Kinetic behaviour and stability of Escherichia coli ATCC27257 alkaline phosphatase immobilised in soil humates

Alkaline phosphatase (EC 3.1.3.1) extracted from Escherichia coli ATCC27257 was immobilised by co‐flocculation with soil humates in the presence of Ca²⁺. The effects of time, temperature, pH and concentration of enzyme and support on immobilisation were studied. Between 58 and 92% of the added phosphatase was strongly bound to the humates, depending on the conditions of immobilisation used. Some characteristics of the humate–phosphatase complexes and of the free enzyme were compared. The enzymatic complexes showed values of K_m (2.22 mM ) and activation energy (33.4 kJ mol^?1) similar to those of the free enzyme (2.00 mM and 27.6 kJ mol^?1). The pH/activity profiles revealed no change in terms of shape or optimum pH (10.5) upon immobilisation of alkaline phosphatase. However, the immobilised enzyme showed maximal activity in the range of 80–100 °C, while the free enzyme had its highest activity at 60 °C. The thermal stability of alkaline phosphatase was enhanced by complexation to the soil humates. © 2003 Society of Chemical Industry     

Characterization of Sultaniye grape (Vitis vinifera L. cv. Sultana) polyphenol oxidase

Polyphenol oxidase (PPO) was extracted from Sultaniye grapes grown in Turkey, and its characteristics in terms of pH and temperature optima, thermal inactivation, kinetic parameters and potency of some PPO inhibitors were studied. Optimum pH and temperature for grape PPO were found to be 3.4 and 30 °C, using catechol as substrate. K_m and V_max values were found to be 44.5 ± 5.47 mm and 0.695 ± 0.0353 OD₄₁₀ min^?1, respectively. Four inhibitors were tested in this study and the most potent inhibitor was sodium metabisulphite, followed by ascorbic acid. From the thermal inactivation studies in the range of 65–80 °C, the half‐life values of the enzyme ranged between 2.6 and 49.5 min. Activation energy (E_a) and Z values were calculated to be 208.5 kJ mol^?1 (r² = 0.9544) and 10.95 °C (r² = 0.9517), respectively.     

Low‐temperature wine‐making using yeast immobilized on pear pieces

A biocatalyst was prepared by the immobilization of Saccharomyces cerevisiae AXAZ‐1 yeast cells on pear pieces and tested for grape must fermentation in both batch and continuous conditions. The immobilized yeast cells were stable and active even at low temperatures (<10 °C). Wine production under batch fermentation at 8 °C was completed within 15 days while at 3 °C it took 36 days. In continuous fermentation, the bioreactor was operated for 33 days, then stored for 12 days at 10 °C, and re‐run for another 15 days without any diminution of the ethanol productivity. Total acidity of the produced wines remained within the ranges usually observed in dry wines, while volatile acidity was found in rather increased levels. The concentrations of higher alcohols (1‐propanol, isobutyl alcohol and amyl alcohols) were relatively low, while ethyl acetate was detected at up to 118 mg l^?1, contributing to the fruity aroma of the wines produced. Preliminary sensory evaluations carried out in the laboratory indicated the fine quality of the produced wines. Copyright © 2004 Society of Chemical Industry     

Kinetics of ascorbic acid degradation and colour change in ground cashew apples treated at high temperatures (100–180 °C)

Ascorbic acid (AA) degradation and colour changes, measured by the lightness index (L*), were determined in cashew apples (at low dissolved O₂ concentrations) heated at high temperature (100–180 °C) in a hermetically sealed cell. A nonisothermal method was developed to estimate thermal degradation kinetics. The results showed that reaction kinetics during heat treatments were well represented by first‐order reactions. The temperature dependence of the kinetic constants was described by an Arrhenius type equation. The activation energy (E_a) for AA degradation and lightness index were 94 ± 3 and 98 ± 3 kJ mol^?1, respectively. The reaction rate constant at 140 °C for AA degradation (64 × 10^?5 ± 3 × 10^?5 s^?1) was twice that for the lightness index change (33 × 10^?5 ± 2 × 10^?5 s^?1). Results allow generating temperature profiles of heat processes that would help preserve the AA of cashew apples as well as control the colour formation during high‐temperature processes.     

