Browsing by Author "Mukama, Matia"

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    Advances in design and performance evaluation of fresh fruit ventilated distribution packaging : a review
    (Publishers version, 2020-02-17) Mukama, Matia; Ambaw, Alemayehu; Opara, Umezuruike Linus
    This review was initiated to realise the state-of-the art in optimising the ventilation and structural requirements of corrugated packaging carton design. Researchers have been using computational methods: computational fluid dynamics, particularly, the finite volume method, to analyse the airflow and heat transfer performances, and computational structural dynamics, particularly, the finite element method, to analyse the loss of compression strength due to vent-holes. Models are validated using actual testing: wind tunnel based forced air cooling system to study the produce cooling kinetics and box compression test machine for the package industry to study the structural dynamics. Studies on the rate and uniformity of produce cooling and the loss of structural strength in corrugated cartons as a function of size, shape, and location of vent-holes are reviewed. Based on experimental data, results show that the loss in strength can range between 10–40 % on addition of vent and hand holes on cartons, and reasonable increase in cooling rates is only achieved with increase in carton face ventilation area only up to 7–8 %. With regards to internal packaging components, increasing awareness of consumers to the environmental degradation of especially disposable plastic packaging means packers and suppliers must devise means to cut back and eventually eliminate plastic packaging from fruit and vegetables.
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    Optimising ventilated package design for postharvest handling of pomegranate fruit in the cold chain
    (Stellenbosch : Stellenbosch University, 2019-12) Mukama, Matia; Opara, Umezuruike Linus; Tsige, Alemayehu Ambaw; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Packaging is an indispensable unit operation in handling and distribution of fresh fruit. Studies on postharvest handling of a number of horticultural products highlighted the importance of package design and knowledge of fruit and package thermophysical properties to effectively accomplish the precooling, cold storage, and refrigerated transport processes. However, the thermal properties of pomegranate fruit and its parts are unknown, and packages for postharvest handling of pomegranates have not been properly investigated. The aim of this study was to address the multi-parameter design requirements of ventilated packages for handling pomegranate fruit to ensure efficient cooling, high precooling throughput, reduction in packaging material used, and improved space utilization during cold storage and refrigerated transport. Firstly, the thermal properties of whole fruit and the parts (epicarp, mesocarp, and arils) of early (‘Acco’) and late (‘Wonderful’) commercial pomegranate cultivars were determined experimentally using a transient heating probe. The values of thermal conductivity and diffusivity of both cultivars increased significantly with an increase in tissue temperature. The aril part was observed to have the highest thermal conductivity and specific heat capacity, respectively. For example, at 7 °C, the thermal conductivity (W m-1 K-1) of ‘Acco’ was 0.419 ± 0.047, 0.352 ± 0.040, and 0.389 ± 0.030 for arils, mesocarp, and epicarp, respectively. Next, a survey of the packaging used for pomegranate fruit in South Africa was conducted. Over 10 different corrugated fibreboard carton designs, with largely open tops, were found with different ventilations, ranging from 0.74–4.66% on bottom, to 0.71–5.33% on short (width), and 4.60–13.82%on the long (length) faces. The cartons were largely poorly ventilated on the short faces that leads to vent-hole misalignment and vent-hole blockage on pallet stacking which increases fruit cooling time and energy requirements. Then, a virtual prototype approach based on computational fluid dynamics (CFD) was used to redesign the ventilation of one of the most commonly used pomegranate fruit cartons with intent to improved cooling performance. Fruit cooled in the new design had more uniform temperature distribution and significantly cooled faster (1.6 hours faster in fruit in polyliner) compared to fruit in the commercial design. This result highlights the need of proper carton vent design and vent-hole alignment in stacks. Furthermore, a virtual prototype approach, based on CFD and computational solid dynamics (CSD) was used to design new ventilated corrugated paperboard cartons that hold pomegranate fruit in multilayers. Running virtual airflow and strength measurements enabled selecting the best alternatives, the ‘Edgevent’, and ‘Midvent’, which were then manufactured and evaluated for cold chain performance. The new designs improved fruit throughput by over 1.8 tonnes more fruit in a reefer compared to commercial single layer designs. For similar volume of fruit contained, the new designs saved over 31% cardboard material and an estimated equivalent of 11 trees per fully loaded 40-ft refrigerated container. Overall, the ‘Midvent’ performed best under cold chain conditions in terms of cooling efficiency and mechanical strength requirements. This warrants its commercialisation. Lastly, the quality of fruit stored in ‘Midvent’ for 12 weeks under cold chain condition (7 ± 1 °C, 90% RH) and an additional 2 weeks at ambient (shelf life) condition (20 ± 1 °C, 65% RH) was compared with fruit in commercial carton under similar conditions. Fruit respiration followed a similar pattern in both carton designs marked by a 64% reduction after precooling. At the end of the shelf life period, fruit weight loss was 5.7% and 8.9% in the ‘Midvent’ and commercial design, respectively. Sensory attributes, decay incidence and colour changes were similar in new and commercial carton designs over the storage period. Overall, research reported in this thesis has provided new data on thermophysical pomegranate fruit and has applied the virtual prototyping tool for horticultural packaging design. The new ‘Midvent’ carton design provides additional benefits in savings in packaging material, energy for fruit cooling, and bioresources efficiency. Future research should focus on performance test of this carton design in the commercial chain. New data on the thermal properties of pomegranate fruit provide needed input towards the modelling and prediction of fruit internal temperature profile during cooling processes.
