Wheat Fusarium Protease Specificity and Effect on Dough Properties.

Ray Bacala,Katherine Cordova,Dave W Hatcher,Bin Xiao Fu

doi:10.3390/foods10071585

Abstract

Fusarium infection is a worldwide agricultural problem of billion dollar proportions globally, and it has increasingly threatened entire regional food supplies. In addition to the toxin deoxynivalenol (DON), Fusarium species express digestive enzymes that degrade starch and protein, affecting the quality of infected grains, especially wheat processing performance which depends largely on gluten proteins. In this study, the impact of Fusarium protease on the functionality of Canada Western Red Spring (CWRS) wheat was assessed by adding Fusarium-damaged kernels (FDK) to a FDK-free base wheat sample. Digestion of beta-casein by extracts of flours, milled from sound and FDK-spiked wheat samples, demonstrated elevated cleavage in FDK-spiked flour extracts as follows: N-terminal to lysine (eight-fold), N- and C-terminal to isoleucine (four-fold and three-fold, respectively), N-terminal to tyrosine (three-fold) and C-terminal to arginine at P1′ (five-fold). Comparison of abbreviated (45 min) and standard (135 min) extensigraph test results indicated that desirable increases in dough resistance to extension (Rmax) due to gluten re-polymerization after longer resting were partially to completely counteracted in FDK-spiked flours in a dose-dependent manner. Baking tests confirmed that while loaf volume is similar, proofed dough from FDK-spiked samples caused detectable loaf collapse at 3% FDK. Extensigraph Rmax and Fusarium protease levels were inversely related, and effected by both the extent and severity of infection. While the current FDK tolerances for grading Canadian wheat can effectively control protease damage, prevalence of deoxynivalenol (DON) weak- and non-producing Fusarium strains/species (e.g., F. avenaceum) in some growing regions must be considered to protect functionality if grading is solely based on DON content.

Highlights

Fusarium infection in wheat is a global problem involving a large number of Fusarium species, each with a different prevalence in different parts of the world
Fusarium-damaged kernels (FDK) were handpicked by trained Canadian Grain Commission (CGC) inspectors from Fusarium-infected samples into three categories based on infection severity: mycelia (FDK-M; presence of mycelia beyond the seed crease, but otherwise sound), affected (FDK-A; close to normal kernel weight and shape with chalky seed coat) and distorted (FDK-D; reduced seed size, thin seeds with chalky seed coat)
The extensigraph Rmax (135 min) of the flour samples milled from the wheat blends (Figure 1a, solid lines) decreased from sound base (445 ± 20 BU SD for FDK-A and FDKD, 457 ± 20 BU for FDK-M) significant enough to indicate a loss of dough strength at

Summary

Introduction

Fusarium infection in wheat is a global problem involving a large number of Fusarium species, each with a different prevalence in different parts of the world. In addition to the severe economic loss and potential threat to regional food supplies, some of these species are capable of causing fusariosis in immunocompromised humans; a treatment-resistant infection that is rare but globally on the rise [1]. In addition to the toxin deoxynivalenol (DON), Fusarium species produce degradative enzymes that aid initial infection and provide sustained nourishment for the established infection. Proteomic analysis of the extracellular proteins (exoproteome) produced by Fusarium graminearum cultured with plant cell wall isolates revealed F. graminearum produced all required digestive enzymes for complete cell wall degradation [2]. These enzymes include both polysaccharide-metabolizing enzymes and proteases, which are primarily involved with initial infection [3]. While DON production typically increases several days after infection, production of secreted proteases and polysaccharide-digesting enzymes peaks within 2 days of infection [3]

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