Flowability, Wet Agglomeration, and Pasta Processing Properties of Whole‐Durum Flour: Effect of Direct Single‐Pass and Multiple‐ Pass Reconstituted Milling Systems

Received: 11 December 2018 | Revised: 24 March 2019 | Accepted: 13 May 2019 DOI: 10.1002/cche.10167

RESEARCH ARTICLE

Flowability, wet agglomeration, and pasta processing properties of whole‐durum flour: Effect of direct single‐pass and multiple‐ pass reconstituted milling systems

Lingzhu Deng | Frank A. Manthey

Cereal Science Graduate Program, Department of Plant Sciences, North Abstract Dakota State University, Fargo, North Background and objectives: Flowability and wet agglomeration can affect pasta Dakota processing properties of whole‐wheat flour (WWF). Direct single‐pass and multi‐

Correspondence pass reconstituted milling are common methods to produce WWF. The flowability, Frank A. Manthey, Cereal Science Graduate wet agglomeration, and pasta processing properties of WWF were compared under Program, Department of Plant Sciences, these two systems where direct single‐pass system consisted of fine (24,000 g with North Dakota State University, Fargo, ND. Email: [email protected] 250 μm mill screen aperture) and coarse (15,400 g, 1,000 μm) grinds on an ultra‐centrifugal mill and the multiple‐pass reconstituted milling systems consisted of roller Funding information milling to produce semolina and bran and blending reground fine/coarse bran back North Dakota Wheat Commission to durum flour/semolina. Findings: Particle sizes were similar for direct fine grind WWF and multiple‐ pass durum flour:fine bran and for direct coarse grind WWF and multiple‐pass semolina:coarse bran flour. Direct coarse grind and semolina:coarse bran had better flowing properties than direct fine grind and durum flour:fine bran. Wet agglomerates were smaller with coarsely ground semolina/bran than finely ground flour/bran. Specific mechanical energy needed to extrude semolina, durum flour:WWF doughs were similar and not affected by milling system. Conclusions: Flow and wet agglomeration properties of direct coarse grind and reconstituted WWF of semolina and coarse bran were better than those of finely ground WWF for whole‐wheat pasta production. Significance and novelty: This research adds to the limited information available concerning the impact of milling process on the flow, agglomeration, and pasta processing properties of WWF. This information is useful to pasta manufacturers when adjusting equipment involved in movement of raw ingredients and in pasta production.

KEYWORDS flowability, processing, wet agglomeration, whole‐wheat flour, whole‐wheat pasta

1 | INTRODUCTION grain. The whole‐wheat flour (WWF) can be made either by direct conversion of grain into WWF (meal) or by reconsti- Whole‐wheat pasta is made from flour that contains bran, tuting the flour by mixing ground bran and germ into flour germ, and endosperm in the same ratio as found in wheat or semolina (Deng & Manthey, 2017; Miller Jones, Adams,

