Preparation, characterisation, stability, and application of tocotrienol nanoemulsion stabilised by pea protein isolate and flaxseed gum complexes

In recent times, there has been a growing demand for full plant-based encapsulating agents to replace the commonly used animal-based or synthetic emulsifiers. However, native pea protein isolate (PPI) has the major drawback of low solubility at neutral pH and unable to stabilize emulsion under storage period. Tocotrienol-rich fraction (TRF) derived from red palm oil has gained significant attention due to its health benefits. However, incorporating it into food products has been challenging due to its poor water solubility. Therefore, this study aimed to enhance the solubility of native PPI followed by complexation with flaxseed gum (FG) to create a stable delivery system to form TRFbased nanoemulsions. Firstly, the solubility of treated pea protein isolate (TPPI) was enhanced through pH adjustment and thermal treatment. TRF-based oil-in-water nanoemulsions were prepared under pH 6 using 2% w/w of soluble treated pea protein isolate- flaxseed gum (TPPIFG) complexes at different ratios (ranging from 3:1 to 11:1). The results indicated that the nanoemulsion prepared using TPPI-FG (3:1) exhibited the highest stability, as evidenced by its increased viscosity, emulsifying activity index, and emulsion stability index. During a 7-day storage study, the nanoemulsion stabilized by TPPI-FG (3:1) remained the most stable, with only a slight increase in droplet size, the lowest rise in polydispersity index, and creaming index. The morphology study further revealed that no coalescence was observed in this nanoemulsion. Subsequently, the optimized TPPI-FG (3:1) stabilized nanoemulsion was spray-dried using different core-to-wall ratios, wall material compositions, and mixing ratios. The microcapsule formed at a 1:4 M ratio exhibited higher microencapsulation efficiency (MEE), improved water solubility index, increased retention of tocopherol and tocotrienol, and excellent flowability. When the 1:4 core-to-wall ratio was employed, Maltodextrin (M) was mixed with starch sodium octenyl succinate (OSS) and inulin (INU) at mixing ratios of 9:1 and 8:2, to create microcapsules. It was observed that the 1:4 M:OSS (8:2) microcapsule achieved the highest MEE, retained the most tocopherol and tocotrienol, demonstrated excellent flowability, and exhibited low cohesiveness. This microcapsule also possessed the highest sphericity, featuring a smooth and dense external surface without cracks. Next, the optimised TRF-based microcapsule produced from the 1:4 M:OSS (8:2) ratio were examined for storage stability, release characteristics, and bioaccessibility of tocotrienol. Over 13 weeks of storage at 40 °C, the microcapsules displayed a slight increase in cohesiveness and lightness, along with a minor decrease in MEE, yellowness, and chroma. Additionally, the microcapsule remained stable against oxidation during storage, as indicated by a low peroxide value, and degradation of tocopherol and tocotrienol isomers. These microcapsules proceed to be stable under various ionic strengths (ranging from 0 to 200 mM) and pH (ranging from 3 to 9). Furthermore, they exhibited higher bioaccessibility and release compared to bulk oil. Finally, the optimised TRF-based microcapsules were added to mayonnaises (M-mayo) and stored at 4 °C for one month. M-mayo remained stable throughout storage, showing only a slight increase in lightness, redness, yellowness, firmness, consistency, and viscosity. By the fourth week, M-mayo had a low peroxide value and minimal degradation of tocopherol and tocotrienol isomers. Sensory evaluation indicated that Mmayo received the highest rating for color, while other sensory attributes (aroma, taste, creaminess, sourness, and overall acceptability) received similar ratings with other samples. This demonstrated that M-mayo is equally well-liked as the original mayonnaise. In conclusion, this study successfully addresses the challenge of incorporating TRF into food products using a fully plant-based emulsifier. The optimized delivery system shows excellent stability, bioaccessibility, and acceptance, making it a promising approach for enhancing the nutritional value of food products

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