Progress in Fishery Sciences (Jun 2024)
Effect of Drying Methods on the Flavor of Cololabis saira Assessed by GC-MS Coupled with Electronic Tongue
Abstract
Flavor is an important characteristic of seafood products, and drying can produce unique pleasant flavors. Drying is among the most common methods for processing seafood products. It can improve quality and shelf-life of seafood products and produce unique flavors. Oxidative hydrolysis of lipids during dry fish processing in the presence of light, photosensitizers, heat, oxygen, transition metal ions, and microorganisms produces volatile small molecules, including alcohols, ketones, aldehydes, and acids, which contribute to the flavor profile of dried fish. Volatile compounds are important components of seafood flavor. Flavor analyses are usually performed using gas chromatography-ion mobility spectrometry (GC-IMS) and gas chromatography-mass spectrometry (GC-MS) in combination with electronic nose/tongue techniques, which not only characterizes the molecular composition of volatile components in the sample, but also yields macroscopic results via the electronic nose/tongue, ultimately combining instrumental analysis with quantitative sensory data for a comprehensive evaluation of sample flavor. Currently, the market sales model of Cololabis saira is mainly based on a single frozen whole C. saira, and excludes most types of deep-processed products. There is an urgent need to enrich research into processing effects on C. saira quality and flavor, and further develop markets for deep-processed C. saira products. To explore the effects of different drying methods on C. saira flavor, we assessed flavor molecule profiles using GC-MS and electronic tongue techniques. This study aimed to provide a theoretical basis for improving C. saira product flavor, thereby enhancing the economic impact of the C. saira industry. In this study, C. saira was thawed in low-temperature air, and the giblets were removed and diagonally cut. Pre-treated fish were then soaked in 15% salt water for 1 h, drained naturally, and subjected to natural drying (natural air-drying on a sunny day in autumn for 3 days, environmental temperature 10~20 ℃, humidity 25%~42%), cold air-drying (continuous cold air-drying for 3 days, setting temperature (15±2) ℃, relative humidity 38%~40%), and UV with cold air-drying (continuous UV with cold air-drying for 3 days, ultraviolet lamp irradiation, setting temperature (15±2) ℃, relative humidity 38%~40%). The flavor profiles of fresh fish (CK), cured fish (0 d), naturally dried fish (N), cold air-dried fish (C), and UV treated cold air-dried fish (U) were compared. Significant differences were observed in the odor and taste of dried C. saira among products of the different drying methods. GC-MS results showed that a total of 58 volatile flavor substances were detected, including aldehydes, alcohols, ketones, acids, hydrocarbons, and nitrogenous compounds. Increased alcohols, aldehydes, and ketones enriched the fatty aroma of the three dried C. saira samples to varying degrees. Among them, the contents of cis-2-heptenal, octylaldehyde, 2-ethylfuran and other substances in U group increased significantly, increasing to 64.96,569.48 and 189.27 μg/kg, respectively, so that the U group had richer fat flavor. Hexanal, heptanal, Z-4-heptenal, octanal, nonanal, (E, E)-2,4-heptadienal, (E, E)-2,6-nonandialdehyde, 1-octen-3-ol, heptanol, 2,3-pentanedione, 3,5-octadien-2-one, and trimethylamine were the odor-active substances common to the five C. saira samples and were used as flavor compounds to characterize the oily and fishy taste of C. saira. E-2-nonenal, 2-ethylfuran, E-2-octenal, 2-nonanone, 2-undecanone, and 1-nonanol are three odor-active substances specific to dried C. saira, with E-2-octenal, 1-nonanol and 2-undecanone, which have an oily smell, and 2-ethylfuran, which has a burnt smell, having the highest odor aroma-active in the U group. Salty taste, richness, bitterness, astringency, and sourness of the fish increased after the drying process, especially salty taste and richness. Only fresh taste was significantly reduced relative to fresh fish. Saltiness, freshness, and richness of dried fish are important taste indicators. Salty taste and richness increased significantly after the three drying processes, whereas freshness decreased. Group U exhibited the highest salty taste and richness. In conclusion, the volatile odor and profile of C. saira changed significantly with each of three drying processes (natural drying, cold air drying, and UV with cold air drying), all of which increased the fatty flavor and considerably reduced the fishy flavor. Moderate oxidation positively contributes to C. saira flavor. Increased fatty flavor reduces the proportion of fishy substances, thus improving C. saira flavor. UV irradiation with cold air drying promoted lipid oxidation to some extent, producing more fatty substances, as well as cis-2-heptenal and 2-ethylfuran, which enriched the roasted, charred flavor of dried C. saira. Salinity, freshness, and richness are important taste indicators of dried C. saira. All three drying methods enhanced the salinity and richness of C. saira, and UV irradiation with cold air-drying significantly improved the salinity and richness of the fish and enriched its taste and aftertaste. Therefore, among the three drying methods, the method involving UV with cold air drying significantly enriched the flavor of C. saira to the greatest extent.
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