708 | © 2019 AACC International, Inc. wileyonlinelibrary.com/journal/cche Cereal Chemistry. 2019;96:708–716. DENG and MANTHEY | 709 Harriman, Miller, & Van der Kamp, 2015). These two meth- agglomeration of durum semolina and found that a decrease ods produce WWFs that differ in their individual particle in semolina particle size led to an increase in agglomerate composition. The direct conversion method produces flour size. Stickiness associated with agglomeration can result in where the bran and germ are adhered to endosperm particles; particles adhering to metal surfaces which can reduce total whereas in the reconstituted method, the bran and germ par- flow or output and represents a potential food safety concern ticles are loose and mixed among the endosperm particles. (Manthey, Yalla, Dick, & Badaruddin, 2004). Flow and agglomeration properties of these two forms of Bran particles have been reported to affect pasta extrusion WWF have not been evaluated. Flowability of ground ingre- (de la Peña & Manthey, 2017; de la Peña, Manthey, Patel, & dients is an important attribute for material handling and food Campanella, 2014). In the extrusion barrel, the screw rotates processing. Flour ingredients are often moved by pneumatic at a constant speed and pushes semolina dough forward and or mechanical conveying from silo to mixing chamber and through the pasta die. The mechanical energy required to ex- ultimately to food processing equipment. Poor flow is as- trude pasta and the rate of extrusion can be affected by dough sociated with clogging of sifters, conveying lines, blenders, strength (Yalla & Manthey, 2006). Manthey et al., (2004) and discharging hoppers (Bian, Sittipod, Garg, & Ambrose, found that extruding dough containing semolina and bran 2015). Agglomeration of ingredients occurs in the mixing flour required 50% less mechanical energy than extruding chamber. Problems occur when the agglomerates become too dough from semolina alone. large and form bridges over the chute of discharge hopper, Limited information is available concerning the effect which prevents the movement of hydrated ingredients be- of different milling systems on particle characteristics and tween the main mixer and the extrusion screw (de la Peña & agglomeration, and pasta processing of WW durum flour. Manthey, 2012). Bridging of the hydrated material will block Therefore, the objective of this research study was to investi- the flow of material and the force a shutdown of the pasta gate the effect of direct single‐pass and multiple‐pass recon- production line. stituted milling systems on flowability, wet agglomeration Flow properties and agglomerate formation could differ and pasta processing properties of WW durum flour. between WWFs when bran is adhered to endosperm (direct grind) compared to when the bran is loose among endosperm particles (reconstituted WWF). Previous research has shown 2 | MATERIALS AND METHODS that particle size and shape of bran differ from semolina or flour. Bran particles are often thin, rectangular, irregular 2.1 | Samples shape compared to a more blocky, angular shape of semo- This study is the continuation of previous published research lina. Particle size, shape, and roughness have been identified where direct single‐pass milled and multiple‐pass reconsti- as key physical determinants of ingredient flowability (Jan, tuted WWF qualities were compared (Deng & Manthey, Ghoroi, & Saxena, 2017). 2017). A bulk sample of durum wheat grown at Casselton, Flow properties tend to be favored by coarse particles ND 2015 was used in this study. The quality of the durum with uniform shape and smooth surface (Jan et al., 2017). sample was good and sound (Deng & Manthey, 2017). The Rough irregular shaped particles tend to interlock with each durum wheat sample was stored at 12°C until used. other and resist flow. Flowability generally decreases with the fine particles due to the cohesive forces between particles (Fitzpatrick, Barringer, & Iqbal, 2004). Small flour particles 2.2 | Whole‐wheat flour milling have a large surface area which allows a large number of con- The WW durum flour was made using the direct single‐pass tact points for inter‐particle bonding and interactions. and multiple‐pass reconstituted milling methods described During pasta processing, agglomeration of semolina oc- by Deng and Manthey (2017). In the single‐pass milling sys- curs after hydration in the mixing chamber. Agglomerate tem, the durum wheat sample (1 kg) was air‐dried to 9.0% formation has been attributed to the different hydration prop- moisture and directly ground into fine and coarse WWFs erties of nontraditional ingredients when compared to semo- with 24,000 g rotor speed, 250 µm screen aperture size, and lina (Kratzer, 2007; Traynham, Myers, Carriquiry, & Johnson, 15,400 g and 1,000 µm on an ultra‐centrifugal mill, respec- 2007). Hydration of WWF could differ depending if bran is tively (ZM 200; Retsch). The multiple‐pass reconstituted sys- adhered to endosperm or if loose and mixed with semolina. tem involved a roller mill (MLU 202; Bühler) with two Miag Differences in hydration properties could affect formation purifiers and an ultra‐centrifugal mill. The durum wheat was and size of agglomerates. When flour particles are hydrated, tempered to 17.5% moisture using a three‐step tempering wet agglomerates can be formed due to adhesive and cohesive process. Durum wheat was milled into semolina, bran/germ, forces caused by liquid bridges between partly or completely and shorts on the roller mill. The bran/germ and shorts frac- filled pore spaces of individual particles (Schubert, 1981). tions were ground into fine and coarse particles as described Bellocq, Duri, Cuq, and Ruiz (2018) investigated the wet above on the ultra‐centrifugal mill. Semolina was milled into 710 | DENG and MANTHEY durum flour using the ultracentrifuge mill configured with 2.6 Pasta extrusion 24,000 g rotor speed and 250 µm screen aperture size. Four | WWFs were made from blending durum semolina/flour and Semolina was hydrated to 33%, while durum flour and fine/coarse bran (SFB: semolina blended with finely ground WWFs were hydrated to 34% moisture as described in wet bran, germ, and shorts; SCB: semolina blended with coarsely agglomeration section above and were extruded under vac- ground bran, germ, and shorts; FFB: durum flour blended uum as spaghetti using a semi‐commercial, single screw, with finely ground bran, germ, and shorts; and FCB: durum laboratory extruder (DEMACO) as described by de la Peña flour blended with coarsely ground bran, germ, and shorts; and Manthey (2017). Specific mechanical energy was deter- Deng & Manthey, 2017). mined. The mechanical energy required to operate the empty pasta press was subtracted from the mechanical energy required to operate the press under load. Specific mechanical 2.3 | Whole‐wheat flour quality energy (J/g) was calculated as the mechanical energy (J/s)