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    Resistance to airflow, cooling characteristics and quality of pomegranate fruit inside ventilated packaging
    (Stellenbosch : Stellenbosch University, 2015-12) Mukama, Matia; Opara, Umezuruike Linus; Stellenbosch University. Faculty of Agrisciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Ventilated packaging has found wide scale industry applications in fresh fruit handling and cooling operations. Given variations in fruit physical and thermal properties, optimal package design for a particular product and supply chain requires a multi-parameter approach incorporating cooling, mechanical and economic performance, as well as resource utilisation efficiency. A wide range of ventilated package designs are used in postharvest handling and marketing of fresh fruit, and several studies have investigated the cooling performance of fruit such as apples, citrus and table grapes; however, very little is known about the performance of pomegranate ventilated packaging. Therefore, the overall aim of this study was to evaluate the cold chain performance of some of frequently used ventilated cartons and internal packages (liners) during forced-air cooling (FAC) and cold storage in the South African pomegranate industry, in terms of resistance to airflow (RTA), cooling characteristics, energy efficiency and fruit quality. The two studied carton designs, CT1 and CT2 had 5.4% difference in total ventilation. CT2 had relatively higher ventilation in both length and width directions (8.82% and 6.67%, respectively) compared to CT1 (6.52% and 2.86%). In a stack of cartons packed with fresh pomegranate fruit (cv. Wonderful), this resulted into a generally faster fruit cooling rate (29.19%) in CT2. However, the obstruction of vent-holes in the lengthwise orientation of the stack of CT2 resulted in over 50% higher RTA compared to CT1. The results also showed that packaging fruit inside a liner offered up to 50% greater RTA than fruit packaging with no liner. Consequently, the use of liners also delayed fruit cooling and increased energy consumption, with seven-eighths cooling times close to 3 times those of fruit inside packaging with no liner. Packaging fruit with liner required about 3.9 and 8.7 times more energy to cool fruit in CT1 and CT2, respectively, compared with no-liner. Fruit in carton stacks also exhibited a heterogeneous cooling pattern, with fruit in the upstream position to incoming air cooling about 36% faster compared to fruit at back stack position. During FAC of fruit over a period of 11.6 and 4.5 hours in liner and no liner, respectively, the use of humidification to maintain 95±1% relative humidity (RH) minimised weight loss by about 13.63% compared to precooling fruit inside cold room at 90±1% RH. Fruit packaged without liners also lost about 17.39% more weight during precooling compared to fruit packaged with liners. Fruit in liners and without liners which took longer to cool to set temperature (7ᵒC) lost more weight than fruit that got to set storage temperature faster. A further study into the effects of RH on pomegranate fruit quality during ambient (20ᵒC) storage showed that storing fruit under high RH (95%) minimised weight loss, maintained fruit colour, firmness and physicochemical quality attributes. Storing fruit under low RH (65%) led to excessive weight loss up to 29.13±1.49% after 30 days (compared to 5.78±0.44% at 95% RH), thereby resulting into an estimated financial loss of ZAR7.78 kg⁻¹ and ZAR1.54 kg⁻¹ at low and high RH storage conditions, respectively. The onset of visible signs of shrivels occurred when fruit weight loss reached about 5.16%. Linear regression equations developed to estimate weight loss in pomegranates during ambient storage gave a high goodness-of-fit (R²) of 0.9931 and 0.9368 for low and high RH environments, respectively. This research has provided an insight into the effects of packaging design used in the pomegranate industry on cooling performance and impacts on fruit quality. Although the use of internal packaging (liners) minimised fruit weight loss, it increased RTA, precooling time, energy consumption and cooling costs. Cold room humidification offered potential remedy to the problem of high moisture loss of pomegranates. Further studies are warranted to optimise the vent design of pomegranate packaging, including the use of perforated liners, to improve cooling performance cost-effectively without compromising structural/mechanical performance in the cold chain.