Dehydration kinetics of red pepper (Capsicum annuum L var Jaranda)

Shredded and whole red pepper samples were dehydrated in a laboratory drier with a through‐flow air velocity of 0.5 m s^?1 at 50, 55, 60 and 70 °C. Shredded peppers dried faster than whole peppers. The drying behaviour of whole samples was characterised by a constant‐ and a falling‐rate drying period, whilst that of shredded samples was characterised by a falling‐rate drying period only. The mass transfer coefficient for whole samples during the constant‐rate period was computed experimentally. The effect of temperature on the mass transfer coefficient was described by the Arrhenius model. The activation energy was 58 kJ mol^?1. In the falling‐rate period the mass transfer was described by a diffusional model, and the effective diffusion coefficient at each temperature was determined. Diffusion coefficients were estimated to lie between 4.38 × 10^?11 and 10.99 × 10^?11 m² s^?1 for whole peppers and between 37.23 × 10^?11 and 99.61 × 10^?11 m² s^?1 for shredded peppers. The effect of temperature on the effective diffusion coefficient was described by the Arrhenius equation, with an activation energy of 44 kJ mol^?1 for whole peppers and 56 kJ mol^?1 for shredded peppers. © 2003 Society of Chemical Industry     

Combination of UV‐C Treatment and Metschnikowia pulcherrimas for Controlling Alternaria Rot in Postharvest Winter Jujube Fruit

The potential of using antagonistic yeast Metschnikowia pulcherrimas alone or in combination with ultraviolet‐C (UV‐C) treatment for controlling Alternaria rot of winter jujube, and its effects on postharvest quality of fruit was investigated. The results showed that spore germination of Alternaria alternata was significantly inhibited by each of the 3 doses (1, 5, and 10 kJ m^?2) in vitro. In vivo, UV‐C treatment (5 kJ m^?2) or antagonist yeast was capable of reducing the percentage of infected wounds and lesion diameter in artificially inoculated jujube fruits, however, in fruit treated with combination of UV‐C treatment and M. pulcherrima, the percentage of infected wounds and lesion diameter was only 16.0% and 0.60 cm, respectively. The decay incidence on winter jujube fruits treated with the combination of UV‐C treatment and M. pulcherrima was 23% after storage at 0 ± 1 °C for 45 d followed by 22 °C for 7 d. None of the treatments impaired quality parameters of jujube fruit. Thus, the combination of UV‐C radiation and M. pulcherrima could be an alternative to synthetic fungicides for controlling postharvest Alternaria rot of winter jujube.     

Kinetic and thermodynamic investigation of mancozeb degradation in tomato homogenate during thermal processing

BACKGROUND: The kinetic and thermodynamic parameters of mancozeb degradation in tomato homogenates under the conditions prevailing in the manufacture of tomato products (at 60–100 °C for 0–60 min) were investigated. A gas chromatography–mass spectrometry method was used to analyse residual mancozeb in tomato homogenate. Ethylenethiourea (ETU), the main toxic degradation product of mancozeb, was measured by high‐performance liquid chromatography (HPLC)–with photodiode array detector (PDA). RESULTS: The degradation of mancozeb and the formation of ETU in tomato homogenates were adequately described as first‐order kinetics. Dependence of the rate constant followed the Arrhenius relationship. Apparent activation energies, temperature coefficients, half time and time to reduce to 90% of the initial value of mancozeb were calculated as kinetic parameters. The thermodynamic parameters of mancozeb were also described as Δg^d = ? 2.440 and 7.074 kJ mol^?1; Δh^d = ? 32.555 and ? 42.767 kJ mol^?1; Δs^d = ? 0.090 and ? 0.150 kJ mol^?1 K^?1; K_e = 0.414 and 9.797 L g^?1 for 333 and 373 K respectively. CONCLUSION: Current findings may shed light on the reduction of mancozeb residue and its toxic degradation product during thermal processing of tomatoes and may also be valuable in awareness and prevention of potential risks from dietary exposure. Copyright © 2011 Society of Chemical Industry     

