Changes in Volatile Flavor Compounds of Tender Kelp during the Processing of Freeze-dried Soup Cubes

To investigate the effects of key processing techniques—namely boiling, drying, and vacuum freeze-drying—on the volatile flavor compounds of tender kelp during the processing of freeze-dried soup cubes, this study analyzed changes in volatile flavor compounds of tender kelp under various boiling times (0, 1, 2, 3, 4, and 5 min) and drying temperatures (60, 70, 80, 90, and 100 ℃). Furthermore, the study identified key volatile flavor compounds by calculating odor activity values (OAV). The results indicated that the boiling process significantly (P<0.05) reduced both the variety and the relative content of volatile flavor compounds in tender kelp. However, boiling time had no significant effect on the relative contents of aldehydes, acids, esters, and furans. In contrast, the relative content of ketones and 1-octen-3-ol significantly (P<0.05) decreased with increasing boiling time. The variation in the number of key flavor compounds in tender kelp across different boiling times was relatively minor. The OAV value of 1-octen-3-one was the highest among all samples, significantly exceeding that of other compounds, thereby indicating its critical role as the most important volatile flavor compound in boiled tender kelp. Its OAV value was lowest at a boiling time of 3 min. As the drying temperature increased, the number of types of volatile flavor compounds initially rose and then declined, with the 70 ℃ group exhibiting the most diverse range of flavor compounds. However, the content of each compound didn't follow a consistent pattern with variations in drying temperature. The OAV values of β-ionone and 2-undecanone were highest in the 60 ℃ group, while the OAV values of aldehydes and fishy compounds were relatively low, suggesting that 60 ℃ was the optimal drying temperature for tender kelp powder seasoning. The vacuum freeze-drying process didn't significantly (P>0.05) affect the variety, relative content, and composition of key flavor compounds in tender kelp, indicating this method didn't substantially alter the overall flavor. However, the OAV values of various compounds generally decreased, primarily leading to a reduction in flavor intensity. In conclusion, selecting a boiling time of 3 minutes and a drying temperature of 60 ℃ contributed to enhancing the flavor of freeze-dried soup cube products.

为探究沸腾、干燥及真空冷冻干燥等关键加工工艺对冻干汤块制备过程中青嫩海带挥发性风味成分（volatile flavor compounds）的影响，本研究针对不同沸腾时长（0、1、2、3、4、5 min）与干燥温度（60、70、80、90、100 ℃）下青嫩海带的挥发性风味成分变化展开分析。此外，本研究通过计算气味活性值（odor activity values, OAV）筛选出核心挥发性风味成分。研究结果显示，沸腾处理显著（P<0.05）降低了青嫩海带中挥发性风味成分的种类与相对含量。但沸腾时长对醛类、酸类、酯类及呋喃类物质的相对含量无显著影响。与之相反，酮类与1-辛烯-3-醇（1-octen-3-ol）的相对含量随沸腾时长增加显著（P<0.05）下降。不同沸腾时长下青嫩海带核心风味成分的种类变化幅度相对较小。所有样品中，1-辛烯-3-酮（1-octen-3-one）的气味活性值最高，显著高于其余化合物，表明其为沸腾处理后青嫩海带中最关键的挥发性风味成分。其气味活性值在沸腾时长为3 min时达到最低。随着干燥温度升高，挥发性风味成分的种类先上升后下降，其中70 ℃组的风味成分种类最为丰富。但各化合物的含量随干燥温度变化并未呈现统一规律。β-紫罗兰酮（β-ionone）与2-十一烷酮（2-undecanone）的气味活性值在60 ℃组中最高，而醛类及腥味物质的气味活性值相对较低，表明60 ℃为制备青嫩海带粉调味料的最优干燥温度。真空冷冻干燥工艺对青嫩海带核心风味成分的种类、相对含量及组成无显著影响（P>0.05），表明该工艺未对整体风味造成显著改变。但各类化合物的气味活性值整体呈下降趋势，主要导致风味强度降低。综上，选择3 min的沸腾时长与60 ℃的干燥温度，有助于提升冻干汤块产品的风味品质。