Edible protein coatings on pears show potential

PRINCIPAL INVESTIGATORS: Dr Nomusa Dlamini and Dr Ian Crouch
Dr Nomusa Dlamini: +27 12 841 3097 / nrdlamini@csir.co.za
Dr Ian Crouch: +27 21 887 1134 / ian@experico.co.za
DURATION: Two years
Phi-1 CONTRIBUTION: R430 831
LEAD INSTITUTIONS: Council for Scientific and Industrial Research (CSIR) and ExperiCo (Fruit Technology Solutions)
BENEFICAIRY: The pome fruit sector

It is standard pack house procedure to apply wax coatings on certain kinds of fruit like avocados, mangoes, citrus and some pome fruit varieties before packing. Wax helps to protect fruit against moisture loss, shrivelling and decay and it provides an attractive surface sheen. However, low storage temperatures can cause the wax to harden and peel off. Wax is also not intended for consumption, which is inconvenient in fruit with an edible peel. The disadvantages of traditional wax coatings led to a project that explored the potential of an edible alternative.

The effect of kafirin protein coating on the quality and ripening of pears

The project was collaborated between the CSIR/Biosciences and ExperiCo. Edible protein coatings were developed and tested on optimum harvested ‘Packham’s Triumph’ and ‘Forelle’ pears. Kafirin, an alcohol soluble sorghum prolamin protein, was assessed for coating. It also has hydrophobic properties, which could potentially shield fruit against moisture loss and shrivelling and provide a barrier against gas exchange to replace the requirement for modified atmosphere packaging (MAP).

  • The CSIR team, led by Dr Nomusa Dlamini, conducted laboratory tests to determine the appropriate coating formulation.
  • A kafirin coating solution was prepared for application on the pears.
  • Dr Ian Crouch led the ExperiCo team, which was responsible for the large-scale coating trials.
  • Fruit maturity and ripening rates were monitored throughout the study.
  • Maturity was determined at the time of coating, after six weeks and after ten weeks of storage in regular atmosphere conditions at 20°C.
  • An additional seven-day shelf life period was introduced after six weeks and after ten weeks of storage.
  • After six weeks and ten weeks of storage, a small sample of fruit from each treatment was ripened for fourteen days for observational purposes.
  • The effect of the kafirin coating on fruit quality was evaluated in terms of taste, appearance, skin colour development, flesh firmness, total soluble solids, total titrable acids, shrivelling incidence and signs of decay.

Outcome of collaborated trials

  • Coating application was more effective as a dip than by atomisation.
  • Kafirin maintained flesh firmness and background skin colour successfully during cold storage and after shelf life.
  • Kafirin treated fruit exhibited a subtle lustre and was more attractive than untreated fruit.
  • However, the kafirin coating did not control moisture loss and shrivelling. It can therefore not replace the MAP requirement of plastic liners.
  • Kafirin treated fruit, ripened for an extended shelf life period of fourteen days, resulted in excellent eating quality.
  • The collaboration has also contributed towards a publication in a peer reviewed journal: Buchner, S., Kinnear, M., Crouch, I.J., Taylor, J. and Minnaar, A. (2011) Effect of kafirin protein coating on sensory quality and shelf life of ‘Packham’s Triumph’ pears during ripening. Journal of the Science of Food and Agriculture, 91:2814-2820.

Benefits to industry

  • Overall, kafirin coating indicated an improved post-storage quality of pears, including better taste, skin colour development and flesh firmness.
  • These findings can lead to increased market acceptability and can be expanded to other fruit sectors.
  • The kafirin coating can be applied in other food products in order to preserve their quality and can also serve as an effective gas barrier under some selected storage conditions.