Barley starch composition

This review has shown that most studies on barley starches have been focused on understanding the fine structures, particle size distribution, chemical composition, gelatinization properties and susceptibility towards enzyme hydrolysis. However, there is a dearth of information on the rheological and retrogradation characteristics of barley starches from different cultivars. Furthermore, the response of small and large barley starch granules towards physical and chemical modification needs investigation. Research in the above areas is underway in our laboratories. It is hoped that this study may improve the utilization of different types of barley starches for specific products within the food and paper industry. 

TABLE 1.4 Starch composition of quinoa, rice, barley (% dry basis)... 

Morrison, W., Scott, D., and Karkalas, J. (1986). Variation in the composition and physical properties of barley starches. Starch/St drke 38, 374-379. 

Hull-less barley varieties have been developed, in which the hull separates during threshing. These varieties contain more protein and less fibre than conventional barley, and theoretically should be superior in nutritive value to conventional barley. However, Ravindran et al. (2007) found that the ME (N-corrected basis) was similar in hull-less and hulled barley. The chemical composition of six Brazilian hull-less barley cultivars was studied by Helm and de Francisco (2004) and reported as follows. The highest constituents were starch (575-631 g/kg), crude protein (125-159 g/kg) and total dietary fibre (TDF 124-174g/kg), the starch and crude protein contents being in agreement with those previously reported for Swedish (Elfverson et al., 1999) and Canadian (Li et al., 2001) varieties. The other reported values (g/ kg) were ash content 15.1-22.7, ether extract 29.1M0.0, starch 574.6-631.4, insoluble dietary fibre 80.7-121.6, soluble dietary fibre 43.0-64.5 and p-glucan 37.0-57.7. 

Li, J.H., Vasanthan, T., Rossnagel, B. and Hoover, R. (2001) Starch from hull-less barley I. Granule morphology, composition and amylopectin structure. Food Chemistry 74, 395-405. 

The ratio of amylose to amylopectin also varies, depending on the source of the starch it ranges from 17 to 70% amylose and a corresponding 83 to 30% amylopectin. SeeO Table 2 for a list of different starches and their composition of amylose and amylopectin. Usually amylopectin is present as the major component, with a common ratio of 1 3 or 25% amylose and 75% amylopectin. There are mutants, however, such as, waxy barley, waxy maize, waxy rice, waxy potato, and waxy sorghum that are 100% amylopectin and there are the high-amylose starches. 

The majority of starches have nearly identical ratios of amylose to amylopectin. The most prevalent composition—found in corn, wheat, arrowroot, potato starches, etc.—is 20 to 28% amylose and 72 to 80% amylopectin. So-called waxy or glutinous starches from waxy varieties of corn, sorghum, rice, barley, and millet contain only amylopectin, or if amylose is present it is so in amounts of not more than about 6%. On the other hand, a few starches, such as special mutant varieties of corn, are known that contain up to 65 to 77 % amylose (90). 

The starch content and its composition (amylose content) in some foods is given in Table 4.25, amylopectin content is the difference to make up the 100%. The main sources of starch in foods and industrial sources of starch are potatoes [Solanum tuberosum, Solanaceae) and cereals, especially wheat Tritkum aestivum, Poaceae), rye Secale cereale), barley Hordeum vulgare), oats... 

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