Particle size distribution test, geometric mean diameter (dgw), to extrude pasta divided by the amount of spaghetti extruded and geometric standard deviation (sgw) by mass of WWF (g/s). Rate of pasta extruded was also determined by measur- particle size measurements were described in Deng and ing spaghetti length/min. Manthey (2017). Water holding capacity was measured using AACC International Approved Method 56‐30.01 (AACC 2.7 Scanning electron microscopy International, 2010). | Dry WWFs and agglomerates were applied to adhesive car- bon tabs on cylindrical aluminum mounts and coated with a 2.4 | Flow properties of whole‐wheat flour conductive layer of gold using a Cressington 108 auto sputter Whole‐wheat flour sample (100 g) was weighed and poured coater (Ted Pella Inc.). Sample images (×25 1 mm magni- into a cylinder. Bulk density of WWF (g/cm3) was measured fication and resolution for dry WWF and ×150 100 µm for as flour weight divided by the volume of the flour after tapping agglomerate) were obtained using a JEOL JSM‐6490LV the cylinder for 5 min. Flow properties of WWF were measured scanning electron microscope (JEOL USA) at an accelerat- on angle of slide and angle of repose. The angle of slide was ing voltage of 15 kV. measured as described by Chang, Kim, Kim, and Jung (1998). WWF sample (200 g) was poured into a stainless steel cylin- 2.8 Statistical analysis der (8 cm id) and then formed a conical heap on a horizontal | stainless steel plane after lifting and removing the cylinder. The The experimental design was randomized complete block. plane was inclined gradually at one end until the flour material The experiment had six different treatments of fine and slid down from the plane. The angle of slide (°) was recorded coarse direct ground WWFs and semolina/durum flour as the inclination of the plane to the horizontal when the mate- and fine and coarse bran blends. Each treatment had three rial slid down. Similarly, WWF sample (200 g) was poured replicates. Each replicate was done on a separate day. into a stainless steel cylinder and then formed a solid pile after Data were subjected to analysis of variance (ANOVA) lifting and removing cylinder on a horizontal plane. The angle using Statistical Analysis System v 9.4 (SAS Institute). of repose (°) is measured as the inclination of the free surface Treatment means were separated by Fisher's Protected to the horizontal of the bulk solid pile (Ileleji & Zhou, 2008). Least Significant Different (LSD) at p ≤ 0.05. Pearson's simple linear correlation coefficient was obtained using the “CORR” procedure in Statistical Analysis System 9.4 2.5 | Wet agglomeration of whole‐ (SAS Institute). wheat flour Whole‐wheat flour sample (250 g) was hydrated to 34% 3 RESULTS AND DISCUSSION moisture content and mixed for 4 min in a mixer (3.3 L | KitchenAid Mixer) with a paddle. Wet agglomerates were 3.1 Whole‐wheat flour qualities formed after hydration and mixing. The agglomeration prop- | erties were measured according to the methods described by 3.1.1 Particle size distribution de la Peña, Wiesenborn, and Manthey (2016). The agglom- | eration properties were measured by agglomerate weight Scanning electron micrographs in Figure 1a–f show the percentage retained on stacked sieves of 6.35, 2.83, 0.125, relative particle sizes and shapes of dry WWFs produced 0.044 mm and bottom after shaking 5 min, respectively. The by direct single‐pass and multiple‐pass reconstitution mill- agglomeration size distribution was recorded the weight per- ing systems. As previously reported in Deng and Manthey centages retained on stacked sieves. (2017), direct fine grind (Figure 1a) and durum flour:fine DENG and MANTHEY | 711 FIGURE 1 The Scanning Electron Micrographs of Dry whole‐wheat flours. (a) DF: Direct fine ground flour; (b) DC: Direct coarse ground flour; (c) SFB: Semolina blended with fine reground bran, germ, and shorts; (d) SCB: Semolina blended with coarse reground bran, germ, and shorts; (e) FFB: Durum flour blended with fine reground bran, germ, and shorts; (f) FCB: Durum flour blended with coarse reground bran, germ, and shorts (a) DF (b) DC

