Some characteristics of polyphenol oxidase purified from edible yam (Dioscorea cayenensis-rotundata cv. Longbô) cultivated in Côte d'Ivoire

Polyphenol oxidase (PPO_Y) of edible yam ( Dioscorea cayenensis-rotundata cv. Longbô ) cultivated in Côte d'Ivoire was purified to homogeneity by a procedure that included ion exchange chromatography, ammonium sulphate fractionation, gel filtration and hydrophobic chromatography using dopamine as a substrate. The relative molecular weight of the PPO_Y was estimated to be 94.75 ± 0.63 and 151.56 ± 2.75 kDa by SDS–PAGE and gel filtration on Sephacryl S100 HR, respectively, indicating this PPO_Y as a multimer. Maximal PPO_Y activity occurred at 30 °C and pH 6.6. The enzyme was stable at 25 °C and its pH stability was in the range of 6.0–7.0. The values V _max/ K _m showed that the enzyme had the greatest reactivity towards dopamine among the substrates used. PPO_Y showed no activity toward the monophenols and was completely inhibited by beta-mercaptoethanol, sodium thiosulphate, l -ascorbic acid, sodium bisulphite and l -cysteine. Data generated by this study might help to better prevent edible yam browning.     

Optimising the free radical scavenging activity of shrimp protein hydrolysate produced with alcalase using response surface methodology

Response surface methodology (RSM) was used to optimise the hydrolysis parameters of Acetes chinensis by Alcalase 2.4L in order to obtain a hydrolysate with potent radical scavenging activity. The parameters were temperature, pH and enzyme concentration/substrate concentration (E/S) ratio with degree of hydrolysis (DH) being the response. The results showed that the optimum condition was: temperature at 57 °C, pH at 8.0, E/S ratio at 2.6AU 100 g⁻¹ shrimp, hydrolysis time 3 h. The DH was 26.32%, the hydroxyl radical scavenging activity was up to 88.12% and the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was 35.61%. The gel column filtration chromatography by a Sephadex G-25 column yielded five fractions. The molecular weight of the most potent free radical scavenging activity fraction ranged from 915 to 207 Da, its IC₅₀ for hydroxyl radical was 0.03 mg mL⁻¹, and IC₅₀ for DPPH radical was 8.86 mg mL⁻¹.     

Extracellular protease from Mucor pusillus: purification and characterization

Extracellular protease from Mucor pusillus was purified 18-fold with 7.56% recovery by ion-exchange chromatography and gel filtration. The enzyme was found to be monomeric in nature, having a molecular mass of 49 kDa. The enzyme acted optimally at 50°C and was stable in the temperature range 30–50°C. It was completely inactivated by heating for 30 min at 65°C. The optimum of activity for the purified extract was observed at milk CaCl₂ concentration of 0.02  m and at milk pH of 5. These properties, except for temperature, were similar to those of rennet.     

Partial purification and characterisation of banana [Musa (AAA Group) 'Gros Michel'] polyphenol oxidase

Polyphenol oxidase (PPO) from pulp of banana [Musa (AAA Group) 'Gros Michel'] was extracted and precipitated with 80% saturated ammonium sulphate followed by conventional column chromatography on Sephacryl S-200 HR and fast protein liquid chromatography on Mono Q column. The lyophilised PPO obtained from Sephacryl S-200 HR column was used for characterisation and inhibition studies. The partially purified PPO obtained from the Mono Q column exhibited at least three isoenzymes. The banana PPO had optimum pH for activity at 7 and it was stable around the same pH. Only 48% of initial enzyme activity was lost after heating at 70 °C for 30 min. The enzyme was completely inhibited by 2 m m sodium metabisulphite, 2 m m l -cysteine, 4 m m ascorbic acid, and 100 m m 4-hexylresorcinol. The K _m and V _max of banana PPO for dopamine were 2.08 m m and 0.124 m m  min⁻¹ respectively.     

