Continuous mixed-culture lactic acid fermentation of dairy effluent: Effects of magnetite supplementation and recycle
Lactic acid (LA) is an important industrial compound used in pharmaceuticals and food. It is considered as an alternative to petrochemical polymers. The global LA market reached USD 3.2 billion in 2021 and is expected to grow to USD 6.9 billion by 2030. LA can be produced through chemical synthesis or microbial fermentation, with the latter being the primary method. However, current commercial LA fermentation processes are costly, energy-intensive, and time-consuming. To address these issues, studies have explored mixed-culture fermentation using organic waste as a substrate, eliminating the need for sterilization. However, mixed-culture fermentation faces challenges in maintaining high LA selectivity and substrate utilization efficiency. To promote the dominance of lactic acid bacteria (LAB) and achieve high LA selectivity, low pH conditions and reduced retention times have been used. However, these strategies may hinder LA yield and productivity due to factors like feedback inhibition, low substrate conversion efficiency, and nutrient deficiencies. Previous studies have shown that iron supplementation, particularly iron oxides like magnetite, can enhance enzyme activity in fermentative bacteria. However, the application of magnetite supplementation and recycling in continuous mixed-culture fermentation has not been reported. This study aims to investigate how magnetite supplementation and recycling affect the performance of mixed-culture LA fermentation using whey as a substrate. The study will analyze various fermentation parameters and microbial community structures to gain insights into the fermentation process.