Abstract
Among organic acids, citric acid (CA) features the highest production volume and the greatest economic potential. The steadily increasing demand for CA necessitates the improvement and diversification of the corresponding production techniques via the incorporation of more environmentally friendly and less costly processes such as the bioconversion of agroindustrial by-products. Musa paradisiaca, known as plantain, is a food product of global importance; however, the related by-products are scarcely utilized. Herein, we investigate CA production from M. paradisiaca peels via fermentation with Aspergillus niger. Compositional analysis shows that the above peels contain 623 g·kg−1 total carbohydrates, 374 g·kg−1 starch, and 91 g·kg−1 protein and therefore are rather rich in carbon, with other elements contained in substantial amounts corresponding to K (28 g·kg−1), N (10 g·kg−1), Fe (39 mg·kg−1), Na (71 mg·kg−1), Zn (16 mg·kg−1), and Cu (18 mg·kg−1). Evaluation of solid-substrate fermentation conditions (pH and inoculum loading) reveals that CA production is maximized (29 g·kg−1) at 10% consistency, 30°C, pH 1.4, and inoculum loading = 20 mg, demonstrating that pH is the most important parameter determining fermentation efficiency. As a result, M. paradisiaca peels are concluded to be a suitable substrate for CA biosynthesis via fermentation with A. niger under optimal nutritional conditions.
Highlights
Some studies have shown that Citric acid (CA) can be produced by solid-state fermentation (SSF) of low-cost agroindustrial by-products such as apple pulp, banana peel, cassava bagasse, coffee husk, corn cob, mango peel, orange peel, papaya peel, pineapple waste, sugar cane bagasse, and others [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] (Table 1)
Chemical Composition of M. paradisiaca Peel. e total carbohydrate, starch, reducing sugar, and protein contents of plantain peel were determined as 623 ± 20, 374 ± 2, 33 ± 3, and 91 ± 1 g·kg− 1, respectively, which showed that this material was rather rich in carbon and protein
High nitrogen levels increase the consumption of sugars and the growth of fungi, decreasing CA production [50]
Summary
Citric acid (CA; 2-hydroxypropane-1,2,3-tricarboxylic acid), one of the most important and versatile among the currently produced organic acids, is widely used in food, cosmetics, agricultural, pharmaceutical, chemical, and metallurgical industries [1,2,3] because of its antioxidant, pH-regulating, acidulant, and metal ion-sequestering properties. e worldwide commercial demand for CA in 2017 equaled 1,977 kilotons [4] and is expected to increase by 3.5–4% every year [5]. Some studies have shown that CA can be produced by solid-state fermentation (SSF) of low-cost agroindustrial by-products such as apple pulp, banana peel, cassava bagasse, coffee husk, corn cob, mango peel, orange peel, papaya peel, pineapple waste, sugar cane bagasse, and others [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] (Table 1). Ere are several agroindustrial substrates of great potential that can be used for the production of CA, such as Musa paradisiaca (plantain) peel, a substrate with a high potential for obtaining various substances. In Panama, plantain peels are not utilized for any particular purpose and are promising raw materials for the production of industrially valuable chemicals. In Panama, plantain peels are not utilized for any particular purpose and are promising raw materials for the production of industrially valuable chemicals. erefore, we investigate CA production by fermentation of M. paradisiaca peel with A. niger and establish optimal operation conditions. is is one of the first works on the use of this substrate for obtaining CA by SSF
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