Zahia Meraihi

Improving Bread Quality with the Application of a Newly Purified Thermostable α-Amylase from Rhizopus oryzae FSIS4

A new thermostable α-amylase from Rhizopus oryzae FSIS4 was purified for first time and recovered in a single step using a three-phase partitioning (TPP) system. The fungal α-amylase, at a concentration of 1.936 U per kg of flour, was used in bread-making and compared to the commercial enzyme. The results showed a significant effect of the recovered α-amylase in the prepared bread and allowed us to improve the quality of the bread. The study indicated clearly that the recovered α-amylase is a potential candidate for future applications in the bread-making industry and in other food biotechnology applications.

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

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.

Improvement of Fungal Cellulase Production by Solid State Fermentation

Cellulase production studies have been carried out using the fungal strains Trichoderma longibrachiatum and Aspergillus terreus by using two different lignocellulosic materials for solid state fermentation (SSF). The effect of basic fermentation parameters (substrate, moisture content and the fermentation time) on enzyme production was studied. Maximum cellulase production (FPA and endoglucanase) of Trichoderma longibrachiatum were 33.83 U/gds and 167.4 U/gds, respectively, which represented a 1.75 fold improved activities than that of Aspergillus terreus (21.5 U/gds and 95.82 U/gds, respectively) using wheat bran as substrate. The optimal conditions for cellulase production with wheat bran were found to be: initial moisture content 70% and the optimal incubation time for production was three days. The endoglucanase of Trichoderma longibrachiatum was thermostable and showed a half-life of 1 hour at 70°C, while the filter paper activity (APF) lost its total activity after 1 hour at 70°C. Results indicate the scope for further optimization of the production conditions to obtain higher cellulase titres using the Trichoderma longibrachiatum strain under SSF.