Carrier‐free,continuous primary beer fermentation

Developing a sustainable continuous fermentation reactor is one of the most ambitious tasks in brewing science, but it could bring great benefits regarding volumetric productivity to modern breweries. Immobilized cell technology is often applied to reach the large densities of yeast needed in a continuous fermentation process. However, the financial cost associated with the use of carriers for yeast immobilization is one of the major drawbacks in the technology. This work suggests that yeast flocculation could address biomass immobilization in a gas‐lift reactor for the continuous primary fermentation of beer. Nearly 25 g dry wt L^?1 of yeast was flocculated in the reactor before interruption of the fermentation. Stable sugar consumption and ethanol production (4.5% alcohol by volume) from an 11°P wort was evidenced. The key esters and higher alcohols measured in the young beer met the standards of a finished primary beer fermentation. Copyright © 2014 The Institute of Brewing & Distilling     

The Effect of Proanthocyanidins on Growth and Alcoholic Fermentation of Wine Yeast under Copper Stress

Proanthocyanidins (PAs) derived from the grape skin, as well as from grape seeds, grape stems, are an important group of polyphenols in wine. The aim of this study was to understand the effect of PAs (0.1, 1.0 g/L) on growth and alcoholic fermentation of 2 strains of Saccharomyces cerevisiae (commercial strain FREDDO and newly selected strain BH8) during copper‐stress fermentation, using a simple model fermentation system. Our results showed that both PAs and Cu²⁺ could pose significant inhibition effects on the growth of yeast cells, CO₂ release, sugar consumption, and ethanol production during the initial phase of the fermentation. Compared to PAs, Cu²⁺ performed more obvious inhibition on the yeast growth and fermentation. However, adding 1.0 g/L PAs increased in the vitality and metabolism activity of yeast cells at the mid‐exponential phase of fermentation in the mediums with no copper and 0.1 mM Cu²⁺ added, shortened the period of wine fermentation, and decreased the copper residues. It indicated that PAs could improve the ability of wine yeast to resist detrimental effects under copper‐stress fermentation condition, maintaining cells metabolic activity, and fermentation could be controlled by manipulating PAs supplementation.     

Rheological behaviour and colour changes of ginger paste during storage

Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high‐density‐polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20–80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s^?1 in 3 min, followed by a steady shear at 200 s^?1 for 3 min and finally decreasing linearly from 200 to 0 s^?1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel–Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol^?1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers.     

Urea and Heat Unfolding of Cold-Adapted Atlantic Cod(Gadusmorhua)Trypsin and Bovine Trypsin

The reversible unfolding reactions for phenylmethylsulphonyl fluoride (PMSF)-modified trypins from Atlantic cod (cod PMS-trypsin) and cattle (bovine PMS-trypsin) were monitored by fluorescence spectrophotometry as a function of urea concentration and temperature. For urea unfolding at 25°C, the free energy change at zero concentration of urea (ΔG(H₂O)) for cod PMS-trypsin was 11(±4·4) kJ mol⁻¹ compared with 18(±1·14) kJ mol⁻¹ for bovine PMS-trypsin, while the mid-point concentration for urea unfolding curve ([urea]_1/2) was 3·0(±0·57) M and 4·1(±0·16) M, respectively. From studies of enzyme heat unfolding, the mid point temperature of the thermal unfolding curve ( T _m ) was 46(±1·4)°C for cod PMS-trypsin compared with 57(±2)°C for bovine PMS-trypsin. The standard free energy change (Δ G° ) for reversible thermal unfolding of cod PMS-trypsin was 9(±1) kJ mol⁻¹ compared with 19(±1) kJ mol⁻¹ for bovine PMS-trypsin. Values for the enthalpy (Δ H _m ), entropy (Δ S _m ) and heat capacity (Δ C _p ) for heat unfolding are compared. Results from urea and thermal unfolding studies show that cod PMS-trypsin has a significantly lower conformational stability than bovine PMS-trypsin.     

