Use of Agro-Industrial Waste as Substrates in Citric Acid Production: A Review
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Due to its antioxidant, acidifying, and flavor-enhancing properties, citric acid is one of the most versatile organic acids, with high demand in the food and beverage industry. Although the conventional system utilizes the fungus Aspergillus niger in media based on sugarcane molasses, the need for economic and environmental optimization has directed research toward alternative substrates and microorganisms. This review aims to conduct a literature survey of the potential use of agro-industrial waste as carbon and nitrogen sources in citric acid production. A structured literature search was conducted in the ScienceDirect, PubMed, SciELO and Google Scholar databases, covering studies published between 1977 and 2026, from which 65 production records were compiled. Data analysis shows that the diversity of available waste, combined with new fermentation strategies, allows not only for the reduction of operational costs but also for the mitigation of environmental impacts. A critical analysis further shows that yield variability within a single substrate class often exceeds the variability between different classes, indicating that inducer supplementation, pretreatment and nutrient balance are stronger determinants of performance than substrate identity alone.
