Abstract

Encapsulation serves as a critical strategy for the preservation of sensitive bioactive compounds, ensuring their stability and functionality within complex food matrices. Cellulose nanocrystals (CNCs) upcycled from by-products are being favoured as wall materials because they offer a sustainable yet powerful solution for maintaining compound stability. This study evaluated the encapsulation of fish oil (FO) within a nanocomposite matrix of garlic skin-derived cellulose nanocrystals (GCNCs) and soy protein isolate (SPI). The synergistic effects of FO loading and GCNC:SPI ratios on the microcapsules’ structural, physicochemical, and digestive properties were investigated. Higher FO loading significantly reduced the moisture content of the resulting microcapsule powders while increasing bulk and tapped densities by minimising internal porosity. Microstructural analysis showed irregularly shaped agglomerates. Higher FO loading also increased surface oil retention and inter-particle adhesion of the microcapsule powders; however, elevated SPI levels effectively counteracted these effects. Colour analysis further revealed that higher FO loading reduced powder lightness (L*) and increased yellowness (b*), while greater GCNC content positively influenced redness (a*). The formulation containing 10% FO, 3% GCNCs, and 7% SPI was identified as the optimal treatment. This ratio achieved the highest encapsulation efficiency (65.77% ± 1.10) and demonstrated superior flowability, characterised by the lowest Carr’s Index (20.65% ± 0.29) and Hausner Ratio (1.23 ± 0.05). Additionally, it maintained oxidative stability, with TBARS values (2.42 ± 0.08 mg MDA/kg oil) remaining consistently below the established 3 mg MDA/kg threshold. Fourier Transform Infrared Spectroscopy confirmed the successful entrapment of FO within the GCNC–SPI matrix. According to the in vitro digestion assays, the wall material provided a durable barrier in acidic media because the gastric release (28.04–55.28%) was significantly lower than the intestinal release (64.38–77.62%). The predominant fatty acids identified in both encapsulated and unencapsulated products were myristic acid (saturated fatty acid), elaidic acid (monounsaturated fatty acid), and docosadienoic acid (polyunsaturated fatty acid). Superior nutritional quality index (NQI) values in the encapsulated samples underscore the effectiveness of the wall material in providing a critical defence against fatty acid degradation and preserving overall oil quality. These findings suggest that the GCNC/SPI binary system is a highly effective delivery vehicle for protecting sensitive polyunsaturated fatty acids in functional food applications.

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