved starch/sample weight (db)×400 % (2) 2.4.5 Rheological properties The rheological properties were investigated on 40 % (w/v, db) pyrodextrin solutions at 20 °C, except for treatment and 10 (both replicates of the central point), according to Le Thanh-Blicharz et al (2016) with modifications After solubilized and before rheological analysis, all pyrodextrin solutions were centrifuged at 2120 × g for 15 to remove particulate materials The rheological behavior of solutions was evaluated using a TA Instrument Rheometer (AR-550, New Castle, USA) with cone and plate geometry (40 mm, 1° cone and 28 μm gap) at shear rate from to 600 s−1 The rheological parameters were calculated using the Herschel − Bulckley model employing the TA Data Analysis software (TA instruments Inc., New Castle, USA), according to Eq (3): 2.4 Digestibility and physicochemical characterization 2.4.1 Available starch The AS content of native starch and pyrodextrins were assessed following the multienzymatic protocol of Holm, Björck, Drews, and Asp, (1986) with minor modifications AS represents the digestible fraction once the starch was gelatinized A starch suspension (300 mg, db dispersed in 20 mL of distilled water) was incubated for 20 at boiling temperature with 100 μL of a heat-stable α-amylase (200 U/ mL) from Bacillus licheniformis (A-3306: Sigma-Aldrich Co., USA) and an aliquot was digested with amyloglucosidase from Aspergillus niger (A7095: Sigma-Aldrich Co., USA) at 60 °C for 30 (3.5 U/mL) Released glucose was quantified with glucose oxidase/peroxidase colorimetric assay (Glicose Liquiform kit; Labtest Diagnóstica S A, Brazil) Standard calibration curve using glucose solution (0 to 0.8 mg/mL) was constructed for the calculation of glucose released σ = σ0 + Ky n̊ (3) −1 where σ (Pa), σ0 (Pa), K (mPa.s ), ẙ (s ), and n (dimensionless) were the shear stress, the yield stress, the consistency coefficient, the shear rate and the flow behavior index, respectively n 2.5 Statistical analysis For the statistical analysis were applied Statistica 10.0 software (StatSoft, Inc.) The response variables were fitted by a second-order polynomial regression model, using a multiple regression analysis The quality of prediction and fitting of the polynomial model was evaluated through the coefficient of determination R2, adjusted R2 (Adj-R2) and analysis of variance (ANOVA) A lack-of-fit test was run and the adequate precision value was calculated for the three models to assist in their validation (Germec, Ozcan, & Turhan, 2019; Noordin, Venkatesh, Sharif, Elting, & Abdullah, 2004) To describe both isolated and combined effects of the independent variables of pyrodextrinization on the three responses, 3D response surface plots were also developed Data were also analyzed using one-way ANOVA followed by Duncan's test as 2.4.2 Color parameters Color parameters were measured according to Le Thanh-Blicharz et al (2016) by the reflection method on a Konica Minolta Chromameter (CR-410, Osaka, Japan) and the classification system of the CIEL*a*b* ΔE index was determined by comparison to the native Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al 3.2 Yield and effects of pyroconversion process Table Chemical characterization of native starch isolated from yam tubers grown in Brazil.a Component Composition (%) Moisture Crude protein Crude fat Ash Amylose Available starch 13.8 0.71 0.24 0.21 9.33 96.6 ± ± ± ± ± ± The Table presents the yield, the digestibility and some physicochemical characteristics of yellow pyrodextrins obtained by pyroconversion of yam starch The yield of pyrodextrinization ranged from 97 to 99 % db, higher than reported by Falade and Ayetigbo (2015) for acid hydrolyzed and acid modified yam starches A relatively mild treatment (< g of HCl/kg of starch) such as Pyr-1 and Pyr-5 had no impact on AS content (P > 0.05) but yielded markedly lighter products (P < 0.05) than stronger treatment (< 2.5 g of HCl/kg of starch) such as Pyr-3, Pyr-4 and Pyr-6, which were the less available pyrodextrins compared to native starch (P < 0.05) In