EFFECT OF LOW-MOLECULAR ADDITIVES ON PRECIPITATION OF POTATO FRUIT JUICE PROTEINS UNDER DIFFERENT TEMPERATURE REGIMES

The effects of two mineral and two organic acids, four organic solvents (methanol, ethanol, 2-propano and acetone) and three inorganic metal salts in combination with temperature regimes 0 and 22C on the yield and resolubility of potato tuber proteins were studied. Using acids, the yield of precipitated protein ranged from 22.3% (citric acid, 0C) to 54.5% (acetic acid, 22C) of total protein; however, the resolubility was generally very low. The precipitation with organic solvents resulted in significantly higher yield as well as resolubility ( P   <  0.05) when precipitated at low temperatures. The yield ranged from 23.4% (ethanol, 22C) to 64.5% (2-propanol, 0C) of total protein. The use of the salts resulted in precipitates with high resolubility regardless of the temperature regimes. The yield of precipitated protein ranged from 25.8% (ZnCl₂, 0C) to 86.4% (FeCl₃, 0C) of total protein.

PRACTICAL APPLICATIONS

The work studied the possibility of isolation of native potato proteins from potato fruit juice (PFJ) resulting from starch manufacturing process. Ethanol and FeCl₃ were evaluated as the most promising precipitators for the recovery of potato tuber proteins from PFJ. However, ethanol usage for industrial isolation of potato proteins is strongly limited by the temperature regime in contrast to FeCl₃, which could be used in a much wider range of temperature regimes without significant difference in protein yield and resolubility.     

PARTIAL PURIFICATION AND CHARACTERIZATION OF α-GALACTOSIDASE FROM ASPERGILLUS ORYZAE

A crude extract of α-galactosidase obtained by fermenting Aspergillus oryzae on wheat bran was purified 35 fold by ethanol precipitation, gel filtration and ion-exchange chromatography. The final preparation was free of protease activity but contained invertase activity. The molecular weight of the enzyme was estimated as 64,000 daltons. The pH and temperature optima were 4.0 and 60°C, respectively. The enzyme was stable over the pH range 3–7.5 and at temperatures up to 55°C (pH 4.0). The K_m values for p-nitrophenyl α-Dgalactopyranoside (PNPG) and raffinose were 4.0 × 10⁻⁴M and 1 × 10⁻²M, respectively. Divalent cations were not required for activity. More than 80% of the oligosaccharides in soy milk were hydrolyzed after 3 h at 50°C using 0.113 PNPG units/mL milk.     

Natural preservative ingredient from marine alga Ulva lactuca L.

The contents of total chlorophyll (T-Chl), carotenoids and phenolics compounds were quantified in the biomasses of Ulva lactuca grown either in normal or artificial sea water under indoor conditions. The antioxidant and antibacterial activities of U. lactuca crude organic extracts ( Ulva- COEs) were determined. Thirty-four compounds in Ulva- COEs were characterised by thin layer chromatography and high-performance liquid chromatography. The major compounds were chlorophyll a (Chl a ) (15.60–30.90%) and b (Chl b ) (12.20–14.89%) , 9-cis β-carotene (13.12–14.47%), α-carotene (11.44–11.47%) and all-trans β-carotene (6.16–29.70%, of total carotenoids).The Ulva- COEs exhibited remarkable antioxidant activity, with an IC₅₀ (concentration which causes a 50% of DPPH radical scavenging activity) values ranged from 16.5 and 18.7 μg mL⁻¹, which could be compared with the synthetic antioxidants: α-tocopherol (14.4 μg mL⁻¹), butylated hydroxyanisol (13.1 μg mL⁻¹) and butylated hydroxyltoluene (13.1 μg mL⁻¹). Also, Ulva- COEs exhibited great potential antibacterial activities against six bacterial strains, with minimal inhibitory concentration values ranged from 0.40 to 0.35 mg mL⁻¹.     

PURIFICATION AND CHARACTERIZATION OF POLYPHENOL OXIDASE FROM POTATO: I. PURIFICATION AND PROPERTIES

Polyphenol oxidase (Isozyme I) from potato was extracted and purified with ammonium sulfate, cation-exchange (Bio-Rad Bio-Scale S2) and Sephadex G-100 column chromatography. The enzyme was purified 11.8 fold resulting in a specific activity of 250.3 units/mg. Optimum pH of the enzyme was 6.6. Optimum temperature of the enzyme was 40C and its half-life was 0.8 min at 70C. The K_mfor catechol, pyrogallol, 4-methyl catechol, caffeic acid and L-DOPA were 4.11 mM, 0.61 mM, 0.78 mM, 0.50 mM and 32 mM, respectively. However, monophenols such as tyrosine, p-cresol and 1-naphtol did not show any activity. Data for V_max/K_m which represents catalytic efficiency show that 4-methyl catechol has the highest value. The molecular weight of the active enzyme was 86,000 Da, composed of two identical subunits. The number of Cu²⁺ ions bound was found to be 2 per enzyme molecule.     

