Analysis of volatiles during grape deterioration using FTIR

Abstract

Grape is very perishable in transportation and storage, so its early warning is particularly important to lower the risks of large-scale deterioration. In order to study grape deterioration process, we analyzed the volatile compounds from grapes using Fourier transform infrared (FTIR) spectroscopy. Several grapes were put in the sample compartment of the FTIR spectrometer for 2 h per day. Then, the volatile compounds vaporized from the grapes were measured directly using the spectrometer. A high energy ceramic IR-source was used to improve the signal-to-noise ratio. We collected the FTIR spectrum before sample was put in as a background to eliminate the influence of air. Spectral signatures of the volatiles from grapes were analyzed and used to classify the grape samples into deterioration or not. By spectral analysis, the volatile mainly includes ethyl acetate, ethanol and carbon dioxide. The above three volatile vaporized more and more from the grapes during deterioration process. We also found that the release rates of volatile compounds get its highest value when the grapes just started deteriorating, so, this value could be used to monitor the beginning of deterioration. The methods to classify grapes deterioration levels were also studied. Firstly, grape deterioration processes were divided into three stages, fresh, slight deterioration and severe deterioration, by appearance and sensory evaluation. Then, a principle compounds analysis (PCA) was used for unsupervised classification to FTIR spectra. Results showed that this method could distinguish grapes into fresh and deterioration by choosing proper data pre-processing algorithms. This paper provides a new way to study the fruit deterioration mechanism, and premise a foundation for developing early-warning equipment for evaluation and monitoring fruit deterioration during its storage and transportation. Furthermore, because of the step change of release rates of volatile compounds at the beginning of deterioration, this kind of classifying method and monitoring system may not influenced by grapes quantity and store patterns. © 2013 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.