general, a longer heating time such as Pyr-8 led to a lower AS content than shorter treatments such as Pyr-11 and Pyr-7, all with 1.82 g of HCl/kg of starch This tendency was also observed under condition of 0.99 g/kg, but interestingly, not with 2.65 g/kg As expected, the yam starch was rapidly pyroconverted using a high acid concentration, and no significantly differences in AS content were found after increasing incubation time from 90 to 270 (Pyr-3 and Pyr-4, respectively) Luo et al (2019) reported that in the first 60 of pyroconversion, the resistant fraction content in enzyme-resistant dextrins increases sharply with the increasing the heating time, then, the increase slowly diminishes with longer treatment times 0.2 0.28 0.04 0.02 0.18 2.1 a Values (% db, except for moisture) are given as the mean ± standard deviation of three replicates post hoc comparison of means and simple correlations (P < 0.05), employing the same software Results and discussion 3.1 Starch extraction and chemical characterization The chemical composition of yam starch extracted is showed in Table The moisture content (13.8 ± 0.2 %) was in the range reported for Dioscorea spp and commercial starches (Jiang et al., 2012; Swinkels, 1985), as were also the crude protein, ash and crude fat contents (Amani et al., 2004; Nwokocha & Williams, 2011) The high AS content reported reflect the presence of low levels of non-starch components in this preparation (protein < %, fat and ash < 0.3 %), and it is indicative of adequate purity level The total starch content in yam starch (not determined) could be expected to be similar to the recorded AS content because raw starches not contain retrograded fractions that would decrease AS content, as reported by Lovera et al (2017) The apparent amylose content of yam starch was lower than those reported for Dioscorea spp., which are in the range of 13.58 − 20.05 % (amylopectin: 79.95 − 86.42 % vs 90.67 %) (Jiang et al., 2012) The amylose content recorded here was also quantified by the iodine binding-colorimetric method but using non-defatted samples, and this usually gives lower amylose contents than defatted samples, because lipids can form inclusion complexes with amylose (Zhu, 2015) This low amylose content was consistent with a high digestibility of yam starch, as reported by Riley et al (2014) for low-amylose yam starches 3.2.1 Available starch Pyrodextrins AS content was always lower (P < 0.05) than native starch, with the exception of Pyr-1 and Pyr-5 Yam pyrodextrins produced were grouped into four categories based on their reduction in AS content compared to native starch, an easier way to estimate the indigestible fraction reported by Laurentin et al (2003) These groups were: those treatments with the highest reduction in digestibility with 52 − 54 % (Pyr-3, Pyr-4, Pyr-6 & Pyr-8), the intermediary group with 44 − 48 % (Pyr-9, Pyr-10 & Pyr-11), followed by the group with a 30 % decrease in AS (Pyr-2 & Pyr-7) and finally, those with the smallest fall in AS content and statistically similar (P > 0.05) to native yam starch (Pyr-1 & Pyr-5) Pyrodextrin AS content was negatively correlated with ΔE index, DE value and water solubility of sample (rΔE = −0.844; rDE = −0.850; rS = −0.798; P < 0.05; n = 33) The acid concentration, incubation time and their interaction had significant influence (P < 0.05) on AS content of pyrodextrins (Table S1) The acid concentration had the largest influence on the AS content of pyrodextrins, being linear and second order coefficients significant However, the acid concentration and incubation time linear terms negativity affected the AS content, although the interaction had a positive effect on this variable (Fig 1a) The mathematical model (R2 = 0.9861; Table Yield, digestibility and physicochemical characterization of yellow pyrodextrins produced from yam starch.1,2,3 Pyrodextrins Pyr-1 Pyr-2 Pyr-3 Pyr-4 Pyr-5 Pyr-6 Pyr-7 Pyr-8 Pyr-9 (C) Pyr-10 (C) Pyr-11 (C) Native starch Yield AS Fall in (%, db) (%, db) AS (%) 97.4 98.3 97.5 97.5 97.2 97.1 97.0 98.0 97.9 