Isolation, Identification, and Screening of Citric Acid-Producing Fungi from Fermented Orange, Pawpaw, and Banana Peels

AJIBOYE, A.E., YUSUF, N.A. and ADESOKAN, T.E.*

Department of Microbiology, Faculty of Pure and Applied Sciences, Kwara State University, Malete, Nigeria.

*Corresponding author: adesokantiti@gmail.com  

ABSTRACT 

The high demand for citric acid in diverse industries is increasing annually. Fruit peels which serve as wastes can be utilized as valuable substrates for cultivating fungi that can be used to produce citric acid through fermentation. The present study was conducted to isolate, identify, and screen citric acid-producing fungi from selected fruit peels. Orange, pawpaw, and banana peels were obtained from Ipata market, Ilorin, Kwara State, Nigeria. They were rinsed, dried, and pulverized. Submerged fermentation of the peels was carried out for 14 days to isolate naturally occurring fungi. The peels were fermented singly and combined as pawpaw and orange, pawpaw and banana and banana and orange. Isolation was performed using the pour plate method, identification was made using macroscopic and microscopic characteristics of the isolates, while screening for citric acid was done using Czapek-dox agar and bromocresol green as indicator. The highest fungal count was obtained from fermented pawpaw peels (49.0 ± 2.83 x 103 cfu/g), while banana peels had 43.00 ± 0.71 x 103 cfu/g and orange peels 40.50 ± 0.71 x 103 cfu/g. Fermented banana and orange peels had the highest fungal count of 38.00 ± 1.41 x 103 cfu/g, while fermented pawpaw and orange peels had a fungal count of 28.00 ± 1.41 x 103 cfu/g. A total of five fungi were isolated and identified as Aspergillus niger, Fusarium sp, Aspergillus flavus, Mucor sp, and Penicillium sp. Four of the fungal isolates screened positively with yellow halos surrounding the colonies except for Fusarium sp. which screened negatively. Aspergillus niger had the highest zone of yellow coloration with a diameter of 41.00 mm, followed by Penicillium sp. (33.00 mm), Mucor sp (29.00 mm), and A. flavus (0 mm). It can be concluded that orange, pawpaw, and banana peels are potential substrates for cultivating citric acid-producing fungi and A. niger screened best for citric acid production.

Keywords: Citric acid, Fruit peels, Submerged Fermentation, Fungal Isolates.

RESUME

La forte demande d’acide citrique dans diverses industries augmente chaque annĂ©e. Les Ă©corces de fruits qui servent de dĂ©chets peuvent ĂȘtre utilisĂ©es comme substrats prĂ©cieux pour la culture de champignons pouvant ĂȘtre utilisĂ©s pour produire de l’acide citrique par fermentation. La prĂ©sente Ă©tude a Ă©tĂ© menĂ©e pour isoler, identifier et sĂ©lectionner les champignons producteurs d’acide citrique Ă  partir d’Ă©corces de fruits sĂ©lectionnĂ©s. Des Ă©corces d’orange, de papaye et de banane ont Ă©tĂ© obtenues sur le marchĂ© d’Ipata, Ilorin, État de Kwara, Nigeria. Elles ont Ă©tĂ© rincĂ©es, sĂ©chĂ©es et pulvĂ©risĂ©es. La fermentation immergĂ©e des Ă©corces a Ă©tĂ© rĂ©alisĂ©e pendant 14 jours pour isoler les champignons naturels. Les Ă©corces ont Ă©tĂ© fermentĂ©es seules ou combinĂ©es sous forme de papaye et d’orange, de papaye et de banane et de banane et d’orange. L’isolement a Ă©tĂ© rĂ©alisĂ© Ă  l’aide de la mĂ©thode de la plaque coulĂ©e, l’identification a Ă©tĂ© effectuĂ©e Ă  l’aide des caractĂ©ristiques macroscopiques et microscopiques des isolats, tandis que la recherche de l’acide citrique a Ă©tĂ© effectuĂ©e Ă  l’aide de la gĂ©lose Czapek-dox et du vert de bromocrĂ©sol comme indicateur. Le nombre de champignons le plus Ă©levĂ© a Ă©tĂ© obtenu Ă  partir des Ă©corces de papayes fermentĂ©es (49,0 ± 2,83 x 103 ufc/g), tandis que les Ă©corces de banane en prĂ©sentaient 43,00 ± 0,71 x 103 ufc/g et les Ă©corces d’orange 40,50 ± 0,71 x 103 ufc/g. Les Ă©corces de banane et d’orange fermentĂ©es avaient le nombre fongique le plus Ă©levĂ© de 38,00 ± 1,41 x 103 ufc/g, tandis que les Ă©corces de papaye et d’orange fermentĂ©es avaient un nombre fongique de 28,00 ± 1,41 x 103 ufc/g. Au total, cinq champignons ont Ă©tĂ© isolĂ©s et identifiĂ©s comme Ă©tant Aspergillus niger, Fusarium sp, Aspergillus flavus, Mucor sp et Penicillium sp. Quatre des isolats fongiques ont Ă©tĂ© dĂ©pistĂ©s positivement avec des halos jaunes entourant les colonies, Ă  l’exception de Fusarium sp. qui a Ă©tĂ© dĂ©pistĂ© nĂ©gativement. Aspergillus niger avait la zone de coloration jaune la plus Ă©levĂ©e avec un diamĂštre de 41,00 mm, suivi de Penicillium sp. (33,00 mm), Mucor sp (29,00 mm) et A. flavus (0 mm). On peut conclure que les Ă©corces d’orange, de papaye et de banane sont des substrats potentiels pour la culture de champignons producteurs d’acide citrique et que A. niger est le mieux sĂ©lectionnĂ© pour la production d’acide citrique.

Mots clés : Acide citrique, écorces de fruits, fermentation immergée, isolats fongiques.

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