Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruit

Abstract

Zhang X., Shao X. (2015): Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruit. Czech J. Food Sci., 33: 109-117.Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a new loquat fruit cultivar (Ninghaibai) and characterised using reliable spectrophotometric methods. In both cases, the optimum pH for PPO was 4.5 and 5 for POD, and their optimum temperatures were 30 and 35°C, respectively. Both enzymes followed Michaelis-Menten kinetics, showing K m = 47.11 mmol/l for PPO with catechol as the substrate and K m = 153.00 mmol/l for POD with guaiacol as the substrate. PPO was much more thermolabile than POD, losing more than 40% of relative activity after 30 min of heating at 40°C. PPO activation energy was much lower than POD activation energy (ΔE # = 39.74 and 94.65 kJ/mol for PPO and POD, respectively): Both enzymes activities showed decreasing patterns as the compound concentration in the assay medium increased. 4-hexylresorcinol (4-HR), oxalic acid, and l-cysteine showed strongly inhibitive effects on the enzymes. Changes in L*, a*, and b* values were chosen to describe the browning of loquat pulp. Only PPO displayed a higher negative correlation with L* values, which indicated that PPO plays an important role in the browning of stored loquat cv. Ninghaibai.

Processing potential of jellies from subtropical loquat cultivars

“…Since color parameter a* significantly varied from 6.71 (Kurisaki) to 11.53 (Fukuhara) (Table 1), the Fukuhara cultivar characterized by having more intense red color when compared to the other cultivars. These results are in agreement with Zhang & Shao (2015) who also found L* values around 68.00 in different loquat cultivars, but the b* values were lower than those found in the present study. As noted for firmness, color may also reflect differences among cultivars and possible differences in the fruit maturation stage.…”

Purification and characterization of peroxidase from zucchini ( Cucurbita pepo L.)

“…POD activity decreased with the temperature increasing from 35°C to 60°C, manifesting that the optimum temperature of zucchini POD was 35°C. The same optimum temperature was detected for PODs from turnip and loquat fruit (Motamed, Ghaemmaghami, & Alemzadeh, ; Zhang & Shao, ). Usually, the POD activity lost severely above 40°C because higher temperature could disrupt structure of POD and lead to the enzyme denature (Gerday et al, ).…”

“…POD from the pearl millet grains exhibited maximum activity at approximate pH 6.6, which was accordance with our results (Goyal & Chugh, ). However, the PODs from Leucaena leucocephala , loquat fruit and Kalipatti sapota exhibited maximum activity at pH 5.0 (Chandrahas et al, ; Pandey & Dwivedi, ; Zhang & Shao, ). In the case of green gram root POD, the optimum pH was 5.5, which was different from our results (Basha et al, ).…”

Assessment of Enzymatic Browning and Evaluation of Antibrowning Methods on Dates

“…Peroxidase Activity. Peroxidase enzyme as it was described earlier contributes besides PPO to the browning reactions through reduction of diphenols [28]. Figure 2 shows the changes in POD enzyme activity over 100 days of storage.…”