Defects
Crop defects may have genetic, physiological, pathological or mechanical origins, or alternatively result from the presence of extraneous organic or inorganic items. Defects inherent in the crop resulting from interactions between genotype, environment and microbial pathogens are dealt with later in this chapter.
Surface blemishes, insect deposits, fungal growth, necrotic zones and virus-induced yellowing can all constitute defects of Brassica crops. Mechanical damage includes cuts, bruises and discoloration resulting from the harvesting processes. Cauliflower is probably the most easily damaged Brassica crop since rough handling will result in bruising and consequently the downgrading or rejection of heads. Where Brussels sprout buds are harvested mechanically, the failure to sharpen and adjust the stripper's blades correctly can ruin previously high-quality crops very quickly.
The effects of mechanical stress (dropping, compression and trimming) on Chinese cabbage cv. Yuki were tested by Porter et al. (2004). Dropping and compression did not affect marketable quality where the produce was sold immediately. Storage of damaged produce for 9 weeks (at 2°C), however, impaired quality. Heads that were repeatedly trimmed produced less ethylene at the end of the storage period compared with the start. This reflected the removal of outer senescing and rotting leaves. Marketable yield was not improved by trimming, emphasizing the point that treatments after harvest cannot improve on quality but only maintain what has already been established in the field.
The presence of extraneous items will also ruin crop quality. Prepackaging by the grower for the supermarkets pre-supposes that there will be strict adherence to quality standards set as part of the contract. These are easily forfeited where, for example, leaves are packed with Brussels sprout buds or soil is allowed into the package along with cauliflower florets.
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