Starch Conversion

[Shetty, 2006]:

• gelatinization: heating in excess water, endothermic reaction, loss of crystalline order
• irreversible w/r to the shape of the granule
• amylopecting and amylose may form new structures when cooled down -> retrogradation
• during heating -> swelling to up to 30x its weight. reversible process
• retrogradation is cause for hard stale bread

[Donald, 2004]

• irreversible order -> disorder transition called gelatinization.
• swell, absorb water, leach amylose, loose crystallinity.
• birefringence is lost
• range is quite large for all granules 56-64 for wheat and potato but much smaller (1 C) for individual granules
• substantial swelling
• inital water absorption in the amorphous growth rings
• swelling driven process
• crystalline regions break open b/c of the swelling
• if water is limited (high density or presence of sugars) swelling doesn't take place as well and a melting of the crystalline sections needs to happen
• gelatinization temperature increases
• Maize starch: from 70C to 78C when placed in 25% sugar solution.
• sugar removes free water

[Briggs, 2004]

• sugar concentration raises gelatinization temperature
• enzymatic breakdown should happen before retrogradation occurs
• some starches require cooking temps between 90 and 120C (194-248F) before amylose lipid complexes are broken -> one of the reasons why cooking of some adjuncts is necessary.

[Narziss, 2005]

• starch is insoluble in cold water
• granules start to swell (50C +)
• then they get small fissures
• amylose leaches out
• amylopectin separates as gelatenous sheet
• viscous and sticky mass is formed\
• doesn't happen in mashing b/c of the enzymes
• but may cause problems in cereal cookers (especially rice)

[Kunze, 2007]

• 4 phases: ungelatenized, gelatinization, liquification, saccharification
• gelatinization temp dependent on growing conditions and crop year : 59 - 65C

• gelatinization
• active enzymes
• emzyme temperature and pH optima
• mash parameters affecting conversion

References

[Valclavik] Vickie A. Valclavik, Elizabeth W. Christian, Essentials of Food Science, Third Edition, Springer

[Champe] Pamela C, Champe, Richard A. Harvey, Denise R. Ferrier, Biochemistry, Lippincott's Illustrated Reviews

[Kunze, 2007] Wolfgang Kunze, Technologie Brauer und Maelzer, 9. Auflage, VLB Berlin

[Narziss, 2005] Prof. Dr. agr. Ludwig Narziss, Prof. Dr.-Ing. habil. Werner Back, Abriss der Bierbrauerei, Technische Universitaet Muenchen (Fakultaet fuer Brauwesen, Weihenstephan). WILEY-VCH Verlags GmbH Weinheim Germany, 2005

[Donald, 2004] A. M. Donald, Understanding Starch Stucture and Functionality, Chapter 5 in Starch in Food: Structure, Function and Applications By Ann-Charlotte Eliasson, CRC Press, 2004

[Shetty, 2006] Kalidas Shetty, Food Biotechnology, CRC Press, 2006