Harnessing valorization potential of whey permeate for D-lactic acid production using lactic acid bacteria

Global milk production has increased by 59% since 1988, reaching 944 million tonnes in 2023. This surge has resulted in an annual by-product, whey, totalling 200 million tonnes. Despite half of this whey being utilized in the food and pharmaceutical sectors, significant quantities are discarded, posing environmental challenges due to its high biological oxygen demand. Whey proteins and lipids are recovered from whey, and the resultant whey permeate stream is rich in lactose is a viable carbon source for value-added biochemical. D(-)lactic acid (DLA) is a versatile organic acid molecule widely used in the synthesis of thermostable biodegradable polymers viz., polylactic acid (PLA). However, the DLA market faces constraints; downstream demand is unsaturated, and upstream production is restricted, leading to elevated costs and posing challenges to its growth and profitability, which affect PLA manufacturing. This review study addresses a novel techno-economic approach involving strategies for genetic engineering of lactic acid bacteria and process intensification towards efficient valorization of whey permeate into DLA. This review enumerates a circular bioeconomy approach offering both environmental benefits and revenue opportunities for the dairy sector, revolutionizing by-product utilization and enhancing the industry's sustainability.