Stability of pigments and oil in pistachio kernels during storage

This work tested the stability of pigments (chlorophyll [chl] a and chlorophyll [chl] b, and lutein] and oil in pistachio kernels stored up to 14 months at three different temperatures: 10, 25 and 37 °C. The samples were hermetically packaged using two films (nylon and ethylene vinyl alcohol) with and without oxygen scavengers. For each temperature, reference samples were packaged in open bags. For both the oil and pigments, no differences were observed during storage, irrespective of packaging or oxygen scavengers. After 14 months, the oil showed very few changes: a slight increase in acidity and peroxide value (PV) irrespective of storage temperature; the spectrophotometric indices K₂₃₂ and K₂₆₈ remained the same. As for pigment stability, the lowest concentrations were observed at 37 °C with a degradation of about 62% for chl a, 44% for chl b and 57.5% for lutein. At 10 and 25 °C, the samples showed slight differences, the pigments degradations were about 46% for chl a, 33% for chl b and 37% for lutein. The degradation rate constants for the three pigments fitted a pseudo‐zero‐order kinetic in which Ea was 11.7 kJ mol^?1, 12.1 kJ mol^?1 and 18.2 kJ mol^?1 for chl a, chl b and lutein respectively.     

Desulphiting dried apricots by exposure to hot air flow

Sulphited dried apricots were exposed to hot air flows at 40, 50 and 60 °C and the removal of SO₂ was investigated as their moisture content fell from an initial value of 193.2 g kg^?1 to a final value of 80–90 g kg^?1. A first‐order kinetic model was found for the removal of SO₂ between 40 and 60 °C. Temperature quotients (Q₁₀) for the removal of SO₂ were 2.84 between 40 and 50 °C and 4.93 between 50 and 60 °C; the activation energy (E_a) was 114.40 kJ mol^?1 between 40 and 60 °C. Analysis of the kinetic data also suggested a first‐order reaction for non‐enzymatic browning, with Q₁₀ values of 2.34 between 40 and 50 °C and 5.36 between 50 and 60 °C and an E_a value of 109.36 kJ mol^?1 between 40 and 60 °C. Exposure of dried apricots to a 60 °C air flow resulted in a rate constant for brown pigment formation that was 12 and 5 times higher than those at 40 and 50 °C respectively. © 2002 Society of Chemical Industry     

Comparison of the performances of different fermentation strategies on cell growth and bacteriocin production by Lactobacillus curvatus CWBI‐B28

The dynamics of cell growth and bacteriocin production by Lactobacillus curvatus CWBI‐B28 in modified De Man/Rogosa/Sharp (mMRS) broth with various concentrations of glucose and complex nitrogen source (CNS; peptone, yeast extract and meat extract) was investigated in flask fermentations and in a laboratory fermentor using batch and fed‐batch cultivations. In fed‐batch fermentation the rate of feeding of the reactor with the substrates was either maintained constant (0.12 L h^?1) or varied exponentially as a function of time. The results showed that both cell growth and bacteriocin activity were influenced by changes in the concentrations of glucose and CNS. Optimal growth and bacteriocin activity were obtained in mMRS broth containing 40 g L^?1 glucose and 40 g L^?1 CNS (mMRS_40/40). A bacteriocin titre of 4266 AU mL^?1 and a cell count of 8.7 log colony‐forming units (cfu) mL^?1 were recorded when this medium was used for cultivation. In batch fermentation using the same medium, a higher cell count (9.5 log cfu mL^?1) and twice as much bacteriocin as in flask fermentation were produced. The highest bacteriocin titre (8533 AU mL^?1) was obtained with fed‐batch fermentation at an exponentially varying rate of feeding. Bacteriocin activity and cell dry mass did not always correlate. Copyright © 2007 Society of Chemical Industry     

