Αpplication of Aspergillus niger for Extracellular Tannase and Gallic Acid Production in Non-sterile Table Olive Processing Wastewaters

Waste and Biomass Valorization https://doi.org/10.1007/s12649-023-02242-0 ORIGINAL PAPER Αpplication of Aspergillus niger for Extracellular Tannase and Gallic Acid Production in Non-sterile Table Olive Processing Wastewaters Eugenia Papadaki1 · Fani Th. Mantzouridou1 Received: 21 January 2023 / Accepted: 22 July 2023 © The Author(s) 2023 Abstract Aspergillus niger B60 was screened for the first time toward extracellular tannase and gallic acid production by submerged fermentation using synthetic media supplemented with tannic acid as the sole carbon source at a wide concentration range (5–150 g/L). Maximum tannase (47 IU/mL) and gallic acid production (36 g/L) was obtained at initial tannic acid concentration 100 g/L. For this study, it was of interest to valorize non-sterile table olive processing wastewaters for fungal tannase production. In particular, lye and washing water effluents from Spanish-style green olive processing enriched with 100 g/L tannic acid provided effective alternative substrates for the production of tannase (21 IU/mL and 17 IU/mL, respectively) and gallic acid (22 g/L and 14 g/L, respectively). The fungal growth and tannase production kinetics were described by the Logistic and Luedeking–Piret models, respectively. The maximum dry biomass content and the maximum specific growth rate were more pronounced in the tannic acid-rich effluents (16–18 g/L and 0.5–0.6 1/h, respectively) than in the synthetic medium (11 g/L and 0.4 1/h, respectively) although in all cases tannase production was growth-associated. These novel findings cast a new light on successful biorefinery strategies of the effluents and warrant further investigation via process scaling-up and optimization. Graphical Abstract Keywords Tannase · Gallic acid · Aspergillus niger B60 · Table olive processing wastewaters · Luedeking–Piret model · Logistic model Extended author information available on the last page of the article 13 Vol.:(0123456789) Waste and Biomass Valorization Statement of Novelty Tannase, is a vital enzyme used for the production of foods, beverages, animal feed, pharmaceuticals and chemicals. Among these valuable products, tannase is primarily used in the manufacture of gallic acid that has also a plethora of commercial applications, including therapeutics, cosmetics, dyes, photography, foods, antimicrobials and radioprotection. Following the sustainability-oriented global trends, several studies have been carried out toward the exploitation of tannin-rich agricultural substrates for the production of fungal tannase. In this direction, the prospect of utilizing effluents from table olive manufacturing as raw materials in a biorefinery, although challenging, still remains largely unexplored. This study proposes a novel process for the the production of extracellular tannase by the robust Aspergillus niger B60 using tannic acidenriched non-sterile wastewaters from the processing of Spanish−style Chalkidiki green olives. The novel findings cast a new light on successful biorefinery strategies of the effluents and warrant further investigation via process scaling-up and optimization. Introduction The industrial production of enzymes is of high importance worldwide toward their effective use in the processing line of high-quality foods and specialty pharmaceuticals. Specifically, the global market value of enzymes was valued at $9.8 billion in 2019 and is projected to reach $16.69 billion in 2027 with an annual growth rate of 6.9%. In 2019, about 61% of the enzyme market share was held by microorganisms. Such production systems are developed because they have simple adaptability and low production cost. Among the different types of microorganisms, fungi are the main source of industrial enzymes [1]. Tannase, also known as tannin acyl hydrolase (EC 3.1.1.20), is a vital enzyme used as a catalyst in the hydrolysis of ester and depside bonds in tannins to release gallic acid and glucose [2]. The catalytic versatility of tannase renders it suitable for the production of foods, beverages, animal feed, pharmaceuticals and chemicals. Among these valuable products, tannase is primarily used in the manufacture of gallic acid, instant tea, acorn liquor and coffeeflavored refreshing drinks. Also, the enzyme can serve as a clarifying agent in wines, beers and fruit juices [3, 4], and as a bioremediation agent in the treatment of tannery wastewaters [5]. Focusing on gallic acid, it has also a plethora of commercial applications, including therapeutics, cosmetics, dyes, photography, foods, antimicrobials and radioprotection [2]. Acid hydrolysis of tannic acid is the conventional 13 method for gallic acid production. Because of its drawbacks in terms of product purity and yield, microbial or enzymatic hydrolysis is considered to be a prominent alternative ecofriendly method for producing gallic acid [6–8]. Filamentous fungi are the most widely used microorganisms for tannase production as they have a strong tolerance and biodegradation potential for tannins [5, 9]. Particularly, various strains of Aspergillus niger can survive at the highest levels of tannic acid concentrations (100–150 g/L) reported in literature and have shown the strongest biodegradation ability at these levels (up to 73% reduction of tannic acid concentration) [10–12]. Notably, tannase derived from A. niger belongs to the list of commercial enzymes marketed in the European Union [13]. Submerged fermentation is advantageous for the industrial production of extracellular tannase as it ensures the sterility of the process, the effective control of the process conditions (e.g. temperature, pH, agitation and aeration), the construction of accurate and feasible process kinetic models, the short fermentation time, the sufficient substrate uptake as well as the simple and efficient methods for enzyme extraction [2]. Tannase is an inducible enzyme produced by microorganisms in a strain-specific matter. In this view, related literature data are focused on the performance evaluation of different autochthonous and allochthonous tannase producing strains in media containing a wide concentration range of tannic acid that induces tannase production [2, 3]. Following the sustainability-oriented global trends, some studies have been carried out toward the combined supplementation of the liquid nutrient media with pure tannic acid (10–22 g/L) and tannin-rich solid agricultural substrates (rice flour, Emblica officinalis powder, pomegranate rind powder, leaves powder from various fruits, grape pomace) [14–18]. It should be pointed out that the agricultural substrates contain complex tannins that are not easily biodegradable and, thus, the simultaneous addition of pure tannic acid favors the microbial performance [17]. Effluents from olive oil and table olive manufacturing create severe environmental problems in the olive producing areas. Specifically in the Mediterranean region, large volumes of the above-mentioned was (...truncated)