(e) FFB (f) FCB

bran (Figure 1e) produced fine particles with a narrow size dry sample) were higher than semolina (0.59 ml water/g distribution (dgw = 92 and 105 μm and sgw = 42 and 43 μm, dry sample, Table 1) which reflects the high amount of respectively), where dgw measures the geometric mean diam- fiber components in the bran associated with WWF. The eter of flour particle and sgw the dispersion of particle frac- direct fine grind WWF and durum flour:fine/coarse bran tions retained on a set of sieves. Durum flour:coarse bran had high water holding capacity (0.72–0.79 ml water/g (Figure 1f) and semolina:fine bran (Figure 1c) produced had dry sample). While, direct coarse and semolina:fine/ intermediate particle size and distribution with dgw = 125 coarse bran had low water holding capacity (0.61– and 183 μm and sgw = 81 and 108 μm, respectively. Direct 0.62 ml water/g dry sample). SEM showed small bran and coarse grind (Figure 1b) had similar coarse and wide parti- flour particles in direct fine grind (Figure 1a) and durum cle size distribution as semolina:coarse bran (Figure 1d) with flour:fine bran blends (Figure 1e). The large surface dgw = 216 and 215 μm and sgw = 163 and 131 μm. area of these small particles increased the water absorption of WWF during hydration. This explains the negative correlation between WWF particle size (geometric 3.1.2 | Water holding capacity diameter mean) and water holding capacity (r = −0.84, Water holding capacity was determined as the maximum p ≤ 0.05, data not shown in Tables). No significant dif- amount of water that material absorbs and retains under ference in water holding capacity was found between low‐speed centrifugation after hydration. Water holding semolina:fine bran and semolina:coarse bran or between capacity is dependent on the absorption and water reten- durum flour:fine bran and durum flour:coarse bran. The tion of protein, starch, and fibers within the hydrated ma- semolina/durum flour is the main component of WWF terials (Damodaran, 1997; Mudgil & Barak, 2013). The and would mask differences in water absorption associ- water holding capacities of WWFs (0.62–0.79 ml water/g ated with fine and coarse bran. 712 | DENG and MANTHEY TABLE 1 Means for water holding Water hold- Flour bulk capacity, flour bulk density, and flow ing capacity density Angle of slide Angle of repose properties of whole‐wheat durum flours ml water/g Durum flours dry sample g/cm3 ° Single‐pass DF 0.79 a 0.82 a 44 a 37 a DC 0.61 c 0.82 a 17 e 30 cd Multi‐pass SFB 0.62 c 0.78 b 34 c 31 cd SCB 0.62 c 0.69 c 23 d 28 d FFB 0.77 ab 0.79 b 43 ab 36 ab FCB 0.72 b 0.79 b 37 bc 33 bc Control S 0.59 0.71 23 23 F 0.71 0.88 60 33

Note: Values followed by different letters in the columns are significantly different at p ≤ 0.05. Abbreviations: DC, direct coarse ground flour; DF, direct fine ground flour; F, durum flour; FCB, durum flour blended with coarse reground bran, germ, and shorts; FFB, durum flour blended with fine reground bran, germ, and shorts; S, semolina; SCB, semolina blended with coarse reground bran, germ, and shorts; SFB, semolina blended with fine reground bran, germ, and shorts.

