Browsing by Author "Lufu, Robert"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Evaluation of the airflow characteristics, cooling kinetics and quality keeping performances of various internal plastic liners in pomegranate fruit packaging
    (Elsevier, 2020-10-23) Lufu, Robert; Ambaw, A.; Berry, Tarl M.; Opara, Umezuruike Linus
    There is a trade-off to be optimised carefully as plastic liners deal with postharvest cooling processes as well as the produce quality and sustainability requirements. Understanding the implementation of plastic liners in the fresh fruit cold chain is required to reconcile the opposing roles. In this paper, the performances of four types of internal packaging plastic liners were studied. The airflow characteristics, cooling rate, cooling uniformity and quality keeping performances were measured. Cases: no liner, non-perforated liner, micro-perforated liner, macro perforated liner with 2 mm diameter holes, macro perforated liner 4 mm diameter holes were investigated. Generally, the liners delayed the cooling rate significantly. Non-perforated and micro-perforated liners are similar in terms of airflow resistance and cooling rate, both delayed the optimum cooling time by 5 h compared to the plastic-free case. On the other hand, macro-perforated liners cause a delay of only 3 h.
  • Thumbnail Image
    Item
    Transport Phenomena in Pomegranate Fruit: Mechanisms of Weight Loss and Control Strategies
    (Stellenbosch : Stellenbosch University, 2020-04) Lufu, Robert; Opara, Umezuruike Linus; Tsige, Alemayehu Ambaw; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: The revived interest in this ancient fruit Pomegranate (Punica grantum L) has resulted in increased production, consumption and intensified research owing to its health and nutritional benefits. Pomegranates are considered luxurious fruit that sell well in the higher market segment and there has been a growing demand for high quality, healthy and exotic fruit both for fresh use and for processing into juices and other products. However, the fruit is classified as highly perishable and specifically being prone to moisture loss, irrespective of its thick rind and tough leathery outer skin. Water loss can easily cause a huge financial loss to the industry through direct loss of marketable fresh weight and the associated diminished commercial value of affected fruit. Therefore, the overall aim of this research was to investigate the mechanisms of weight loss in pomegranate fruit by characterising associated structural and quality changes in the fruit, quantifying the water transport properties of fruit tissues, developing a water transport model and to assess various techniques to control fruit water loss. The research methodology followed a multifaceted approach which included the application of imaging and computational techniques in combination with several laboratory experiments. The experimental studies established that ‘Wonderful’ and ‘Herskawitz’ pomegranate cultivars are more susceptible to water loss than ‘Acco’ due to differences in aril-peel ratio and moisture content. The thick non-edible peel (rind) is the major source of water loss compared to the edible portion (arils). Overall, mean fruit water loss was 0.31, 0.34 and 0.26 g cm⁻² for ‘Wonderful’, ‘Herskawitz’ and ‘Acco’, respectively, after 16 d in shelf storage at 23 ⁰C and 58 % relative humidity (RH). Analysis of fruit micro-structures showed that the arils (edible portion) are protected against excessive moistures loss by the inner epidermis membrane (white membrane) covering the aril sacs. This membrane had a lower water permeability (0.14 × 10⁻ ¹¹ kg m⁻¹ pa⁻¹ s⁻¹) compared to the exocarp (1.31-1.43 × 10⁻¹¹ kg m⁻¹ pa⁻¹ s⁻¹) and mesocarp (13.51-16.37 × 10⁻¹¹ kg m⁻¹ pa⁻¹ s⁻¹) peel tissues under ambient conditions (23 ⁰C and 58 % RH). Transpiration is the major process of water loss in pomegranate fruit; however, this study showed that water loss due to the respiratory process contributed up to 35 at high 93 % RH. The qualitative studies on fruit peel microstructure using scanning electron microscopy (SEM) identified a higher count of lenticels, larger lenticel size and a generally low peel thickness on the top and mid spatial locations along the fruit surface as compared to the bottom locations. Furthermore, X-ray examination revealed higher porosity in the exocarp than in the mesocarp peel fractions and that porosity increased from bottom to middle to top locations in the exocarp fraction. This suggests that the pomegranate fruit is more susceptible to moisture loss at the top and mid locations compared to the bottom location. In addition, a distinctively bright waxy cuticle was identified on the surface of the peel using confocal laser scanning microscopy (CLSM). A decreasing profile of the waxy cuticle thickness, increased fragmentation of waxy cuticle, widening and deepening of micro-cracks and general decrease in peel thickness were observed during fruit storage. These micro-structural features predispose the fruit to increasing water loss during storage. The study has also demonstrated the use of non-invasive technology such as magnetic resonance imaging (MRI) to assess transient water profiles across intact fruit. Furthermore, the study developed and validated a water transport model that can be used to study water loss and control strategies in future. Assessing fruit weight loss control strategies proved that surface waxing is a potential environmentally friendly solution for minimising water loss in pomegranates. However, modelling of gas transport is required for accurate optimisation of surface waxing application. Future research should also consider coupling of water transport model and mechanical deformation model to account for shrinking (also referred to as shrivelling, wilting) of the fruit due to moisture loss.
