Effect of annealing on the structure and properties of barley starches

Waduge, Renuka Nilmini (2005) Effect of annealing on the structure and properties of barley starches. Masters thesis, Memorial University of Newfoundland.

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Abstract

Starches from normal (CDC McGwire, SR 93102), waxy (CDC Fibar, HB 364), and high-amylose (SB 94897, SB 94893) hull-less barley cultivars were isolated and their structure, morphology, and properties studied before and after one step annealing (50°C for 72h at a moisture content of 75% ). The starches from all genotypes consisted of a mixture of large (spherical, disk, lenticular) and small (irregular) granules. Pores were present on the granule surface of all starches. The total amylose content, the bound lipid content and the total phosphorous content ranged from 0.00 to 55.30%, 0.10 to 0.72%, and 0.024 to 0.060%, respectively. The amylopectin structure of all starches was nearly identical. The X-ray pattern of CDC Fibar, HB 364, and CDC McGwire starches was of the 'A'- type. Whereas, SR 93102, SB 94897, and SB 94893 starches exhibited a mixed 'A+B'- type pattern. The relative crystallinity (RC), swelling factor (SF), amylose leaching (AML), gelatinization temperature range (GTR), enthalpy of gelatinization (AH), amylose-lipid complex melting temperature (Tpcx) and the enthalpy of melting of the amylose-lipid complex (ΔHcx) ranged from 37.0 to 44.3%, 41.0 to 54.2% (at 90°C), 4.0 to 31.0% (at 90°C), 11.4 to 22.5°C, 6.0 to 13.0 Jig, 84.9 to 89.1°C and 0.4 to 1.8 J/g, respectively. The RC of CDC Fibar, HB 364, SR 93102 and CDC McGwire starches increased on annealing, whereas, it remained unchanged in SB 94897 and SB 94893 starches. The 'A'- type X-ray pattern of CDC Fibar, HB 364, and CDC McGwire starches remained unchanged on annealing. However, the 'A+B'- type X-ray pattern of SR 93102, SB 94897 and SB 94893 starches resembled more closely the 'A'- type pattern on annealing. In all starches, the X-ray intensity of the V-amylose-lipid complex peak increased on annealing. Annealing increased the gelatinization transition temperatures and decreased the GTR in all starches. The ΔH of SB 94893 starch increased on annealing, whereas it remained unchanged in the other starches. Tpcx of SR 93102 and SB 94897 remained unchanged on annealing, whereas Tpcx of CDC McGwire increased slightly. ΔHcx of native and annealed CDC McGwire, SR 93102 and SB 94897 were similar. Tpcx and ΔHcx were not detectable in annealed SB 94893 starch. In all starches, SF decreased on annealing. Annealing decreased AML in SR 93102, SB 94897 and SB 94893 starches in the temperature range of 50-90°C, but increased AML in HB 364 and CDC McGwire starches at higher temperatures. Annealing decreased acid hydrolysis in CDC Fibar starch during the early stages of hydrolysis. Thereafter, both native and annealed CDC Fibar starches were hydrolyzed to the same extent. However, all other starches showed no significant changes in acid hydrolysis on annealing.

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