## 3 PPO Activity Assessment
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & \multicolumn{3}{c}{**Spectrophotometric Determination**} \\ \cline{3-5}
**Produce** & **Reference** & **PPO Extraction** & **Substrate Solution** & **pH** & **Wavelength (nm)** \\ \hline \multirow{2}{*}{Lettuce} & [15] & PVPP and phosphate buffer & \multirow{2}{*}{Catechol} & \multirow{2}{*}{6.5} & \multirow{2}{*}{400} \\  & & (pH 6.5) & & & \\ \hline \multirow{2}{*}{Lettuce} & [30] & PVPP and phosphate buffer & \multirow{2}{*}{Catechol} & \multirow{2}{*}{7.0} & \multirow{2}{*}{420} \\  & & (pH 7.0) & & & \\ \hline \multirow{2}{*}{Lettuce} & [31] & Acetone, MBTH and citrate & \multirow{2}{*}{DOPAC} & \multirow{2}{*}{7.0} & \multirow{2}{*}{505} \\  & & phosphate buffer (pH 7.5) & & & \\ \hline \multirow{2}{*}{Lettuce} & [32] & Phosphate buffer (pH 7.0) & MBTH & 7.0 & 467 \\ \hline \multirow{2}{*}{Lotus root} & [33] & PVPP and phosphate buffer & \multirow{2}{*}{Catechol} & \multirow{2}{*}{7.0} & \multirow{2}{*}{410} \\  & & (pH 7.0) & & & \\ \hline \multirow{2}{*}{Mushroom} & [34] & PVPP and NaCl (pH 6.5) & & & \\ \hline \multirow{2}{*}{Mushroom} & [35] & PVPP, triton and phosphate & \multirow{2}{*}{Catechol} & \multirow{2}{*}{6.8} & \multirow{2}{*}{420} \\  & & buffer (pH 6.8) & & & \\ \hline \multirow{2}{*}{Potato} & [36] & PVPP and phosphate buffer & \multirow{2}{*}{4-methylcatechol} & \multirow{2}{*}{6.0} & \multirow{2}{*}{410} \\  & & (pH 6.0) & & & \\ \hline \multirow{2}{*}{Potato} & [37] & Phosphate buffer (pH 6.5) & & & \\ \hline \multirow{2}{*}{Potato} & [38] & PBS (pH 6.8) & & & \\ \hline \multirow{2}{*}{Potato} & [39] & PVP, triton and phosphate & \multirow{2}{*}{Catechol} & \multirow{2}{*}{7.0} & \multirow{2}{*}{475} \\  & & buffer (pH 6.8) & & & \\ \hline \multirow{2}{*}{Red beet} & [40] & NaCl, PVP and & \multirow{2}{*}{Pyrocatech} & \multirow{2}{*}{6.5} & \multirow{2}{*}{420} \\  & & phosphate-citrate buffer (pH 6.5) & & & \\ \hline \multirow{2}{*}{Red beet} & [41] & NaCl and phosphate buffer & \multirow{2}{*}{Pyrocatech} & \multirow{2}{*}{7.0} & \multirow{2}{*}{420} \\  & & (pH 6.0) & & & \\ \hline \multirow{2}{*}{Sweet peppers} & [42] & Acetone and citrate phosphate & \multirow{2}{*}{DOPAC} & \multirow{2}{*}{7.0} & \multirow{2}{*}{505} \\  & & buffer (pH 7.5) & & & \\ \hline \multirow{2}{*}{
\begin{tabular}{} \end{tabular} } & DOPAC = 3,4-dihydroxyoxyphenyl acetic acid; EDTA = Ethylenediamineinetetraacetic acid; MBTH = 3-methyl-2-benzothiolone hydrazine; PBS = Phosphate buffered saline; PMSF = Phenylethylsulphonyl fluoride; PVP = Polyvinylpyrrolidone; PVDF = Polyvinyl polypropylene. \\ \end{tabular}
\end{table} 
Table 1: _Cont._ \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Spectrophotometric Determination**} \\ \cline{3-5}
**Produce** & **Reference** & **PPO Extraction** & **Substrate Solution** & **pH** & **Wavelength (nm)** \\ \hline \multirow{2}{*}{Apple} & [19] & PVPP and phosphate buffer (pH 7.0) & Catechol & 5.8 & 420 \\ \hline \multirow{2}{*}{Apple} & [43] & PVPP and phosphate buffer (pH 5.0) & 4-methylcatechol & 5.0 & 494 \\ \hline \multirow{2}{*}{Apple} & [44] & Triton and phosphate buffer (pH 7.2) & Chlorogenic acid & 5.2 & 420 \\ \hline \multirow{2}{*}{Apple} & [45] & PVPP, triton and Phosphate buffer & \multirow{2}{*}{Citrate-phosphate} & \multirow{2}{*}{5.0} & \multirow{2}{*}{420} \\  & & (pH 7.0) & & & \\ \hline \multirow{2}{*}{Apple} & [46] & Potassium phosphate buffer (pH 7.0) & Sodium acetate & 5.5 & 405 \\ \hline \multirow{2}{*}{Banana} & [18] & PVPP, triton and phosphate buffer & \multirow{2}{*}{Catechol} & \multirow{2}{*}{6.5} & \multirow{2}{*}{420} \\  & & (pH 6.5) & & & \\ \hline \multirow{2}{*}{Carambola} & [47] & PVPP, KCl and phosphate buffer (pH & \multirow{2}{*}{Catechol} & \multirow{2}{*}{7.2} & \multirow{2}{*}{410} \\  & & 6.8) & & & \\ \hline \multirow{2}{*}{Carambola} & [48] & PVPP, KCl and phosphate buffer (pH & \multirow{2}{*}{Catechol} & \multirow{2}{*}{7.2} & \multirow{2}{*}{410} \\  & & 6.8) & & & \\ \hline \hline \end{tabular}
\end{table}