ffects of cinnamic acid treatment on aroma of Kyoho grape during low temperature storage

【Objective】Kyoho grape (Vitis vinifera × V. labrusca) is highly favored by consumers for its unique flavor, and the quality of aroma is one of the key factors determining its flavor and thus acceptance. During the stage of Kyoho grape berries, the internal aroma components undergo a series of complex changes over time, which are directly related to its economic value and popularity in the market. Cinnamic acid, a phenolic compound widely found in nature, is known for its excellent antibacterial and antioxidant properties and is believed to play an active role in maintaining the stability of grape aroma and enhancing quality. Against the backdrop that food industry continuously pursues natural and safe preservation methods, cinnamic acid, as a green natural preservative, has attracted increasing attention and research for its ability to effectively inhibit the oxidative degradation of lipids, thereby enhancing the quality and nutritional value of food. This study focused on the specific impact of cinnamic acid treatment on the changes in aroma of Kyoho berries during storage and systematically evaluated its potential application value as a natural preservative in the post-harvest treatment of grapes, with the aim of providing a scientific basis and theoretical support for extending the shelf life of Kyoho grape and ensuring the stability of its aroma quality.【Methods】This experiment selected Kyoho grape as the research subject. At 10 days before the expected harvest date, cinnamic acid solutions with concentrations of 0, 1, 5, and 10 mmol·L-1 were evenly and meticulously sprayed on the surface of the grape clusters. The group treated with 0 mmol·L-1 was set as the control group (CK). The entire spraying process followed strict operational standards to ensure uniformity and consistency till drip. After the grape berries reached harvest ripeness, samples were quickly transported to the laboratory of the College of Horticulture and Forestry, Tianjin Agricultural University, within 48 hours through a cold chain logistics system. All grape samples were stored in a 4 ℃ refrigerator. At 0, 7, and 14 of storage, the advanced headspace solid- phase microextraction technology combined with gas chromatography- mass spectrometry (HSSPME/GC-MS) was used to detect and analyze the volatile compounds released by the berries. On this basis, a variety of analytical methods, including variance analysis, correlation analysis, aroma profiling, and entropy weight TOPSIS evaluation method, were comprehensively applied to systematically organize and deeply mine the experimental data, thereby selecting the cinnamic acid treatment concentration that achieves the best preservation effect.【Results】A total of 32 compounds were identified, 13 of which had an odor activity value (OAV) of 1 or higher. There were 13 aroma-active compounds which were significantly affected by the treatments, including 5 esters, 2 aldehydes, 2 aromatics, 2 terpenes, 1 alcohol, and 1 ketone. Specifically, ethyl butyrate and methyl butyrate were higher at the early stages of storage (days 0 and 7), especially under the treatment with 10 mmol·L-1 cinnamic acid, where their content was significantly higher than in the other treatments. In contrast, hexanal and trans-2-hexenal were at their lowest levels on day 0, and the 10 mmol·L-1 cinnamic acid treatment caused significantly reduction in their contents. Benzaldehyde showed significant differences among the treatments after 7 days of storage, with the treatment at 5 mmol·L-1 being the highest while the 10 mmol·L-1 treatment the lowest. Analysis of the contents of different types of aroma compounds in Kyoho grape berries during storage found that on day 0, the content of ester and alcohol compounds varied significantly under different treatments. The content of ester compounds was the lowest at 5 mmol · L- 1 treatment and significantly higher in 10 mmol·L-1 treatment than in the control. For alcohol compounds, their content in treatments at 5 mmol·L-1 was significantly higher than the control and lowest at 10 mmol·L-1 treatment. By day 7, the content of ester, alcohol, and aromatic compounds all had changed significantly, with ester compounds dominating in the 10 mmol · L- 1 treatment. On day 14, only the content of alcohol compounds still showed significant differences, with the highest content in the 5 mmol·L-1 treatment group. Correlation analysis between different types of aroma compounds and cinnamic acid treatment during storage revealed that cinnamic acid treatment had a significant impact on the aroma compounds in the berries, especially promoting ester and terpene compounds, while showing a negative correlation with aldehyde and alcohol compounds. However, this impact tended to gradually weaken over time. Aroma profiling results clearly show that throughout the storage process, fruity notes always dominated, followed by floral, fatty, herbal, and chemical notes. Cinnamic acid treatments effectively enhanced the richness of fruity notes at each storage stage, significantly improved the aroma quality of the fruit. Finally, the comprehensive evaluation results based on the entropy weight TOPSIS method showed that the 10 mmol·L-1 cinnamic acid treatment performed the best in enhancing aroma quality, followed by the 1 mmol · L- 1 and 5 mmol · L- 1 treatments.【Conclusion】In summary, cinnamic acid, as a potential natural preservative, can effectively improve the storability of Kyoho grape by significantly increasing the contents of ester and terpene compounds in the fruit, thereby enhanced the fruity, floral, and fatty notes and thus comprehensive aroma quality. This study provides a new method for post-harvest preservation and quality enhancement in Kyoho grape, which has a broad application prospect and a high practical value.