Modeling of Respiration Rate of Litchi Fruit under Aerobic Conditions

Respiration of the produce and permeation of gas through the packaging films are the processes involved in creating a modified atmosphere inside a package that will extend shelf life of agricultural perishables. Thus modeling respiration rate of the selected produce is crucial to the design of a successful modified atmosphere packaging system. Two different models based on regression analysis and enzyme kinetics were developed with the help of respiration data generated at temperatures 0, 5, 10, 15, 20, 25, and 30 °C for litchi fruit using the closed system method. Temperature was found to influence the model parameters. In the model, based on enzyme kinetics, the dependence of respiration rate on O₂ and CO₂ was found to follow the uncompetitive inhibition. The enzyme kinetic model parameters, calculated from the respiration rate at different O₂ and CO₂ concentration were used to fit the Arrhenius equation against different storage temperature. The regression coefficients values were used for the prediction of respiration rate using regression model. The activation energy and respiration pre-exponential factor were used to predict the model parameters of enzyme kinetics at any storage temperature. The developed models were tested for its validity at 2 °C. The models showed good agreement with the experimentally estimated respiration rate.     

Mode of inhibition of finger millet malt amylases by the millet phenolics

The effect of millet polyphenols on starch hydrolysis catalyzed by amylases developed during malting were investigated. The enzyme kinetic studies using Michaelis–Menten and Lineweaver–Burk equations showed the K_m remained constant (0.625%) but the maximum velocity (V_max) decreased in the presence of a crude extract of millet polyphenols, indicating mixed non-competitive inhibition. On the other hand, gallic acid, vanillic acid, quercetin and trans-cinnamic acid isolated from the polyphenol extract of the millet showed uncompetitive inhibition. Kinetic studies of amylase inhibition by phenolic compounds indicated the presence of secondary binding sites in malted finger millet amylases similar to other cereal amylases.     

Modeling the effect of storage temperature on the respiration rate and texture of fresh cut pineapple

The effect of temperature on the respiration rate and texture of fresh cut pineapple was studied over the course of 10 days of storage. The thermal exchange between the pineapple trays and the cooling environment was simulated using the finite element method and tested at 6 °C. The temperatures on pineapple wedges differed between the cold point and points near the surface, indicating that the respiration rate may be affected in pineapple subjected to temperature abuse. The experimental respiration rates obtained were used to develop a model relating respiration to O₂ and CO₂ concentrations at different temperatures using the closed system method. The O₂ consumption and CO₂ production of pineapple wedges was accurately modeled using Michaelis–Menten kinetics. The texture degradation of pineapple wedges follows a zero-order kinetic reaction at different temperatures and the thermal dependence of the model’s parameters for both respiration rate and texture degradation was described by Arrhenius-type equations.     

Peroxidase-like activity of aminopropyltriethoxysilane-modified iron oxide magnetic nanoparticles and its application to clenbuterol detection

A magnetic nanoparticle-linked immunosorbent assay for clenbuterol (CL) was developed using aminopropyltriethoxysilane (APTES)-modified Fe₃O₄ magnetic nanoparticles (MNPs) as a replacement for horseradish peroxidase (HRP) in conventional ELISA configurations. The catalytic activity of the as-synthesized APTES-MNPs is, like HRP, dependent on pH, temperature, and H₂O₂ concentration. The optimal reaction conditions for APTES-MNPs require a pH of 4 and a temperature of 40 °C. However, APTES-MNPs need a higher H₂O₂ concentration than HRP to reach maximal activity. Catalysis follows Michaelis–Menten kinetics. The calculated kinetic parameters exhibit a strong affinity to substrates and high catalytic activity. Comparative studies for CL demonstrate that the IC₅₀ values of CL for APTES-MNPs are 34% lower than that for HRP. The differences in limit of detection and cross-reactivity are not significant between APTES-MNPs and HRP. The proposed approach confirms that the APTES-modified Fe₃O₄ MNPs not only possess peroxidase activity but also show potential application in a variety of simple, robust, and cost-effective ELISAs in the future.     

