The effect of pH, phenolic substrates, and food additives on polyphenoloxidase (PPO) activity and on tissue browning was studied in fresh-cut 'Rocha' pear. Substrates 4-methylcatechol, caffeic acid, (+)catechin hydrate, catechol, chlorogenic acid, dopamine hydrochloride, and pyrogallol, were prepared in citric acid-phosphate buffer at pHs ranging from 3.0 to 8.0. pH optima for PPO activity depended on the phenolic substrate. Activity was optimal at pH 5.0 for catechol and 4-methylcatechol; pH 6.0 for chlorogenic acid; pH 7.0 for dopamine, caffeic acid, and catechin; and pH 8.0 for pyrogallol. Discrepancies were observed between the pH dependency of PPO activity and browning, as assessed by objective color measurement. Significant correlations were obtained between enzyme activity and metric-hue difference (H*) over the pH range 3.0-8.0 for four of the eight phenolics. Chlorogenic acid, the main PPO substrate in 'Rocha' pear, induced high tissue browning but very low PPO activity at pH 3.0-4.0. Chemical inhibition of PPO was tested using catechol as substrate, and buffer solutions containing 250 mM Ca 2+ in four salts (ascorbate, chloride, lactate and propionate), 57 mM ascorbic acid, 61 mM N-acetyl-l-cysteine and 3 mM 4-hexylresorcinol. PPO inhibition by additives was affected by the pH of the buffer, and was more effective with ascorbic acid, N-acetyl-l-cysteine and calcium ascorbate. It was concluded that inferences on tissue browning based on PPO activity can be misleading. Measurement of tissue color is proposed as a reliable means to assess the antibrowning effectiveness of additives and the pH of additives for cut pear should be corrected to reduce the browning potential.

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Fresh figs are very appreciated and have been associated with health benefits. However, these fruits are highly perishable. In this study, edible coatings were studied envisaging their positive effect in enhancing figs’ shelf-life. Fig fruits cv. ‘Pingo de mel’ were harvested at commercial ripening stage and single emulsion-based coatings, composed of chitosan + olive oil and alginate + olive oil, were applied. After coatings application by dipping each fruit in the emulsion-based solutions at 4 °C and drying, the coated fruits were sprayed with crosslinking solutions (6% tripolyphosphate and 1% calcium chloride for chitosan and alginate-based coatings, respectively). Then, were maintained at 4 °C and analyzed after 1, 7, 14 and 19 days of storage. After each time interval, fruits were further maintained at 25 °C for 2 days. The results have shown that coatings were effective on delaying fungal decay and postharvest ripening indicators (respiration rate, mass loss, softening and total soluble solids/titratable acidity ratio). The results foresee a fruits’ shelf life between 14 and 19 days under refrigeration at 4 °C that may be followed up to 2 days at ambient temperature, higher than that estimated for uncoated fruits (less than 14 days at 4 °C plus to 2 days at ambient temperature).

We study the Shannon entropy of the cluster size distribution in classical as well as explosive percolation, in order to estimate the uncertainty in the sizes of randomly chosen clusters. At the critical point the cluster size distribution is a power-law, i.e. there are clusters of all sizes, so one expects the information entropy to attain a maximum. As expected, our results show that the entropy attains a maximum at this point for classical percolation. Surprisingly, for explosive percolation the maximum entropy does not match the critical point. Moreover, we show that it is possible determine the critical point without using the conventional order parameter, just analysing the entropy's derivatives.