Enhanced fresh-keeping capacity of printed surimi by Ca2+-nano starch-lutein and its nondestructive freshness monitoring based on 4D printed anthocyanin

To solve undiscernible freshness changes of printed functional surimi while maintaining printed shape, 4D printable color-changing material were prepared. Firstly, based on results of printing properties and fresh-keeping of Ca2+-NS-L-surimi, it showed better printing effects (enhanced mechanical strength) and good preservation (inhibition of amino acids decomposition, bacterial growth). However, freshness changes of printed Ca2+-NS-L-surimi were not distinguished directly. To avoid that, 4D printable color-changing material-anthocyanin-hydroxypropyl methyl cellulose-xanthan gum-carrageenan (AHXK) was prepared for indicating freshness through discoloration. Printing results showed AHX with 5 % K had the most suitable mechanical strength (appropriate gel strength, texture, rheology) for printing. Based on that, AHXK had stable color (ΔE fluctuation <5) and was sensitive to pH and ammonia (obvious discoloration; ΔE > 10). Actual freshness monitoring results (co-printing of AHXK-surimi) exhibited significant discolorations, especially for HXK with 0.75 % A. It became green during refrigeration of 3-5 d (keeping fresh, ΔE < 4), brighter green at 7 d (decreased freshness, ΔE > 6), turned yellow at 9 d (spoilage, ΔE > 16), which were distinguished significantly with naked eyes rather than traditional freshness determining. In conclusion, printed AHXK-functional surimi exhibited good printing, preservation and nondestructive freshness monitoring, facilitating application of 3D printed functional surimi.

Effect of Ca2+ on 3D printing accuracy and antioxidant efficacy of nano starch-lutein surimi: mechanical properties, chemical bonds and release rate

BACKGROUND

Nano starch-lutein (NS-L) can be used in 3D printed functional surimi. However, the lutein release and printing effect are not ideal. The purpose of this study was to facilitate the function and printing properties of surimi by adding the combination of Ca²⁺ and NS-L.

RESULTS

Printing properties, lutein release and anti-oxidation of printed Ca²⁺ -NS-L-surimi were determined. The NS-L-surimi with 20 mM·kg^-1 Ca²⁺ had the best printing effects (fine accuracy, 99 ± 1%). Compared to NS-L-surimi, the structure became denser after adding Ca²⁺ , the gel strength, hardness, elasticity, yield stress (τ), water holding capacity of Ca²⁺ -NS-L-surimi increased by about 17 ± 4%, 3 ± 1%, 9 ± 2%, 20 ± 4%, 40 ± 5% respectively. These enhanced mechanical strength and self-supporting ability to resist binding deformation and improve printing accuracy. Moreover, salt dissolution and increased hydrophobic force by Ca²⁺ stimulated protein stretching and aggregation, leading to enhancement of gel formation. Decreased printing effects of NS-L-surimi with excessive Ca²⁺ (> 20 mM·kg^-1 ) caused by excessive gel strength and τ, leading to strong extrusion force and low extrudability. Additionally, Ca²⁺ -NS-L-surimi had higher digestibility and lutein release rate (increased from 55 ± 2% to 73 ± 3%), because Ca²⁺ made NS-L-surimi structure porous, which promoted contact of enzyme-protein. Furthermore, weakened ionic bonds reduced electron binding bondage that combined with released lutein to provide more electrons for enhancing anti-oxidation.

CONCLUSION

Collectively, 20 mM·kg^-1 Ca²⁺ could better promote printing process and function exertion of NS-L-surimi, facilitating the application of 3D printed functional surimi. This article is protected by copyright. All rights reserved.