Low field NMR relaxation time assessment of Cucumaria frondosa sea cucumber quality during heat-induced autolysis enzyme inactivation

Low field NMR relaxation time assessment of Cucumaria frondosa sea cucumber quality during heat-induced autolysis enzyme inactivation

 

*María Gudjónsdóttir1,2, Qian Zhang3,4

1University of Iceland, Reykjavík, Iceland,

2Matís Food and Biotech R&D, Reykjavík,Iceland,

3Dalian Ocean University, Dalian, China,

4 Huazhong Agricultural University,

Wuhan, China.

*mariagu@hi.is

 

Boiling or steaming, are commonly used heat treatments to inactivate autolysis enzymes

present in the sea cucumber species Cucumaria frondosa. This is necessary to allow transport

of this fragile product from Icelandic waters to its market in China. The aim of this project was

to explore optimized heating treatments of Icelandic sea cucumber by comparing the effects of

boiling and steaming, respectively, at different heating times, and temperatures. Moreover, to

analyse the correlation of protein degradation, low-field Nuclear Magnetic Resonance (LF-

NMR) relaxometry and Texture Profile Analysis (TPA) parameters to provide more insights

into the relationship between physicochemical properties and structure changes of C. frondosa

during the heat treatments.

The LF-NMR T2 relaxation times of the black wall, middle tissue and tendons of the sea

cucumbers were assessed using a mq20 Bruker Minispec, applying a CPMG pulse sequence (τ

100 μs, 13 μs 90° pulse and 26 μs 180° pulse, 8 scans, 10 s repetition delay, and 8000 echoes

per scan). The obtained NMR relaxation data was maximum normalized and then processed

firstly by principal component analysis (PCA) in Unscrambler (CAMO, Trondheim, Norway),

and secondly by discrete relaxation fitting to a multi-exponential model.

The first two principal components described 96% and 3% of the sample variation, respectively

with regards to the LF-NMR response. The wide distribution of samples in the PCA indicated

that the heating processes had quite different effects on the different sea cucumber tissues.

Discrete fittings of the relaxation data to a multi-exponential model confirmed significant

differences in the water distribution of the three tissues. Two to four proton populations were

observed in the different tissues, depending on tissue, cooking method, temperature, and

heating time. T2 parameters were relatively stable in the middle portion, except for a clear

exchange of water between the two intermediate populations during the first 15 min of

steaming (A22 → A23). This behaviour was even stronger in the body wall and the tendon parts,

indicating that these parts were more vulnerable towards water loss and denaturation. All

relaxation times increased in the black body wall during the first 45 min of steaming, and in

the T24 relaxation time in the tendon part. This increase in relaxation times during the first 45

min of cooking can be associated to protein denaturation in the sea cucumber body wall and

tendons. Furthermore, the analysis showed that the tendons are especially vulnerable towards

this protein denaturation during steaming. Smaller variations were observed in the relaxation

times in the boiled samples, indicating less protein denaturation compared to the steamed

samples.

Comparisons of physicochemical parameters as presented by Zheng et al. (2022) and the LF-

NMR parameters indicated that boiling at 60℃ caused obvious proteins denaturation. This

denaturation led to changes in water holding capacity, texture properties, and enzyme activities.

When all indices were taken into account, 45 min boiling at 100°C was concluded to be a

sufficient heat treatment of Cucumaria frondosa to limit autolysis enzymes activities, as well

as limiting heat-induced protein denaturation.

References

1. Zhang Q, et al. Processes 10, 847 (2022).