Sea bass (Lateolabrax japonicus) is known for its unique flavor and high nutritional value. In this study, the influence of slaughter methods on the volatile compounds (VOCs) in sea bass was investigated using electronic nose (E-nose) technology and gas chromatography-ion mobility spectrometry (GC-IMS). VOCs in raw and cooked sea bass resulting from different slaughter methods were effectively distinguished using both techniques. Aldehydes, ketones, and alcohols were associated with the basic flavor of sea bass, whereas esters, organic acids, and furans enriched the aroma. In raw sea bass, the fishy odor was the strongest in the HSD group (head shot control death), followed by that in the IFD (ice faint to death) and BDS (bloodletting to death) groups. The VOC content increased and stabilized after steaming, enhancing pleasant odors such as fatty and fruity aromas. In cooked sea bass, the content of diacetyl and ethanol was the highest in the EAD group (eugenol anesthesia to death), which may be a residue of eugenol, imparting a distinct irritating chemical odor. Furthermore, abundant (E)-2-octenal, 2-heptanone, benzaldehyde, and esters in the BDS group imparted a strong, pleasant aroma. The findings indicate that heart puncture and bloodletting is the preferred slaughter method to maintain sea bass quality, providing new insights into the volatile changes in sea bass induced by different slaughter methods.

The biotransformation of L-glutamic acid (L-Glu) to γ-aminobutyric acid (GABA) using glutamate decarboxylase (GAD) in microbial whole cells represents an ideal approach for biosynthesis of food-grade and pharmaceutical-grade GABA. To overcome the cell membrane barrier, enhance mass transfer efficiency in the whole-cell reaction system, and improve GABA biosynthesis efficiency, we established a novel ethanol-enhanced whole-cell biocatalytic co-reaction system through systematic investigations on the enzymatic characteristics of GAD in Pediococcus pentosaceus whole cells and the regulatory effects mediated by ethanol. The results showed that the optimal reaction pH and temperature for GAD in P. pentosaceus whole cells were 4.2 and 32 °C, respectively. A 7.5% (v/v) ethanol concentration significantly promoted the activity of whole-cell GAD, but reduced its stability. Through orthogonal test optimization, the optimal reaction conditions for ethanol-promoted GABA synthesis via P. pentosaceus whole-cell transformation were as follows: mixing 0.3 M monosodium glutamate (MSG) solution with 100 mg/ml cell suspension at a 1:1 volume ratio, adding 40 g/l of L-Glu/MSG (2:1) solid mixture, adjusting the final ethanol concentration to 3.75% (v/v), reacting at pH 4.2, 28 °C for 40 h. Under these conditions, the GABA yield reached 366.07 ± 5.57 mM, which was 21.44 ± 1.85% higher than that of the control group without ethanol. As an enhancer, ethanol demonstrates great application potential in GABA production via whole-cell transformation due to its high safety and ease of use.

Maintaining cell envelope integrity and intracellular enzyme stability while alleviating transmembrane mass-transfer limitations is important for sustained