Advanced GC-Based Analysis for Decoding Off-Flavors in Reheated Ready-to-Heat Roasted Catfish

A joint study conducted by members of the Hubei Academy of Agricultural Sciences, the Hubei University of Technology, the Wuhan Institute of Technology, and Huazhong Agricultural University (all in Wuhan, China) employed gas chromatography-electronic nose (GC-E-Nose), GC-ion mobility spectrometry (GC-IMS), and GC-olfactory-mass spectrometry (GC-O-MS) techniques, along with odor recombination and omission experiments to characterize the off-flavors in commercially available ready-to-heat roasted catfish after reheating. A paper based on their work was published in Food Chemistry: X (1).

A high-quality freshwater fish that is well-suited for processing, channel catfish meat is flavorful, rich in fat and various nutrients, offers a unique taste, and does not possess intermuscular spines (1). Channel catfish is currently made into frozen fillets, frozen balls, and roasted and sold ready-to-heat (2). Ready-to-heat roasted catfish is a semi-finished product created through a pre-treatment process which includes open back curing, roasting, and quick-freezing; this allows consumers to eat the product after simple reheating, which has made it widely popular in the consumer market. However, roasted catfish will often develop an undesirable sensory characteristic during the reheating process known as “off-flavor,” encompassing fishy notes and “warmed-over flavor” (WOF) which reduces the overall olfactory enjoyment of the product and has impeded the advancement of the prepared food industry (3). While there have been studies focusing on the investigation of off-flavor formation in meat products (4—6), corresponding studies addressing aquatic products have been limited, with existing research focusing primarily on surimi (7). The researchers report that, at this time, research off-flavor substances in ready-to-heat aquatic products have not been reported, inspiring their work (1).

Three top-selling roasted catfish products (Youyuyao, Deyan, and Huihaiying) were purchased from online retailers, with 10 units of each brand, prepared as ready-to-heat roasted products. This was done by opening the back, curing at 6–10°C for 3–5 h, roasting at 180–190°C for 25–30 min, and subsequently freezing at −40°C ± 5°C. The ready-to-heat roasted catfish products, frozen for six months, were then transported to the laboratory where the analysis would take place, via cold chain logistics and stored in a refrigerator at −80°C. During the measurement process, the samples were thawed in a refrigerator at 4°C until the center temperature reached 0°C. The samples were then reheated according to the optimal reheating method specified by the product. All three of the products were made from channel catfish, with raw materials tested for quality at the factory prior to processing (1).

A total of 19 (DR), 11 (HR), and 21 (YR) characteristic compounds were identified across the three samples. The 19 characteristic compounds from the DR group were reconstituted to develop recombination and omission models. The resulting model demonstrated the highest similarity (84.98 %) to the original sample while retaining some odor information from the other two sample groups. The 12 key off-flavor substances were identified through the omission model and were subsequently subjected to multivariate recombined. The contribution of these off-flavors was further validated via omission testing (1).

The research indicated that the main off-flavors in reheated ready-to-heat roasted catfish (characterized primarily by fatty, grassy, hard-boiled egg, metallic, and fishy notes) were attributed to hexanal, heptanal, (E)-2-hexenal, octanal, 3-methyl-1-butanol, 1-octen-3-ol, and (E,E)-2,4-heptadienal; these markers predominantly occur due to lipid oxidation. Furthermore, compounds such as sulfide, allyl methyl, d-limonene, and linalool may function as masking agents, affecting the awareness of off-flavor. In addition, the loss of aroma compounds exacerbates off-flavor, drawing the researchers to the conclusion that the increase in lipid oxidation products, protein degradation, and the introduction of exogenous aroma spices, along with their interactions, may significantly influence the emergence of off-flavor. This led the research team to recommend that further research occur to illuminate the mechanisms underlying off-flavor production, as well as to investigate the integration of masking agents to enhance the quality of flavor in prepared products (1).

References

1. Zhou M, Lu Y, Yu J, Wang C, Yu W, Shi L, Wu W, Wang L, Qiao Y. Characterization of off-flavor compounds in ready-to-heat roasted catfish after reheating by sensomics approach. Food Chem X. 2025 Aug 7;30:102872. DOI: 10.1016/j.fochx.2025.102872
2. Zhong, L. Q.; Song, C.; Chen, X. H. et al.Channel Catfish in China: Historical Aspects, Current Status, and Problems. Aquaculture 2016, 465, 367-373. DOI: 10.1016/j.aquaculture.2016.09.032
3. Tims, M. J.; Watts, B. M. Protection of Cooked Meats with Phosphates. Food Tech.1958, 12, 240-243
4. Zang, M.; Wang, L.; Zhang, Z. et al. Changes in Flavour Compound Profiles of Precooked Pork After Reheating (Warmed-Over Flavour) Using Gas Chromatography Olfactometry-Mass Spectrometry with Chromatographic Feature Extraction. Int. J. Food Sci. Tech.2020, 55 (3), 978-987. DOI: 10.1111/ijfs.14306
5. Konopka, U. C.; Grosch. W. Potent Odorants Causing the Warmed-Over Flavour in Boiled Beef. Zeitschrift für Lebensmittel-Untersuchung und -Forschung1991, 193, 123-125. DOI: 10.1007/BF01193360
6. Liu, J.; Deng, S.; Wang, J. et al. Comparison and Elucidation of the Changes in the Key Odorants of Precooked Stewed Beef During Cooking-Refrigeration-Reheating. Food Chem. X2024, 23, 101654. DOI: 10.1016/j.fochx.2024.101654
7. Y. An, Y.; L. Wen, L.; W. Li,W. et al. Characterization of Warmed-Over Flavor Compounds in Surimi Gel Made from Silver Carp (Hypophthalmichthys molitrix) by Gas Chromatography-Ion Mobility Spectrometry, Aroma Extract Dilution Analysis, Aroma Recombination, and Omission Studies. J. Agric. Food Chem.2022, 70 (30), 9451-9462. DOI: 10.1021/acs. jafc.2c02119