Assessing banana and rice waste for postbiotics production

Abstract

The growing demand for sustainable solutions in biotechnology has encouraged the use of agri-food residues as alternative raw materials for producing value-added compounds. Accordingly, this study aimed to propose a sustainable biotechnological strategy for valorizing residues, focusing on banana peel and rice bran, through the microbial production of health-promoting compounds. In line with the principles of the circular economy, the work sought to demonstrate that food by-products can be converted into bioactive compounds, thereby combining environmental responsibility with applications relevant to the health sector. Initially, both residues were characterized to evaluate their suitability for bioprocessing. Although an attempt to extract ellagic acid from banana peel using ultrasound-assisted extraction (UAE) was performed, the compound was not detected. Consequently, the investigation shifted towards the microbial production of γ-aminobutyric acid (GABA). To this end, the residues were subjected to enzymatic hydrolysis with two proteases, alcalase and P24, to increase the availability of glutamic acid (Glu). Subsequently, the resulting hydrolysates were fermented with co-cultures of Saccharomyces cerevisiae and either Lactobacillus brevis or Lactobacillus plantarum. Samples were collected at 0, 48 and 72 hours for GABA and Glu quantification. The results indicated that rice bran was a more suitable substrate than banana peel for GABA production, primarily because of its higher protein content and greater release of Glu after hydrolysis with P24. Moreover, the co-culture with L. brevis yielded higher GABA levels at earlier fermentation stages, whereas L. plantarum displayed a slower and more gradual profile. This contrast highlights distinct fermentation dynamics and suggests different strategies for process optimization depending on the microbial consortium and production goals. Overall, this study demonstrates the potential of fermentation-based approaches for the valorization of agro-industrial residues. Not only did the process prove effective in generating GABA from rice bran, but it also pointed to possible strategies for improving the use of banana peel. Therefore, future studies should focus on optimizing fermentation conditions to enhance both efficiency and applicability.

Date of Award	24 Oct 2025
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Ana Raquel Madureira (Supervisor)