Vine Trimming Shoots as Substrate for Ferulic Acid Esterases Production

Rice Husk, Brewer's Spent Grain, and Vine Shoot Trimmings as Raw Materials for Sustainable Enzyme Production

Solid by-products with lignocellulosic structures are considered appropriate substrates for solid-state fermentation (SSF) to produce enzymes with diverse industrial applications. In this work, brewer's spent grain (BSG), rice husk (RH), and vine shoot trimmings (VSTs) were employed as substrates in SSF with Aspergillus niger CECT 2088 to produce cellulases, xylanases, and amylases. The addition of 2% (NH4)2SO4 and 1% K2HPO4 to by-products had a positive effect on enzyme production. Substrate particle size influenced enzyme activity and the overall highest activities were achieved at the largest particle size (10 mm) of BSG and RH and a size of 4 mm for VSTs. Optimal substrate composition was predicted using a simplex centroid mixture design. The highest activities were obtained using 100% BSG for β-glucosidase (363 U/g) and endo-1,4-β-glucanase (189 U/g), 87% BSG and 13% RH for xylanase (627 U/g), and 72% BSG and 28% RH for amylase (263 U/g). Besides the optimal values found, mixtures of BSG with RH or VSTs proved to be alternative substrates to BSG alone. These findings demonstrate that SSF bioprocessing of BSG individually or in mixtures with RH and VSTs is an efficient and sustainable strategy to produce enzymes of significant industrial interest within the circular economy guidelines.

Characterization of Feruloyl Esterase from Klebsiella oxytoca Z28 and Its Application in the Release of Ferulic Acid from De-Starching Wheat Bran

Feruloyl esterase (EC3.1.1.73; FAE) can degrade biomass to release ferulic acid (FA), which has a high application in bioprocessing, food, pharmaceutical, paper, feed, and other industrial fields. A strain of Klebsiella oxytoca Z28 with ferulic esterase activity was screened from Daqu. In addition, the FAE gene was expressed in Escherichia coli BL21 (DE3). The enzyme consists of 340 amino acids with a molecular mass of 37.7 kDa. The FAE enzyme activity was 463 U/L when the substrate was ethyl 4-hydroxy-3-methoxycinnamate and the optimum temperature and pH were 50 °C and 8.0, respectively. The enzyme had good stability at temperatures of 25-40 °C and a pH of 8.0. Ba²⁺, Cu²⁺, Mn²⁺, and Ca²⁺ had a strong inhibitory effect on the enzyme activity, and Na⁺ had a promotive effect on the enzyme activity. The de-starching wheat bran was degraded by KoFAE, and the FA release was up to 227.15 µg/g. This indicated that the heterologous expression of KoFAE from Klebsiella oxytoca Z28 in E. coli had a certain potential of biodegradation, which can be applied to the degradation of agricultural waste to obtain high value-added FA products.

Statistical approach to evaluate effect of temperature and moisture content on the production of antioxidant naphtho-gamma-pyrones and hydroxycinnamic acids by Aspergillus tubingensis in solid-state fermentation

Non-ochratoxigenic Aspergillus tubingensis G131 is a filamentous fungus that can produce naphtho-gamma-pyrones (NγPs), polyketide pigments that exhibit interesting antioxidant properties. This study aims to investigate the effect of two critical parameters, temperature and moisture content on the fungus grown in solid-state fermentation using agricultural by-products (vine shoots and wheat bran) as sole medium. From the kinetic productions of secondary metabolites NγPs (asperpyrone E, dianhydroaurasperone C, fonsecin, fonsecin B and ustilaginoidin A), alkaloids (nigragilin and aspernigrin A), degradation products from the solid medium (β-D-glucose, p-coumaric acid and trans-ethyl ferulate), ergosterol and conidia obtained for different temperatures and moisture contents, a principal component analysis (PCA) was carried out to highlight the production patterns of these compounds. This approach allowed us to determine that fonsecin, the compound of higher interest-exhibiting the most interesting antiradical potential-is particularly more produced at 25 °C and 66% of moisture content. This study underlines the importance of temperature and moisture content on naphtho-gamma-pyrones and hydroxycinnamic acid production using solid-state fermentation and contributes to the development of agroindustrial by-product valorization.