1141 Prediction of Spinach Quality Based on Pre- and Postharvest Conditions E. Gutiérrez-Rodríguez, J.H. Lieth, J.A. Jernstedt and T.V. Suslow Department of Plant Sciences University of California Davis, CA 95616 USA Keywords: spinach, nitrogen, organic acids, ammonium, glutamine synthetase, storage Abstract Nitrogen amendments and water availability have a significant effect on the nutritional quality of spinach. Despite this established knowledge, the specific influence of these interacting factors on overall postharvest quality is poorly under- stood. Determined by interviews with multiple growers, current agronomic practices in California and Arizona routinely include the application of 100 to 350 kg/ha total N. Preharvest trials and postharvest evaluations with field and hydroponically-grown spinach were conducted to elucidate how this fertility management practice influences quality. Additionally, quantitative evaluations were performed to identify predictors of market quality at harvest and during storage. Preharvest nitrogen availability greater than 100 ppm coupled with high temperature during cultivation reduced the overall quality of spinach. Color (hue) of spinach grown under various N rates and stored at 7.5°C (in perforated polymer-film packaging) did not reliably predict the key phyto- nutrient composition and marketable shelf life. Marketable shelf life was initially defined as a combination of visual quality score (OVQ) ≥6.5 (on a 9 point hedonic scale), decay <1%, and ascorbic acid concentrations ≥35 mg/100 g FW. Ammonium accumulation more reliably anticipated the reduction of quality during storage than other parameters taken as single assessment indicators. Changes in respiration rates, chlorophyll and carotenoid concentrations during storage were poor indicators of marketable shelf life. More accurate quality retention projections were achieved by combining ammonium concentrations with measurements of glutamine synthetase (GS) activity at harvest. Total organic acids (TOA) and sugar content >3.5 mg/g FW at harvest were negatively associated with quality retention. Although storage tempera- tures significantly affect quality retention in spinach, the initial quality at harvest is the main factor that influences inherent postharvest potential. Spinach pre- and postharvest quality is best predicted by analysis of TOA, sugar concentrations and the relationship between ammonium and GS at harvest while during storage OVQ, TOA and ammonium concentrations were practical descriptors of marketable shelf life. INTRODUCTION Postharvest management for spinach focuses mainly on temperature control and water loss. Because of its high respiration rates (40-70 ml CO 2 /kg-h at 10°C) and its high sensitivity to ethylene and elevated CO 2 concentrations, spinach needs to be cooled in an expedited manner soon after harvest (Suslow and Cantwell, 2009). Once spinach has been packaged, high oxygen and low carbon dioxide concentrations at temperatures close to 0°C favor high spinach quality (Cantwell et al., 1998; Suslow and Cantwell, 2009). There have been several attempts to describe the postharvest quality of spinach during storage at different temperatures based on color and visual quality measurements as well as chlorophyll, and carotenoid content. Although reproducible results were described, the marked differences in storage temperatures were the driving factor in the quality assessments reported. The objective of this study was to characterize those quality assessments at harvest that could predict the postharvest quality of spinach during storage associated with N fertilization. Proc. XXVIII th IHC – IS on Postharvest Technology in the Global Market Eds.: M.I. Cantwell and D.P.F. Almeida Acta Hort. 934, ISHS 2012