BACKGROUND: The koji mold Aspergillus sojae, an industrially important microorganism, can produce high levels of pectinases utilizing agro-industrial wastes. This study introduces apricot and peach pomace, two agro-industrial wastes barely considered as raw material for the generation of value-added products, and focuses on its utilization together with orange peel for polygalacturonase production in submerged cultures using A. sojae.

One hundred and three yeasts isolated from soil samples from King George Island and Tierra del Fuego province were screened in relation with their capability to produce pectinolytic enzymes. Although all the yeasts showed well-developed colonies at 20 °C, only eight showed a clear halo around the colony, indicative of pectin degradation. A secondary screening demonstrated that only four yeasts were capable to produce pectinases at low temperatures (8 °C). It could be seen that the selected yeasts were able to grow and produce high levels of polygalacturonase activity when submerged fermentations were performed using pectin-containing fruit wastes as substrates. None of the strains produced neither lyase nor rhamnogalacturonan hydrolase activities. Regarding pectin esterase activity, it was only produced in lower amounts by G. pullulans 8E (0.022 U ml). A TLC analysis of the substrate cleavage pattern of the pectinolytic systems was consistent with an endo-type activity. The clarification of apple juice was only accomplished by G. pullulans pectinolytic system, with a clarification of 80% (%T) using 4 U/ml of enzyme at 20 °C. As far as we concern this work describes for the first time the production of pectinases by the cold-adapted yeasts species Cystofilobasidium infirmominiatum, Cryptococcus adeliensis and G. pullulans.

An endo-polygalacturonase secreted by Aspergillus sojae was characterized after being purified to homogeneity from submerged cultures with orange peel as the sole carbon source by gel filtration and ion-exchange chromatographies. According to SDS-PAGE and analytical isoelectric focusing analyses, the enzyme presents a molecular weight of 47 kDa and pI value of 4.2. This enzyme exhibits considerable stability under highly acidic to neutral conditions (pH 1.5-6.5) and presents a half-life of 2 h at 50°C. Besides its activity towards pectin and polygalacturonic acid, the enzyme displays pectin-releasing activity, acting best in a pH range of 3.3-5.0. Thin-layer chromatographic analysis revealed that tri-galacturonate is the main enzymatic end product of polygalacturonic acid hydrolysis, indicating that it is an endo-polygalacturonase. The enzyme exhibits Michaelis-Menten kinetics, with K_M and V_MAX values of 0.134 mg/mL and 9.6 µmol/mg/min, respectively, and remained stable and active in the presence of SO₂, ethanol, and various cations assayed except Hg²⁺.

BACKGROUND Soybean hulls result from the processing of the bean for producing oil and protein products. This by‐product generated massively in America has virtually no commercial value, so substantial effort is being applied to its exploitation for generating value‐added goods. This work evaluates soybean hulls as inducer of the production of pectinolytic enzymes, through optimization studies regarding polygalacturonase production by Aspergillus sojae in submerged cultures. RESULTS A 2‐fold improvement in polygalacturonase yield was found by varying the initial pH of the culture in a very narrow acid pH range (2.40–2.80). The optimized fermentation process was successfully transferred to stirred‐tank bioreactors in terms of volumetric productivity, and final polygalacturonase yields were 42 U mL‐1 and 1.39 U g‐1 soybean hulls, which are among the highest reported with this by‐product. Morphological characterization of A. sojae during cultivation showed that the fungus mainly developed in dispersed mycelia at initial pH of 2.40–2.80 while, conversely, fungal pellets predominated in cultures performed at initial pH of 5.40. CONCLUSION High enzyme titers are possibly connected to the formation of dispersed mycelia, as well as to acid‐induced expression of the respective gene/s. It is foreseen that this data will be helpful regarding the production of fungal pectinases or other acid‐induced enzymes. © 2017 Society of Chemical Industry

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