Coating of pears (Var. ‘Packhams Triumph’) with kafirin protein and its effect on postharvest physiology and shelf-life

Abstract

In order to reduce postharvest losses of exported Pome fruit and increase export revenue, export quality pears require a reduction in stem-end shrivelling and an extension in shelf-life, regardless of the presence or absence of refrigerated storage. A kafirin coating may fulfil these requirements during export and at the export destination, in retail and at fresh fruit markets. A two-phased approach was followed. During Phase 1, the physiological and biochemical behaviour of ’Packham’s Triumph’ pears were studied under ideal refrigerated (-0.5°C), temperature-abused (10°C) and typical ripening (20°C) conditions. These storage conditions were selected to simulate potential conditions during the export process. Phase 2 involved the development and application of a kafirin-based coating to increase the shelf-life of pears. In Phase 1, two experiments were conducted concurrently on freshly harvested, uncoated pears. In Experiment 1, pears were stored at –0.5, 10 and 20°C and 95 to 98% RH for 42, 42 and 21 d respectively. An increase in storage temperature increased the metabolic activity of the pears and the rate of quality deterioration. Very few quality changes occurred in pears during storage at -0.5°C. Pears stored at 20°C ripened and became senescent in approximately half the time taken by pears at 10°C. However, fully ripe ‘Packham’s’ pears from 10 and 20°C exhibited similar final colour and firmness values. Stem-end shrivelling was exacerbated by storage at 20°C after only 4 days but not observed during storage at -0.5 or 10°C. In Experiment 2, ‘Packham’s Triumph’ pears were stored at -0.5 and 10°C (95 to 98% RH) for 42 and 35 days, respectively before being ripened at 20°C for 7 days. Storage of pears at 10°C prior to ripening accelerated softening and yellowing in the pears, when compared to pears from -0.5°C storage. Storage duration prior to ripening at 20°C also resulted in pears of increasing softness and yellowness by the end of 7 days at 20°C. The effect of storage duration at -0.5°C was less severe on the ripening rate and intensity of softening and yellowing than storage at 10°C. Thus, storage at -0.5°C extended pear shelf-life and resulted in pears of better quality after ripening than storage of pears at 10°C. In Phase 2, pears from Controlled Atmosphere (CA) storage were coated with a kafirin-based coating and stored at 20°C (35 to 45% RH) for 24 days. The ripening rate and the physiological behaviour and physico-chemical changes of pears used in Phase 2 were probably accelerated by 18 weeks under CA conditions and one week under RA conditions prior to the start of the shelf-life study. The kafirin coating did not retard ripening, which was probably already induced during storage before coating, but senescence in the coated pears was delayed by approximately 6 days. The rate of respiration, ethylene production, flesh softening and especially yellowing, was delayed by the coating. Coated and uncoated pears exhibited no growth of coliforms or lactic acid bacteria. Overall, coated pears had lower levels of aerobic mesophiles and yeast and mould growth than uncoated pears. Unfortunately, pear surface-shrivelling was intensified by the coating, probably due to the dehydrating action of the ethanol in the coating solution during dipping. However, the kafirin coating was able to extend pear shelf-life by delaying senescence and microbiological growth. The coating formulation may require a higher concentration of kafirin to increase its hydrophobicity and reduce pear shrivelling. The kafirin coating has possible potential to markedly extend the quality and shelf-life of ‘Packham’s Triumph’ pears, provided that the pears are coated after minimal RA storage when pears are in the pre-climacteric phase. Copyright 2007, University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. Please cite as follows: Buchner, S 2007, Coating of pears (Var. ‘Packhams Triumph’) with kafirin protein and its effect on postharvest physiology and shelf-life, MSc(Agric) dissertation, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-02242012-113144/ > E549/gm