Effect of pH on specific oxidative enzyme activity (nmol mL^-1s^-1) of enzyme extracts from the larvae of <i>T</i>. <i>molitor</i> (A), <i>A</i>. <i>diaperinus</i> (B) and <i>H</i>. <i>illucens</i> (C).

<p>L-DOPA (red), L-DOPA+H₂O₂ (orange), L-dopamine (light blue), L-tyrosine (green) or ABTS (purple) were used as substrates and buffer (dark blue) as negative control (n = 2, error bars represent absolute deviation).</p

AEC fractionation pattern (black line) at 214 nm for <i>T</i>. <i>molitor</i> (A) and <i>A</i>. <i>diaperinus</i> (B).

<p>The panels also report the increase of absorbance at 520 nm per day for each fraction, when assayed with L-DOPA (red) and L-tyrosine (green) (n = 2), error bars represent absolute deviation).</p

Color formation directly after grinding in MilliQ water and centrifugation of <i>T</i>. <i>molitor</i>, <i>A</i>. <i>diaperinus</i> and <i>H</i>. <i>illucens</i>.

<p>Color formation directly after grinding in MilliQ water and centrifugation of <i>T</i>. <i>molitor</i>, <i>A</i>. <i>diaperinus</i> and <i>H</i>. <i>illucens</i>.</p

Correction: Involvement of phenoloxidase in browning during grinding of <i>Tenebrio molitor</i> larvae

Correction: Involvement of phenoloxidase in browning during grinding of <i>Tenebrio molitor</i> larva

Overview of reactions between different enzymes and substrates which occur (+).

<p>Overview of reactions between different enzymes and substrates which occur (+).</p

Reaction products formed after incubation of pooled fractions T_I-V from <i>T</i>. <i>molitor</i> with substrates L-tyrosine and L-DOPA; + formed, × not found, = substrate constant, − substrates decreases, n/a not applicable.

<p>Reaction products formed after incubation of pooled fractions T_I-V from <i>T</i>. <i>molitor</i> with substrates L-tyrosine and L-DOPA; + formed, × not found, = substrate constant, − substrates decreases, n/a not applicable.</p

Native PAGE stained with 3 mM L-DOPA (left) showed active bands for extract of <i>Tenebrio molitor</i> (T), <i>Alphitobius diaperinus</i> (A) and <i>Hermetia illucens</i> (H).

<p>Two pooled active fractions from the same insects were subjected to PAGE analysis (T_III, T_IV, A_III, A_IV, H_III and H_IV). Numbering on the left highlights the bands excised and further subjected to proteomic analysis. A similar gel was stained with Coomassie (right).</p

Potato and Mushroom Polyphenol Oxidase Activities Are Differently Modulated by Natural Plant Extracts

Enzymatic browning is a major quality issue in fruit and vegetable processing and can be counteracted by different natural inhibitors. Often, model systems containing a single polyphenol oxidase (PPO) are used to screen for new inhibitors. To investigate the impact of the source of PPO on the outcome of such screening, this study compared the effect of 60 plant extracts on the activity of PPO from mushroom (Agaricus bisporus, AbPPO) and PPO from potato (Solanum tuberosum, StPPO). Some plant extracts had different effects on the two PPOs: an extract that inhibited one PPO could be an activator for the other. As an example of this, the mate (Ilex paraguariensis) extract was investigated in more detail. In the presence of mate extract, oxygen consumption by AbPPO was found to be reduced >5-fold compared to a control reaction, whereas that of StPPO was increased >9-fold. RP-UHPLC-MS analysis showed that the mate extract contained a mixture of phenolic compounds and saponins. Upon incubation of mate extract with StPPO, phenolic compounds disappeared completely and saponins remained. Flash chromatography was used to separate saponins and phenolic compounds. It was found that the phenolic fraction was mainly responsible for inhibition of AbPPO and activation of StPPO. Activation of StPPO was probably caused by activation of latent StPPO by chlorogenic acid quinones