## 4 Conclusions  
Our method using an infrared camera combined with the iodine-turbidimetric method was able to simplify the instrument design and replace the traditional optical instruments used in the VC analytics of fruits and VC tablets. This demonstrated the feasibility of a new method for VC measurements. By adding a VC solution to an iodine ethanol solution to form a suspension with the remaining iodine, the VC concentration was obtained by measuring the turbidity of the suspension with an infrared camera. The designed measuring device and image processing software were able to accurately acquire the corresponding color components of the suspension. The proposed method had high accuracy in standard solution measurements and no significant difference to the spectrophotometry in the VC measurements of the fruits and VC tablet, therefore, the method was proven to be effective.  
Compared to the established VC measuring methods, the proposed method had the advantages of simple design and operation, visualization, as well as easy miniaturization and broadened the application scope of the image detection and turbidimetric methods. However, a disadvantage is that temperature had a great influence on the experimental results, which was found experimentally. This is because temperature can affect the solubility of iodine and, therefore, the reaction between iodine and VC. The method was not implemented on more tissue-dense foods. Therefore, following works should test the feasibility of this method on a wider range of foods and complete the compensation algorithm for different temperatures, which will provide more functionality to the method.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/8/2655/s1](http://www.mdpi.com/2076-3417/10/8/2655/s1)]([http://www.mdpi.com/2076-3417/10/8/2655/s1](http://www.mdpi.com/2076-3417/10/8/2655/s1)).  
Conceptualization, Y.M. and S.L.; Formal analysis, Y.Z.; Funding acquisition, S.L.; Investigation, W.Z. and X.Z.; Methodology, Y.M.; Project administration, S.L.; Resources, Y.M. and C.J.; Software, Y.M.; Supervision, S.L.; Validation, H.M. and H.G.; Visualization, Y.M.; Writing--original draft, Y.M.; Writing--review and editing, H.G. All authors have read and agreed to the published version of the manuscript.  
This work is partially supported by the National Natural Science Foundation of China (no. 61671434) and the Natural Science Fund for Colleges and Universities of Anhui Province (No. KJ2017 ZD32).  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Method**} & **VC Found** & **Relative Standard** & **VC Added** & **VC Found** & \multirow{2}{*}{**Recovery**} & \multirow{2}{*}{**RSD**} \\  & & **(n = 5,** & **Deviation (RSD)** & **(n = 5,** & **after Adding** & **(n = 5,** & **(n = 5,** \\  & **\(\mu\)g/mL)** & **(n = 5,** & **\(\mu\)g/mL)** & **(n = 5,** & **\(\mu\)g/mL)** & **(n = 5,** \\ \hline
1 & L & 1.67 & 3.10 & 1 & 2.64 & 96.80 & 3.81 \\  & grayscale & 1.66 & 6.05 & 1 & 2.69 & 102.42 & 4.60 \\  & log-grayscale & 1.67 & 5.96 & 1 & 2.69 & 102.49 & 4.55 \\ \hline
2 & L & 3.24 & 3.26 & 1 & 4.23 & 99.33 & 4.17 \\  & grayscale & 3.25 & 1.85 & 1 & 4.26 & 101.13 & 3.08 \\  & log-grayscale & 3.24 & 1.83 & 1 & 4.24 & 99.85 & 3.09 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Analytical results of the recovery tests.