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.

Thirteen Non-Conventional Yeasts (NCYs) have been investigated for their ability to reduce activated C=C bonds of chalcones to obtain the corresponding dihydrochalcones. A possible correlation between bioreducing capacity of the NCYs and the substrate structure was estimated. Generally, whole-cells of the NCYs were able to hydrogenate the C=C double bond occurring in (E)-1,3-diphenylprop-2-en-1-one, while worthy bioconversion yields were obtained when the substrate exhibited the presence of a deactivating electron-withdrawing Cl substituent on the B-ring. On the contrary, no conversion was generally found, with a few exceptions, in the presence of an activating electron-donating substituent OH. The bioreduction aptitude of the NCYs was apparently correlated to the logP value: Compounds characterized by a higher logP exhibited a superior aptitude to be reduced by the NCYs than compounds with a lower logP value.

Fourty-two yeast strains were isolated from natural sources in Algeria. Based on the sequence analysis of the 26S ribosomal RNA D1/D2 domain they were identified to be of 8 species belonging to the genera Aureobasidium, Candida, Clavispora, Hanseniaspora, Pichia, Rhodotorula and Vishniacozyma. All yeast isolates were screened for cellulase, amylase, protease and lipase production. Six strains of Aureobasidium pullulans, Rhodotorula diobovata and Vishniacozyma tephrensis demonstrated ability to produce at least one extracellular enzyme. The enzyme activity index (EAI) for cellulase was noted to be prominent in the isolates of A. pullulans (A1, A3, A5) and V. tephrensis A4 as 2.3 and 2.1, respectively. Highest EAI for amylase and protease was also seen in A. pullulans isolate A1 (EAI = 2.9) and isolate A3 (EAI = 1.9), respectively. For lipase, the EAI was superior in V. tephrensis A4 (EAI = 1.5) when compared to the isolates of R. diobovata (B1, O5) (EAI =1.4) and A. pullulans A5 (EAI =1.3). To the best of our knowledge, this is the first report of cellulase and/or lipase activity in V. tephrensis and R. diobovata strains associated with apple, orange and beet peels in Algeria. Furthermore, the strain A. pullulans A5 showed enzymatic activities for all the enzymes screened in the current work. Thus, our study can provide further information about the diversity and enzyme production by yeasts and demonstrated the potential for yeast isolated from fruit and beet peels as sources for extracellular hydrolytic enzymes.