Alternative, Sustainable, and Bioactive Additives with Potential Application in Aquaculture
Author: Alan Carvalho de Sousa Araujo (Currículo Lattes)
Advisor: Dr. José María Monserrat
Abstract
This study aimed to evaluate the bioactive properties of microbial flocs from the BFT system and protein hydrolysates from the giant mealworm Zophobas morio to promote more sustainable aquaculture. For this purpose, their nutritional content and biological properties (chlorophyll a and carotenoids) were determined. The study was divided into three chapters. In Chapter 1, the influence of the drying process (oven and freeze-drying) on the nutritional parameters and biological properties of biofloc samples (photoautotrophic and heterotrophic) was evaluated. Additionally, the samples were dissolved in different solvents (water, ethanol, and methanol) and assessed for their bioactive properties. Freeze-drying resulted in a higher protein content in the photoautotrophic sample, whereas oven drying led to higher protein levels in the heterotrophic sample. Regarding total amino acids (TAA) and hydrophobic amino acids (HAA), freeze-drying yielded higher values for both types of flocs, with the heterotrophic sample having higher total essential amino acids (TEAA) compared to the photoautotrophic one. Chlorophyll a and carotenoid levels were higher in the photoautotrophic sample. Antioxidant capacity (DPPH and ABTS) and polyphenol content were higher in processed samples and in aqueous extracts, with the best values in the photoautotrophic sample (both oven-dried and freeze-dried), followed by the heterotrophic sample dried in the oven. In Chapter 2, the use of different proteases in the enzymatic hydrolysis of giant mealworm flour was compared. Higher degrees of hydrolysis (DH) and lower water activity (aw) values were obtained in samples treated with Alcalase and Protamex enzymes. Regarding functional properties, hydrolysis time negatively affected water solubility of the hydrolysates; however, the samples showed good oil-holding capacity, foaming ability, and emulsifying properties. Nutritional content increased in the hydrolysates (68.74–57.63% total protein) compared to insect flour (47.09%). Higher levels of TEAA and TAA were observed in the hydrolysate obtained with Alcalase, while higher HAA content was found in the Protamex hydrolysate. Hydrolysates produced with Alcalase and Protamex showed antimicrobial effects against Gram-negative microorganisms (Vibrio coralliilyticus, Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli). In contrast, the hydrolysate obtained with Flavourzyme showed no activity against the tested microorganisms. Antioxidant activity analysis indicated that the hydrolysates had better ABTS radical scavenging ability. The Protamex hydrolysate exhibited the highest antioxidant capacity in both the ABTS assay and the ferric reducing antioxidant power (FRAP) assay. Finally, in Chapter 3, the effect of microencapsulation using different wall materials (maltodextrin/MD and gum arabic/GA) on the hydrolysates obtained with Alcalase and Protamex was evaluated. The microencapsulated hydrolysates had lower water solubility compared to the free hydrolysates. Zeta potential results indicated a tendency for aggregation in aqueous media. Antioxidant capacity followed the same trend as the free hydrolysates, with higher ABTS radical scavenging capacity. Thermal and FTIR analyses confirmed successful encapsulation. Finally, in the C. elegans in vivo assay under thermal and oxidative stress conditions, nematodes showed growth, although survival was lower compared to treatments with free hydrolysates. Overall, the hydrolysate obtained with Protamex and microencapsulated with maltodextrin showed the best growth and survival results in the evaluated assays compared to other treatments.