Potato Sprout Inhibition and Tuber Quality after Treatment with High-Energy Ionizing Radiation

American Journal of Potato Research, Jan/Feb 2006 by Frazier, Mary Jo, Kleinkopf, Gale E, Brey, Richard R, Olsen, Nora L

ABSTRACT

The use of industrial-type linear accelerators may be an alternative treatment for controlling sprouts in potatoes during long-term storage. The technical aspect of treatment has been described and may include large-scale treatment of bulk potatoes as they are moving along a system of conveyors either to or from storage. The objective of the study was to evaluate the use of a linear accelerator for long-term sprout control under commercial storage conditions and the effects on tuber quality. An 18-MeV linear accelerator was used to provide sprout-inhibiting irradiation to various lots of 'Russet Burbank' potatoes. Successful sprout suppression was achieved with doses of 40 to 50 Gy (0 g sprout weight after 9 months of storage at 7.2 C) while higher doses caused undesirable increases in reducing sugars in the tubers. Glucose concentrations of treated tubers (0.25% fresh tuber weight) were higher after treatment than the untreated controls (0.08%), but returned to control levels after 2 to 6 months in storage. Glucose concentrations in treated tubers were significantly reduced with storage management for reconditioning by increasing the storage temperature for one month (from 7.2 C to 14.4 C) resulting in glucose concentrations near control concentrations. By increasing the dose-rate from the accelerator, recovery of tuber glucose concentration due to radiation treatments was significantly faster than when the dose was given more slowly. Potato tubers irradiated with high rates (100 Gy) of high-energy electrons exhibited an increase in soft rot and dry rot incidence in storage. Disease development in potatoes treated with sprout inhibiting doses of radiation (50 Gy) increased in lots with a high rot potential. Treated lots with low rot potential were successfully stored for 8 months or more without an increase in rot potential or shrinkage. Selection of lots for irradiation treatment should include some preliminary evaluation for development of disease in long-term storage.

RESUMEN

El uso de acelerador linear de irradiación de tipo industrial puede ser un tratamiento alternativo para controlar el brotamiento de los tubércules de papa durante periodos largos de almacenaje. El aspecto técnico del tratamiento ya fue descrito anteriormente y puede incluir el tratamiento en gran escala de grandes volúmenes de papa a medida de que se transportan del o hacia el almacén. El objetivo de este estudio fue evaluar el uso de un acelerador lineal para controlar el brotamiento por largo tiempo, bajo condiciones comerciales de almacenamiento y su efecto sobre la calidad del tubérculo. Se utilizó un acelerador lineal 18-MeV para aplicar la irradiación de inhibición del brotamiento a varios lotes de papa 'Russet Burbank'. Se consiguió una mejor supresión de brotes con dosis de 40 a 50Gy (0g de peso de brotes después de nueve meses de almacenaje a 7.2 C), mientras que dosis más altas causaron el aumento indeseable de azúcares reductores en los tubércules. Las concentraciones de glucosa de los tubérculos tratados (0.25% del peso fresco del tubérculo) fueron más altas después del tratamiento que en los testigos sin tratar (0.08%), pero volvieron a niveles del testigo después de dos a seis meses de almacenaje. Las concentraciones de glucosa en los tubérculos tratados se redujeron significativamente con un manejo de reacondicionamiento del almacén, incrementando la temperatura por un mes (de 7.2 C a 14.4 C), lo que dio como resultado que las concentraciones de glucosa estuvieran cercanas a las del testigo. Incrementando la velocidad de aplicación del acelerador, la recuperación de la concentración de glucosa de los tubérculos, debida a los tratamientos de radiación fue significativamente más rápida que cuando se aplicó más lentamente. Los tubérculos de papa irradiados con tasas altas (100 Gy) de electrones de alta energía mostraron en el almacén un incremento en pudrición blanda y pudrición seca. El desarrollo de enfermedades en papa tratada con cantidades de radiación inhibidoras de brotes (50 Gy) incrementó el potencial de pudrición. Los lotes tratados, con potencial bajo de pudrición fueron muy bien almacenados por ocho meses sin presenter un incremento de pudrición o arrugamiento. La selección de lotes para el tratamiento de irradiación debería incluir evaluación preliminar para el desarrollo de enfermedades en almacenamiento prolongado.

Accepted for publication 4 August 2005.

ADDITIONAL KEY WORDS: linear accelerator, reducing sugars, long-term storage

ABBREVIATIONS: MeV, Megaelectron volts; µS, Microseconds; g, grams; Gy, gray (the derived SI unit for the absorbed dose of ionizing radiation, equal to absorption of 1 joule per kilogram); mL, milliliters; NIST, National Institute of Standards and Technology

INTRODUCTION

Consumers and the potato (Solanum tuberosum L.) processing industry are accustomed to having fresh, high-quality potatoes available year round from long-term storage. The use of chemical sprout inhibitors, mainly chlorpropham (Isopropyl N-(3-chlorphenyl)carbamate, CIPC), has made this possible. During 2002, the Food Quality Protection Act required a reevaluation of CIPC, which resulted in a proposed reduction of 40% allowable residual of CIPC on fresh potatoes. This reduction emphasizes the need to evaluate alternative sprout control methods. Without effective spout inhibition the economics of the potato industry would be drastically altered. Guenthner et al. (1999) have estimated the value of CIPC to the U.S. potato industry at $56 million per year. Without sprout suppressants, potatoes for the fresh market would have to be stored at temperatures cold enough to prevent sprouting or shipped long distances from winter production areas. Potatoes for processing cannot be stored at cold temperatures because of the resulting accumulation of reducing sugars that negatively affect quality of the processed product. Processing would then be limited to the period from harvest to dormancy break and the output of all processing facilities would be drastically reduced.