  • Thumbnail Image
    Item
    Unpacking the influence of internal packaging on cooling characteristics and postharvest quality of pomegranate fruit
    (Stellenbosch : Stellenbosch University, 2017-03) Lufu, Robert; Opara, Umezuruike Linus; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH SUMMARY: Plastic films (liners) are commonly used inside packages of pomegranates. Liners can create modified atmosphere around fruit (MAP) and minimize fruit moisture loss. However, the barrier nature of liners affects cooling characteristics by increasing resistance to airflow (RTA), delaying cooling and promoting condensation, leading to fruit spoilage. During this research the impact of liners on the characteristics and postharvest quality of pomegranate fruit during cold storage and subsequent shelf life was investigated. The role and impact of liner perforations was highlighted. The effect on RTA by non-perforated ‘Decco’, micro-perforated Xtend®, macro-perforated ‘Decco’ liners (2 mm × 70 and 4 mm × 18) and macro-perforated high density polyethylene (HDPE) liners (2 mm × 54 and 4 mm × 36), was studied in a wind tunnel. Generally, fruit stack packed with non-perforated ‘Decco’ and micro-perforated Xtend® liners increased the RTA of the no-liner packed fruit by 175.7 and 238.4 %, respectively. However, using macro-perforated 2 and 4 mm ‘Decco’ liners increased the RTA of the no-liner packed fruit by only 69.2 and 113.6 %, respectively. The impact of non-perforated ‘Decco’ and micro-perforated Xtend® liners on cooling characteristics was carried using a forced-air cooling (FAC) setup. The 7/8 cooling time of fruit stack packed with no-liner was 3.5 ± 0.2 h, compared to 8.1 ± 0.1 h with non-perforated ‘Decco’ and 8.5 ± 0.1 h with micro-perforated Xtend® liners. As a result, more energy was consumed in pre-cooling fruit packed in liners than with no-liners. However a higher stack cooling uniformity (81.6 ± 1.7 and 78.7 ± 1.5 %) was obtained for fruit packed with non-perforated ‘Decco’ and micro-perforated Xtend® liners, respectively, compared to fruit packed with no-lines (64.2 ± 0.2 %). The effect of non-perforated (‘Decco’ and ‘Zoe’), micro-perforated (Xtend®), macro-perforated 2 and 4 mm HDPE liners on fruit quality during storage at 5 o C and 90 ± 5 % relative humidity (RH) for 12 weeks and subsequently 5 days at 20 o C, was evaluated. At the end of 12 weeks of cold storage, the no-liner fruit lost 15.6 ± 0.3 % of its initial weight. Non-perforated (‘Decco’ and ‘Zoe’) liners minimized weight loss by 95.0 % compared to Xtend® micro-perforated (73.2 %), 2 mm macro-perforated HDPE (84.3 %) and 4 mm macro-perforated HDPE (62.5 %) liners, respectively. Fruit packed in perforated and non-perforated liners maintained a lower respiration rate and retained better peel colour than fruit with no-liners. Micro- and macro-perforation of liners increased diffusion of moisture lost from the fruit across film to the room atmosphere. This minimized moisture condensation inside the liners leading to a reduced fruit decay, with acceptable shrivel severity. The type of liner and perforation quality (size and number) did not have a significant impact on total soluble solids (TSS), titratable acidity (TA), juice colour, total phenolic concentration and antioxidant activity. Overall, the use of perforated liners reduced RTA, energy consumption and moisture condensation associated with non-perforated liners, and yet retained fruit texture, colour, weight and chemical quality attributes during and after prolonged cold storage.