Browsing by Author "Caleb, Oluwafemi James"
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- ItemEnzyme kinetics modelling approach to evaluate the impact of high CO2 and super-atmospheric O2 concentrations on respiration rate of pomegranate arils(Taylor & Francis, 2017) Belay, Zinash A.; Caleb, Oluwafemi James; Opara, Umezuruike LinusSuper-atmospheric O2 has been shown to affect respiration rate (RR), but no model describing its effect on RR for pomegranate arils has been reported. This study investigated the effects of four different gas compositions (5 kPa O2, 10 kPa CO2 and 85 kPa N2; 10 kPa O2, 5 kPa CO2 and 85 kPa N2; 70 kPa O2, 10 kPa CO2 and 20 kPa N2; and air) on RR of pomegranate arils (cv. Wonderful) stored at 5°C. Michaelis–Menten enzyme kinetics models were used to investigate the effect of CO2 inhibition on O2 consumption rate. Respiratory quotient was used to determine fermentation threshold. The O2 consumption rate increased from 0.87 to 2.81 mL/kg h, with increase in O2 concentration from 5 kPa to 70 kPa. All enzyme kinetics model parameters adequately described the influence of gas concentration on aril RR with correlation coefficient (R2adj = 81–91%).
- ItemMicrobial community structure as an indicator of soil health in apple orchards(Stellenbosch : University of Stellenbosch, 2010-03) Caleb, Oluwafemi James; Jacobs, Karin; Du Plessis, K.; University of Stellenbosch. Faculty of Science. Dept. of Microbiology.ENGLISH ABSTRACT: The relationship between various land management practices, soil properties and the soil microbial communities are complex and little is known about the effect of these interactions on plant productivity in agricultural systems. Although it would be advantageous to have a single organism or property that can be used as a measure of soil health, it may not be possible. Soil organisms which include both the microorganisms as well as soil fauna are subjected to the effect of their immediate environment. This microenvironment in turn is determined by the soil properties as well as above ground flora and their interactions. Most soil indicators interact with each other, and these interactions can modify or influence the soil properties. The complexities of the interactions between critical soil indicator values often preclude its practical use by land managers and policy makers. However, soil microbial communities (e.g. diversity and structural stability) may serve as a relative indicator of soil quality. These communities are sensitive to land management practices and changes in the microenvironment. The objective of this study was to gain an understanding of the complex relationships by investigating the effect of conventional, integrated and organic apple production systems on the physical, chemical and biological (particularly soil microbial diversity) properties of the soil. Automated Ribosomal Intergenic spacer analysis (ARISA) was used to characterise fungal (F-ARISA) and bacterial (B-ARISA) communities from soil samples obtained from an experimental apple orchard in Elgin, Grabouw. The intergenic spacer (ITS) region from the fungal rRNA operon was amplified using ITS4 and fluorescently FAM (6- carboxylfluorescein) labelled ITS5 primers. Similarly, the 16S-23S intergenic spacer region from the bacterial rRNA operon was amplified using ITSR and FAM-labelled ITSF primers. The sensitivity of the technique allowed us to discriminate between the soil microbial communities of the different treatments. From our results we observed significant increase (p < 0.05) in the fungal community diversity between the February and April samples, while the bacterial community diversity was consistent (p > 0.05). Also, treatments with mulch showed a significantly higher microbial diversity than the other treatments at a 5 % significance level. Fungal communities showed significant correlation with the potassium concentration in the soil, while bacterial communities depicted a significant correlation with the soil phosphorous concentration. Based on the results we concluded that different management practices have a significant effect on the soil microbial communities and that these communities are particularly sensitive to small changes in the environment. However, there is still a need to determine what the composition of the soil microbial communities are to be able to correlate our observations with soil health.
