Effect of Sorghum on Rheology and Final Quality of Western Style Breads: a Literature Review
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foods Review Effect of Sorghum on Rheology and Final Quality of Western Style Breads: A Literature Review Rubina Rumler and Regine Schönlechner * Department of Food Science and Technology, University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna, Austria; [email protected] * Correspondence: [email protected]; Tel.: +43-147-6547-5240 Abstract: Due to the extreme weather conditions, caused by the climate change, the usual wheat harvest yield and quality in the Western countries were difficult to maintain in the past few years. The altered wheat quality was primarily characterized by a rising protein content. The application of high protein wheat flours in baking products leads to baking difficulties due to its elastic dough behavior. As these issues will further face the Western cereal cultivation, heat resistant cereals, like sorghum, are attracting increasing interest. A partial substitution of wheat with sorghum might offer one possible solution to address the current challenging situation. To introduce sorghum in the Western cereal and baking industry, the grain and its unique chemical and rheological properties need to be more widely promoted. Until now, several authors have conducted studies in order to emphasize the high potential of sorghum. The aim of the present review is to broaden the current knowledge of the chemical, rheological and baking properties of sorghum in comparison to wheat. The review further demonstrates promising approaches, which might be from interest in order to achieve higher wheat-sorghum bakery end product qualities. Citation: Rumler, R.; Schönlechner, Keywords: sorghum; western bread; rheology; baking; wheat sorghum blends R. Effect of Sorghum on Rheology and Final Quality of Western Style Breads: A Literature Review. Foods 2021, 10, 1392. https://doi.org/ 1. Introduction 10.3390/foods10061392 The wheat grain industry already experienced the effects of the climate change in the past few years. Dry climate with low rainfall was responsible for crop failures of Academic Editors: Manuel Gomez wheat. According to a study, 60% of the current wheat growing areas could be affected by and Lillian Barros insufficient water supply by the end of this century [1]. However, due to the climate change not only wheat harvest losses happened, but also the wheat protein contents increased in Received: 17 May 2021 the last few years [2]. A suitable solution must be found to compensate for the loss of wheat Accepted: 12 June 2021 Published: 16 June 2021 in the grain and baking industry and to deal with the altered quality. A possible way to address these challenges could be the use of food additives or to import wheat from other Publisher’s Note: MDPI stays neutral countries. A more sustainable, customer-friendly and innovative option could be the use with regard to jurisdictional claims in of regional grains, preferable gluten-free grains, in wheat products. A partial replacement published maps and institutional affil- by gluten-free cereals might offer an option in order to compensate for the changed protein iations. content of wheat. Sorghum, which is gluten-free and heat resistant, presents a promising grain in this context. The use of sorghum in wheat products could be a possible future solution to counteract the high climate-induced protein content of wheat. In addition, end products consisting of sorghum can gain valuable nutrients [3]. In order to introduce sorghum into the Western diet, the nutritional and technological Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. challenges have to be considered. Mainly the altered protein composition, due to the This article is an open access article absence of gluten results in changed dough rheological parameters and end-product distributed under the terms and qualities [4–7]. However, like other cereals sorghum contains tannins, trypsin inhibitors conditions of the Creative Commons and phytic acids, which are known to impair protein digestion and mineral absorption [8]. Attribution (CC BY) license (https:// Sometimes these values are higher than in other cereals. In addition, sorghum prolamins, creativecommons.org/licenses/by/ called kafirins, are known to have a low digestibility, especially in prepared foods [9], which 4.0/). is mainly due to their crosslinking properties upon processing. Sorghum possesses higher Foods 2021, 10, 1392. https://doi.org/10.3390/foods10061392 https://www.mdpi.com/journal/foods Foods 2021, 10, x FOR PEER REVIEW 2 of 15 Foods 2021, 10, 1392 2 of 15 which is mainly due to their crosslinking properties upon processing. Sorghum possesses higher crosslinking properties than wheat for example. However, if this protein cross- crosslinking properties than wheat for example. However, if this protein cross-linking linking could in turn offer beneficial viscoelastic properties in food is still unknown [10]. could in turn offer beneficial viscoelastic properties in food is still unknown [10]. This review summarizes the main chemical properties of sorghum and highlights its This review summarizes the main chemical properties of sorghum and highlights its uniqueunique nutritional nutritional profile, profile, reveals reveals the the current current state state of of research research on on the the use use of of sorghum sorghum in in wheatwheat doughs doughs and and suggests suggests promising promising technologies technologies that that could could lead lead to to improvements in in wheat-sorghumwheat-sorghum doughs. doughs. 