Modelling the effect of superatmospheric oxygen concentrations on in vitro mushroom PPO activity

The kinetics of polyphenol oxidase (PPO, EC 1.14.18.1) with respect to oxygen concentrations from 5 to 100% using chlorogenic acid (CGA) as substrate was examined. In vitro mushroom PPO activity was determined by measuring the consumption of oxygen during the oxidation reaction. A differential Michaelis–Menten model was fitted to the obtained total depletion curves. The product concentration as well as the concentration of oxygen had a clear inhibitory effect on the reaction rate. However, the inhibitory effect of oxygen was more evident at low product concentration. A linear mixed inhibition model that considered both the product (oxidised CGA) and oxygen as inhibitors was developed. A model with the product as a competitive inhibitor and oxygen as an uncompetitive inhibitor was the most appropriate to explain the reaction kinetics. The values of the inhibition constants calculated from the model were 0.0032 mmol L⁻¹ for K_m (Michaelis–Menten constant related to oxygen), 0.023 mmol L⁻¹ for K_mc (constant for competitive inhibition due to the product), 1.630 mmol L⁻¹ for K_mu (constant for uncompetitive inhibition due to oxygen) and 1.77 × 10⁻⁴ mmol L⁻¹ s⁻¹ for V_max (maximum reaction rate). The results indicate that superatmospheric oxygen concentrations could be effective in preventing enzymatic browning by PPO. Copyright © 2006 Society of Chemical Industry     

Measurement and Modeling of Respiration Rate of Guava (CV. Baruipur) for Modified Atmosphere Packaging

Several experiments were conducted at different storage temperatures for generating respiration data using close system method for respiration. A respiration rate model, based on enzyme kinetics and the Arrhenius equation was proposed for predicting the respiration rates of Guava as a function of O₂ and CO₂ concentrations and storage temperature. Temperature was found to influence the model parameters. In this model, the dependence of respiration rate on O₂ and CO₂ was found to follow the uncompetitive inhibition. The enzyme kinetic model parameters, calculated from the respiration rate at different O₂ and CO₂ concentration were used to fit the Arrhenius equation against different storage temperature. The activation energy and respiration pre-exponential factor were used to predict the model parameters of enzyme kinetics at any storage temperature between 0–30°C. The developed models were tested for its validity at 12°C and it was found to be in good agreement (the mean relative deviation moduli between the predicted and experimental respiration rates were found to be 8.95% and 8.02% for O₂ consumption and CO₂ evolution, respectively) with the experimentally estimated respiration rates.     

Model for Fresh Produce Respiration in Modified Atmospheres Based on Principles of Enzyme Kinetics

A respiration model, based on enzyme kinetics, was proposed for predicting respiration rates of fresh produce as a function of O₂ and CO₂ concentrations. In this model, the dependence of respiration on O₂ was assumed to follow a Michaelis-Menten type equation (r = V_m[O₂]/{K_m+ [O₂]}), and the effect of CO₂ on respiration to follow an uncompetitive inhibition model (r = V_m[O₂]/{Km + (1 + [CO₂]/ Ki) [O₂]}). The model predictions agreed well with published data for a variety of commodities and with experimental data for cut broccoli. Fresh produce respiration rates (O₂ consumption or CO₂ evolution) at various O₂ and CO₂ concentrations, as well as transient and equilibrium gas concentrations within permeable packages, could be accurately predicted with the model equations.     

Development and comparison of multivariate respiration models for fresh papaya (Carica papaya L.) based on regression method and artificial neural network

Respiration modelling is the fundamental of the packaging and storage of fresh fruit and vegetables. Previous model of respiration rate accounted for external forcing from temperature and modified atmosphere but did not attempt to predict internally generated natural variability such as maturity. We present two types of respiration models here that predict the respiration rate of fresh papaya in response to changes of temperature, CO₂/O₂ concentrations and maturity as well. These two models were separately developed using a quadratic polynomial with four parameters and fifteen coefficients and using an artificial neural network (ANN) model with 4-15-2 architecture trained by Levenberg–Marquardt algorithm, in which the maturity of papaya covers skin yellowing from 10 to 90% and the temperatures vary over 10–30 °C. Comparison between the two types of respiration models shows a predictive superiority of the ANN-based model over the regressive one, demonstrating that the use of ANN technique can provide a reliable and effective approach to describe papaya’s respiration rate as a function of multivariate influencing factors.     

Modeling Respiration Rate of Strawberry (cv. San Andreas) for Modified Atmosphere Packaging Design

A model for strawberry (Fragaria × ananassa cv. San Andreas) respiration rate was determined as a function of O₂ and CO₂ concentrations and temperature. Strawberries were enclosed in containers under different gaseous compositions (0–24% O₂ and 0–15% CO₂) and temperatures (10, 19, 23°C). Respiration rate was determined as O₂ consumption and CO₂ production. Respiration rate data was fitted to Michaelis-Menten models, with temperature dependence according to Arrhenius type equation. Non–linear regression was applied to calculate model parameters. No CO₂ inhibition was verified, so a simple Michaelis–Menten model was selected (R² = 0.91).     

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.     