Thermo‐physical properties of composite bread dough with maize and cassava flours

Composite wheat–cassava and wheat–maize flours were produced in ratio 100:0. 60:40, 50:50, 40:60 and 0:100 respectively. Thermo‐physical properties of bread dough were determined. For wheat –cassava composite bread dough, moisture content ranged between 44.02 ± 2.04 to 51.31 ± 2.99% dry basis (db), density (1035.2 ± 20.4 to 975.6 ± 12.6 kg m^?3), specific heat capacity (2.51 ± 0.61 to 3.01 ± 0.42 kJ kg^?1 K) and thermal conductivity (0.362 ± 0.13 to 0.473 ± 0.12 W mK^?1). While wheat–maize mixture gave 44.14 ± 1.94 to 45.09 ± 1.26%(db) of moisture content, 981.4 ± 16.3–960.4 ± 22.5 kg m^?3 density, 1.77 ± 0.17–2.61 ± 0.63 kJ kg^?1 K specific heat capacity and 0.36 ± 0.07–0.39 ± 0.02 W mK^?1 thermal conductivity. Effects of substitutions was significant on moisture content and thermal conductivity of dough while non significant influence was recorded on density and specific heat capacity at P < 0.05.     

Short chain xylooligosaccharides: a potential prebiotic used to improve batter fermentation and its effect on the quality attributes of idli,a cereal–legume‐based Indian traditional food

Xylooligosaccharides (XOS), a potential prebiotic exhibits important technological characteristics and interesting nutritional properties. The major fraction in XOS produced enzymatically from corncob was characterised as β‐d ‐xylopyranosyl‐(1,4)‐d ‐xylanopyranose (xylobiose) using ¹³C and 2D‐HSQC NMR. The use of this XOS as a prebiotic in idli, a cereal/legume‐based fermented cake, and its effect on texture, fermentation and sensory characteristics was investigated. Idli batter was fermented with different concentrations of XOS (0, 0.2, 0.4 and 0.6% w/v) for 4–18 h conventionally. The addition of XOS markedly increased lactic acid bacteria number (9.88 ± 0.08 log cfu g^?1) which resulted in rapid reduction in pH (4.61 ± 0.03) and specific gravity after 6 h of fermentation when compared to conventional batter fermentation for 18 h without XOS (9.46 ± 0.06 log cfu g^?1). Instrumental (colour and texture) and sensory evaluation indicated that the optimum conditions were 0.4% XOS and 6 h fermentation. Idlis with XOS had higher moisture content and a softer texture. Addition of XOS benefits both fermentation and idli quality.     

Descriptive analysis of bacterial profile,physicochemical and sensory characteristics of grape juice containing Saccharomyces cerevisiae cell wall‐coated probiotic microcapsules during storage

In this study the feasibility of incorporation of probiotic microcapsules coated with fragmented yeast cell wall in grape juice was evaluated during 60 days at 4 °C. Lactobacillus acidophilus and Bifidobacterium bifidum were encapsulated in alginate microbeads and coated with fragmented Saccharomyces cerevisiae cell wall and calcium alginate and were added into grape juice. At the end of storage, the survival of probiotics was higher than recommended minimum value (10⁷ cfu mL^?1) and the results demonstrated that applying yeast cell wall layer for L. acidophilus microcapsules significantly enhanced its survival while did not affect the survival of B. bifidum (P > 0.05). Generally, probiotic grape juice showed decrease in °Brix, pH and colour and increase in acidity and turbidity during storage and the presence of yeast wall layer had no significant effect on its properties expect colour and turbidity. Overall acceptance of grape juices containing yeast cell wall‐coated microcapsules scored the least.     