97.7 98.5 − 95.4 ± 2.9a 67.4 ± 1.7b 44.1 ± 1.7d 44.2 ± 3.2d 86.2 ± 6.9a 44.2 ± 1.4d 67.6 ± 6.3b 46.6 ± 2.3d 49.8 ± 5.5c, d 53.4 ± 5.3c 54.2 ± 3.9c 96.6 ± 2.1a 1.2 30.2 54.4 54.3 10.7 54.2 30.0 51.7 48.4 44.7 43.9 − Color parameters L* 92.3 93.4 60.4 63.5 91.4 56.3 83.6 83.4 80.2 80.4 76.7 94.6 ± 0.03c ± 0.04b ± 0.51h ± 0.51g ± 0.16c ± 0.78i ± 0.22d ± 0.46d ± 0.09e ± 0.15e ± 0.13f ± 0.62a DE a* b* ΔE (%, db) 0.11 ± 0.00g −0.28 ± 0.00h 5.3 ± 0.04c 5.8 ± 0.06b 0.49 ± 0.07e 6.0 ± 0.12a −0.46 ± 0.07i 0.43 ± 0.04e 1.2 ± 0.02d 1.2 ± 0.03d 1.2 ± 0.06d 0.29 ± 0.07f 7.3 ± 0.07j 10.0 ± 0.03i 30.5 ± 0.24b 31.4 ± 0.18a 9.6 ± 0.27i 28.8 ± 0.32c 20.4 ± 0.23h 25.1 ± 0.06d 23.6 ± 0.11f 24.7 ± 0.24e 21.3 ± 0.12g 4.0 ± 0.46k 4.0 ± 0.0h 6.2 ± 0.0g 43.5 ± 0.2b 41.7 ± 0.3c 6.5 ± 0.2g 45.9 ± 0.5a 19.7 ± 0.3f 23.9 ± 0.2e 24.3 ± 0.1e 25.0 ± 0.3d 24.9 ± 0.1d − 2.8 ± 0.0d 3.4 ± 0.0c 7.4 ± 0.1a 7.3 ± 0.1a 1.6 ± 0.0f 7.5 ± 0.2a 7.3 ± 0.1a 6.6 ± 0.1b 6.4 ± 0.1b 6.6 ± 0.1b 6.6 ± 0.2b 1.8 ± 0.1e Values are means ± standard deviation of triplicate analysis Means in columns not sharing same superscript letters are significantly different (P < 0.05; Duncan's test) Fall in AS content was calculated as (AS native – AS pyrodextrinized) × 100/AS native ΔE, color difference; AS, available starch; C, central point; db, dry mass basis; DE, dextrose equivalent; Pyr, pyrodextrins Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al Fig Pareto chart of standardized effects of the acid concentration (X1) and incubation time (X2) on pyrodextrins characteristics: (a) AS content, (b) ΔE index and (c) DE value Adj-R2 = 0.9721; P < 0.05) that illustrates the behavior of the AS content, in terms of the coded independent variables is represented by Eq (4): AS (%) =178.08–73.10 X1 +9.88 X12 –0.372 X2 +0.00034 X22 +0.094 X1 X2 color and were characterized by smaller values of the whiteness (L*) and higher values of a* and b* parameters than native yam starch (Table 3) The lightest and darkest materials were Pyr-5 and Pyr-6, respectively An inverse correlation between L* and parameters a* and b* (ra* = −0.944; rb* = −0.872; P < 0.05; n = 33) and a positive relationship between a* and b* (r = 0.744; P < 0.05; n = 33) were found These correlations indicated a predominance of red and yellow colors in the pyrodextrins and reinforce the idea of the progress of the caramelization The whiteness of pyrodextrins decreased with the increasing concentrations of HCl, which was consistent with the reduction of the whiteness degree reported for pyrodextrins prepared from Chinese yam starch using the same acid (Luo et al., 2019) The acid concentration, incubation time and their interaction had significant influence (P < 0.05) on pyrodextrin ΔE index (Table S2) Similar to AS response, significance analysis on coefficients of each factor showed that the acid concentration had the largest influence on the ΔE index of pyrodextrins, linear and second order coefficients were significant Incubation time had a smaller but significant effect on the ΔE index, linear and quadratic coefficients were also significant Linear terms of acid concentration and incubation time positively affected the ΔE index, although the interaction had a negative effect on this variable (Fig 1b) The final estimative regression model (R2 = 0.9776; AdjR2 = 0.9552; P < 0.05) for the ΔE index of pyrodextrins is represented by Eq (5): (4) Starch pyroconversion produced a decrease in AS content as reported previously by different authors (Campechano-Carrera et al., 2007; Laurentin et al., 2003) Laurentin et al (2003) reported a 55 − 65 % decrease in digestibility for pyrodextrins from cassava starch, using the same pyroconversion conditions as for Pyr-1, Pyr-2, Pyr-3, Pyr-4 and the central point, although spraying a constant volume (0.5 mL) of the acid solution onto the starch powder These authors reported that non-digestible fractions produced by pyroconversion differ depending on the starch source It was reported for yam starch that a low amylose content could predispose the starch to acidic and thermal