Postharvest Biology and Technology 60 (2011) 130–135 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio Testing of a local approach for the prediction of quality parameters in intact nectarines using a portable NIRS instrument María-Teresa Sánchez a,∗ , María-José De la Haba a , José-Emilio Guerrero b , Ana Garrido-Varo b , Dolores Pérez-Marín b,∗ a Department of Bromatology and Food Technology, University of Cordoba, Campus Rabanales, 14071 Cordoba, Spain b Department of Animal Production, University of Cordoba, Campus Rabanales, 14071 Cordoba, Spain article info Article history: Received 3 September 2010 Accepted 10 December 2010 Keywords: NIR spectroscopy Nectarine Portable sensor Quality parameters LOCAL algorithm abstract The nectarine sector requires rapid, economical and non-destructive methods for monitoring physical–chemical quality changes taking place not only during fruit development and at harvest, but also postharvest, thus allowing fruit quality to be evaluated at any stage in the commercial chain from grower to consumer. The use of sensors based on Near Infrared Spectroscopy (NIRS) technology, in conjunction with chemometric data treatment models, has already been studied for this quality-control purpose in nectarines. The critical challenge is to develop robust and accurate mathematic models based on hun- dreds of highly heterogeneous nectarine samples in order to represent the large natural variability of the fruit. This paper evaluates and compares the performance of MPLS regression and a local regression method for the prediction of major quality parameters including size (weight and diameter), flesh firm- ness and soluble solids content (SSC), in nectarines representing different harvests and crop practices. The results showed that the LOCAL algorithm offered no advantages over MPLS regression for the pre- diction of SSC and diameter, and only slight benefits in weight determination. For firmness evaluation, however, application of the LOCAL algorithm yielded a major improvement, reducing the standard error of prediction (SEP) by 27%, increasing the coefficient of determination (r 2 ) by 44% (from 0.47 to 0.68), and reducing bias by 88.5% (from 6.95 N to 0.80 N). Thus, use of the LOCAL algorithm proved to be valuable in minimizing the error in NIRS models for predicting a parameter as complex as firmness. © 2010 Elsevier B.V. All rights reserved. 1. Introduction The stonefruit sector requires rapid, nondestructive analytical techniques for assessing external and internal fruit quality charac- teristics, enabling on-site and in-line classification and certification of fruit, based on quality criteria prior to harvest, in packaging plants, and even in supermarkets. Near infrared spectroscopy (NIRS) has been developed and used as a convenient nondestructive technique for the indi- vidual quantitative and qualitative characterization of many kinds of fruit, avoiding possible discrepancies between differ- ent batches and samples, and giving rise to a new approach to market segmentation and fruit evaluation in both fresh and processed markets (Bureau et al., 2009). Previous research has demonstrated the potential of NIR spectroscopy for the predic- tion of quality parameters in stonefruit (Nicolaï et al., 2007; ∗ Corresponding authors. Tel.: +34 957 212576; fax: +34 957 212000. E-mail addresses: teresa.sanchez@uco.es (M.-T. Sánchez), dcperez@uco.es (D. Pérez-Marín). Fu et al., 2008; Paz et al., 2008; Pérez-Marín et al., 2009, 2010). In a previous paper, Pérez-Marín et al. (2009) developed NIRS models for the simultaneous prediction of three major quality parameters in nectarines: size (weight and diameter), flesh firm- ness, and SSC, using MPLS regression and two types of instruments, a MEMS-based spectrometer highly suited to field measurement, and a diode-array spectrometer better suited to on-line use in the packing house. Their results confirmed the feasibility of NIRS tech- nology for monitoring key nectarine quality attributes both in the field and in the laboratory. Although better results were obtained with the diode-array instrument, the handheld spectrometer also proved to be a promising instrument for the nondestructive in-field evaluation of nectarine quality, particularly for measuring SSC and firmness, as well as affording the additional advantages of porta- bility and low cost. Using the handheld instrument, suitable for routine use under field conditions in order to predict more precisely the timing of harvest operations and thus ensure the highest-possible fruit qual- ity, the present paper sought to update the calibrations employing samples drawn from later harvests under a range of agronomic 0925-5214/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2010.12.006