3.1.3 | Bulk density 3.2 | Whole‐wheat flour flow properties Direct fine and direct coarse ground flours had similar bulk density (0.82 g/cm3). Bulk density was greater with WWF 3.2.1 | Angle of slide from single‐pass milling system than from multiple‐pass The angle of slide of WWFs was significantly affected by reconstituted milling system (0.69–0.79 g/cm3). The bran/ particle size. Direct fine grind and durum flour:fine bran germ remained adhered to the endosperm particles pro- had high angle of slide (44 and 43°, respectively, Table duced by direct milling but were separated from the en- 1). The angle of slide for both finely ground WWFs (43– dosperm (semolina/flour) by the multi‐pass reconstitution 44°) was less than that for durum flour (60°) followed by milling system. Bulk density is determined by the density durum flour:coarse bran and semolina:fine bran of 37 and of individual particles and their spacial arrangement in a 34°. Those WWFs had small particle size (geometric di- container. The density of individual particles where the ameter mean: 92–183 μm) and small particles associated bran/germ is adhered to the endosperm is probably greater with fine grinding/regrinding required a high slope to slide than the density of bran/germ particles found in the recon- down the stainless steel plate. The small particles resisted stituted samples. Loose bran particles appeared to be long flow due to their high surface area and associated increased rectangular as compared to more square, blocky shape of friction and cohesive forces that occur between particles semolina/flour particles (Figure 1c–f). These findings in- (Fitzpatrick et al., 2004). Furthermore, Landillon, Cassan, dicate that the loose bran associated with the reconstituted Morel, and Cuq (2008) reported that small particles had poor WWF's probably interfered with particle packing, which flowability due to mechanical linkage and increased inter‐ resulted in lower bulk density. Within the reconstituted particle interaction by van der Waals forces. Direct coarse WWF's, semolina:fine bran, flour:fine bran, and flour grind and semolina:coarse bran required the lowest angle coarse bran had similar bulk densities of 0.78, 0.79, and of slide (17 and 23°). Larger particles of direct coarse grind 0.79 g/cm3, respectively. Semolina:coarse bran had the and semolina:coarse bran (geometric diameter mean: 215– lowest bulk density (0.69 g/cm3). Air space between large 216 μm) were more susceptible to flowing (sliding) on the particles of semolina and coarse bran resulted in loosely stainless steel surface. The lower angles of slide for WWFs packed, less dense material. Knowing the bulk density is (37–44°) compared to durum flour (60°) reflect the positive important in ensuring proper rate of ingredient delivery to effect of bran particles either adhered (direct grind) or loose mixers and extruder whether using volumetric or gravimet- and mixed with durum flour (reconstituted) had on flowabil- ric feeders. ity. Conversely, loose fine bran particles seemed to reduce DENG and MANTHEY | 713 TABLE 2 Mean size distribution of wet agglomerates made from flowing properties (European Pharmacopoeia Commission, whole‐wheat durum flours 2010), particles with angle repose of ˃35° are fair‐good

Mesh sieve (mm) flowing property and those with 30–35° and ˂30° are shown good and free flowing properties, respectively. Direct fine 6.35 2.83 0.125 0.044 <0.044 grind and durum flour:fine bran showed fair‐good flowing, Single‐pass as their angle of repose is >35° (Table 1). The bulk piles DF 4 ab 15 c 35 39 ab 7 of coarse particle are cone shape with a round bottom base DC 2 a 9 ab 45 41 b 3 that narrows to a point at the top (apex). However, the fine Multi‐pass particle piles were irregular shape. It might have caused from the high inter‐particle interactions between fine parti- SFB 6 b 11 bc 39 38 a 6 cles that restrained the particles flowing into a cone shape. SCB 1 a 9 ab 41 42 b 7 Followed by those two fine WWFs, durum flour:coarse bran FFB 6 b 14 c 43 32 a 5 and semolina:fine bran had angle of repose of 33 and 31°, FCB 1 a 7 a 40 45 b 7 respectively, which both showed good flowing properties. Control The direct coarse grind and semolina:coarse bran had small S 5 14 39 36 7 values (30 and 28°, respectively). The coarse particles of F 5 12 42 35 6 those two showed free flowing properties.