resistance (Amani et al., 2005), this suggests that it would need a more extreme pyroconversion condition to decrease its digestibility In general, the pyroconversion results in a substantial reduction of digestibility relative to that of the native starch (Laurentin et al., 2003; Le Thanh-Blicharz et al., 2016; Lin et al., 2018) Pyrodextrins prepared using similar conditions as here have been structurally characterized (Bai & Shi, 2016; Laurentin, 2004; Le Thanh-Blicharz et al., 2016; Luo et al., 2019; Okuma & Matsuda, 2002), reporting the presence of 1→2, 1→3 and 1→6 glycosidic linkages in either α- or β-anomers, with a reduction of 1→4 bonds occurrence Similar glycosidic linkage patterns are expected to be formed under the conditions tested (Table 1), independently of starch source used The indigestibility of pyrodextrins has been mainly attributed to the formation of these atypical linkages during transglucosydation reactions (Siljeström, Björck, & Westerlund, 1989), because the retrograded starch is very low for both native and modified samples, according to Laurentin et al (2003) ΔE =–19.81+18.43 X1 +1.02 X12 +0.100 X2 –0.00019 X22 -0.013 X1 X2 (5) The color difference shows its direct dependence on pyrodextrinization conditions, where extreme conditions lead to more variation in color, as it was reported elsewhere (Campechano-Carrera et al., 2007; Laurentin et al., 2003; Lin et al., 2018; Terpstra, Woortman, and Hopman, (2010) produced yellow pyrodextrins by heating potato starch for h at 165 °C (with ∼1.85 g of HCl/kg of starch) and they reported the presence of significantly different aggregate-like structures made of small starch fragments which were intensely colored, physically linked, and probably still susceptible to repolymerization and 3.2.2 Color parameters The Fig presents the visual aspects of native yam starch and pyrodextrins All pyrodextrins presented a cream or yellowy-brownish Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al Fig Native yam starch and pyrodextrins visual aspects from CCRD 22 matrix desired as significant lack-of-fit indicates that there might be contributions in the regressor–response relationship that are not accounted for by the model (Noordin et al., 2004) Nevertheless, the adequacy of the models was also investigated calculating the signal to noise ratio or adequate precision, which compares the range of the predicted values at the design points to the average prediction error, and ratios greater than indicate adequate model discrimination (Noordin et al., 2004) For the three responses AS, ΔE and DE, the adequate precision values were 23.1, 18.7 and 23.4, respectively; indicating that there were adequate signals Therefore, the models for responses were reliable and can be used to navigate the design space, as reported by Germec et al (2019) Therefore, the predictive models (Eqs 4–6) were successful to precisely predict the AS, ΔE and DE in pyrodextrinization of yam starch Eqs (4)–(6) are plotted in Fig 3a–c, respectively as 3D response surface plots As can be observed from Fig 3a, increasing the acid concentration and incubation time caused a decrease in the AS content of pyrodextrins However, at the pyrodextrinization conditions used in this study, the response reached a minimum value instead of reaching the optimum value The critic values to obtain a minimum AS content of 41.6 % were 3.18 g/kg of HCl and 109 of heating For ΔE index and DE value (Fig 3b & c, respectively) a high acid concentration caused an increases in both responses, reaching a saddlepoint value instead of optimum value This behavior was more evident with response DE value, with a predicted value of 7.5 % using 2.59 g/kg of HCl and 215 of incubation time Pyr-3, Pyr-4, Pyr-6 and Pyr-8 were the less digestible and the darkest pyrodextrins, with the exception of Pyr-8 According to these results, the use of 1.82 g/kg acid concentration with 307 of heating time at 140 °C, appears to be an appropriate condition for preparing a yam pyrodextrin with the lowest AS content and ΔE index Even though