Application of Portable NIR for Measuring Soluble Solids Concentrations in Peaches J.B. Golding and S. Satyan Gosford Horticultural Institute NSW Department of Primary Industries Gosford NSW 2250 Australia C. Liebenberg and K. Walsh Plant Sciences Group Central Queensland University Rockhampton Qld 4702 Australia W.B. McGlasson Centre for Horticulture and Plant Sciences University of Western Sydney Locked Bag 1797, Penrith S DC NSW 1797 Australia Keywords: near infrared spectroscopy, non-destructive, fruit maturation Abstract A prototype portable near infrared (NIR) spectrometer was evaluated using several varieties of peaches and nectarines, including fruit ranging from immature to tree ripe. The NIR unit was pre-calibrated with different varieties of peaches and nectarines. A series of NIR measurements were made on up to 12 locations on each fruit. Cores of flesh were removed from each of these locations and juice was expressed to enable measurements of soluble solids concentrations (SSC) with a temperature compensated digital refractometer. The NIR and SSC readings were highly correlated. SSC values at different locations within each fruit varied by up to 4%. Based on these data we suggest that a minimum of two NIR readings on opposite sides of the fruit in the equatorial plane are required to give a reliable measure of the average value for each fruit. We found that the NIR unit gave accurate measurements of SSC over four harvests of a yellow flesh peach variety ranging from small immature fruit to large tree ripe fruit. INTRODUCTION A minimum soluble solids concentration (SSC) of 11% is required if peaches have to satisfy most consumers. However, under commercial conditions a large proportion of the crop may not reach this level for a number of reasons, including unsuitable cultivars, adverse weather conditions, injudicious use of fertilisers, insufficient fruit thinning and inadequate summer pruning. Even under good growing conditions the SSC can range from 9-16% in a population of fruit that has excellent visual quality (Fig. 1). Fruit at the low end of the range should be excluded from controlled ripening programs. On-line NIR (near infra-red spectroscopy) is being used in some pack houses in Australia to detect sub-standard fruit but packers are reluctant to discard these fruits if their visual quality is high. The task of raising SSC above 11% and reducing variability within a population of fruit must begin in the orchard. Central Queensland University has developed portable NIR that can be used in the orchard or in the pack house (Fig. 2). This paper reports initial investigations with this equipment. The aims were: • Determine the internal variability in SSC in fruit, • Determine the predictability of SSC based on NIR measurements, • Where on the fruit and how many measurements per fruit are required and • Whether the instrument can be used on growing green fruit through to fruit that is tree ripe. MATERIALS AND METHODS Fruits were obtained from commercial orchards and from the University of Western Sydney Research Station. The NIR instrument was calibrated using a population 461 Proc. 6 th Intl. Peach Symposium Ed. R. Infante Acta Hort. 713, ISHS 2006