Production, purification and thermal characterisation of invertase from a newly isolated Fusarium sp. under solid-state fermentation

Production of invertase employing a newly isolated Fusarium sp. under solid-state fermentation was optimised. Different process parameters were optimised. The maximum enzyme activity under optimum conditions was 47.23 ± 2.12 U gds⁻¹ with nitrogen additives. The enzyme was purified by ammonium sulphate precipitation, diethylaminoethyl cellulose ion-exchange chromatography and Sephadex gel filtration. This protocol gave 20.25-fold purification and 5.53% recovery. The optimum pH and temperature for activity were 5.0 and 50 °C. The K _m and V _max values for the enzyme were 8.33 m m and 21.48 μmol min⁻¹, respectively. A detailed kinetic study of thermal inactivation has been carried out. Enthalpy of activation (Δ H *) decreased when entropy (Δ S *) of activation increased at higher temperatures. Moreover, free energy of denaturation (Δ G *) increased at higher temperature making the enzyme thermally stable. A possible explanation for the thermal inactivation of invertase at higher temperatures is also discussed.     

Water desorption isotherms of two varieties of sweet potato

Water desorption isotherms were determined for New Zealand sweet potato at 25, 40 and 55°C, and for Philippines sweet potato at 28°C. The isotherms were sigmoid in shape and of type II according to the BET classification. The data were fitted to eight two-parameter equations reported in the literature. The effect of water activity, a_w, and temperature, T °C, on the equilibrium moisture content, M _e g water/100g dry solids, was best described for New Zealand sweet potato by: Me = 20.51 T-^0.204 (a_w/(1-a_w)0.39 for a_w= 0.06–0.81     

EFFECT OF DIFFERENT STORAGE CONDITIONS ON THE LIPID FRACTION OF A VEGETABLE CREAM

Fatty acids (free and esterified), diglycerides, peroxides and total sterols were determined in a vegetable cream. Cream samples were analyzed when fresh and after storage for 3 and 6 months at 4, 15, 30C and room temperature (10–25C). The product showed a higher amount of unsaturated fatty acids ( ≈ 50% of total fatty acids) with respect to milk fat and a low level of cholesterol ( < 0.01%). The phytosterol content ( ≈ 14 mg/100 g of cream) was not high enough to contribute to a decrease in cholesterolemia. Lipid oxidation remained low during storage (peroxides: 2.0–3.0 meq O₂/kg of fat), but a small increase was observed at room temperature after 6 months (about 6.0 meq O₂/kg of fat). Free fatty acids never exceeded 0.3% of fat. Storage at 4C and 15C delayed lipolysis in comparison to storage at 30C and room temperature.

PRACTICAL APPLICATIONS

The analysis of a vegetable cream demonstrated that it was a shelf-stable product, showing a high stability toward lipid oxidation and lipolysis. Such a product might be employed as vehicle for healthy fat compounds like long-chain polyunsaturated fatty acids, phytosterols and fat-soluble vitamins.     

Texture of rehydrated dried bell peppers modified by low-temperature blanching and calcium addition

Diced green bell pepper was blanched twice, once at 51–79 °C for 19–61 min, and once at 95 °C for 3 min, and dried. The firmness of rehydrated samples was measured by puncture, and optimum conditions assessed by response surface methodology. The optimized model showed that, blanching at 65 °C for 49 min gave a 64% increase in puncture force over the control. The optimum temperature was used to evaluate the effect of adding CaCl₂. The dices were blanched twice, once at 65 °C for 3 min in either 0 or 4% CaCl₂, secondly in either 0 or 2% CaCl₂ solution at 95 °C for 3 min. In the second case the dices had been held at room temperature for 0–30 min before treatment. Adding CaCl₂ increased puncture force significantly ( P  ≤ 0.05). The best results, those which gave greatest firmness, were obtained by blanching at 65 °C for 3 min in 4% CaCl₂, holding for 16 min after blanching, followed by a secondary blanching at 95 °C in 2% CaCl₂.     

