Study on volatile flavor compounds of Enteromorpha prolifera during the drift of green tide in the Yellow Sea
Enteromorpha prolifera green algae are widely distributed around the world, some growing in seawater or freshwater rivers, and some growing on the upper mouth of attached bases such as rocks or mud beaches in intertidal zones. There are currently over 80 known species of Enteromorpha prolifera worldwide, with approximately 11 species in China. Some green algae grow rapidly and gather together, causing a green tide. The outbreak of green tide will bring a series of secondary environmental problems, such as a large number of algae floating on the surface of seawater, causing shading effects and leading to the degradation and death of bottom vegetation due to the inability to carry out photosynthesis; Algae accumulate on the shore, decay and emit a foul odor, and even breed bacteria; After settling on the seabed, algae can cause hypoxia and sediment degradation, changing the physical and chemical properties of the bottom water and sediment, thereby causing serious impacts on the marine ecological environment and ecological service functions.
Since 2007, large-scale green tide disasters have occurred in the Yellow Sea of China for 14 consecutive years, causing huge economic losses and even threatening the ecological security of China’s coastal areas. At present, domestic and foreign researchers have conducted in-depth research on the source exploration, outbreak mechanism, drift path, prediction and early warning of the Yellow Sea green tide, and have achieved a series of important results. The dominant species causing the outbreak of green tide in the Yellow Sea, Ulva prolifera, is actually an economic seaweed. According to the “Compendium of Materia Medica” and “Sui’enju Dietary Catalogue”, it has the effects of cooling blood, relieving heat, diuresis, reducing phlegm, softening hardness, and lowering cholesterol. Modern research mainly focuses on polysaccharides from Enteromorpha prolifera, which have been proven to have pharmacological activities such as lowering blood lipids, antioxidation, enhancing immunity, and inhibiting skin cancer. In addition, Enteromorpha prolifera also has functions such as sterilization and washing, fiber spinning, sound-absorbing materials, and restoration of eutrophic marine ecosystems. In recent years, Enteromorpha prolifera has been increasingly used in the food industry. In Japan and South Korea, Enteromorpha prolifera is a luxury seasoning that is only used in high-end cuisine and is expensive. In China, Enteromorpha prolifera is ground into algal powder, which can be added to other foods. At present, it has industrialized the production of shrimp, noodles, Fried Dough Twists and other products of Enteromorpha prolifera. The application of Enteromorpha prolifera is mainly attributed to its unique aroma. Therefore, understanding the volatile flavor compounds and components in the green tide seaweed body is crucial for the rational utilization and development of green tide resources.
At present, research on green tide algae in China is commonly focused on its species identification, life history, tissue culture, experimental ecology, and other aspects. There has been some progress in the analysis of the nutritional components of green tide algae, but it is mostly concentrated on the component analysis of green tide algae in a specific location or sea area. There are few reports on the changes in the components of green tide algae during the entire drift process, especially the changes in volatile flavor compounds of green tide algae during the entire drift process. This study collected samples from various stages of green tide drift and conducted analysis of volatile flavor compounds. Combined with aroma thresholds, the main aroma components of the dominant species of green tide, Enteromorpha prolifera, in different regions were screened and determined, providing a foundation for the development and resource utilization of green tide Enteromorpha prolifera food.

This study used HSSPME to extract volatile flavor compounds from floating green tide seaweed in 8 different urban areas of the Yellow Sea. GC-MS analysis showed that the main flavor components and contents of floating seaweed in these 8 areas were not completely the same. Alcoholic compounds generally have a soft odor and a plant fragrance, which has a beneficial effect on the overall odor of green algae. The Rudong region has a relatively rich variety of green tide algae alcohol substances; Among them, 1-penten-3-ol and heptanol both have aromatic odors, and the octadecanol content in Sheyang green tide algae is relatively high, which has a fragrance and makes a significant contribution to the odor of green tide algae. For other regions, especially in the late stage of green tide drift near the coast of Shandong, the content and types of alcohol substances are significantly decreasing.
Among all the volatile components detected in Rudong, Dafeng, and Rushan green tide algae, olefins are the most abundant, mainly 8-heptacene, limonene, styrene, etc; Among them, green tide algae in the Rudong and Dafeng regions contain a high content of 8-heptacene, while green tide algae in Rizhao, Qingdao, and Haiyang were not detected. 8-heptacene is a characteristic flavor substance shared by large seaweeds and has been detected in sauerkraut, seaweed, and red seaweed; And 8-heptacene is a type of chemical sensing substance generated by enzymatic reactions. As a bioinformatics element that plays a certain role in callus formation, 1-dodecene is present in Sheyang, Lianyungang, and Rushan green tide algae, which has a strong pungent odor and has an adverse effect on the flavor of green tide algae.