Beer metabolomics: molecular details of the brewing process and the differential effects of late and dry hopping on yeast purine metabolism

The flavour of beer is complex, based upon changes at the molecular level in the key raw materials, notably grain, hops and yeast, as well as during the process stages that comprise malting and brewing. As analytical techniques evolve in their sophistication and sensitivity, there are opportunities to delve ever more deeply into the fate of small molecules in brewing. To this end, ¹H nuclear magnetic resonance (NMR) metabolomics was used to follow the progression of 76 metabolites in four different late or dry hopped beers (brewed in triplicate) at five time points throughout the brewing process. The majority of the metabolites identified, including sugars, amino acids and nucleotides, significantly decreased in concentration from the start of the boil to post‐secondary fermentation, whereas energy‐related and fatty acid associated metabolites significantly increased in concentration as wort nutrients were consumed by the yeast. Adenine was significantly higher in the dry hopped brews than in the late hopped brews after both primary (p = 2.1 × 10^?6) and secondary (p = 2.7 × 10^?9) fermentation, while 2′‐deoxyadenosine (after primary, p = 1.1 × 10^?2, after secondary, p = 3.2 × 10^?5) and adenosine (after primary, p = 2.6 × 10^?8; after secondary, p = 3.1 × 10^?7)were significantly lower in the dry hopped beers at these time points. These results give molecular insight into the brewing process and the differential effects of hopping methods on yeast purine metabolism. Copyright © 2016 The Institute of Brewing & Distilling     

Production, purification and characterisation of polysaccharides from Pleurotus ostreatus with antitumour activity

BACKGROUND: Mushroom polysaccharides play an important role in functional foods because they exhibit biological modulator properties such as antitumour, antiviral and antibacterial activities. The present study involved the production, purification and characterisation of intracellular and extracellular free and protein‐bound polysaccharides from Pleurotus ostreatus and the investigation of their growth‐inhibitory effect on human carcinoma cell lines. RESULTS: Several fermentation parameters were obtained: batch polysaccharide productivities of 0.013 ± 8.12 × 10^?5 and 0.037 ± 0.0005 g L^?1 day^?1 for intracellular and extracellular polysaccharides respectively, a maximum biomass concentration of 9.35 ± 0.18 g L^?1, P_max = 0.935 ± 0.018 g L^?1 day^?1, µ_max = 0.218 ± 0.02 day^?1, Y_EP/X = 0.040 ± 0.0015 g g^?1 and Y_IP/X = 0.014 ± 0.0003 g g^?1. Some polysaccharides exhibited superoxide dismutase (SOD)‐like activity of 50‐200 units. Fourier transform infrared analysis of the polysaccharides revealed absorption bands characteristic of such biological macromolecules. Cytotoxicity assays showed that both intracellular and extracellular polysaccharides exhibited antitumour activity towards several tested human carcinoma cell lines in a dose‐dependent manner. CONCLUSION: The polysaccharides of P. ostreatus exhibited high SOD‐like activity, which strongly supports their biological effect on tumour cell lines. The extracellular polysaccharides presented the highest antitumour activity towards the RL95 carcinoma cell line and should be further investigated as an antitumour agent. Copyright © 2012 Society of Chemical Industry     

Inactivation Kinetics of Enzymes by Using Continuous Treatment with Microbubbles of Supercritical Carbon Dioxide

ABSTRACT Enzyme inactivation using a new apparatus for continuous treatment with microbubbles supercritical carbon dioxide (SC-CO₂) was investigated. D value of a-amylase (5.0±1.2 min) subjected to microbubbles of SC-CO₂ treatment (microbubbles-SCT) at 35 °C, 30 MPa was lower than that (227 ± 15.9 min) subjected to heat treatment (HT) at 70 °C. D value of acid protease was reduced by microbubbles-SCT at 50 °C, 30 MPa (15.4 ± 4.1 min), compared to HT at 50 °C (233 ± 15.2 min). The activation energy for the inactivation of acid protease (135 ± 8.3 kJ mol^-1) by microbubbles-SCT was 1 half of that (259 ± 9.0 kJ mol^-1) by HT. These results indicated that continuous treatment with microbubbles of SC-CO₂ was effective for enzyme inactivation.