Effects of Initial Density on Biochemical Composition and Texture Characteristics of Nostoc sphaeroides Under Long-Term Outdoor Cultivation

Nostoc sphaeroides is a cyanobacterium known for its valuable health benefits, including antioxidant, anti-inflammatory, and immune-boosting properties, making it a promising addition to functional foods. However, large-scale cultivation has remained necessary due to economic value and decreased yield. This study focused on the effect of varying inoculation densities and seasonal conditions on the growth and quality of N. sphaeroides. The main results were as follows: The highest average fresh weight productivity per unit volume was observed in summer and autumn at an inoculation density of 10 g·L−1, with values of 0.26 g·L−1·d−1 and 0.31 g·L−1·d−1, respectively. In winter and spring, the highest productivity was achieved at an inoculation density of 15 g·L−1, with values of 0.52 g·L−1·d−1 and 1.40 g·L−1·d−1, respectively. Nutritional components varied seasonally, with chlorophyll and carotenoid contents peaking in spring and phycobiliproteins, including phycocyanin, allophycocyanin, and phycoerythrin, reaching their highest levels in summer. The dry weight was greatest in summer, while the total protein content was highest in autumn, with values of 40.87%, 39.66%, and 41.44% for 5 g·L−1, 10 g·L−1, and 15 g·L−1, respectively. In terms of texture, the hardness of N. sphaeroides was highest in autumn at inoculation densities of 5 g·L−1 and 15 g·L−1, with values of 153.96 g and 146.88 g, respectively. At 10 g·L−1, the highest hardness was observed in spring (109.67 g). The elasticity and chewiness of the algae were best in spring across all inoculation densities, with elasticity values of 2.86, 2.54, and 2.07, and chewiness values of 112.37, 120.67, and 75.96 for 5 g·L−1, 10 g·L−1, and 15 g·L−1, respectively. In conclusion, the optimal inoculation density for summer and autumn is 10 g·L−1, while for winter and spring, it is 15 g·L−1. N. sphaeroides exhibits better texture in spring. This study offers valuable information for the large-scale cultivation and functional food applications of N. sphaeroides.