Department of Horticulture

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Browsing Department of Horticulture by Author "Berry, Tarl Michael"

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    Resistance to airflow and the effects on cooling efficiency of multi-scale ventilated pome fruit packaging
    (Stellenbosch : Stellenbosch University, 2013-12) Berry, Tarl Michael; Opara, U. L.; Delele, M. A.; Meyer, Chris J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticultural Science.
    ENGLISH ABSTRACT: Inadequate cooling of produce after it has been packed into ventilated packaging can result in inconsistent fruit quality. Misalignment of ventilation holes during stacking as well as the use of internal packaging, such as trays, polyliner bags and thrift bags reduces airflow distribution through the packaging. Consequently, the complex needs of maintaining the cold chain of perishable produce and the considerable variations in packaging designs have made it challenging to find an optimal ventilated package and stacking arrangement. The aims of this study were, therefore, to assess the status of ventilated packaging in the South African pome fruit industry, and to characterize the effects of package design and multi-scale packaging components on the resistance to airflow and cooling performance of apples under forced-air cooling conditions. A survey of the pome fruit industry identified over twenty packaging designs which were grouped into eleven unique designs and further categorised into either ‘display’ or ‘telescopic’ designs. Although South African fruit industry standards recommend ventilation areas of at least 5%, the ventilation areas of package designs identified from the survey varied considerably between <1 and 11%. Furthermore, the study showed that use of stacking renders many of the ventilation holes ineffective, due to blockages from adjacent cartons. The contribution of each component of the multi-scale packages used for handling apples was determined by analysis of pressure drop during forced-air cooling. The results showed when utilising a combination of cartons, fruit trays and plastic liner bags, the total pressure drop contribution of the cartons (8%) and fruit trays (3%) was minimal, while the use of plastic liner bags contributed 89%. However, in a carton and thrift bag packaging combination, the thrift bags contributed 66% to the pressure drop while the carton contributed 34%. The cooling results indicated a negative correlation between the total stack ventilation area and the cooling heterogeneity. In addition, the airflow velocity was correlated positively with fruit cooling rate and negatively with total moisture loss. Fruit packed inside polyliner bags had cooling rates four times slower than fruit on trays and three times slower in thrift bags. The use of liner bags blocked the ventilation holes, thereby reducing the airflow velocity. As a result of the longer cooling times in the polyliner bags, fruit remained at higher temperatures for longer periods, resulting in up to three times more moisture loss during forced-air cooling. In addition, a temperature gradient formed due to a progressive increase in air temperature through the stack, thereby resulting in a similar gradient of moisture loss. This research showed that airflow velocity and distribution were the most important factors contributing to the effectiveness of fruit cooling in multi-scale packaging. From a cold chain perspective, future packaging designs should therefore focus on optimising ventilation characteristics and alignment during stacking to ensure adequate airflow. Given the contribution of internal packaging to high resistance to airflow, such packaging components should be used with caution and only when necessary to meet physiological and market requirements.