food and bioproducts processing 87 (2009) 237–246 Contents lists available at ScienceDirect Food and Bioproducts Processing journal homepage: www.elsevier.com/locate/fbp Pneumatic separation of hulls and meats from cracked soybeans Murilo D.M. Innocentini a,b,* , Wellington S. Barizan a , Maicon N.O. Alves a , Reinaldo Pisani Jr a,b a Chemical Engineering Course, University of Ribeirão Preto-UNAERP, Av. Costábile Romano 2201, Ribeirânia, 14096-900 Ribeirão Preto, SP, Brazil b Post-graduation Program in Environmental Technology, University of Ribeirão Preto-UNAERP, Av. Costábile Romano 2201, Ribeirânia, 14096-900 Ribeirão Preto, SP, Brazil abstract The dehulling process of cracked soybeans was experimentally investigated in this work. The mean Sauter diame- ter (d v,s ) of as-received material was 2.70mm, with an average proportion of 95% meats and 5% hulls for a moisture content of 11.8%. The true densities of hulls and meats were 1090 and 1267 kg/m 3 , with d v,s of 2.11 and 2.74 mm, respectively. Hulls were mostly elutriated around 2.7–4.5m/s and meats around 9.1–13.7m/s. The overlap of ter- minal velocity profiles required a combination of pneumatic and sieving operations for optimized separation. The influence of particle concentration on continuous dehulling was investigated for three solid-to-air ratios (W/Q). The procedure that maximized particle separation was a sequence of pneumatic dehulling with v s = 7.4–9.1m/s and W/Q = 1.05 kg solids /m 3 air , followed by screening of lifted material with sieve ASTM no. 6 and a final pneumatic sepa- ration of small hulls and meats at v s = 3.9 - 4.1m/s. An industrial scale pneumatic dehuller was built and tested for W = 6973 kg/h, v s = 7.6–8.2m/s and W/Q = 0.97 kg solids /m 3 air . The efficiency of the pneumatic device to remove hulls from the cracked soybean was very high, with the recovery of meats with purity around 99%. © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Soybean; Hulls; Pneumatic dehulling; Terminal velocity; Elutriation 1. Introduction Soybean is the agricultural crop with the largest planted area in Brazil. The country was the second-largest world producer and exporter of this oilseed crop in 2007, just behind the United States. The expectation for the next years is still opti- mistic, especially because of the increasing demand of oil sources for the food industry and recently for the biodiesel pro- duction. This fact has motivated Brazilian industries to search for cost-reducing technologies to improve the market compet- itiveness of soybean byproducts, especially the meal fraction, a rich protein–carbohydrate–fiber ingredient for livestock and food production. Whole soybeans have a typical size of 5–8 mm (Duarte et al., 2004; Kocabiyik et al., 2004) and, on a dry weight basis, con- tain about 40% proteins, 20% lipids (oil), 35% carbohydrate and about 5% ash. The grain comprises approximately 92% kernel ∗ Corresponding author at: Chemical Engineering Course, University of Ribeirão Preto-UNAERP, Av. Costábile Romano 2201, Ribeirânia, 14096-900 Ribeirão Preto, SP, Brazil. Tel.: +55 16 3603 6784. E-mail address: muriloinnocentini@yahoo.com.br (M.D.M. Innocentini). Received 19 July 2008; Received in revised form 31 October 2008; Accepted 5 November 2008 or meat (90% cotyledons and 2% germ) and 8% seed coat or hull (Erickson, 1995; Liu, 1997; Francis, 1999). Cleaned hulls typically have thickness of 0.4–0.5 mm (Raji and Famurewa, 2005) and contain 9.4% crude protein and 86% complex car- bohydrates, a composition that makes hulls an important source of dietary fiber (Erickson, 1995). The insoluble car- bohydrate fraction of hull cell walls consists of 30% pectin, 50% hemicellulose, and 20% cellulose (Gnanasambandam and Proctor, 1999; Mullin and Xu, 2001). A unique aspect of soy- bean hulls is that the fiber content is low in lignin and is highly digestible; therefore hulls are recognized as an excel- lent source of readily available energy in forage-based diets (Löest et al., 2001). Soybean hulls are poor in oil content and are fairly abrasive. Thus it is convenient to remove them from the meat prior to the oil extraction to avoid reduction in the oil yield and wear of flaking machines (Erickson, 1995). 0960-3085/$ – see front matter © 2008 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.fbp.2008.11.001