The research team, led by Annamalai Jeyakumari with Vinod Abhiroop and Krishnamoorthy Elavarasan, prepared four sardine fish oil emulsion formulations, coded SE1 through SE4, using low- and medium-molecular-weight chitosan as the variable biopolymer. Low-molecular-weight chitosan, derived from shrimp shell with a viscosity of 75.2 centipoise, was paired with bovine gelatin and maltodextrin in SE1 and SE2, while medium-molecular-weight chitosan, with a viscosity of 386 centipoise, formed the basis of SE3 and SE4. The fish oil-to-wall material ratio was maintained at 1:4 by weight across all formulations, and the oil loading differed between the pairs, with SE1 and SE3 containing 0.5 percent fish oil and SE2 and SE4 containing 1.0 percent. Wall materials were dissolved in 1 percent acetic acid solution, the oil was added gradually under magnetic stirring, and the coarse emulsions were homogenized at 20,000 rpm for 5 minutes before being converted into powder by spray drying at an inlet air temperature of 160 degrees Celsius and an outlet temperature of 70 degrees Celsius.

The choice of chitosan as an encapsulating biopolymer rests on its structure, a beta (1,4)-linked copolymer of D-glucosamine and N-acetyl-D-glucosamine, which confers biodegradability, biocompatibility, film-forming capacity, and inherent antioxidant and antimicrobial activities. However, chitosan alone performs poorly as an emulsifier, so it must be combined with complementary wall materials. Bovine gelatin, extracted by hydrolyzing collagen, contributes excellent film-forming, emulsifying, and gelling properties, while maltodextrin acts as a drying aid with high water solubility, low hygroscopicity, and good powder-forming ability. Tween 20 was included as a non-ionic emulsifier to reduce interfacial tension and facilitate the formation of fine oil droplets. The interplay of these polymers determines how effectively the wall matrix wraps around the lipid droplets during the rapid moisture evaporation that characterizes spray drying, and the study set out to quantify precisely how chitosan molecular weight alters that interplay.

Measurements of the emulsions with a nanoparticle analyzer revealed significant differences in droplet size, polydispersity index, and viscosity among the formulations. SE1 exhibited the smallest droplet size at 1023 nanometers, followed by SE2 at 1258 nanometers, while SE3 and SE4 produced larger droplets of 1638 and 1845 nanometers respectively. The increase in particle size with rising chitosan molecular weight was attributed to enhanced intermolecular interactions and chain entanglement, which form larger droplets during emulsification. Polydispersity index values were lower for the low-molecular-weight formulations, 0.40 to 0.41, indicating narrower droplet size distributions, whereas the medium-molecular-weight systems showed higher values of 0.51 to 0.56, suggesting greater heterogeneity. Viscosity increased dramatically from roughly 9 centipoise in the low-molecular-weight emulsions to about 93 to 94 centipoise in the medium-molecular-weight systems, a more than tenfold jump that reflects the stronger chain entanglement of the longer chitosan molecules.

When the emulsions were spray dried, the resulting powders showed moisture contents ranging from 2.49 to 4.23 percent, all within the acceptable range for spray-dried lipid powders, which is critical for suppressing microbial growth, caking, and oxidative deterioration during storage. Encapsulation efficiency, the key indicator of how well the wall matrix retains oil within the microcapsules and minimizes surface oil exposed to pro-oxidant conditions, varied significantly from 53.26 to 82.06 percent. SE3, the medium-molecular-weight chitosan formulation with 0.5 percent fish oil, achieved the highest encapsulation efficiency at 82.06 percent, while SE2, the low-molecular-weight system with 1.0 percent oil, recorded the lowest at 53.26 percent. Protein content of the powders ranged from 21.00 to 36.75 percent, reflecting the proportion of gelatin in each wall blend, while fat content varied between 10.18 and 11.88 percent and ash remained low at 0.46 to 0.49 percent.