Note: Values followed by different letters in the columns are significantly differ- Samples with angles of repose above 35° flow more ent at p ≤ 0.05. poorly than those samples that have angles <30°, which is Abbreviations: DC, direct coarse ground flour; DF, direct fine ground flour; F, confirmed by the positive correlation between angle of re- durum flour; FCB, durum flour blended with coarse reground bran, germ, and pose and angle of flow (r = 0.70, p ≤ 0.05). Fine particle shorts; FFB, durum flour blended with fine reground bran, germ, and shorts; S, sizes have more friction to resist flow and form compact and semolina; SCB, semolina blended with coarse reground bran, germ, and shorts; SFB, semolina blended with fine reground bran, germ, and shorts. high piles. Also, the angle of repose had a negative correlation with sgw (r = −0.78, p ≤ 0.05), which was similar to the angle of slide (r = −0.93, p ≤ 0.05). Uniformity in particle the flowability of semolina as the angle of slide was 34° with size distribution increased particle flow difficulties of WWF semolina:fine bran compared to 23° for semolina alone. blends. Angle of slide with WWF blends containing coarse bran was lower than those containing fine bran, irrespectively of milling system. SEM images clearly show large pieces 3.3 | Whole‐wheat flour wet agglomeration of bran in the WWF blends (Figure 1b,d,f). With the large Agglomerates >6.4 mm can cause bridging and disrupt the bran pieces, the sgw of flour blends was increased from 38 extrusion process (de la Peña & Manthey, 2012). More large to 121 μm, reflecting wider dispersions of particle fractions agglomerates (>6.35 and 2.83 mm) were made from WWFs of WWF retained on a number of sieves compared with fine containing fine bran (direct fine grind, semolina:fine bran, bran blends. The wide dispersion reduced the uniformity of and durum flour fine bran) than those containing coarse flour blend and the heterogeneous particles flow more easily bran (direct coarse grind, semolina:coarse bran, and durum due to decreased inter‐particle interactions. This is also evi- flour:coarse bran; Table 2). Coarse bran particles seemed to dent from the negative relationship between sgw and angle of reduce the formation of large agglomerates. Agglomerates slide (r = −0.93, p ≤ 0.05). made from direct fine grind (Figure 2a) and from durum flour:fine bran (Figure 2e) appear to be more dense than those made from semolina (Figure 2c,d) or those containing 3.2.2 | Angle of repose coarsely ground bran (Figure 2b,d,f). de la Peña et al. (2016) Angle of repose is measured as the inclination of the free reported that the particle size of flour impacted the wet ag- surface to the horizontal of the bulk pile. Angle of re- glomerate formation and shape. Fine flour particles of direct pose can be used to predict behavior during bulk load- fine grind (Figure 2a) and durum flour:bran blends (Figure ing. Difficulties can occur during filling of bulk bags or 2e,f) have large solid–liquid contact area, which favors water silos with ingredients that result in a high angle of repose. movement into the capillary pores and the formation of ag- Ingredients with a high angle of repose have the potential glomerates. As granules collide with other particles during to back fill into the fill head and limit the amount of ma- mixing, water migrates outwards, which promotes adhesion terial that can be placed into the bag or silo. Undesirable interaction for agglomerate development. Thus, a greater filling properties can be ameliorated by the use of vibration number of large agglomerates are formed under the adhe- during filling. Angle of repose can also be used to predict sion interaction between fine flour particles than from coarse particle flow properties. According to the criteria of particle particles. In addition, direct fine grind and durum flour:fine 714 | DENG and MANTHEY FIGURE 2 The Scanning Electron Micrographs of whole‐wheat flour agglomerates. (a) DF: Direct fine ground flour; (b) DC: Direct coarse ground flour; (c) SFB: Semolina blended with fine reground bran, germ, and shorts; (d) SCB: Semolina blended with coarse reground bran, germ, and shorts; (e) FFB: Durum flour blended with fine reground bran, germ, and shorts; (f) FCB: Durum flour blended (a) DF (b) DC with coarse reground bran, germ, and shorts

