Development of Virgin Coconut Oil Emulsified Surimi Gel with Nutraceutical Properties

Abstract

Effects of virgin coconut oil (VCO) at various levels (0-25%) on the properties of croaker surimi gels were studied. As the levels of VCO increased up to 15%, breaking force continuously decreased (p < 0.05). No differences in breaking force, deformation and fracture constant were noticeable when VCO of 15-25% was incorporated (p > 0.05). Based on texture profile analysis (TPA), hardness and chewiness decreased as the level of added VCO increased up to 10% (p <0.05), while no marked changes were observed with the addition of 10-25% VCO (p > 0.05). Addition of VCO had no profound impact on springiness and cohesiveness. No remarkable change in protein pattern among all surimi gel samples was noticed, regardless of VCO levels. Lower elastic (G') as well as loss moduli (G") of surimi paste were attained when VCO was added, compared to the control. Nevertheless, there was no marked difference in the moduli among samples containing VCO at all levels. Whiteness of surimi gel increased, whereas expressible moisture content decreased as VCO levels increased (p < 0.05). Microstructure study revealed that VCO droplets were distributed uniformly in gel network. Overall likeness of surimi gel was also increased for gel added with VCO. To minimize the interfering effect of VCO on gel properties, pre- emulsified VCO was incorporated in the form of VCO nanoemulsion. Nanoemulsion based on 5% virgin coconut oil (VCO) was prepared with the aid of ultrasound using sodium caseinate (2 and 3%) as emulsifier for various ultrasonication times (5-20 min). The smallest average particle size of resulting nanoemulsion (3.88 nm) was obtained when 3% sodium caseinate and ultrasonication of 5 min were used. Nevertheless, the nano droplets were flocculated when visualized using confocal laser scanning microscope. The effects of VCO and nanoemulsion at a level of 5% on properties of croaker surimi gel with the mixing time of 3 and 5 min were studied. No differences in breaking force, deformation and fracture constant were observed between the control gel and that added with nanoemulsion, regardless of mixing time (p > 0.05). No difference in TPA parameters was found between the control gel and that added with nanoemulsion, however mixing time had a significant impact on the hardness and chewiness (p<0.05). No change in protein pattern of all the surimi gel samples was found for both mixing times, irrespective of VCO or nanoemulsion added. No remarkable effect on elastic (G') as well as loss (G") moduli of surimi paste was noticeable with the addition of either VCO or nanoemulsion, but higher G' was generally attained for the control. Whiteness increased, while the expressible moisture decreased with the addition of either VCO or nanoemulsion. VCO droplets from nanoemulsion were embedded in the gel matrix and distributed uniformly. In general overall likeness was increased for the gels added with VCO nanoemulsion, compared to the control, most likely owing to the increased whiteness. To elucidate the effects of B-glucan on surimi gel, VCO nanoemulsion stabilized by ẞ-glucan at levels of 5-20% (based on solid weight of surimi) on croaker surimi gel were comparatively studied. Increases in breaking force, deformation and fracture constant were found in surimi gel containing VCO nanoemulsion stabilized by 5% B-glucan, whereas the decrease in all properties were observed as level of ẞ- glucan in nanoemulsion increased. The addition of B-glucan solutions led to continuous decreases in breaking force, deformation and fracture constant, compared to the control. Addition of both B-glucan stabilized VCO nanoemulsion (BG-V-N) and B-glucan solutions resulted in the decreases in viscoelastic moduli. Power law mo del represented viscoelastic behavior of all the gels. Expressible moisture content decreased, while whiteness increased with the addition of BG-V-N, compared with gel containing VCO. However, both expressible moisture content and whiteness increased with the addition of ẞ-glucan solutions, at all levels used. Addition of BG- V-N resulted in finer gels, than the control gel added with only VCO. Generally, overall likeness score was increased for gel containing VCO nanoemulsion stabilized by 5% B-glucan. To improve the storage stability and enhance value, addition BG-V-N containing epigallocatechin gallate (EGCG) and a-tocopherol at levels of (0-0.3%) on properties and storage stability of surimi gel were investigated. Augmented breaking force, deformation and fracture constant were obtained in gels containing 0.2% EGCG or 0.1% a-tocopherol (p<0.05). Expressible moisture content increased as EGCG levels were higher than 0.2%. Smoother microstructure was observed in gels containing 0.2% EGCG. No change in protein pattern of gels was observed, regardless of antioxidant incorporation. The incorporation of 0.2% EGCG or 0.1% α- tocopherol lowered the decrease in G'. Gels containing EGCG and a-tocopherol at selected levels had the improved oxidative stability and lowered microbial loads. To investigate digestibility and bioactivity of surimi gels containing BG- V-N, gel samples were subjected to simulated gastrointestinal digestion system and the resulting digest was analyzed for nutraceutical properties. BG-V-N remarkably improved antioxidant activities of the surimi digest. When EGCG was added in nanoemulsion, the surimi digest showed the highest antioxidant activities. Antidiabetic activity of the digest was also improved by the addition of BG-V-N comprising EGCG. Nevertheless, the addition of BG-V-N lowered ACE inhibitory activity of surimi digest. The surimi digest from the gel added with BG-V-N possessed an inhibitory effect on five cancer cell lines including HEK (human embryonic kidney 293 cells), MCF-7 (breast cancer cell line), U87 (human glioma), HeLa (human cervical cancer), and IMR-32 (human neuroblastoma), regardless of EGCG or a- tocopherol incorporated. This study demonstrated that surimi gel supplemented with BG-V-N in the presence of EGCG exhibited nutraceutical potential and could be used as a functional food.