Ethylene production,respiration and gas exchange modelling in modified atmosphere packaging for banana fruits

A mathematical model was developed from experimental measurements to describe the evolution of the O₂, CO₂ and ethylene in a modified atmosphere packaging system for Cavendish bananas. The respiration and ethylene production in the fruits were experimentally obtained from a closed system method and then represented by Michaelis–Menten equations of enzyme kinetics. The gas transfer through the packaging was described by a Fick's diffusion equation, and the temperature dependence was represented based on the Arrhenius law. The model was validated by packaging the fruit in perforated bags of polypropylene and low density polyethylene at 12 °C for a period of 8 days. With the developed model it was possible to satisfactorily describe the experimental evolution of the gas content in the headspace of the packages, obtaining coefficients of determination (R²) of 0.93 for the O₂ levels, 0.90–0.91 for the CO₂ levels, and 0.89–0.93 for the ethylene levels.     

Respiratory parameters of onion bulbs (Allium cepa) during storage. Effects of ionising radiation and temperature

The O₂ and CO₂ respiration rates of untreated and irradiated onion bulbs (Allium cepa) at 0.15 and 0.30 kGy were measured at 4, 10 and 20 °C. The O₂ respiration rate increased for 24 h after treatment from 0.19 mmole kg⁻¹ h⁻¹ at 20 °C for control samples up to 0.26 and 0.39 mmole kg⁻¹ h⁻¹ for 0.15 and 0.3 kGy irradiated onions respectively. Respiratory quotient (RQ) increased with temperature. The Q₁₀ of the respiration of the control samples (1.61) was lower than that of any other plant tissue, but it increased with storage duration and irradiation dose. The respiration rate of control onions increased steadily over 25 weeks of storage at 4 °C, while that of the irradiated samples decreased during the same period after a peak observed after irradiation treatment. The apparent K_m for the Menten–Michaelis equation was determined on a new respirometer and averaged 1.6 kPa at 10 °C and 6.3 kPa at 20 °C. However, at this higher temperature (20 °C) apparent K_m varied with O₂ partial pressure, proving that the respiration of onion bulbs does not follow a Menten–Michaelis‐like process. The Fermentative Index (FI) of onions was measured under anoxic conditions as CO₂ production rates in mmole kg⁻¹ h⁻¹ at 4, 10 and 20 °C. © 2000 Society of Chemical Industry     

Respiration Rate of a Dry Coleslaw Mix Affected by Storage Temperature and Respiratory Gas Concentrations

The respiration rate of dry coleslaw mix at different concentrations of O₂ and CO₂ was determined in an open flow-through respirometer at 5°C. Product O₂ consumption rate fitted an enzyme kinetics model. V_m and K_m values of 22.72 mlkg^-1h^-1 and 1.083 %O₂, respectively were calculated. CO₂ had an inhibitory effect on respiration rate. The effect of CO₂ on respiration gave a good fit with an uncompetitive inhibition enzyme kinetics model (E = 5.11%). Product respiration rate increased with temperature by an Arrhenius type relationship. Activation energies for O₂ consumption and CO₂ evolution were 74.8 kJ/kg and 84.2 kJ/kg respectively. These results provide information essential for the design and optimization of modified atmosphere packs for this product.     

Modeling of Enzymatic Hydrolysis of Whey Proteins

The aim of this work was to emphasize the limitations of modeling complex phenomena under unrealistic model assumptions. As a case study, the whey protein hydrolysis mechanism was modeled. A stirred batch reactor was used to study the degree of hydrolysis of sweet whey protein concentrate by using the protease alcalase. A completely random two-factorial experimental design was used, three levels of initial enzyme concentrations (E ₀) (1.58, 3.18, 6.36 AU (Anson units)/L) times three levels of initial substrate concentrations (S ₀) (18.73, 38.45, 81.16 g/L). All treatments were carried out at optimal alcalase—activity conditions: pH 8 and 50 °C. Reactions were monitored for 180 min. The degree of hydrolysis (h) curves was finally adjusted for each treatment to the exponential model using nonlinear regression techniques but not assuming a Michaelis–Menten relationship. From the estimation process, the coefficient b was constant (27.26 ± 1.37) and independent of E ₀ and S ₀, while coefficient a depended directly on the ratio E ₀/S ₀, ranging from 0.0017 to 0.0497. A noncritical strategy of forward modeling based on unrealistic assumptions was misleading in the face of complex phenomena; instead, a modeling strategy moving from data to the identification and estimation of parameters of practical interest must be considered.     

Properties of thermostable extracellular FOS-producing fructofuranosidase from <Emphasis Type="Italic">Cryptococcus</Emphasis> sp.