- ItemModeling the effect of time and temperature on respiration rate of pomegranate arils (cv. ‘‘Acco’’ and ‘‘Herskawitz’’)(Wiley Blackwell, 2012-03) Caleb, Oluwafemi James; Mahajan, Pramod V.; Opara, Umezuruike Linus; Witthuhn, Corli R.Abstract: Understanding the effect of time and temperature on the respiration rate (RR) of fresh-cut produce, towards the design of a suitable modified atmosphere packaging (MAP) system, requires an adequate mathematical model for prediction of RR as a function of both time and temperature. This study investigated the effect of temperature (5, 10, and 15 ◦C) and storage time (1 to 5 d) on the RR (RO2 and RCO2 ) of 2 pomegranate cultivars (cv. ‘‘Acco’’ and ‘‘Herskawitz’’) fresh arils. RO2 and RCO2 were 3 to 4 folds significantly higher with increased temperature from 5 to 15 ◦C and were within the range of 2.51 to 7.59 mL/kg h and 2.72 to 9.01 mL/kg h, respectively, for both cultivars. At 15 ◦C RCO2 increased significantly from 8.4 to 25.96 mL/kg h from day 1 to 5, respectively, while at 5 ◦C RCO2 changed from 2.9 to 2.05 mL/kg h from day 1 to 5. Temperature had the greatest influence on RR and the interaction of time and temperature also significantly affected RO2 and RCO2 . The respiratory quotient (RQ) estimated by linear regression was 0.98 at 95% significant level. The dependence of RR on temperature and time was accurately described with a combination of an Arrhenius-type and power equation model for RO2 and RCO2 of fresh pomegranate arils.
- ItemModelling the respiration rates of pomegranate fruit and arils(Elsevier, 2012-02) Caleb, Oluwafemi James; Mahajan, Pramod V.; Opara, Umezuruike Linus; Witthuhn, Corli R.The design of modified atmosphere packaging (MAP) for fresh and fresh-cut fruit requires adequate prediction of respiration rates (RRs). A study was conducted to determine the influences of storage temperature (5, 10 and 15 ◦C) and duration on RR of whole pomegranate fruit and arils of two pomegranate cultivars (‘Acco’ and ‘Herskawitz’). The RR of whole fruit was two to three folds higher, in comparison to those of the fresh arils across all storage temperatures. Temperature had a significant influence on RR. Over the range of storage temperatures studied, RO2 and RCO2 increased from 4.53 to 14.67 mL/kg h and 5.67 to 18.53 mL/kg h, respectively, for whole fruit, while RO2 and RCO2 of fresh arils ranged from 2.51 to 7.59 mL/kg h and 2.72 to 9.01 mL/kg h, respectively. The cultivar ‘Acco’ had higher respiration rates (mL/kg h CO2 production) than ‘Herskawitz’, especially as the length of storage increased at higher temperature conditions. The respiration quotient (RQ) for the whole fruit of both cultivars ranged from 1.14 to 1.26, while that of fresh arils ranged between 1.06 and 1.62. Experimental evidence showed that the significant influence of higher temperature in increasing the RQ of pomegranate arils was more pronounced towards the end of the storage period. The effects of temperature on rates of O2 consumption and CO2 production of whole fruit and arils were adequately described by an Arrhenius type model. The model was validated for whole fruit stored at 8 ◦C, and a good agreement was found between experimental and predicted data.
