Observation of the Effects of Spray Drying and Freeze Drying on the Physical Structure of Catfish Gelatin Using SEM

Abstract

Catfish production ( Ictalurus punctatus ) in the United States was annually above 250 thousand tons in 2003 but dropped to approximately 150 thousand tons in 2012 and in 2023 reached approximately 170 thousand tons annually. Mississippi, Alabama, Arkansas, and Texas account for approximately 96% of total catfish sales. Approximately 55% of the whole weight of catfish is considered a by-product with 98% of it being sold as offal for ~3 cents per pound. Of this, 25% is skin and frame which contains collagen. This collagen can be extracted through partial hydrolysis to yield edible gelatin that can be utilized in value-added food and cosmetic products. Thus, catfish by-products are of great interest in the catfish industry. The objective of this research was to extract gelatin from channel catfish skins and compare the structural impacts of subsequent dehydration methodologies for targeted food applications. Catfish skins were sourced from a regional commercial processing plant. Structural disintegration was achieved via acid hydrolysis to transition the skins into a gelatin solution. The solution was filtered sequentially through cheesecloth to remove macro-particulates and activated charcoal to remove micro-particles, residual fats, and off-odors. The purified yield was split into two equal treatments: one portion was freeze-dried (FD) and the other was spray-dried (SD). Structural characterization was performed via a JEOL 6390 LV Scanning Electron Microscope (SEM). SEM micrographs revealed distinct morphological divergences: the SD treatment formed dimpled globular spheres, whereas the FD treatment exhibited a porous, interconnected fibrous sheet network. These microstructural variations alter the texturizing, hydrating, and encapsulating properties of the gelatin, establishing a processing-driven mechanism to customize byproduct gelatin for specialized functional niches in food formulation.