Molecular Structure and Pasting Properties of Normal Barley Starches.

Abstract

(1-21-24, Korimoto, Kagoshima 890-0065, Japan)The molecular structure and pasting properties of the starches from seven normal cultivars of barley were examined and compared with those of normal maize, rice and wheat starches. The bar ley starches had an actual amylose content of 24.3-27.9%. The starches had different pasting prop erties, such as maximum viscosity and breakdown, and different amylose gelatinization. A positive correlation was found between the maximum viscosity and the gelatinization degree of amylose, suggesting that low amylose gelatinization restrains the swelling of starch granules. The amylopec tins had a low iodine affinity (0.42-0.70 g/100 g) and resembled each other in chain-length distri bution with the individual peaks of B 1 and A chains. The amyloses had DPn of 810-1410 with 3.6-5.2 chains per molecule, indicating that barley amyloses differed in molecular structure with the cultivars. Among the cereal starches, barley starches were similar to wheat starch in amylose content and molecular structure, especially molecular size of amylose and chain-length distribution of amylopectin.Barley is one of the major cereals along with maize, rice and wheat, and is mainly used for livestock feed and raw material for the production of alcoholic beverages. Recently, barley has also been used as food, such as a rice substitute, and in breads and noodles. Starch is the main component of barley grains (65% by wet weight).1) However, structural characteristics of barley starches have been less well established compared with those of other major cereals such as maize,2,3) rice4-6) and wheat.7,8) We recently examined the molecular structure of starches from some barley cultivars with different amylose content, one waxy (0% amylose), two low-amylose (2 and 11% amylose), two normal (23 and 25% amylose) and two high amylose (33 and 41% amylose) barley starches.9,10) The barley amylopectins from starches with differ ent amylose content were similar in molecular structure, while the amyloses had different molecu lar structures. The amyloses from the normal culti vars were similar in size to those of high-amylose cultivars but smaller than those of low-amylose cultivars. To date there is only limited literature in which the molecular structure of normal barley starches is examined9-12) although many varieties are cultivated. Moreover, in most studies,13-18) their structural analyses were conducted using whole starch. In this study, seven normal barley starches were characterized in molecular structure of frac tionated amylose and amylopectin and starch pasting properties in order to elucidate both similarities and differences among the normal varieties.

Molecular Structure and Some Physicochemical Properties of Buckwheat Starches

“…Buckwheat amylopectins showed a similar chain-length distribution among the cultivars with a peak at DP 11-12 and a shoulder at DP 18. These distributions were similar to those for wheat (Shibanuma et al 1996) and barley (Takeda et al 1999;Yoshimoto et al 2001Yoshimoto et al , 2002.…”

“…Ranges for the first transition were 59.5-64.1°C for onset (T o ), 63.7-68.4°C for peak (T p ), and 81.7-85.8°C for complete (T c ) temperatures, and ∆H values were 14.5-15.0 J/g. These values were higher than those of barley starches (T o 53.6-57.0°C, T p 56.9-60.0°C, T c 72.1-77.7°C, ∆H 12.1-13.0 J/g) (Yoshimoto et al 2001) examined under the same experimental conditions, indicating that buckwheat starches had a larger crystalline region, to which size and perfection of crystallite contribute. Because the first transition corresponded to melting of crystallite of starch, which is mainly amylopectin (Morrison et al 1993), the number of long chains of amylopectin also is a factor affecting the thermal properties.…”

“…The IA values were higher than those for maize (0.80-1.10) (Takeda et al 1988a;Takeda and Preiss 1993), wheat (0.40-1.12) (Shibanuma et al 1994(Shibanuma et al , 1996, and barley (0.42-0.70) (Takeda et al 1999;Yoshimoto et al 2000Yoshimoto et al , 2001Yoshimoto et al , 2002 amylopectins but comparable to those of indica rice amylopectins (1.62-2.57) (Takeda et al 1987a). The CL was 23-24 determined by three independent methods of rapid Smith-degradation, isoamylolysis, and fluorescent labeling/ HPSEC.…”

“…The average number of chains was 3.1-4.3, which is in the range for cereal amyloses (1.8-6.5). Buckwheat amyloses had a β-amylolysis limit (76-82%) similar to those of cereal amyloses (74-86%) (Takeda et al 1986(Takeda et al , 1988a(Takeda et al , 1989(Takeda et al , 1999Takeda and Preiss 1993;Shibanuma et al 1994Shibanuma et al , 1996Yoshimoto et al 2000Yoshimoto et al , 2001Yoshimoto et al , 2002.…”

“…The amyloses were similar in IA (19.3-20.2 g/100 g), blue value (1.36-1.48), and λ max (645-657 nm), and had DP n of 1,020-1,380. Buckwheat amyloses were slightly larger than maize (830-990) (Takeda et al 1988a;Takeda and Preiss 1993) and rice (920-1,110) (Takeda et al 1986(Takeda et al , 1989 amyloses, and in the range of wheat (830-1,570) (Shibanuma et al 1994(Shibanuma et al , 1996, and barley (810-1,570) (Takeda et al 1999;Yoshimoto et al 2000Yoshimoto et al , 2001Yoshimoto et al , 2002 amyloses. The DP n values were in agreement with those determined by the fluorescent labeling/HPSEC method.…”