Application of e-nose and e-tongue to measure the freshness of cherry tomatoes squeezed for juice consumption

The freshness of fruit is relatively easy to authenticate by its morphological characteristics, while processing fruits into juices makes the freshness difficult to identify. In this paper, cherry tomatoes at different storage temperatures (4 and 25 degrees C) and shelf lives (SLs, 16 days at 4 degrees C and 8 days at 25 degrees C) were squeezed for use in 100% juices. Quality indices (SL, pH, soluble solids content (SSC), vitamin C (VC) concentration and firmness) of these cherry tomatoes were determined through analysing the juices using two sensor systems - an e-nose and an e-tongue. Support vector regression (SVR) was applied to predict the quality indices. The prediction performances based on a one sensor system, as well as a combination of two systems, were compared. The results showed that the e-tongue, which presents a similar prediction performance to the combination system, presents a better prediction performance (with higher squared correlation coefficients (R-2) and a lower standard error of prediction (SEP)) than the e-nose. For tomatoes stored at 4 degrees C, the prediction parameters (R2, SEP) based on the e-tongue data for the SL, pH, SSC, VC concentration and firmness are (0.998, 0.295 d), (0.971, 0.022), (0.906, 0.075 degrees Brix), (0.978, 1.005 mg per 100 g) and (0.906, 0.292 N), respectively. For tomatoes stored at 25 degrees C, the prediction parameters (R2, SEP) based on the e-tongue data for the SL, pH, SSC, VC concentration and firmness are (0.997, 0.193 d), (0.934, 0.017), (0.957, 0.075 degrees Brix), (0.902, 0.897 mg per 100 g) and (0.908, 0.593 N), respectively. These results prove that it is possible to measure the freshness of fruits that are squeezed for juice consumption using sensor systems, and that the combination of sensor systems is not always better than using a one sensor system.