Gelatins, extracted from various animal tissues, are widely used in diverse fields including food science, due to their functional properties that are dependent on their source and extraction methods. Fish oil, rich in omega-3 fatty acids, offers significant health benefits but suffers from limitations like fishy odor, poor water solubility, and susceptibility to oxidation. Encapsulation techniques, particularly complex coacervation using gelatins, have been employed to overcome these challenges, but encapsulation efficiencies often remain below 90%. A recent advancement achieved >95.2% encapsulation efficiency using a combination of gelatin-sodium hexametaphosphate (SHMP) complex coacervation and freeze-drying aided by starch sodium octenyl succinate (SSOS). However, the detailed effects of gelatin type and concentration on the resulting fish oil powder properties remain unclear. This study aims to comprehensively analyze these effects using four gelatin types (PSG, BSG, FG, and CFG) across varying concentrations, focusing on the preparation process, physicochemical properties, and in vitro digestion behavior of the resulting fish oil@gelatin-SHMP@SSOS powders.

Existing literature highlights the diverse applications of gelatin, emphasizing the influence of its source and extraction method on its functional properties. Numerous encapsulation methods exist for fish oil, including complex coacervation, spray-drying, freeze-drying, and electrospraying. Complex coacervation, utilizing gelatins as wall materials, has gained popularity, with previous studies exploring various combinations like gelatin with acacia gum, SHMP, anionic gum Arabic, and almond gum. However, these studies generally reported encapsulation efficiencies below 90%. The current study builds upon a previously developed method that yielded significantly higher encapsulation efficiency (>95.2%) by combining gelatin-SHMP complex coacervation and SSOS-aided freeze-drying. This prior work provided a foundation for this current research by investigating the specific impacts of gelatin type and concentration.

The study employed a combination method of gelatin-SHMP complex coacervation and SSOS-aided freeze-drying to prepare fish oil powders. Four types of gelatin (PSG, BSG, FG, and CFG) were used at three concentrations (60, 80, and 100 mg/mL). Fish oil-loaded gelatin-stabilized emulsions were first prepared via homogenization. Complex coacervates were then formed by mixing the emulsion with SHMP solution and adjusting the pH. The effects of gelatin type and concentration on coacervate formation were investigated using optical microscopy. Freeze-drying, aided by SSOS, produced the fish oil powders. The powders' microscale morphologies were observed using SEM. Physicochemical properties (bulk and tapped densities, moisture content, water activity, loading capacity, encapsulation efficiency, surface oil content, and encapsulation yield) were determined. Oxidative stability was evaluated using a Schaal oven test by measuring peroxide values. Powder stability at acidic (pH 2.0) and neutral (pH 7.0) pH was assessed using digital camera and optical microscopy. Finally, in vitro digestion behavior was analyzed using a simulated gastrointestinal model, with free fatty acid (FFA) release percentages measured in the small intestinal phase. Statistical analysis was performed using one-way ANOVA.

CFG, unlike other gelatins, failed to form complex coacervates due to its unobvious isoelectric point, lower molecular weight, higher number of hydrogen bonds, and longer gel formation time. Gelatin type and concentration significantly influenced the physicochemical properties of the powders. Peroxide values were lowest for PSG and highest for FG at 3 hours under the Schaal oven test. Acidic and neutral pH did not dissolve the complex coacervates. In vitro digestion studies revealed that the powders dissolved quickly to form emulsion droplets in the gastric phase, and SSOS significantly enhanced oil digestion. Gelatin type and concentration also affected FFA release percentages in the small intestinal phase, with no clear consistency observed in relation to the powders' physicochemical properties. Encapsulation efficiencies were generally above 95%, except for BSG at 100 mg/mL.

The findings highlight that not all gelatin types are suitable for preparing fish oil powders using this method. The inability of CFG to form complex coacervates underscores the importance of gelatin selection based on its physicochemical properties. The significant impact of gelatin type and concentration on powder properties indicates the need for careful optimization of these parameters for desired product characteristics. The high encapsulation efficiency and relatively low peroxide values of powders suggest that the chosen method represents a promising approach for fish oil encapsulation. The enhanced oil digestion in the presence of SSOS demonstrates its positive role in improving the bioavailability of the encapsulated fish oil. The lack of clear correlations between some physicochemical properties and FFA release emphasizes the complex interplay of factors influencing oil digestion.

This study comprehensively evaluated the influence of gelatin type and concentration on the preparation and properties of freeze-dried fish oil powders. CFG proved unsuitable due to its unique properties. Gelatin type significantly affected physicochemical properties and oxidative stability, while SSOS enhanced digestibility. Future research should investigate the influence of gelatin tissue source, animal source, extraction method, and particle size, aiming to optimize the process for enhanced properties and high-value utilization of by-products. Further investigations into complex coacervation without fish oil could further illuminate the formation mechanisms.

The study primarily focused on four specific gelatin types and a limited range of concentrations. A broader range of gelatin types and concentrations could provide a more comprehensive understanding of the effects. The in vitro digestion model may not fully represent in vivo conditions. Further research using in vivo models is needed to validate the findings regarding bioavailability and digestibility. The Schaal oven test provides accelerated oxidation; further studies under actual storage conditions are needed to verify long-term oxidative stability.