Monday, 17 July 2017 17:57

Factors affecting post-harvest quality

Good quality of fresh cut flowers for export depends on a good understanding of the factors leading to their deterioration. If these factors are taken into account, both the producer and the transporter will be able to develop and implement optimum technologies that ensure the preservation of the quality throughout the process, until reaching the consumer.

 

Maturity of the flowers

 

The minimum cut ripeness for a given flower is the state of development in which the buttons can fully open and display a satisfactory vase life. Many flowers respond well to being cut in the button state, opening after the process of storage, transport and distribution. This technique has many advantages including a reduced growth period for single-crop crops, higher packaging density, simplified handling of temperature, less susceptibility to mechanical damage and less drying. Many flowers are harvested today when the buttons begin to open (pink, gladiolus), although others are cut when they are completely open or close to being (chrysanthemum, carnation). Flowers for the local market are generally harvested much more open than those destined for long-distance storage and / or transport.

 

Temperature

 

Breathing cut flowers, an integral part of growth and senescence, generates heat as a by-product. Additionally, as the ambient temperature rises the rate of respiration increases. For example, a flower at 30 ° C may breathe (and therefore age) up to 45 times faster than a flower at 2 ° C. The rate of aging can be dramatically reduced by cooling the flowers. Rapid cooling accompanied by a stable cold chain are therefore essential to ensure satisfactory quality and vase life of most of the cut flowers currently being marketed.

 

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Although air transport is quick compared to surface transport (lorry, shipping container, etc.), the response of cut flowers and foliage to warm temperatures leads to their rapid deterioration, even during relatively short air transport hours. It has been shown many times that transporting flowers by surface methods that maintain a good cold chain produces better results than air transport without temperature control, and this is mainly due to the dramatic response of flowers to heat. For this reason, air transport is rarely the chosen medium when there are other options that offer a good temperature control. An important objective of this manual is to raise awareness among exporters and traders about the importance of the cold chain in flower quality and to suggest strategies to improve temperature control during air transport.

 

The following photographs demonstrate the effect of storage for four days at different temperatures, on the subsequent quality and vase life of some common cut flowers. One day after being removed from the cold room, the quality of the gerberas is clearly related to adverse temperatures. The twisting of the flower stalks (escapes) of these flowers is a result of the negative geotropism (against gravity) that accelerates when the flowers are stored at a higher temperature. In dragon mouths the effect of storage at different temperatures is dramatic and clearly visible after four days at room temperature. Flowers that remain at temperatures different from the optimum (0 ° C) show a marked loss of quality as they increase. Crooked stems, loss of flowers and poor opening of flower buds are all evident in flowers subjected to higher temperatures. A similar situation is observed in iris stored at different temperatures for four days, and then maintained at room temperature for two days.

 

It has been suggested that the marked effects of temperature could be eliminated or at least minimized by keeping the flowers stored in water - using the so-called aquapacks or Proconas ™. Research shows that this is only partially true. Although flowers stored in water at higher than optimal temperatures perform better than dry stored flowers, this is never the same as flowers stored at the appropriate temperature, either dry or in water.  

 

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The optimum storage temperature for most fresh cut flowers currently marketed is near freezing point - 0 °C. Some tropical flowers such as anthuriums, birds of paradise, some orchids and gingers however, are negatively affected by temperatures below 10 °C. Symptoms of this "cooling damage" include darkening of the petals, Watermarks in them (which are transparent) and in severe cases collapse and death of leaves and petals.

 

*Source Handling and recommendations for postharvest of cut flowers - Author Michael S. Reid.- University of California

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