2.2. Classification Classification and and Morphology Morphology of of Sorghum Sorghum AlthoughAlthough sorghum sorghum is is not not well well known known in in the the West, West, it it is is the the fifth fifth most most produced produced cereal cereal worldwide.worldwide. In In Africa Africa sorghum sorghum is is considered considered to to be be the the most important cereal. Outside Outside of of AfricaAfrica production production takes takes place place mainly mainly in in Indi India,a, USA, USA, Australia, Australia, and and Argentina, Argentina, whereby whereby sorghumsorghum in in the the USA USA and and in in Australia Australia is is mostly mostly used used as as animal animal feed. feed. Five Five races races are are known known underunder sorghum: sorghum: bicolorbicolor, ,kafirkafir, , caudatumcaudatum, , durradurra andand guinea.. All All combinations combinations from from those those mentionedmentioned races races are are called called intermediate intermediate races. races. Of Of all all races, races, SorghumSorghum bicolor bicolor MoenchMoench is is mainlymainly cultivated cultivated [11]. [11]. According According to to Taylor Taylor there there are are different different classification classification systems systems of of sorghum.sorghum. Some Some of of them them seem seem to to be be complex. complex. However, However, like like wheat wheat and and maize maize sorghum sorghum is is classifiedclassified into into the the grass grass family family PoaceaePoaceae asas can can be be seen seen in Figure 11.. SorghumSorghum belongs,belongs, likelike maize,maize, to to the the subfamily Panicoideae andand toto thethetribe tribeAndropogoneae Andropogoneae[ 12[12].]. Due Due to to the the botanical botani- calrelationship relationship sorghum sorghum is often is often compared compared to maize.to maize. FigureFigure 1. 1. FamilyFamily tree tree of of sorghum. sorghum. Modified Modified according according to to Taylor Taylor [12]. [12]. TheThe structure structure of of a asorghum sorghum kernel kernel is comparab is comparablele to the to thestructure structure of a ofcorn a corn kernel, kernel, but inbut general, in general, a sorghum a sorghum grain grain is smaller. is smaller. Awika Awika et al. et [13] al. [determined13] determined the diameters the diameters of dif- of ferentdifferent sorghum sorghum kernels kernels to range to range between between 1.7–2 1.7–2.7.7 mm, mm, and and thethe thousand thousand kernel kernel weight weight of differentof different varieties varieties was was between between 15.2–38.8 15.2–38.8 g. g.The The extent extent of of the the pericarp pericarp thickness thickness and and the the presencepresence of aa testatesta is is variety variety dependent dependent [13 [1].3]. Both Both sorghum sorghum and and maize, maize, have have an endosperm an endo- spermwith a with floury a andfloury a corneous and a corneous part [14 part]. Sorghum [14]. Sorghum kernels appearkernels inappear color nuancesin color nuances of white, ofred, white, brown red, and brown black and (Figure black2). (Figure 2). However, the color of the pericarp is not always indicative of the appearance of sorghum flour. For example, a sorghum kernel which owns a red pericarp, may have a light endosperm color. Therefore, if special food colors are required, the insertion of sorghum fraction flours may be useful in order to achieve appropriate food appearances [15]. Foods 2021, 10, 1392 3 of 15 Foods 2021, 10, x FOR PEER REVIEW 3 of 15 FigureFigure 2. 2.Sorghum Sorghum field field in in Hörsching, Hörsching, Austria Austria (©Rumler, (©Rumler, 2020). 2020). 3. ChemicalHowever, and the Nutritional color of the Properties pericarp ofis not Sorghum always indicative of the appearance of sor- 3.1.ghum Protein flour. For example, a sorghum kernel which owns a red pericarp, may have a light endospermThe protein color. content Therefore, in sorghum if special can befood comparable colors are to required, the protein the content insertion of wheat of sorghum[5,16]. However,fraction flours Tasie may and be Gebreyes useful in [17 order] found to achieve a wide rangeappropriate of 8.20–16.48% food appearances between [15]. different sorghum whole grain varieties. Attempts have often been made to identify correlations between3. Chemical nutrients and Nutritional and the sorghum Properties kernels of Sorghum color. Whether the protein content differs between3.1. Protein red and white sorghum is still poorly understood. A research of Galan et al. [18] detectedThe a protein higher proteincontent contentin sorghum in red can whole be comparable grain sorghum to the flour, protein while content Yousif et of al.