Effects of Cultivation Temperature on Protein Production of Selected Spirulina Strains Under Photobioreactor Conditions

Abstract

Spirulina is cultivated industrially for food supplement applications due to its high protein content and protein quality. This study assessed the influence of cultivation temperature on the productivity of widely accessible, protein-rich Spirulina strains under standardized bubble column photobioreactor conditions, with the goal of identifying strains with consistently high nutritional value across varying temperatures and culture age for outdoor applications. Five strains were first screened for protein content at 30 degrees C, and three with protein contents >60 % dry biomass were selected for cultivation at 25 degrees C, 35 degrees C, and 40 degrees C. Protein content was measured daily to determine variations, and protein quality was assessed at log and stationary growth phases. The metal content was analyzed to assess the toxic heavy metal bioaccumulation potential. At the optimum temperature of 35 degrees C, the strains had similar biomass productivities. However, the protein contents were highly temperature and strain-specific. Based on the strain, under identical process conditions, a relatively stable protein content of around 65 % or a content variation from 30 to 70 % was observed through the cultivation. Growth at 25 degrees C lowered the biomass productivity without affecting the protein contents, and growth at 40 degrees C lowered both parameters. S. platensis UTEX 2340 had consistently the highest protein quality, reflected by its higher cumulative essential amino acid contents and essential amino acid index scores. However, at 35 degrees C, the strain also had a mercury content exceeding the safety limits set for food supplements. These findings demonstrate the importance of strain selection and cultivation temperature in maintaining the nutritional value of Spirulina-based products.