Pyr-8 had a slightly higher AS content (P > 0.05) than Pyr-3, Pyr-4, and Pyr-6, it was selected as the optimum pyrodextrinization treatment because produced a lighter pyrodextrin (Table & Fig 2) Pyr-8 uses the highest heating time with an acid concentration not more than 2.0 g/kg and a temperature commonly used for pyroconversion (Table & Fig 2) In this work, the central point of CCRD design was Laurentin transglucosydation These changes would explain the low digestibility found in Pyr-8 with similar pyroconversion conditions Pyrodextrin ΔE index was positively correlated with DE and water solubility (rDE = 0.846; rS = 0.577; P < 0.05; n = 33), although negatively correlated with AS content; similar results were found by Le Thanh-Blicharz et al (2016) for commercial potato pyrodextrins 3.2.3 Dextrose equivalent The pyroconversion process significantly increased DE values (Table 3), with exception of the Pyr-5 (slightly lower than native starch; P < 0.05), suggesting that this pyrodextrin was poorly hydrolyzed Pyrodextrins from corn and potato starches according to Ohkuma, Hanno, Inada, Matsuda, & Katta, 1997 are preferably between and 10 in DE, such as reported here Nevertheless, the reducing sugar quantification was assayed on gelatinized samples, and since pyrodextrins were not neutralized after pyroconversion, the possibility that digestion had continued during gelatinization cannot be discarded Only acid concentration, but not the incubation time had significant influence (P < 0.05) on DE value (Table S3 and Fig 1c) Both linear and quadratic increases on acid concentration affected the DE value The determination coefficients (R2=0.9784; Adj-R2=0.9639; P < 0.05), exhibited an excellent experimental result which fits the mathematical model proposed for DE value, represented by Eq (6): DE (%) =–3.09+8.51 X1 –1.64 X12 –0.0042 X2 +0.00001 X22 (6) The decrease in DE values at higher acid concentrations was probably associated to thermal decomposition and/or oxidation process of reducing end Le Thanh-Blicharz et al (2016) reported that degree of oxidation is restrained and surprisingly independent of the type of pyrodextrin In this study, DE was positively correlated with ΔE index and water solubility (rS = 0.863; P < 0.05; n = 33), although negatively correlated with AS content The coefficients of determination R2 and Adj-R2 for the three quadratic models were higher than 0.95, which is desired On the other hand, except for ΔE index the probability value of the lack of fit test were insignificant (Table S1, S2 and S3) Insignificant lack-of-fit is Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al Fig 3D response surface plot for pyrodextrins characteristics in function of acid concentration and incubation time (a) AS content, (b) ΔE index and (c) DE value be compatible with beverage products The 40 % pyrodextrin solutions showed pseudoplastic flow behavior index (Table and Table S4); confirming the non-Newtonian flow of concentrated solutions, whose viscosity decreases with increasing shear rate Le Thanh-Blicharz et al (2016) reported a Newtonian behavior in four commercial pyrodextrins even solubilized at 40 % (w/v) Differences between these studies suggest that yam pyrodextrin fluids could be composed of intermediary and high-molecular weight (MW) substances instead of predominantly low-MW sugars In general, all pyrodextrins presented very low yield stress (which indicate a smaller resistance to flow) and shear viscosity (Table and Table S4) The drop in viscosity is not a surprise as native starch is rapidly broken down by acid and heat (Terpstra et al., 2010), even at short reaction time of pyroconversion such in Pyr-7 (53 min) Table shows that pyrodextrins from yam starch did not differ much from four commercial yellow pyrodextrins, obtained by dry roasting of potato starch with an acid catalyst Pyr-8 was the most similar to potato pyrodextrins The almost nil viscosity found with a high content of dry mass could be considered a better functional property for specific applications, for example, to