Influence of milling and extrusion on the sorption properties of sorghum

Abstract

The processing to which a material is subjected can affect its physical or chemical structures, resulting in products with different hygroscopic behaviours. The present work studied the water adsorption properties of sorghum subjected to different types of processing: raw flour (produced by milling whole grain), extrudates (obtained using a double screw extruder) and extruded flour (obtained by milling the extrudates). The isotherms were obtained using an automated instrumental method. The tests were run in duplicate at 25 °C with relative humidity values ranging between 11 and 84%. The water adsorption data fitted the GAB model well, showing high coefficients of determination. The estimated water contents of the adsorption monolayer ranged from 5.3 to 6.9 g of water per 100 g of dry material. The sorption isotherms were affected by the type of processing, extrusion cooking resulting in products with less water in the monolayer (less hygroscopic). The milling process yielded high water contents in the monolayer, probably due to the breakdown of some polymer-polymer interactions, which exposed the binding sites. To ensure microbiological stability, the water contents in the materials should not exceed 6.9 g of water per 100 g of dry material for raw sorghum flour, 5.3 g of water per 100 g for sorghum extrudates and 6.7 g of water per 100 g for extruded sorghum flour. Keywords: Extruded flour; Extrudates; Raw flour; Sorghum bicolor L.; Sorption isotherms. ResumoO processamento ao qual um material é submetido pode afetar sua estrutura física ou química, resultando em produtos com diferentes comportamentos higroscópicos. No presente trabalho, objetivou-se estudar as propriedades de adsorção de água do sorgo em diferentes formas de processamento: farinha crua (produzida pela moagem de grãos inteiros), extrusados (produzidos em extrusora de duplo parafuso) e farinha extrusada (obtida pela moagem dos extrudados). As isotermas foram obtidas usando o método instrumental automatizado. Os testes foram realizados em duplicata, a 25 °C, com valores de umidade relativa variando entre 11 e 84%. Os dados de adsorção de água foram bem ajustados ao modelo de GAB, mostrando altos coeficientes de determinação. O teor estimado de água da monocamada variou de 5,3 a 6,9 g de água por 100 g de material seco. As isotermas de sorção foram afetadas pelo tipo de processamento, sendo que o cozimento por extrusão resultou em produtos com menor valor de monocamada (menos higroscópico). O processo de moagem produziu valores de monocamada elevados, provavelmente devidos à degradação de algumas interações polímero-polímero, que expuseram sítios de ligação. Para garantir a estabilidade microbiológica, o teor de água nos materiais não deve ser superior a 6,9 g de água por 100 g de material seco para a farinha crua de sorgo; 5,3 g de água por 100 g para os extrusados de sorgo, e 6,7 g de água por 100 g para a farinha extrusada. Palavras

Moisture adsorption isotherms of baru almond flours

“…By comparing the present study and Galdeano et al (2018), note that the estimated molecular monolayer moisture values were higher for the WBF (estimated by GAB model) when compared to PDBF at all temperatures. This fact can be explained by the higher oil content of the whole meal flour.…”

“…These values were smaller than raw and extruded sorghum flours, which contained 6.90 and 6.70% (d.b.) water content at X m , respectively at 25 °C, estimated from the GAB model (Galdeano et al, 2018).…”

Comparison and modeling of moisture sorption isotherms of deproteinized rapeseed meal and model extrudate

“…A similar trend was observed by Włodarczyk‐Stasiak and Jamroz (2008) for starch–protein extrudates in comparison to the raw material. Comparing the sorption properties of sorghum flour and extrudate, Galdeano et al (2018) established that the extrusion disrupted the starch structure and changed the biopolymers conformation which allowed the interactions among the food components and, as a consequence, reduction of the sorption capacity. The comparison of the sorption isotherms of raw materials from sour cherry and blackcurrant pomaces and extrudates from the same pomaces with the addition of corn meal showed a reduction of the sorption capacity of the extrudates (Witczak et al, 2020).…”

Evaluation of the Physical, Chemical, Technological, and Sensorial Properties of Extrudates and Cookies from Composite Sorghum and Cowpea Flours

“…The samples were extruded at Embrapa Food Technology, Rio de Janeiro, Brazil, according to the method described by Galdeano et al [27]. The extrusion process was done using an Evolum HT25 co-rotating, intermeshing twin-screw extruder (Clextral Inc., Firminy, France) with the aim of producing expanded or puffed extrudates.…”