CHARACTERIZATION OF DYE-SENSITIZED PHOTOOXIDATION OF MUSHROOM TYROSINASE

Dye-sensitized photooxidation was investigated as a nonthermal means to inactivate food quality-related enzymes, using mushroom tyrosinase as a model. Illumination of tyrosinase in the presence of either rose bengal or riboflavin resulted in an apparent first-order destruction of enzyme activity. Both dye and light were required, and photoinactivation was favored by increasing levels of dissolved oxygen. The rose bengal-sensitized photooxidation was generally more rapid than that caused by riboflavin (at 0.01% dye), with k_i values ranging from 0.74 to 1.66 h⁻¹ and 0.25 to 1.23 h⁻¹, respectively. First-order rate constants for photoinactivation decreased with decreasing temperatures (E_a was 8.4 to 12.2 kcal mol⁻¹ between 20° and 50°C), increasing protein concentration (0.175 to 1.40 mg⁻¹ ml), increasing sodium phosphate buffer concentration (10 to 200 m M) and increasing ionic strength (0.02 to 0.20). The dependence of enzyme photoinactivation rates on pH (between 6.0 and 9.0) resembled a titration curve with a pK of 7.5, and maximal rates were observed at pH 8.0–9.0.     

The Flavonoid Eriodictyol as Substrate of Peach Polyphenol Oxidase

ABSTRACT: Spectral changes produced in the oxidation of eriodictyol by peach polyphenol oxidase were followed over time. A product with λ_max= 390 nm was seen to appear before another with λ_max= 475. The product absorbing at 390 nm must correspond to the o -quinone derived from eriodictyol. The compound absorbing at 475 nm must be derived from this eriodictyol-o-quinone. Progress curves at this wavelength revealed a lag, the length of which varied with enzyme and substrate concentrations. This lag must have been caused by chemical reactions taking place after the enzymatic reaction. When eriodictyol oxidation was studied in the presence of 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH), a potent nucleophilic reagent that reacts with the eriodictyol-o-quinone to form a dark pink product absorbing at 508 nm, the lag disappeared. When the kinetic parameter was evaluated in the presence of MBTH (K_m= 0.6 m M ), the results was similar to those obtained without MBTH. Eriodictyol oxidation was inhibited by tropolone, which behaved as a classic competitive inhibitor (K_I= 15 μ M ). The inhibition results reported show that eriodictyol oxidation was strictly dependent on the presence of polyphenol oxidase. In addition, other oxidase activities, such as laccase and H₂O₂ independent phenol oxidase, were not detected in the enzyme extract.     

Mathematical modelling of O2 consumption and CO2 production rates of whole mushrooms accounting for the effect of temperature and gas composition

Investigation of respiration rate of fresh produce, under different gas composition and temperatures, and respective mathematical modelling is central for the modified atmosphere packaging design. This work investigates the effect of temperature (4, 8, 12, 16, 20 °C) and gas composition (O₂ between 3 to 21% and CO₂ between 0 to 15%) on respiration rate of whole mushrooms. Oxygen and carbon dioxide respiration rates increased significantly (3–4 fold) as the temperature elevated from 4 to 20 °C and were in the range of 13.23 ± 3.12 to 102.41 ± 2.132 mL kg⁻¹ h⁻¹) and 14.33 ± 1.56 to 97.02 ± 2.51 mL kg⁻¹ h⁻¹) respectively. Low O₂ and high CO₂ levels reduced O₂ consumption and CO₂ production rates of whole mushrooms on average by a circa 47–60% at all temperatures as compared to the respiration rate at ambient air. Mathematical models were developed for RO₂ and RCO₂, by combining the Arrhenius and Michaelis–Menten uncompetitive equations. These models predicted well, O₂ consumption and CO₂ production rates of whole mushrooms as a function of both temperature and gas composition.     

Some effects of modified-atmosphere packaging and vacuum packaging in combination with antioxidants on quality and storage life of chilled potato strips

A modified-atmosphere packaging system for chilled fresh potato strips, which rapidly produced oxygen levels < 3%, was identified. This system enclosed the strips within 25 μ low density polyethylene film heat sealed to a fibre tray lined with Surlyn-PVdC-Surlyn, and the package flushed with an initial atmosphere of 5% O₂, 10% CO₂. An equilibrium-modified atmosphere of 3–4% CO₂, 1–2% O₂ was established after 3 days' storage at 5°C. This modified-atmosphere package, used in combination with dipping of potato strips in a 10% ascorbic acid solution, inhibited enzymatic discoloration for 1 week at 5°C. Vacuum packaging within a Surlyn/PVdC-coated polyester film, with or without dipping in ascorbic acid solution, inhibited discoloration of chilled potato strips stored at 5°C for at least 2 weeks.     