(e) FFB (f) FCB

bran had high level of starch damage (7.6%–7.9%; Deng & 3.4 Whole‐wheat flour Manthey, 2017). Broken starch granules can absorb large | processing properties amount of water during hydration (Farrand, 1964), which could promote water absorption and formation of large Specific mechanical energy (SME) did not vary significantly agglomerates. among WWFs (data not presented). These results are simi- Content of small agglomerates was significantly lar to those previously reported by de la Peña and Manthey greater with direct coarse grind, semolina:coarse bran and (2017). They reported that SME required to extrude semo- durum flour:coarse bran (41%–45% retained on 0.044 mm lina, WWF or semolina whole‐wheat flour blend was simi- mesh sieve, Table 2) than direct fine grind, semolina:fine lar when they were hydrated to 34% mb. It was observed bran and durum flour:fine bran (32%–39%). SEM images that agglomeration and stickiness to metal surfaces were show coarse bran of direct coarse, semolina:coarse bran, not a problem and that all the WWF samples had similar and durum flour:coarse bran blends (Figure 2b,d,f) that extrusion rate (data not presented). These observations are are located on the surface of agglomerates or along with reflected in the lack of difference in SME when extruding agglomerates. The coarse bran could affect the movement WW spaghetti. of water to the flour particle (endosperm) and decrease the subsequent formation of large wet agglomerates. SEM images show that some bran pieces contained epicarp 4 | CONCLUSIONS hairs (Figure 2b). The epicarp hairs could disrupt agglomeration process and prevent the development of large Bran remained adhered to the endosperm when durum was agglomerates. milled with the direct single‐pass system but was separated DENG and MANTHEY | 715 from the endosperm when milled with the multiple‐pass Damodaran, S. (1997). Food proteins: An overview. In S. Damodaran reconstituted system. The bran particles separated from & A. Paraf (Eds.), Food proteins and their applications (pp. 12–14). endosperm and reground in multiple‐pass milling system New York, NY: Marcel Dekker Inc. Whole wheat pasta fortified possess different particle size and shape than flour/semo- de la Peña, E., & Manthey, F. A. (2012). with flaxseed flour. In Proceedings of the 64th Flax Institute of the lina from endosperm. The heterogeneity of bran and flour/ United States March 29–30, Fargo, ND. 64:89–94. semolina particles could alter the flow properties during de la Peña, E., & Manthey, F. A. (2017). Effect of formulation and material conveying by their inter‐particle bonding and dough hydration level on extrusion, physical and cooked qualities interaction. of nontraditional spaghetti. Journal of Food Process Engineering, The results showed that bulk density and flowability of 40, 1–12. WWF's were affected by milling system. Bulk density of de la Pena, E., Manthey, F., Patel, B. K., & Campanella, O. H. (2014). WWF's was greater with direct single‐pass system (bran Rheological properties of pasta dough during pasta extrusion: Effect Journal of Cereal Science 60 is adhered to ground endosperm) than with multiple‐pass of moisture and dough formulation. , , 346–351. https://doi.org/10.1016/j.jcs.2014.05.013 reconstitution system (bran particles are loose and mixed de la Peña, E., Wiesenborn, D. P., & Manthey, F. A. (2016). with flour or semolina particles). Direct fine grind WWF Agglomeration properties of semolina and whole wheat flour forti- and multiple‐pass reconstituted durum flour:fine bran fied with flaxseed flour. Journal of Food Process Engineering, 39, had flow difficulties when compared to the direct coarse 400–410. https://doi.org/10.1111/jfpe.12232 grind and multiple‐pass reconstituted semolina:coarse Deng, L., & Manthey, F. A. (2017). Effect of single‐pass and multiple bran. Overall, direct coarse grind had the best flow prop- pass milling system on whole‐wheat flour and whole‐wheat pasta Cereal Chemistry 94 erties. Thus, bulk density and flowability seemed to be quality. , , 963–969. European Pharmacopoeia Commission (2010). Powder flow. pp: 308 influenced by whether or not the bran was adhered to the in European Pharmacopoeia (7th ed.). Strasbourg, France: Council endosperm. of Europe. Whole‐wheat flour