The aim of this study was to investigate the optimum maturity, time of harvest and quality of Western Schley and Wichita pecans grown at Moree, New South Wales (NSW) in Australia. This was achieved by conducting experiments with particular emphasis on changes in physical, chemical and sensory properties of pecans at different maturity levels, based on changes in shuck characteristics (colour and condition) and different harvest dates for two consecutive years (1999 and 2000). No previous research has been conducted in this area in Australia.
A preliminary study of the maturation process of Western Schley pecans was carried out in 1998, the first year of a three-year project. Pecans were harvested at monthly intervals for five months. The chemical composition including moisture, total lipid, sugars, fatty acid profiles and minerals were determined. The sensory properties of the pecans were also evaluated by a sensory taste panel. The results showed that the most important chemical changes were a decrease in moisture content and an increase in total lipid content. However, little changes were found in the sensory characteristics and the overall quality of the pecans did not change with time of harvest. This was due mainly to an abnormally wet period during sample collection.
As time of harvest alone was not a favourable index of maturity, the effect of maturity based on shuck characteristics and time of harvest for both pecan cultivars was investigated in 1999 and 2000. The moisture, total lipid, sugars, total phenolic acids, individual phenolic acid, protein, fatty acid profiles and minerals of the pecans at different levels of maturity were determined. The concentration of total phenolic acids and individual phenolic acid was investigated for the first time in Australian grown pecans in this study. In addition, the sugar, raffinose was detected in pecan kernels for the first time in this study. Maturity and time of harvest showed significant influence on these chemical constituents. It was found that the concentration of moisture decreased rapidly while the concentration of total lipid increased from the early to the middle harvest dates and the levels of both constituents remained constant thereafter. The critical time of harvest for both pecan cultivars grown at Trawalla orchard were from 11 May 1999 and 17 May 2000 onwards when the shuck of the pecans had opened, irrespective of colour.
The effects of maturity and time of harvest on the shelf-life of the pecans were also investigated. This was achieved by conducting an accelerated storage trial in which pecans were aerobically canned and stored at 40 °C for 12 week. After storage, the pecan kernels were analysed for free fatty acid value and peroxide value as well as their sensory properties through the sensory taste panel. A control sample from each treatment was aerobically canned and stored at 0-4 °C and analysed in a similar way to that of the experimental samples. It was found that maturity and time of harvest did not affect the free fatty acid value or the peroxide value of the control, but slightly affected the stored samples. In addition, as a result of accelerated storage, time of harvest and maturity slightly affected the sensory properties of the stored samples. However, maturity and time of harvest affected the sensory properties of the control samples significantly and favourably. As time of harvest was delayed and shuck description changed, both pecan cultivars had naturally developed colour and texture, had less bitterness, less other flavours, more crispness, more pecan nut flavour, more sweetness, and higher overall quality. After accelerated storage the pecan kernels had very low overall quality and had developed rancidity.
The presence of opalescence in both pecan cultivars was also studied. Pecans harvested early in the season had less opalescence than pecans harvested later in the season. However, as the early harvested pecans were too immature for commercial harvesting, a slight increase in opalescence would be compensated by achieving higher quality pecans if harvested later in the season.
Overall, for optimum quality. Western Schley and Wichita pecans grown at Trawalla orchard, Moree, NSW should be harvested after the shuck has opened, irrespective of shuck colour (green, brown). This occurred after 11 May 1999 and 17 May 2000 respectively. Harvesting under these conditions would produce the best quality pecans as well as minimising costs of processing.