- ItemModified atmosphere packaging of pomegranate arils(Stellenbosch : Stellenbosch University, 2013-03) Caleb, Oluwafemi James; Opara, U. L.; Manley, M.; Mahajan, P. V.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.ENGLISH ABSTRACT: Modified atmosphere packaging (MAP) is a dynamic process of altering gaseous composition inside a package. It relies on the interaction between the respiration rate (RR) of the produce, and the transfer of gases through the packaging material. These two processes are dependent on numerous factors such as storage temperature, film thickness and surface area, produce weight as well as free headspace within the pack. Therefore, in order to achieve the desired modified atmosphere in a given package, it is important to understand the three basic disciplines of MAP, namely produce physiology, polymer engineering, and converting technology. In this study the effects of storage conditions and duration on physiological responses i.e. respiration (RR) and transpiration rate (TR) of two pomegranate cultivars ‘Acco’ and ‘Herskawitz’, were investigated and mathematical models were developed to predict these physiological responses at given time and storage conditions. The result of this study showed that RR of whole pomegranate fruit was significantly higher than that of fresh arils, and that temperature had a significant impact on the RR of both whole fruit and fresh arils. The influence of time, and the interaction between temperature and time also had significant influences on RR of fresh pomegranate arils. These findings highlight the significance of maintaining optimal cold-storage condition for packaged arils or whole fruit along the supply chain. In addition, mathematical models based on the Arrhenius-type equation and the power function equation coupled with Arrhenius-type equation accurately predicted the effect of temperature and the influence of time and temperature on the RR of fresh pomegranate arils for both cultivars. Furthermore, the results of experimental and model prediction studies showed that both relative humidity (RH) and storage temperature had significant effects on TR. RH was the variable with the greatest influence on TR, and it was observed that arils were best kept at 5°C and 96% RH to maintain quality for 8 days. The applicability of the transpiration model developed was validated based on prediction of TR of pomegranate arils under different combinations of storage conditions. The model adequately predicted TR and provides a useful tool towards understanding the rate of water loss in fresh pomegranate arils as affected by storage conditions and duration. The effect of passive-MAP engineering design parameters as a function of produce weight contained, storage temperature and duration on fresh pomegranate arils was investigated. The result showed that produce weight of aril content, temperature and the interaction between temperature and time had slight but insignificant effects on measured physicochemical quality attributes. However, headspace gas concentration was significantly influenced by produce weight and storage temperature. Oxygen (O2) composition decline below 2% after day 3 and 5 at 15 and 10 ºC, respectively, while samples at 5 °C did not reach below 2% throughout the study. On the other hand, CO2 levels increased significantly during storage for all packaging conditions. This study showed the importance of a systematic approach to the design of optimal MAP systems. At lowest storage temperature the inability to achieve desired modified atmosphere (MA) required for optimal storage of arils despite the increase in produce weight, suggests that the use of active gas modification (gas flushing with recommended atmosphere) would be necessary. However, the present results show that at higher temperature macro/micro perforations would be required on the polymeric films used in the present study in order to avoid critical levels of O2 and CO2. The influence of passive MAP, storage temperature and duration on volatile composition and evolution of packaged pomegranate arils was investigated. The results showed that changes in aroma compounds were dependent on cultivar differences, storage condition and duration. Using GC-MS analysis of pomegranate juice HS-SPME extracts, a total of 18 and 17 volatiles were detected for ‘Herskerwitz’ and ‘Acco’, respectively. Furthermore, flavour life (7 days) was shorter than the postharvest life (10 days) for both cultivars. There was a decrease in volatile composition during the storage period (aldehydes < alcohols < esters) while the concentration (%) and composition of ethyl esters increased with storage time. These results highlight the need for a more precise definition of flavour shelf life for MApackaged pomegranate arils and other packaged fresh produce. The importance of maintaining optimal cold storage condition, selection of appropriate packaging materials and a systematic approach to the design and application of MAP systems has also been shown.
- ItemModified atmosphere packaging of pomegranate fruit and arils : a review(Springer Verlag, 2011-02) Caleb, Oluwafemi James; Opara, Umezuruike Linus; Witthuhn, Corli R.Ongoing global drive for a healthier diet has led to a rise in demand for convenient and fresh food produce, with high nutritional value and free of additives. Minimally fresh processed fruits and vegetables, satisfies the consumers’ perception of a high nutritional quality and convenience produce. Minimally processed fruit and vegetables are susceptible to increased deterioration in quality and microbial infestation due to increase in endogenous enzymatic processes and respiration rate. Modified atmosphere packaging (MAP) technology offers the possibility to retard produce respiration rate and extend the shelf life of fresh produce. However, it is important to correlate the permeability properties of the packing films with the respiration rate of the produce, in order to avoid anaerobic conditions which could lead into fermentation of produce and accumulation of ethanol. Hence, mathematical prediction modelling is now widely applied in the design and development of effective MAP technology in both whole and minimally processed fresh produce. With increasing global interest in postharvest handling and nutrition value of pomegranate, MAP of minimally processed pomegranate arils offers additional innovative tool for optimal use and value addition, including the utilization of lowergrade fruit with superficial peel defects such as; cracks, splits, and sunburnt. This review paper highlights the current status and applications of modified atmosphere packaging in whole fruit and minimally processed pomegranate arils and identifies future prospects.