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. 2016 Oct 29;5(4):72.
doi: 10.3390/foods5040072.

Production and Properties of a Thermostable, pH-Stable Exo-Polygalacturonase Using Aureobasidium pullulans Isolated from Saharan Soil of Algeria Grown on Tomato Pomace

Leila Bennamoun  1 , Serge Hiligsmann  2 , Scheherazad Dakhmouche  3 , Amel Ait-Kaki  4 , Fatima-Zohra Kenza Labbani  5 , Tahar Nouadri  6 , Zahia Meraihi  7 , Benedetta Turchetti  8 , Pietro Buzzini  9 , Philippe Thonart  10
Affiliations

Production and Properties of a Thermostable, pH-Stable Exo-Polygalacturonase Using Aureobasidium pullulans Isolated from Saharan Soil of Algeria Grown on Tomato Pomace

Leila Bennamoun et al. Foods. .

Abstract

Polygalacturonase is a valuable biocatalyst for several industrial applications. Production of polygalacturonase using the Aureobasidium pullulans stain isolated from Saharan soil of Algeria was investigated. Its capacity to produce polygalacturonase was assessed under submerged culture using tomato pomace as an abundant agro-industrial substrate. Optimization of the medium components, which enhance polygalacturonase activity of the strain Aureobasidium pullulans, was achieved with the aid of response surface methodology. The composition of the optimized medium was as follows: tomato pomace 40 g/L, lactose 1.84 g/L, CaCl₂0.09 g/L and pH 5.16. Practical validation of the optimum medium provided polygalacturonase activity of 22.05 U/mL, which was 5-fold higher than in unoptimized conditions. Batch cultivation in a 20 L bioreactor performed with the optimal nutrients and conditions resulted in a high polygalacturonase content (25.75 U/mL). The enzyme showed stability over a range of temperature (5-90 °C) with an optimum temperature of 60 °C with pH 5.0, exhibiting 100% residual activity after 1h at 60 °C. This enzyme was stable at a broad pH range (5.0-10). The enzyme proved to be an exo-polygalacturonase, releasing galacturonic acid by hydrolysis of polygalacturonic acid. Moreover, the exo-polygalacturonase was able to enhance the clarification of both apple and citrus juice. As a result, an economical polygalacturonase production process was defined and proposed using an industrial food by-product.

Keywords: Aureobasidium pullulans; characterization; exo-polygalacturonase; response surface methodology; tomato pomace.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Parity plot showing the distribution of experimental data versus predicted value by the model for potentiation of PG activity.
Figure 2
Figure 2
Response surface graphs of potentiation of PG activity by Aureobasidium pullulans showing the effect of variables of (a) Lactose–CaCl2, (b) pH–CaCl2, and (c) pH–Lactose.
Figure 2
Figure 2
Response surface graphs of potentiation of PG activity by Aureobasidium pullulans showing the effect of variables of (a) Lactose–CaCl2, (b) pH–CaCl2, and (c) pH–Lactose.
Figure 3
Figure 3
Potentiation of PG activity in shake flasks (a) and a laboratory bioreactor (b) by A. pullulans. The results were presented as mean ± SD, n = 3.
Figure 4
Figure 4
Effect of pH on the activity (A) and stability (B) of PG of A. pullulans isolated strain. Each point represents the mean (n = 3) ± standard deviation.
Figure 5
Figure 5
Effect of temperatures on the activity (A) and stability (B) of PG from A. pullulans isolated strain. Each point represents the mean (n = 3) ± standard deviation.
Figure 6
Figure 6
Thin layer chromatography of the reaction products of polygalacturonic acid hydrolyzed by PG. Hydrolysis times were 30 min and 6 h. Standard was 10 g/L of monogalacturonic acid.
Figure 7
Figure 7
(A) Reduction of the haze of fresh citrus juice by CE (crude extracellular enzymes from A. pullulans); C: without treatment (considered as “control”); (B) Reduction of the haze of fresh apple juice by CE (crude extracellular enzymes from A. pullulans); C: without treatment (considered as “control”).
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