Identifying Key Volatile Compounds in Tilapia during Air Frying by Quantitative GC-IMS

A recent study published in Molecules (1), identified and quantified the volatile compounds (VCs) of tilapia by quantitative gas chromatography–ion mobility spectrometry (GC-IMS), followed by the selection of key VCs based on the calculation of the odor activity value (OAV). The contents of malondialdehyde (MDA), total sulfhydryl, and protein carbonyl were analyzed as well. The relationship among the key VCs and oxidative indexes of proteins and lipids was researched by a correlation analysis to determine the possible formation mechanism.

Tilapia, the world’s third largest freshwater aquaculture fish, has the advantages of fast growth and large yield around the world due to the strong environmental adaptability (2,3). Rich in nutrients such as unsaturated fatty acids and proteins, tilapia is usually processed into frozen filets because of the lack of intermuscular spines (4) Unfortunately, this primary processing method leads to low added value of tilapia, therefore bringing to attention a great need for an alternative technique that can obviously improve the added value of the fish (1).

Aroma is one of the main quality characteristics of roasted fish is aroma, which results from the existence of VCs usually caused by chemical reactions, such as the oxidative decomposition of lipids and proteins in fish during roasting, and their species and contents change significantly along with the roasting (5).

Air frying as a new roasting technique is based on high heat transfer efficiency because of the hot air circulating in the chamber (6). During the process, the high-temperature airflow surrounds the food, simultaneously inducing a fast mass transfer in a transient state among the hot air medium, water, and oil inside the food (7). Air frying can effectively reduce the oil content and produce a similar product appearance with deep-fat frying (8,9), leading to the good texture and mouthfeel of products.

In this study, live tilapia weighing about 1000 g was bought from a local supermarket in Guangzhou, China. The meat was harvested and soused with 0.6% complex phosphate (sodium tripolyphosphate/sodium hexametaphosphate = 1:1) and 6% salt for 40 min. The soused meat was then dried by hot air at 80 °C for 7 min and its surface brushed with 2% soybean oil. After preheating the air fryer at 190 °C for 10 min, the meat was roasted by air frying at that temperature for 40 min. Samples were taken after air frying for 0, 20, 30, and 40 min, respectively. A mixture of 2.0 g ground tilapia and the internal standard substance (1 μg 4-methyl-2-pentanol) was put into a 20 mL headspace bottle and incubated at 60 °C for 15 min. The headspace gas (200 μL) was then analyzed for VCs under the following GC conditions: the initial flow velocity was maintained at 2 mL/min for 2 min, increased to 10 mL/min within 3 min, increased to 100 mL/min within 20 min, and then held at 100 mL/min for 5 min. The compounds were finally identified through the retention index and drift time (1).

A total of 34 VCs were identified and quantified in the air fryer-prepared tilapia by quantitative GC-IMS, and 16 key VCs were determined according to OAV ≥ 1. With the increase in air frying time, the total sulfhydryl content reduced, while the protein carbonyl and MDA content was enhanced. This suggests that the oxidation of the protein and lipid was promoted after air frying. The correlation network showed that the change in total sulfhydryl, protein carbonyl, and MDA was significantly correlated with most key VCs, especially 2-methyl butanal, ethyl acetate, and propanal. This indicates that the oxidation of lipids and proteins after air frying contributed to the flavor improvement in tilapia. The authors of the study believe that their work provides a useful reference for the volatile flavor improvement in a pre-cooked tilapia product (1).

Raw fish fillet of tilapia on a cutting board with lemon and spices. © Elengush - stock.adobe.com

References

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2. Yang, Y.; Wu, Z.; Ren, Y.; Zhou, Z.; Wang, W.-X.; Huang, Y.; Shu, X. Improving Heat Resistance of Nile Tilapia (Oreochromis niloticus) by Dietary Zinc Supplementation. Aquac. Nutr. 2022, 2022, 6323789. DOI: 10.1155/2022/6323789

3. Jinagool, P.; Wipassa, V.; Chaiyasing, R.; Chukanhom, K.; Aengwanich, W. Effect of Increasing Ambient Temperature on Physiological Changes, Oxidative Stress, Nitric Oxide, Total Antioxidant Power, and Mitochondrial Activity of Nile Tilapia (Oreochromis niloticus Linn.). Aquaculture 2024, 589, 741017. DOI: 10.1016/j.aquaculture.2024.741017

4, Li, C.; Chen, S.; Huang, H.; Li, J.; Zhao, Y. Improvement Mechanism of Volatile Favor in Fermented Tilapia Surimi by Cooperative Fermentation of Pediococcus acidilactici and Latilactobacillus sakei: Quantization of Microbial Contribution Through Influence of Genus. Food Chem. 2024, 449, 139239. DOI: /10.1016/j.foodchem.2024.139239

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