particle size showed negative cor- Farrand, E. A. (1964). Flour properties in relation to the modern bread relation with water holding capacity. Regardless of mill- process in the United Kingdom with special reference to alpha‐amy- ing system, flour flow properties were better (low angle lase and starch damage. Cereal Chemistry, 41, 98–111. of slide) with large/coarse particles and wet agglomeration Fitzpatrick, J. J., Barringer, S. A., & Iqbal, T. (2004). Flow prop- was greater with fine particles. Direct coarse grind, semo- erty measurement of food powders and sensitivity of Jenike’s Journal of lina:coarse bran and durum flour:coarse bran had few large hopper design methodology to the measured values. Food Engineering, 61, 399–405. https://doi.org/10.1016/S0260- wet agglomerates. Neither milling system nor particle size 8774(03)00147-X affected pasta processing as evaluated by extrusion rate and Ileleji, E. K., & Zhou, B. (2008). The angle of repose of bulk corn the specific mechanical energy required to extrude WWF's stover particles. Powder Technology, 187, 110–118. https://doi. into spaghetti. org/10.1016/j.powtec.2008.01.029 Jan, S., Ghoroi, C., & Saxena, D. C. (2017). A comparative study of ORCID flow properties of basmati and non‐basmati rice flour from two Frank A. Manthey https://orcid. different mills. Journal of Cereal Science, 76, 165–172. https://doi. org/0000-0003-4134-6932 org/10.1016/j.jcs.2017.05.016 Kratzer, A. M. (2007). Hydration, dough formation and structure development in durum wheat pasta processing. PhD Thesis, Swiss Federal Institute of Technology Zurich. Zurich, Switzerland. REFERENCES Landillon, V., Cassan, D., Morel, M.‐H., & Cuq, B. (2008). Flowability, AACC International (2010). Approved methods of analysis (11th ed.). cohesive, and granulation properties of wheat powders. Journal Method 56‐30.01. Water Holding Capacity of Protein Materials of Food Engineering, 86, 178–193. https://doi.org/10.1016/j.jfood Method. St Paul, MN; AACC International. eng.2007.09.022 Bellocq, B., Duri, A., Cuq, B., & Ruiz, T. (2018). Impacts of the size Manthey, F. A., Yalla, S. R., Dick, T. J., & Badaruddin, M. (2004). distributions and protein contents of the native wheat powders in Extrusion properties and cooking quality of spaghetti containing their structuration behavior by wet agglomeration. Journal of Food buckwheat bran flour. Cereal Chemistry, 81, 232–236. https://doi. Engineering, 219, 29–37. org/10.1094/CCHEM.2004.81.2.232 Bian, Q., Sittipod, S., Garg, A., & Ambrose, R. P. K. (2015). Bulk flow Miller Jones, J., Adams, J., Harriman, C., Miller, C., & Van der properties of hard and soft wheat flours. Journal of Cereal Science, Kamp, J. W. (2015). Nutritional impacts of different whole grain 63, 88–94. https://doi.org/10.1016/j.jcs.2015.03.010 milling techniques: A review of milling practices and existing Chang, K. S., Kim, D. W., Kim, S. S., & Jung, M. Y. (1998). Bulk data. Cereal Foods World, 60, 130–139. https://doi.org/10.1094/ flow properties of model food powder at different water activity. CFW-60-3-0130 International Journal of Food Properties, 1, 45–55. https://doi. Mudgil, D., & Barak, S. (2013). Composition, properties and health org/10.1080/10942919809524564 benefits of indigestible carbohydrate polymers as dietary fiber: A 716 | DENG and MANTHEY review. International Journal of Biological Macromolecules, 61, 1–6. https://doi.org/10.1016/j.ijbiomac.2013.06.044 How to cite this article: Deng L, Manthey FA. Schubert, H. (1981). Principles of agglomeration. International Journal Flowability, wet agglomeration, and pasta processing of Chemical Engineering 21 , , 363–377. properties of whole‐durum flour: Effect of direct Traynham, T. L., Myers, D. J., Carriquiry, A. L., & Johnson, L. A. single‐pass and multiple‐pass reconstituted milling (2007). Evaluation of water‐holding capacity for wheat‐soy flour systems. Cereal Chem. 2019;96:708–716. https://doi. blends. Journal of American Oil Chemists Society, 84, 151–155. https://doi.org/10.1007/s11746-006-1018-0 org/10.1002/cche.10167 Yalla, S. R., & Manthey, F. A. (2006). Effect of semolina and absorption level on extrusion of spaghetti containing non‐traditional ingredients. Journal of the Science of Food and Agriculture, 86, 841–848. https://doi.org/10.1002/jsfa.2425