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Oxidative Gelation – Its Influence on Processing and End-Use in Soft Wheat Flour A.D. Bettge USDA-ARS Western Wheat Quality Laboratory Pullman, WA USA.

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Presentation on theme: "Oxidative Gelation – Its Influence on Processing and End-Use in Soft Wheat Flour A.D. Bettge USDA-ARS Western Wheat Quality Laboratory Pullman, WA USA."— Presentation transcript:

1 Oxidative Gelation – Its Influence on Processing and End-Use in Soft Wheat Flour A.D. Bettge USDA-ARS Western Wheat Quality Laboratory Pullman, WA USA

2 Quality, Variation and Control Controlling, or understanding variation in quality is important, scientifically and economically. Defining the biochemical influence(s) on quality and developing reliable and informative testing methods allows this control or understanding Allows development of new wheat varieties that require reduced processing input to obtain desired quality. Also shortens product label. Viscosity is a little-studied quality attribute.

3 Viscosity and End-Use Quality Variation Viscosity is an important consideration in batter-based processes, i.e. cakes, batter coatings, donuts, pancake mixes, etc Some biochemical components may contribute both to viscosity and to end- product quality Substantial unexplained variation exists

4 Variation in Viscosity Protein, especially HMW glutenins, can influence viscosity. Lactic acid SRC or SDS- sedimentation are tests Other water-absorbing compounds also contribute: arabinoxylans (aka pentosans, hemicellulose, non-starch carbohydrate). Sucrose SRC is the test Leavening gas (bubbles) affect viscosity Focus here is arabinoxylans and protein

5 Arabinoxylans and Viscosity Xylose backbone, variously substituted with Arabinose Degree of substitution and pattern of substitution determines water solubility Broadly, functionally categorized as water soluble or water insoluble Water soluble arabinoxylans also have ferulic acid moieties attached to arabinose side- chains (insolubles already have ferulic acid cross-linked as part of cell walls)

6 Arabinoxylan

7 Arabinoxylan Structure Stone, 1996, Cereal grain carbohydrates in: Cereal Grain Quality eds: Henry and Kettlewell

8 Arabinoxylans and Oxidative Gelation Under appropriate conditions, ferulic acid moieties can cross link with other ferulic acid moieties or protein side chains forming a large polymeric oxidative gel that sequesters water and creates viscosity Water soluble arabinoxylans form oxidative gels; insoluble arabinoxylans do not appear to do so (already cross-linked) Insoluble arabinoxylans adsorb water (not sequester) and affect A w

9 Arabinoxylan cross-linking Arabinoxylan – Protein cross linking Neukom and Markwalder, 1978: Cereal Foods World Protein – Protein (di-Tyrosine) cross linking

10 Modifiers of Arabinoxylan Concentration and Activity Endogenous (sometimes exogenous or added) enzymes Inhibited by TAXI (Triticum aestivum xylanase inhibitor) or XIP (xylanase inhibitor protein) – Courtin and Delcour. pH – elevated pH solubilizes esterified arabinoxylans

11 Oxidative Gelation Long known that gels form: Oxidative arabinoxylan gels are mechanically fragile, hence limiting their impact on mixed doughs (bread, cookie, etc); protein gels may be more robust Cereal Chem. 1925

12 Oxidative Gel Impact on Quality Viscosity can retain leavening gas in low- gluten products, allowing greater volume Potential detrimental effect on low-moisture products such as cookies or crackers through sequestered water, low spread or high volume and “stickiness” Potential beneficial effect on cakes, batters and batter coatings where viscosity prevents the “settling” that causes separation of flour suspensions and loss of leavening gasses

13 Oxidative Gelation Gels form naturally from endogenous, uncontrolled presence of free radicals (i.e. auto-oxidized lipids and fatty acids) Gels can be caused to form by adding free radicals in excess (e.g. H 2 O 2 + peroxidase) Gels are formed from both protein and arabinoxylan Both likely have an end-use impact

14 Oxidative Gelation Test Test developed to assess oxidative gelation as manifested in viscosity Hydrate 20 min, with rocking, 1:2.5 w/v flour:peroxide (75 ppm) Hoseney&Faubion, 1981 Add 60 U horseradish peroxidase Decant into Bostwick Consistometer reservoir; let sit one minute Measure flow distance at 40 sec

15 Equipment

16 Protein and Viscosity

17 Arabinoxylans and Viscosity

18 Antioxidants and Gelation

19 End-Use and Arabinoxylans “MaxR” models constructed to obtain information on most influential factors NOT to be used as predictive equations Provides best model parameters based on combination of factors reflected in F-values and R 2

20 Straight Grade Cookie (sugar snap) F/p-value (+/-) Cake Volume F/p-value (+/-) Flour Protein Px pH Total AX Water Extr. AX Carbonate SRC Lactic acid SRC Model R Model F-value

21 Patent Cookie (sugar snap) F/p-value (+/-) Cake Volume F/p-value (+/-) Water SRC Px pH Xylanase Xylanase + Px + Pxase Feulic + Px + pH Lactic Acid SRC Px Water Brookfield pH Model R Model F-value7.56.2

22 Interpretation (?) Oxidative gelation occurs between: Arabinoxylan polymers, protein polymers and a combination of the two Elevated pH decreases viscosity through inhibition of cross-linking Patent flours are distinctly more prone to oxidative gelation than are straight grade flours (unwitting breeding selection of club wheats?) Flour has sufficient free radicals (likely from lipid auto-oxidation in flours over a couple weeks old) to initiate oxidative gelation without other sources. Flour aging and new/old crop factors? Other oxidative systems (i.e. PPO) may also have a role. Chlorination issues?

23 Interpretation (?) Oxidative gels affect cookie, cracker and cake quality, but especially products with unconstrained viscous flow (pancakes or cake donuts) Nutritionally and functionally, WEAX esterification to gluten proteins may add a form of fiber in hard wheats for bread But at a cost to mixing quality (tolerence) Probably occurs due to reduction in elasticity due to presence of AX in gluten

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