Analysis of Thermal Inactivation Kinetics of Membrane-Bound Polyphenol Oxidases and Peroxidases From Metroxylon Sagu

Abstract

Thermal inactivation kinetics for the purified membrane‐bound polyphenol oxidases (mPPOs) and peroxidases (mPODs) isolated from Metroxylon sagu were analyzed. Each isoenzyme was treated at different time–temperature combinations in the range of 0–70 min and 20–70C. Thermal inactivation rates constant (k) at 70C for mPOD‐I (72.9 × 10‐3/min) and mPOD‐II (97.9 × 10‐3/min) were lower than that of mPPO‐I (379.7 × 10‐3/min) and mPPO‐II (138.1 × 10‐3/min). The activation energy for inactivation of mPPO‐I (32.94 kcal/mol) and mPPO‐II (40.34 kcal/mol) was lower compared with mPOD‐I (45.77 kcal/mol) and mPOD‐II (40.62 kcal/mol). The enthalpy values for mPOD‐I (45.08 kcal/mol) and mPOD‐II (39.94 kcal/mol) were higher than those of mPPOs (mPPO‐I, 32.26 kcal/mol; mPPO‐II, 39.66 kcal/mol). This result implies that both mPOD‐I and mPOD‐II are more thermostable. PRACTICAL APPLICATIONS Sago starch has a great potential for application in various food systems. However, its further development and exploitation was hindered by browning‐associated problems due to polyphenol oxidases and peroxidases. In this work, we have investigated the effect of heat treatment on the stability and inactivation kinetics of membrane‐bound polyphenol oxidases and membrane‐bound peroxidases. The results from this work will enable the food industry to develop optimum process parameters with respect to heating time and temperature during processing and production of sago starch to produce high‐quality starch.

Enzymatic Browning of Fresh-cut Galangal (Alpinia siamense K. Schum) and its Relationship to Oxidative Enzymes

“…Histochemical assay for PPO and POD localization study The localization of PPO and POD in the fresh tissue of peeled galangal rhizomes was investigated using a modified histochemical assay described by Milosevic and Slusarenko (1996) and Onsa et al (2007). Rhizome slices of 3 mm thick consisting of exterior tissue about 5-7 mm wide and interior tissue ≥ 10 mm in diameter were excised from the central part of the peeled rhizome with a sharp knife.…”

Karakter Morfologi dan Potensi Produksi Beberapa Aksesi Sagu (Metroxylon spp.) di Kabupaten Sorong Selatan, Papua Barat

“…LPPO pada tanaman tingkat tinggi terletak di plastid dan membran tilakoid. Aktivitas LPPO akan meningkat 50-120 kali ketika enzim tersebut teroksidasi (Onsa et al, 2007). Selain disebabkan oleh LPPO, warna cokelat juga disebabkan oleh aktivitas enzim peroksidase (POD).…”

“…Aktivitas PPO terkonsentrasi pada amiloplas yang pada akhirnya diserap oleh butiranbutiran pati sehingga menyebabkan warna empulur (pati) berubah menjadi kecokelatan. Enzim tersebut disintesis dan ditranslokasikan dari organel seluler (cellular organelles) ke dinding sel selama proses pematangan tanaman sagu (Onsa et al, 2007). Konsumen lebih menyukai pati yang berwarna putih dari pada cokelat.…”