Powder flow characteristics, evaluated through bulk density, tapped density, Carr’s Index, and the Hausner ratio, differed significantly among the treatments. SE3 exhibited the most desirable flow properties, with the lowest Carr’s Index at 26.93 percent and the lowest Hausner ratio at 1.37, compared with values as high as 47.56 percent and 1.91 in SE2. According to conventional classification, an Hausner ratio above 1.34 and a Carr’s Index above 25 percent indicate poor flowability, and indeed all samples in the study fell into that category, a limitation commonly reported for microencapsulated oil powders. Nevertheless, the relative superiority of SE3 suggests that the denser encapsulating matrix formed by medium-molecular-weight chitosan improved powder handling. Hygroscopicity values ranged narrowly from 8.43 to 9.12 percent, and SE3 combined high encapsulation efficiency with moderate moisture uptake, consistent with the reported negative correlation between encapsulation efficiency and hygroscopicity.

Differential scanning calorimetry added a thermal dimension to the comparison. All formulations displayed a small transition between 50 and 75 degrees Celsius, attributed to the release of physically bound water from the microcapsule matrix, followed by prominent exothermic peaks associated with structural breakdown of the encapsulating wall. These decomposition peaks appeared at 166.15 degrees Celsius for SE1, 152.14 for SE2, 175.96 for SE3, and 167.18 for SE4. SE3 exhibited the highest decomposition temperature, indicating greater resistance to thermal degradation and a more compact, robust microcapsule structure arising from stronger interactions among the wall materials. Because the decomposition temperatures exceeded 150 degrees Celsius, the researchers concluded that the microencapsulated sardine oil could withstand moderate thermal processing conditions common in the food industry, including baking, extrusion, and blending with dry ingredients, without significant degradation of the encapsulating matrix.

The decisive test came from the storage studies, in which the powders were held for 21 days under both ambient conditions at 28 plus or minus 2 degrees Celsius and refrigerated conditions at 4 degrees Celsius, with oxidative stability monitored through thiobarbituric acid reactive substances, expressed as milligrams of malondialdehyde per kilogram. Under ambient storage, SE3 started with the lowest initial TBARS value of 0.41 and fluctuated only between 0.41 and 0.54 throughout the 21-day period, demonstrating an effective barrier against oxygen diffusion. In stark contrast, SE2 and SE4 rose sharply during the first week to 3.82 and 3.51 respectively, and SE1 climbed gradually from 1.77 to 2.57. Under refrigeration, SE3 again maintained the lowest values, ranging from 0.44 to 0.60, while SE4 showed moderate protection at 0.65 to 1.13 and the low-molecular-weight formulations fared worse. The consistently low TBARS values of SE3 under both conditions were linked to its higher encapsulation efficiency and reduced surface oil, which limited the lipid fraction accessible to pro-oxidative attack.

The study concludes that a wall system comprising 0.5 percent medium-molecular-weight chitosan, bovine gelatin, maltodextrin, and 0.5 percent fish oil is an effective carrier for sardine oil, delivering the highest encapsulation efficiency, the lowest oxidation markers, and the greatest thermal resistance among the formulations evaluated. Refrigerated storage provided additional protection for all samples, but the formulation itself proved the dominant factor in preserving oxidative quality. The researchers suggest that these microencapsulated sardine oil powders possess significant potential as omega-3-rich ingredients for functional foods and nutraceutical formulations, from bakery and dairy products to powdered beverages, instant soup mixes, and nutritional supplements, where processing and storage stability are critical for maintaining product quality and nutritional value. By demonstrating that the molecular weight of a single biopolymer can swing encapsulation efficiency by nearly 30 percentage points and suppress oxidation markers by more than sixfold, the work offers food technologists a precise, actionable lever for engineering stable omega-3 delivery systems.

Subject of Research: Microencapsulation of sardine fish oil with chitosan-based polymer blends for oxidative stability

Article Title: Microencapsulation of sardine fish oil using different molecular weight chitosan and polymer blends: a comparative study on oxidative stability and encapsulation characteristics

Article References: Jeyakumari, A., Abhiroop, V., & Elavarasan, K. (2026). Microencapsulation of sardine fish oil using different molecular weight chitosan and polymer blends: a comparative study on oxidative stability and encapsulation characteristics. Frontiers in Marine Science, 13, Article 1906530. https://doi.org/10.3389/fmars.2026.1906530

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1906530

Keywords: fish oil, omega-3, microencapsulation, chitosan, spray drying, oxidative stability, maltodextrin, gelatin, functional foods, sardine oil, sardine, fish