# Evaluation of Table Grape Flavor Based on Deep Neural Networks
## 4 Experiments and Performance Evaluation  
### Data Collection  
#### 4.1.1 Flavor Data Collection  
We selected fresh grapes marketed from June to August 2021, including 15 varieties such as Kyooho, Summer Black, and Shine Muscat, mainly from the provinces of Jiangsu and Zhejiang in China, for a total of 126 batches of samples. After the reaping of grapes, smooth and full fruits were screened out. Jucies were extracted and filtered as samples, and the physical and chemical indicators of the grape pulp were tested according to the methods shown in Table 1.  
We selected five commonly used physicochemical indicators that affect grape flavor and are generalizable to the grape varieties analyzed in the experiments. We present each of these five indicators and explain their influence on grape flavor as follows. Soluble solids are the total amount of sugars and other water-soluble substances in the grapes, and their contents reflect the sweetness and ripeness of the grapes. The higher the soluble solids are, the sweeter the taste is. However, too many soluble solids can also make the grapes cloyingly sweet or sticky. Titratable acid is the total amount of acids in grape juices, usually composed of malic, citric, and other organic acids. It is an essential indicator of the acidity of grape juices \begin{table}
\begin{tabular}{c c} \hline \hline
**Indicator** & **Method** \\ \hline Total soluble solids (TSS) & Brix meter \\ Titratable acid (TA) & Acid-base titration \\ Solid/acid ratio & Calculation \\ Total phenols (TP) & Folin–Cicolteu \\ Volatile substances (VS) & HS-SPME \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Indicators and detection methods. and greatly impacts the flavor and quality of the grapes. Grapes with high titratable acid contents exhibit strong acidity, while grapes with low titratable acid contents exhibit a blander taste. The solid/acid ratio is the ratio of the total acid to soluble solids in grape juices. It is a key indicator of the acidity and sugar content of grapes and reflects the ripeness and flavor of the grapes. Generally, grapes with a low solid/acid ratio have a softer taste and relatively low acidity, while grapes with a high solid/acid ratio have higher acidity and a stronger taste. Total phenols are a mixture of natural compounds present in the skins and seeds of grapes. They include compounds such as tannins, anthocyanins, and flavonoids. Total phenols can increase the bitterness and dryness of grapes. At the same time, total phenols can also enhance the fruitiness and herbaceousness of the grapes, which may give them a more complex and deep flavor. Volatile substances volatilize easily at room temperature and include esters, alcohols, aldehydes, aromatic compounds, etc. In grapes, volatile substances are mainly found in the skin and flesh, and they are one of the primary sources of the aroma and taste of wine. The relationship between the physicochemical indicators of grapes is very complex, and these indicators interact with each other. Therefore, judging the flavor of grapes solely from the content of a single indicator is insufficient. An accurate assessment of the flavor and quality of grapes requires a combination of factors and the contents of multiple indicators. The range of data for each physicochemical index for grape flavor determined experimentally is provided in Table 2.  
This table provides data ranges, means, and standard deviations for five physical and chemical indicators to determine the flavor profile of grapes. These measurements are important in assessing the quality and flavor characteristics of the samples and therefore can be used for model training to ensure the good generalization performance of the model in predicting the sensory quality of different grape varieties. Since these metrics reflect the chemical composition and flavor characteristics of grapes, they are considered the input features of the model to predict the sensory scores of grape flavors.