Partial purification and characterization of polyphenol oxidase from persimmon

Purification and comparison of soluble and membrane-bound polyphenol oxidase from potato (Solanum tuberosum) tubers

Enzymatic browning greatly affects the quality of potato products. Polyphenol oxidase (PPO) is the enzyme mainly responsible for potato enzymatic browning. PPO has soluble polyphenol oxidase (sPPO) and membrane-bound polyphenol oxidase (mPPO) forms. In this study, the properties of sPPO and mPPO were investigated in potato tubers. The molecular weight of potato sPPO and mPPO were estimated to be 69 kDa in the form of homodimers in vivo. The mass spectrometry results showed that the purified sPPO and mPPO protein in potato tubers was mainly tr|M1BMR6 (Uniprot). The optimum pH for sPPO and mPPO was 6.5, and the optimum temperatures were 20 and 30 °C, respectively. The Michaelis constant (K_m) and maximum unit enzyme activity (V_max) of sPPO were 6.08 mM and 2161 U/S when catechol was used as the substrate, whereas those of mPPO were 2.95 mM and 2129.53 U/S, respectively. The mPPO had stronger affinity to the substrate catechol than sPPO, whereas pyrogallic acid was stronger affinity for sPPO. Ascorbic acid and sodium sulfite were inhibitors of sPPO and mPPO, respectively. After understanding the different binding states of polyphenol oxidase, different inhibitors and treatment methods can be used to treat the enzyme according to different enzymatic properties, so as to achieve a greater degree of Browning control. These results will provide a theoretical basis for regulating PPO activity to reduce enzymatic browning during potato processing.

The roles of soluble poly and insoluble tannin in the enzymatic browning during storage of dried persimmon

The roles of total soluble polyphenols (TSP) and insoluble tannins (IST) in the enzymatic browning during the storage of dried persimmon slices packaged by different methods was studied. The color evolution was comprehensively evaluated within 18 weeks of storage, as well as determination the content variation of TSP, IST, and carotenoids. A series of simulated reactions were conducted to investigate the involvement of TSP and IST in PPO-catalyzed reaction. The results showed that N₂-opaque packaging was a good way to alleviate this browning issue. The IST contributed preponderantly to the browning during the whole storage, while the contribution of TSP was little. And the degradation of carotenoids might be related to the color deterioration in the early storage. The IST participated in PPO-catalyzed reaction directly with the insoluble state. By contrast, only a small amount of TSP participated in PPO-catalyzed browning reaction, since it preferentially interacted with IST.

Health Benefits of Plant-Derived Sulfur Compounds, Glucosinolates, and Organosulfur Compounds

The broad spectrum of the mechanism of action of immune-boosting natural compounds as well as the complex nature of the food matrices make researching the health benefits of various food products a complicated task. Moreover, many routes are involved in the action of most natural compounds that lead to the inhibition of chronic inflammation, which results in a decrease in the ability to remove a pathogen asymptomatically and is connected to various pathological events, such as cancer. A number of cancers have been associated with inflammatory processes. The current review strives to answer the question of whether plant-derived sulfur compounds could be beneficial in cancer prevention and therapy. This review focuses on the two main sources of natural sulfur compounds: alliaceous and cruciferous vegetables. Through the presentation of scientific data which deal with the study of the chosen compounds in cancer (cell lines, animal models, and human studies), the discussion of food processing’s influence on immune-boosting food content is presented. Additionally, it is demonstrated that there is still a need to precisely demonstrate the bioavailability of sulfur-containing compounds from various types of functional food, since the inappropriate preparation of vegetables can significantly reduce the content of beneficial sulfur compounds. Additionally, there is an urgent need to carry out more epidemiological studies to reveal the benefits of several natural compounds in cancer prevention and therapy.

Antimicrobial mechanism of reaction products of Morus notabilis (mulberry) polyphenol oxidases and chlorogenic acid

Herein, five polyphenol oxidases (PPOs) obtained from Morus notabilis (Mn) were characterized. Chlorogenic acid was the most readily oxidized substrate by these MnPPOs, and the products derived from the oxidation of chlorogenic acid by MnPPOs were tested for antimicrobial activity. The results showed that products of the five MnPPOs exhibited good inhibitory effects against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Sclerotinia sclerotiorum, and Botrytis cinerea. Because the products of MnPPO1 exhibited the strongest antimicrobial activity, the antimicrobial mechanism of these products was explored. The results showed that the products of MnPPO1 increased cell membrane permeability and chitinase and β-1,3-glucanase activities.

Biochemical Properties of Polyphenol Oxidases from Ready-to-Eat Lentil (Lens culinaris Medik.) Sprouts and Factors Affecting Their Activities: A Search for Potent Tools Limiting Enzymatic Browning

