In vitro study of L-asparaginase enzyme activity by two yeast strains on food matrixes and the relative effect on fungal pathogens growth

Alessandra Di Francesco

doi:10.31083/j.fbe1401006

Abstract

Asparagine is one of the precursors of acrylamide and toxic fungal secondary metabolites, both carcinogenic compounds. In the present study, the optimal conditions to deplete asparagine by Aureobasidium pullulans (L1 and L8) from potato and wheat flour matrices were investigated. Through a colorimetric plate-assay with phenol red as indicator dye, both strains demonstrated to be able to produce L-asparaginase from 20 ∘C to 30 ∘C for L1 and only at 20 ∘C for L8 strain starting from 48 h of incubation. The ability of both yeasts to reduce asparagine content in potato and wheat flour was studied by in vitro spectrophotometric assay. Both strains showed a great ability to totally reduce asparagine at 20 ∘C after 15 min of incubation in potato homogenate, conversely in wheat flour, the highest reduction was detected after a longer exposition time (60 min). As known, L1 and L8 diamine asparaginase to aspartic acid. For this reason, both amino acids were tested to verify the antifungal effect against Rhizoctonia solani (Rs1) and Fusarium graminearum (F3) mycelial growth. Asparagine (120 mg/L) increased Rs1 and F3 mycelial growth respectively by 4.4% and 18.9%; conversely, aspartic acid significantly inhibited both respectively by 8.2% and 12.0%.

Highlights

L-asparaginase is an amid-hydrolase that catalyzes Lasparagine to L-aspartate and L-ammonia [1]
L-asparaginase enzyme is used in the food industry for acrylamide prevention formation in foods processed with high temperatures [3], especially for baked and fried foods
The amino acids involved in the studied food systems such as potato and wheat flour are mainly based on asparagine and aspartic acid

Summary

Introduction

L-asparaginase is an amid-hydrolase that catalyzes Lasparagine to L-aspartate and L-ammonia [1]. L-asparaginase enzyme is used in the food industry for acrylamide prevention formation in foods processed with high temperatures [3], especially for baked and fried foods. Application of L-asparaginase in food process represent an alternative method to reduce acrylamide content in fried, baked, and toasted products. The amino acids involved in the studied food systems such as potato and wheat flour are mainly based on asparagine and aspartic acid. Both amino acids were studied because the first one can be utilized readily by the antagonists and poorly by the pathogens, and the second one showed an inhibiting effect on the growth of some molds [9]. In the case of wheat, Fusarium graminearum can cause severe economic losses for cereal farmers due to significant reductions in grain yield and quality, especially for mycotoxins production [15]

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