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    Resistance to airflow, cooling characteristics and quality of pomegranate fruit inside ventilated packaging
    (Stellenbosch : Stellenbosch University, 2015-12) Mukama, Matia; Opara, Umezuruike Linus; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Ventilated packaging has found wide scale industry applications in fresh fruit handling and cooling operations. Given variations in fruit physical and thermal properties, optimal package design for a particular product and supply chain requires a multi-parameter approach incorporating cooling, mechanical and economic performance, as well as resource utilisation efficiency. A wide range of ventilated package designs are used in postharvest handling and marketing of fresh fruit, and several studies have investigated the cooling performance of fruit such as apples, citrus and table grapes; however, very little is known about the performance of pomegranate ventilated packaging. Therefore, the overall aim of this study was to evaluate the cold chain performance of some of frequently used ventilated cartons and internal packages (liners) during forced-air cooling (FAC) and cold storage in the South African pomegranate industry, in terms of resistance to airflow (RTA), cooling characteristics, energy efficiency and fruit quality. The two studied carton designs, CT1 and CT2 had 5.4% difference in total ventilation. CT2 had relatively higher ventilation in both length and width directions (8.82% and 6.67%, respectively) compared to CT1 (6.52% and 2.86%). In a stack of cartons packed with fresh pomegranate fruit (cv. Wonderful), this resulted into a generally faster fruit cooling rate (29.19%) in CT2. However, the obstruction of vent-holes in the lengthwise orientation of the stack of CT2 resulted in over 50% higher RTA compared to CT1. The results also showed that packaging fruit inside a liner offered up to 50% greater RTA than fruit packaging with no liner. Consequently, the use of liners also delayed fruit cooling and increased energy consumption, with seven-eighths cooling times close to 3 times those of fruit inside packaging with no liner. Packaging fruit with liner required about 3.9 and 8.7 times more energy to cool fruit in CT1 and CT2, respectively, compared with no-liner. Fruit in carton stacks also exhibited a heterogeneous cooling pattern, with fruit in the upstream position to incoming air cooling about 36% faster compared to fruit at back stack position. During FAC of fruit over a period of 11.6 and 4.5 hours in liner and no liner, respectively, the use of humidification to maintain 95±1% relative humidity (RH) minimised weight loss by about 13.63% compared to precooling fruit inside cold room at 90±1% RH. Fruit packaged without liners also lost about 17.39% more weight during precooling compared to fruit packaged with liners. Fruit in liners and without liners which took longer to cool to set temperature (7oC) lost more weight than fruit that got to set storage temperature faster. A further study into the effects of RH on pomegranate fruit quality during ambient (20oC) storage showed that storing fruit under high RH (95%) minimised weight loss, maintained fruit colour, firmness and physicochemical quality attributes. Storing fruit under low RH (65%) led to excessive weight loss up to 29.13±1.49% after 30 days (compared to 5.78±0.44% at 95% RH), thereby resulting into an estimated financial loss of ZAR7.78 kg-1 and ZAR1.54 kg-1 at low and high RH storage conditions, respectively. The onset of visible signs of shrivels occurred when fruit weight loss reached about 5.16%. Linear regression equations developed to estimate weight loss in pomegranates during ambient storage gave a high goodness-of-fit (R2) of 0.9931 and 0.9368 for low and high RH environments, respectively. This research has provided an insight into the effects of packaging design used in the pomegranate industry on cooling performance and impacts on fruit quality. Although the use of internal packaging (liners) minimised fruit weight loss, it increased RTA, precooling time, energy consumption and cooling costs. Cold room humidification offered potential remedy to the problem of high moisture loss of pomegranates. Further studies are warranted to optimise the vent design of pomegranate packaging, including the use of perforated liners, to improve cooling performance cost-effectively without compromising structural/mechanical performance in the cold chain.