The present work was devoted to investigations concerning the fructooligosaccharide producing activity of Cryptococcus sp. LEB-V2 (Laboratory of Bioprocess Engineering, Unicamp, Brazil) and its extracellular fructofuranosidase. After cell separation, the enzyme was purified by ethanol precipitation and anion exchange chromatography. The enzyme showed both fructofuranosidase (FA) and fructosyl transferase (FTA) activity. With sucrose as substrate, the data failed to fit the Michaelis–Menten behaviour, showing a substrate inhibitory model. The K _m, K _i and v _max values were shown to be 64 mM, 3 M and 159.6 μmol mL⁻¹ min⁻¹ for FA and 131 mM, 1.6 M and 377.8 μmol mL⁻¹ min⁻¹ for FTA, respectively. The optimum pH and temperature were found to be around 4.0 and 65 °C, while the best stability was achieved at pH 4.5 and temperatures below 60 °C, for both the FA and FTA. Despite the strong FA activity, the high transfructosylating activity allowed for good FOS production from sucrose (35% yield).     

Modeling the respiration of Pseudomonas fluorescens on solid-state lettuce-juice agar

When modeling gas atmospheres within equilibrium-modified atmosphere packaging it is vital to cover all influences on the atmosphere inside. It is necessary to take the microbial respiration into account when considering an extensive growth of microorganisms on fresh-cut vegetables during shelf life. Therefore the respiration of Pseudomonas fluorescens (due to its frequent occurrence on vegetables) was determined under solid-state conditions. A lettuce-juice agar was chosen to provide similar conditions for the microorganisms. Incubated agar plates were stored in air-tight glass jars at 7 °C for 8 days. The change in gas composition was measured and the data were examined by fitting them to Michaelis–Menten equations. All glass jars were filled with air initially; some of them additionally contained sodium hydroxide to bind the carbon dioxide. In other jars, 26.3% carbon dioxide was added after 4 days of storage whereas the rest of the glass jars were used without any modification. The data were successfully fitted to the Michaelis–Menten equation for substrate limitation (neglecting the influence of CO₂) for the three different experiments. The fit with the Michaelis–Menten equation for competitive inhibition was only successful for the respiration experiments with carbon dioxide added. The order of magnitude of the maximum respiration rate (r_max = 0.289–0.305 mL/(incubated plate (1.7 × 10⁷ cfu) · h)) shows by comparing it with reported respiration rates for fresh-cut vegetables, that the influence of microbial respiration should not be neglected, particularly at the end of the shelf life, where the amount of microorganisms may increase to 10⁷ cfu/g.     

Modelling respiration rate of soybean seeds (Glycine max (L.)) in hermetic storage

The dynamic of oxygen (O₂) and carbon dioxide (CO₂) concentration was characterized in soybean (Glycine max (L.)) samples hermetically stored in glass jars at 15, 25 and 35 °C and 13, 15 and 17% moisture content (m.c., wet base). Two correlations were used for smoothing gas concentration in time: linear and exponential. Then, the respiration rate at each temperature and m.c. combination was calculated as storage time progressed and oxygen was consumed and two predictive models for respiration were proposed: Model I (temperature and m.c. dependent) and Model II (temperature, m.c. and oxygen dependent). It was observed that respiration rate increased with storage m.c. and temperature. However, respiration rate was not mainly affected by O₂ until a critical concentration limit of about 2% was reached. Respiration rates were from 0.341 to 22.684 mg O₂/(kgDM d) and from 0.130 to 20.272 mg CO₂/(kgDM d) for a range of storage condition of 13–17% m.c. and 15–35 °C temperature. The respiration rate of soybean seeds obtained in this study resulted significantly lower than the rates reported in the literature for other grains at similar temperature and a_w (water activity) storage condition. For hermetic storage simulations in which O₂ concentration is not expected to drop below 2%, the simplest model (Model I) could be used, but if the O₂ concentration of the hermetic system is expected to be depleted, Model I would under estimate the time at which O₂ is consumed, and thus a model with O₂ dependency is recommended instead (Model II).     

Modelling perforated mediated modified atmospheric packaging of capsicum

Perforation of a film would otherwise have a low permeability is an alternative to obtain optimum oxygen and carbon dioxide concentration in modified atmosphere packages. In present study, gas exchange was studied through a macroperforated packet containing capsicum having different number of holes, 1–4, of diameter 0.3 mm at temperatures of 5 and 25 °C. A model combining the Michaelis–Menten kinetics to describe the respiration rate of the product with mass transfer equation to describe the gas transfer across the package provided a good fit to the experimental data. Its applicability was further validated in a dynamic test, subjecting a package to a variable temperature programme simulating conditions in distribution chains. Model showed good agreement between predicted and observed values for both storage conditions with constant temperatures and variable temperature conditions of distribution chain, as mean relative deviation modulus (E) value was <10%.