An evaluation of changes in ground colour, firmness, soluble solids and starch as apple maturity indices : a report submitted in partial fulfilment of the requirements for the degree of Bachelor of Horticultural Science (with Honours) in the University of Canterbury, Lincoln College

Abstract

An investigation into the reliability of four apple maturity indices was made using 'Cox's Orange Pippin' and 'Granny Smith' as test populations. Commencing four weeks before normal harvest, samples of 80 apples were obtained at weekly intervals over a seven week period. Determinations were made of ground colour, flesh firmness (four sites/fruit), total soluble solids (four sites/fruit) and percentage starch (iodine test). Trends in each over time were characteristic of maturing fruit but changes were much less pronounced for Granny Smith, except for starch loss. Significant correlations were found for four pairs of Cox maturity indices. Variability increased with time for all parameters except firmness, and was highest for the subjectively assessed ground colour and starch test. Sources of variability were identified and significant differences detected between crown levels for soluble solids and ground colour, and between the red and green sides of fruit for soluble solids and pressure tests. The involvement of light and temperature in contributing to these effects is alluded to. A possible link between soil moisture status and refractometer readings could weaken the reliability of total soluble solids data.