Ketone compounds generally have a floral and fruity aroma. During the drifting process of green tide algae, the content and types of ketone substances in green tide algae in various regions are gradually decreasing. Except for Rushan green tide algae, β – ionone has been detected: β – ionone has a pine like aroma and a purple Roland like aroma when diluted, and is an important synthetic material for vitamin A, which is conducive to the production of the aromatic flavor of green tide algae; In addition, substances such as tea aroma ketone, aromatic acetone, and dihydro – β – violet ketone all have pleasant floral and fruity aromas, but were not detected in the later stage of floating green tide algae.
Aldehyde compounds are closely related to the formation of various specific aroma styles. There are literature reports that aldehyde compounds have a low threshold and contribute significantly to the flavor of products. The content of saffron aldehyde and cyclic citral is relatively high in the green tide algae of Rudong, which have woody, pungent, and sweet aromas. In living organisms, many aldehydes come from fatty acids, such as hexanal and valeraldehyde, which are oxidative cleavage products of linoleic acid; Fatty aldehydes mostly present a strong fruity flavor with a hint of bread aroma. In the late stage of floating green tide algae, trans-2-heptenal was detected, which has a stimulating odor and has an adverse effect on the flavor of the algae.
Among all the volatile components detected in green tide algae, ester compounds have a high content and rich variety. Generally, ester compounds have a pleasant aroma, and the odor threshold of ester compounds is generally low. It is speculated that ester compounds contribute greatly to the overall odor of green tide algae. The research results indicate that with the northward drift of green tide algae, the overall content of ester substances gradually decreases, such as dihydrokiwilactone and methyl palmitate, which both have fruity and woody aromas. Dihydrokiwilactone also has important application value in the food and cigarette industries, but its content gradually decreases with the drift, and its contribution to the overall flavor is also decreasing.
It is worth noting that a certain amount of Cai was detected in the Rushan sample. These compounds are generally formed by the continuous enrichment of environmental pollutants, which may be the reason for the poor flavor of Rushan green tide algae. In addition, only thiazole and pyrazine substances were detected in Rushan samples. According to relevant literature reports, they are related to the bitterness of Enteromorpha prolifera, which indirectly proves the poor flavor of green tide algae in the later stage of drift.
The type and content of volatile flavor compounds determine the quality of green algae. Combining the content and threshold of compounds in 8 different regions of green tide algae, it can be concluded that green tide algae in different regions not only have unique aroma characteristic components, but also have the same key aroma components, such as benzaldehyde, cyclic citral, limonene, β – ionone, etc. Referring to Li’s research results, the changes in volatile components of seaweed are closely related to aquaculture areas, and due to the strong adsorption capacity of seaweed itself for environmental substances. The changes in volatile components may be related to the changes in background substances in aquaculture areas. Based on the molecular identification results of different regions of green tide algae, when the variety of green tide algae is the same, environmental factors have a significant impact on the volatile flavor compounds of green tide algae. In the future, further research can be conducted on the effects of environmental factors such as temperature, light, seawater quality, and nutrient composition on volatile metabolites.
Green tide algae, as a marine resource with various health benefits, have great production and utilization value and market development prospects. This study used headspace solid-phase microextraction to extract the volatile flavor components of green tide algae and combined them with GC-MS analysis to accurately detect the components of volatile flavor compounds in floating green tide algae in the Yellow Sea. The main aroma components of green tide algae in various regions were preliminarily determined. The results showed that the flavor of green tide algae varies in different regions. During the drifting process of green tide algae, the types and contents of volatile substances gradually decreased from Rudong in Jiangsu to Rushan in Shandong, indicating a decline in overall quality. Compared to others, the quality of South Yellow Sea green tide algae is better and can be used for food product production in practical applications; Due to being in the late stage of floating, the volatile flavor of the North Yellow Sea green tide algae is poor, and it can be salvaged for use as feed, fertilizer, and biomass energy development. This study laid the foundation for in-depth research on the flavor compounds of green tide algae and provided a theoretical basis for the development and utilization of green tide algae in the future.