Microbial protein as sustainable feed and food ingredient: Production and nutritional quality of phototrophs and aerobic heterotrophs
22 May 2019
UAntwerpen, Stadscampus, Promotiezaal van de Grauwzusters - Lange Sint-Annastraat 7 - 2000 Antwerpen (route: UAntwerpen, Stadscampus
Organization / co-organization:
Department of Bioscience Engineering
Siegfried Vlaeminck & Pieter Vermeir
PhD defence Maarten Muys - Faculty of Science, Department of Bioscience Engineering
In just over 30 years, we need to produce 50% more protein, while our conventional linear food production system already trespassed the boundaries of sustainability. Microbial protein (MP), the protein-rich biomass of microorganisms, was researched as novel feed and food ingredient in a circular protein production chain. MP production can be based on primary resources to skip nutrient inefficient conventional protein production steps, or it can be based on secondary resources originating from the losses (e.g. wastewater) in the conventional production chain.
Indirect resource recovery was explored by application of struvite as phosphorus and nitrogen source for MP production. Struvite, a recovery product in wastewater treatment, was found to be a high-purity product, making it a selective barrier between waste stream and MP production. Dissolution kinetics and MP growth experiments demonstrated that struvite can be easily dosed in function of the microbial nutrient needs, while problems related to turbidity are avoided, making phototrophic MP production possible.
In contrast, direct resource recovery was considered by studying nutritional value and safety of aerobic heterotrophic bacteria (AHB) produced on processing effluents from 25 companies in the food and beverage sector. Protein and amino acid (AA) content varied notably between companies and within one company through time, while protein content was found to be correlated with nitrogen loading rate and sludge retention time, indicating that process design tailored towards protein production can increase biomass quality. Additionally, feed safety was guaranteed for most contaminants.
In the subsequent chapter, the variability in nutritional quality and safety was studied of commercial microalgae products, cultivated on primary resources. The high nutritional variability observed necessitates further optimization of cultivation conditions. It was also observed that a high protein content does not imply a high overall nutritional quality since digestibility and protein quality can still be unfavorable. Based on measured contaminants a safe consumption dose indicates that microalgae can perfectly be consumed as protein source rather than as food supplement, their current main application. In a final experimental chapter it was studied how the determined variability in microalgal biomass quality can be reduced, and how a stable, high-value biomass production can be established. The influence of harvesting time, operation mode and photoperiod was determined on the biomass, protein and essential AA productivity and optimal production parameters were identified.
In summary, MP production by means of indirect and direct nutrient recovery is promising, while further technological developments and increasing social awareness are expected to facilitate the introduction of novel MP in feed and food markets. As such, they can help to sustainably feed the growing world population.