provide a non-viscous dietary fiber to patients under enteral feeding Even in cooked food preparations could be used because after gelatinization pyrodextrins solutions remain with very low viscosity (data not showed) The shear behavior also found is often required in cosmetic products like emulsions, suspensions and for encapsulating material These features make these pyrodextrins suitable for use in the beverage and food industry, as well as, a promising material for the cosmetic, pharmaceutical and paper industries et al (2003) pyroconversion condition which also proved to be efficient to produce yellow pyrodextrins with similar appearance and digestibility than Pyr-8, but in a shorter time, which is technologically more advantageous 3.2.4 Water solubility and rheological properties of pyrodextrins All pyrodextrins presented a water solubility < 95 %, with the exception of Pyr-1 (58 ± %) and Pyr-5 (32 ± %), and were similar to commercial yellow pyrodextrins from potato starch (Table 4) Pyroconversion considerably increases the solubility as a consequence of the increase in low molecular linear fractions (Campechano-Carrera et al., 2007; Luo et al., 2019) These water-soluble pyrodextrins would Table Comparative between in vitro digestibility and physicochemical properties of potato (commercial) and yam pyrodextrins.1,2 Parameter Digestibility (Fall in AS; %) ΔE L* a* b* DE (%) Water solubility (%) Moisture (%) Rheological parameters Yield stress, σ0 (Pa) Consistency coefficient, K (mPa.sn) Flow behavior index, n (dimensionless) Standard error, S.E Pyrodextrins Potato1 Yam2 Pyr-8 40.6 − 53.9 (46 − 59 %) 15.8 − 25.4 82.7 − 87.4 −0.62 − 0.70 16.2 − 24.6 1.6 − 2.4 > 95 nd 44.1 − 67.6 (30 − 54 %) 6.2 − 45.9 56.3 − 93.4 −0.46 − 6.0 10.0 − 31.4 3.4 − 7.5 > 95 1.3 − 3.2 46.6 (52 %) 23.9 83.4 0.43 25.1 6.6 > 95 2.0 nd 80 − 240 nd 0.251 − 0.717 16 − 132 0.768 − 0.969 0.474 56 0.827 nd 1.5−9.0 2.0 Conclusions To the best of the authors’ knowledge, this paper reports the first documented pyrodextrinization of yam (Dioscorea sp.) starch isolated from tubers grown in Brazil Under the studied experimental conditions, pyroconversion resulted in 30 − 54 % decreases of AS content, with changes in their physicochemical properties The use of 1.82 g HCl/kg of starch acid concentration and ∼ h of heating at nd, not determined; Pyr, pyrodextrin Four yellow pyrodextrins produced from potato starch by WPPZ SA (Lubón, Poland) as reported by Le Thanh-Blicharz et al (2016) The ranges exclude pyrodextrins with AS content similar to the native starch (Pyr-1 and Pyr-5; Table 3) Carbohydrate Polymers 242 (2020) 116382 M Lovera, et al 140 °C was appropriate for preparing a yellow pyrodextrin (Pyr-8) with simultaneously low AS content and ΔE index, and similar physicochemical properties to the commercial pyrodextrins from potato starch, which is a promising material for water-soluble and very low viscous dietary fiber Further research is needed to elucidate the molecular structure of these pyrodextrins, as well as the nutritional effects as potential dietary fiber and carbohydrate prebiotic FAO (2001) Modified starches Compendium of food additive specifications Addendum Joint FAO/WHO expert committee on food additives, 57th session, Rome FAO food and nutrition paper - 52 add Germec, M., Ozcan, A., & Turhan, I (2019) Bioconversion of wheat bran into high valueadded products and modelling of fermentations Industrial Crops and Products, 139, 111565 Han, X., Kang, J., Bai, Y., Xue, M., & Shi, Y C (2018) Structure of pyrodextrin in relation to its retrogradation properties Food Chemistry, 242, 169–173 Holm, J., Björck, I., Drews, A., & Asp, N.