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‐cen- trifugal 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 agglomer- ates 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