Optimisation of the medium composition for production of protease and soybean peptides by Bacillus subtilis SHZ using response surface methodology

Responses surface methodology was employed to enhance the production of protease and soybean peptides by Bacillus subtilis SHZ. For screening of medium composition significantly influencing protease and soybean peptides yield, the two-level Plackett–Burman design was used. Among thirteen variables tested; KH₂PO₄, glucose and defatted soybean flour (DSF) were selected based on their high significant effect on both protease activity and soybean peptides yield. Then, a three-level Box–Behnken design was employed to optimise the medium composition for the production of the protease and soybean peptides in submerged fermentation. Mathematical models were then developed to show the effect of each medium composition and their interactions on the production of protease and soybean peptides. The model estimated that, the maximal protease activity (320 ± 1 U mL⁻¹) could be obtained when the concentrations of glucose, KH₂PO₄, DSF were set at 8–9 g L⁻¹, 2–3 g L⁻¹, 55–65 g L⁻¹, respectively; while a maximal yield of soybean peptides (8.5 ± 0.1 g L⁻¹) could be achieved when the concentrations of glucose, KH₂PO₄, DSF were set at 7–9 g L⁻¹, 3–4 g L⁻¹ and 55–58 g L⁻¹, respectively. These predicted values were also verified by validation experiments.     

Aflatoxin levels in dried figs, nuts and paprika for export from Turkey

Three hundred and thirteen of 2643 dried fig, two of eighty hazelnut, sixteen of twenty-eight pistachio, five of ten peanut and nineteen of twenty-three paprika samples for export from Turkey were contaminated with total aflatoxins in the range of 0.2–162.76, 5.46–6.55, 2.31–63.11, 0.75–26.36 and 1.79–6.55 μg kg⁻¹, respectively. Samples were collected from January to August 2007 and tested for aflatoxins (B₁, B₂, G₁ and G₂) by immunoaffinity column extraction using RP-HPLC. Fifty-six of the 313 dried fig, all of the contaminated hazelnut and pistachio, two of the sixteen peanut and three of the nineteen paprika samples exceeded the regulatory limits of the European Union. The ratio of the different types of aflatoxin present in each sample exhibited great variability. For example, of 313 contaminated fig samples, 159 contained only aflatoxin B₁, eighty-five contained B₁ (49.7%) + G₁ (50.3%), twenty-two contained only G₁, twenty contained B₁ (89.4%) + B₂ (10.6%), thirteen contained B₁ (73.7%) + B₂ (10.8%) + G₁ (15.5%) and fourteen contained all four types, B₁ (26%) + B₂ (2.5%) + G₁ (66.5%) + G₂ (5%).     

Influence of Steeping Solution and Storage Temperature on the Color Change of Garlic

ABSTRACT:  The objective of this study was to investigate the browning of garlic under different steeping conditions and storage temperatures. The brown indices of steeped garlics showed lowest values (7.3 and 7) in 25% and 50% EtOH at 7 d of storage. The degree of browning of steeped garlics was lowest (10.2 in 25% EtOH and 10.4 in 50% EtOH) in the samples soaked for 8 h at 13 d of storage. As the storage temperature was increased from 10 to 40 °C, the brown indices of garlics revealed an increasing trend relative to storage time regardless of steeping treatment. Overall, the kinetic parameters showed relatively low  R ² and irregular reaction constants, but the  k_o  values showed an increasing trend with temperature under a zero-order model. The highest polyphenol content within the garlic bulbs was seen in controls (without steeping treatment, 588.9 μg/g), than 0% EtOH (water, 392.5 μg/g), than 25% EtOH (211.3 μg/g), and finally 50% EtOH (155.6 μg/g). The polyphenol oxidase activity of garlic showed a similar trend to that of polyphenol content. However, the texture properties of garlics steeped with 25% and 50% did not change.
Practical Application: The garlic color preferred by consumers is a creamy-white, but this is susceptible to enzymatic browning when pre-peeled and chopped. When garlic was steeped in the 25% and 50% alcohol, the browning of garlic was prevented during storage.