-G (1986) A rapid method for the analysis of starch Starch‐Stärke, 38, 224–226 Hostettler, F., Borel, E., & Deuel, H (1951) Über die reduktion der 3,5-dinitrosalicylsäure durch Zucher [About the reduction of 3,5-dinitrosalicylic acid by sugars] Helvetica Chimica Acta, 34, 2132–2139 ISO 6647-1 (2007) International Organization for Standardization Rice – Determination of amylose content – Part 1: Reference method Jiang, Q., Gao, W., Li, X., Xia, Y., Wang, H., Wu, S., et al (2012) Characterizations of starches isolated from five different Dioscorea L species Food Hydrocolloids, 29, 35–41 Kapuśniak, K., & Nebesny, E (2017) Enzyme-resistant dextrins from potato starch for potential application in the beverage industry Carbohydrate Polymers, 172, 152–158 Kroh, L W., Jalyschko, W., & Häseler, J (1996) Non-volatile reaction products by heatinduced degradation of α-glucans I: Analysis of oligomeric maltodextrins and anhydrosugars Starch‐Stärke, 48, 426–433 Laurentin, A (2004) Starch pyrodextrins: In vitro fermentation and physiological effects PhD thesis Glasgow University Laurentin, A., & Edwards, C A (2004) Differential fermentation of glucose based carbohydrates in vitro by human faecal bacteria: A study of pyrodextrinised starches from different sources European Journal of Nutrition, 43, 183–189 Laurentin, A., Cárdenas, M., Ruales, J., Pérez, E., & Tovar, J (2003) Preparation of indigestible pyrodextrins from different starch sources Journal of Agricultural and Food Chemistry, 51, 5510–5515 Le Thanh-Blicharz, J., Blaszczak, W., Szwengiel, A., Paukszta, D., & Lewandowicz, G (2016) Molecular and supermolecular structure of commercial pyrodextrins Journal of Food Science, 81, 2135–2142 Le Thanh-Blicharz, J., Sip, A., Malcher, A., Prochaska, K., & Lewandowicz, G (2015) The effect of surface activity of pyrodextrins on their assimilability by selected strains of bacteria from genus Lactobacillus Starch‐Stärke, 67, 267–275 Lefranc-Millot, C (2008) NUTRIOSE® 06: A useful soluble dietary fiber for added nutritional value Nutrition Bulletin, 33, 234–239 Lin, C.-L., Lin, J.-H., Zeng, H.-M., Wu, Y.-H., & Chang, Y.-H (2018) Indigestible pyrodextrins prepared from corn starch in the presence of glacial acetic acid Carbohydrate Polymers, 188, 68–75 Lockyer, A., Spiro, S., & Stanner, S (2016) Dietary fiber and the prevention of chronic disease–should health professionals be doing more to raise awareness? 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Modified starches: Properties and uses (pp 17–40) Boca Raton, FL, USA: CRC Press Zhu, F (2015) Isolation, composition, structure, properties, modifications, and uses of yam starch Comprehensive Reviews in Food Science and Food Safety, 14, 357–386 CRediT authorship contribution statement Mighay Lovera: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, Visualization, Writing original draft, Writing - review & editing, Project administration George Meredite Cunha de Castro: Methodology, Formal analysis Natalia da Rocha Pires: Investigation, Resources Maria Socorro Rocha Bastos: Resources, Funding acquisition Márjory Lima Holanda-Araújo: Conceptualization, Resources, Visualization, Writing - original draft Alexander Laurentin: Conceptualization, Formal analysis, Visualization, Writing - original draft, Writing - review & editing Renato de Azevedo Moreira: Conceptualization, Resources, Supervision, Funding acquisition, Project administration Hermógenes David de Oliveira: Conceptualization, Resources, Writing - original draft, Supervision, Funding acquisition, Project administration Declaration of Competing Interest The authors declare no conflicts of interest Acknowledgements The authors gratefully acknowledge support from the Brazilian Federal Agency for Support and Evaluation of Graduate Education (Coordenaỗóo de Aperfeiỗoamento de Pessoal de Nível Superior – CAPES), and the PAEC OAS-GCUB (Partnerships Program for Education and Training between the Organization of American States and the Coimbra Group of Brazilian Universities) for the international scholarship awarded to the first author The authors also thank to Embrapa Agroindústria Tropical for the technical support Lovera also acknowledges her leave of absence from Central University of Venezuela Appendix A Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.carbpol.2020.116382 References AACC International (2003) Approved methods of analysis (11th ed.) 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