Enzymatic browning of sprouts during storage is a serious problem negatively influencing their consumer quality. Identifying and understanding the mechanism of inhibition of polyphenol oxidases (PPOs) in lentil sprouts may offer inexpensive alternatives to prevent browning. This study focused on the biochemical characteristics of PPOs from stored lentil sprouts, providing data that may be directly implemented in improving the consumer quality of sprouts. The purification resulted in approximately 25-fold enrichment of two PPO isoenzymes (PPO I and PPO II). The optimum pH for total PPOs, as well as for PPO I and PPO II isoenzymes, was 4.5–5.5, 4.5–5.0, and 5.5, respectively. The optimal temperature for PPOs was 35 °C. Total PPOs and the PPO I and PPO II isoenzymes had the greatest affinity for catechol (K_m = 1.32, 1.76, and 0.94 mM, respectively). Ascorbic acid was the most effective in the inhibition of dark color formation by total PPOs, and showed ca. 62%, 43%, and 24% inhibition at 20-, 2-, and 0.2-mM concentrations. Ascorbic acid, l-cysteine, and sodium metabisulfite (20 mM) significantly inhibited color development in the reactions catalyzed by both isoenzymes of PPO. Ba²⁺, Fe³⁺, and Mn²⁺ (10 mM) completely inhibited PPO activity. This study of the effect of antibrowning compounds and cations on PPO activity provides data that can be used to protect lentil sprouts against enzymatic browning during storage and processing.

Efficacy of Pyrus elaeagnifolia subsp. elaeagnifolia in acetic acid–induced colitis model

In Turkish folk medicine, the fruits of Pyrus elaeagnifolia subsp. elaeagnifolia have been used to treat diarrhea and detoxify poisonous snake bites by enlarging the wound. The aim of the study was to confirm the ethnopharmacological usage of the plant using in vivo and in vitro models. Experimental colitis was performed under anesthesia by intrarectal administration of acetic acid in rats, and the extracts were administered orally. The colonic malondialdehyde (MDA), tumor necrosis factor (TNF-α), interleukin-6 (IL-6), and nitrite levels, in addition to the myeloperoxidase (MPO) and caspase-3 activities, were measured to determine the effects of the plant extracts. The methanol (MeOH) extract revealed a significant decrease in MPO and caspase-3 levels. The MeOH extract was found to have the highest total tannin content. It was also found to have significant antioxidant (p ˂ 0.01) and anti-inflammatory activities (p ˂ 0.05) in acetic acid induced colitis rat model . According to our results, the present study exhibited a decrease in MDA, nitrite, IL-6, and TNF-α levels in the colon tissue and blood in the MeOH extract treated group. The findings of this study can help in treating various disorders, such as Clostridium difficile infection, irritable bowel syndrome, and inflammatory bowel diseases.

Catalytic and Structural Characterization of a Browning-Related Protein in Oriental Sweet Melon (Cucumis Melo var. Makuwa Makino)

Polyphenol oxidase (PPO) in plants plays an important role in browning reactions and may affect the quality of sweet melon products. In this study, a browning-related protein (BRP) with PPO activity was partially purified from oriental sweet melon (Cucumis melo var. makuwa Makino) by salt precipitation and column chromatography. The BRP possessed a high degree of identity with several chitinase proteins, particularly defense-related proteins, by MS identification. Pyrogallol was determined as the most appropriate substrate for BRP (K_m = 0.04278 M). BRP exhibited extreme resistance under alkaline and high temperature conditions when pyrogallol was used as substrate. Polyacrylamide gel electrophoresis (PAGE) analysis indicated that BRP was a homo-dimer of two subunits and had a molecular weight of 37 kDa. Structural analysis indicated that the α-helix was the dominant conformation of BRP. The active site of the protein might be buried deeply in the protein, and BRP might be monodispersed in an aqueous system.

Effect of ultrasonic processing on the changes in activity, aggregation and the secondary and tertiary structure of polyphenol oxidase in oriental sweet melon (Cucumis melo var. makuwa Makino)

BACKGROUND

Polyphenol oxidase (PPO) mainly contributes to the browning reaction of fruits and vegetables and causes serious damage to the quality of sweet melon products. However, traditional methods to inactivate browning may induce more unexpected risks than ultrasonic processing. Meanwhile, there are no reports on the effect of ultrasound on PPO directly purified from sweet melon.

RESULTS

The PPO in the original juice was less inactivated than the purified form when treated with ultrasound. As for purified PPO, superior to thermal treatment, less heat was needed to inactivate the PPO with ultrasonic treatment. At intensity lower than 200 W, ultrasound did not significantly affect the structure and activity of PPO (P > 0.05), and latent PPO was activated. At intensity higher than 200 W, ultrasound inactivated PPO, induced aggregation and dissociation of PPO particles and significantly decreased the α-helix structure content.

CONCLUSION

Low-frequency high-intensity ultrasound caused an inactivation effect and conformational changes of purified PPO from oriental sweet melons. Changes in the PPO structure induced by ultrasound eventually inactivated the enzyme. Ultrasound may be a potential method to inactivate PPO in oriental sweet melons. © 2016 Society of Chemical Industry.

Chemistry and Functionality of Bioactive Compounds Present in Persimmon

Extensive research has related the consumption of persimmon with the reduced risk of various diseases and particularly highlighted the presence of bioactive phenolic compounds for their therapeutic properties. Major phenolic compounds present in persimmon are ferulic acid,p-coumaric acid, and gallic acid.β-Cryptoxanthin, lycopene,β-carotene, zeaxanthin, and lutein are important carotenoids having antioxidant potential. They are important to prevent oxidation of low-density lipoproteins, safeguard beta cells of the pancreas, and reduce cardiovascular diseases, cancer, diabetes mellitus, and damage caused by chronic alcohol consumption. In this paper, the chemistry and health benefits of bioactive compounds present in persimmon are reviewed to encourage impending applications and to facilitate further research activities.