Valorisation of white grape pomace sugars for optimized heterotrophic cultivation of Auxenochlorella protothecoides: A sustainable food ingredient

Abstract

Microalgae, such as Auxenochlorella protothecoides, are promising candidates as sustainable food sources due to their high protein content and adaptability to various growth modes. However, traditional fermentation methods are costly and resource intensive. This study explores the use of soluble sugars from white grape pomace, a wine industry by-product, as an alternative and cost-effective carbon source for heterotrophic cultivation. Optimization of the growth medium stablished yeast extract as the best nitrogen source, together with the optimal C:N and C:P ratios of 7:1 and 12:1, respectively. The process was scaled to a 6 L bioreactor, achieving a biomass content of 10.04 g L⁻¹ biomass with a 34.51 % dry weight protein. Two semi-continuous strategies, perfusion and fed-batch, were implemented, increasing biomass concentration by 2.02 and 3.27, respectively. While batch-grown biomass showed superior protein content, fatty acid profile and pigment concentration, all biomasses exhibited rich essential amino acid composition, surpassing FAO/WHO standards. These finding support microalgae's role in sustainable agriculture, integrating waste streams into food production systems, and contributing to the circular bioeconomy.