Managing chilli (Capsicum spp.) quality attributes : the importance of pre-harvest and postharvest factors : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, New Zealand
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Date
2012
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Massey University
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Abstract
Demand for chillies and peppers continues to increase in many parts of the world as
chillies (Capsicum spp.) are a good source of beneficial compounds. Optimising
postharvest storage of chilli fruit is not enough to gain highest quality products in the
market place if there is a significant variation in the quality such as size, colour and
phytochemical compounds at the time of harvest, which may be a result of pre-harvest
factors. The objectives of this research were to understand effects of pre-harvest and
postharvest factors on chilli quality in order to produce consistent quality chilli fruit.
Storing of Habanero and Jalapeño at 8 °C can maintain low respiration rates and delay
loss of firmness without the development of chilling injury symptoms for 4 - 5 weeks,
while Paprika requires warmer storage temperatures as loss of firmness was found
during storage at 8 °C, although overall appearance was still marketable. Chillies were
very susceptible to shrivel when stored above 8 °C. In Jalapeño, water loss occurred
approximately equally through fruit skin and through the calyx and pedicel area until
cracking appeared on Jalapeño fruit which stimulated a significant increase in skin
water loss. A model was developed to predict the shelf life (using 5 % water loss as
time to shrivel development) of Jalapeño during storage by conducting a sensitive
analysis on the potential factors (such as fruit weight, water vapour
permeance (Pf H2O) temperature and RH); RH was the most important factor on the
impact on rate of water loss and time to shrivel. Application of wax on fruit skin or the
whole fruit is recommended as waxing on calyx and pedicel of Jalapeño increased
shelf-life by 10 % compared to control fruit.
Pre-harvest factors such as time of planting, position on plant, maturity at harvest and
crop load significantly influence Jalapeño quality (i.e. fruit size, colour and
phytochemical composition). Fruit weight, colour and ascorbic acid varied with time
of planting and time of fruit set during the season demonstrating that growing
conditions affected plant and fruit growth. Fruit from plants planted late in the season
(October) were small and contained low ascorbic acid concentration. Position on plant
also affected fruit size and ascorbic concentration despite fruit being of the same
maturity stage. Different fruit size may be explained by the competition between plant
Managing chilli quality attributes: the importance of pre-harvest and postharvest factors
and fruit growth and also the distance from nutrients and water supply rather than fruit
to fruit competition as there was no influence of crop load on fruit size. However,
ascorbic acid accumulation in fruit was stimulated by competition between fruit on the
plant as fruit from high crop load plants showed higher ascorbic acid concentration
than fruit from low crop load plants. In addition, it may be influenced by plant age or
time of fruit set during season, as late season or upper node fruit produce low ascorbic
acid concentration. Maturity had a major effect on colour at harvest, but colour change
was influenced by position on plant and growing conditions. Colour development of
fruit at lower nodes which were set at cooler temperatures was slower than fruit at
higher nodes which were set at warmer temperature. Capsaicinoid concentration
seemed to be consistent along the plant. However, the observed results showed that
measurement of total capsaicinoid concentration can be affected by the sub-sampling
error from the proportion of each individual tissue (i.e. pericarp, placenta and seed)
contained in the sample due to large differences in capsaicinoid concentration among
tissues. Similar to capsaicinoids, antioxidant activity (AOX) and total phenolic
concentration (TPC) seemed to be consistent along the plant. A weak correlation was
found between AOX and TPC or AOX and ascorbic acid indicating that ascorbic acid
or TPC was not a major contributor of the AOX in Jalapeño. Further work in this area
is required, but needs to start with harmonisation of extraction solvents.
In conclusion, this research generates an overall understanding on the effects of preharvest
and postharvest factors on chilli quality which will assist chilli growers in
controlling sources of variation and help to produce more uniform chillies. Based on
these results, to produce larger Jalapeño fruit with high concentrations of health
beneficial compounds such as ascorbic acid, Jalapeño plants should be pruned not to
higher than 12 nodes. Thinning leaders during production is essential for decreasing
the risk from plant collapse due to weight but does not influence fruit size. As this
research was focused on plants with two leaders and a single first flush fruit per node
at high crop load, investigating the role of more leaders, a higher number of fruit per
node and the second flush of fruit production should be investigated in future work.
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Keywords
Capsicum, Chillies, Peppers, Jalapeño, Habanero, Chilli peppers, Chilli quality, Chilli storage