39B-5

A. B. NORA¹, C. D. T. Marita², P. Galen², and M. S. Edmundo¹. (1) Departamento de Investigacion y Posgrado en Alimentos, Universidad Autonoma de Queretaro, Centro Universitario S/N, Cerro de las Campanas, Queretaro, 76010, Mexico, (2) Vegetable Crops, University of California, Mann Laboratory, Davis, CA 95616-8746

JUSTIFICATION: The jicama (Pachyrhizus erosus) is a sweet-starchy root with potential as a fresh-cut product. Browning of the cut surfaces can be a problem even during storage at low temperatures. To develop effective discoloration control measures, it is important to know whether discoloration is associated with metabolism of phenolic compounds.

OBJECTIVE: To determine if there are wound-induced changes in phenolic enzyme activities and phenolic concentrations, and whether these changes are associated with discoloration of fresh-cut jicama.

METHODS: Jicama cylinders (1.8 x 0.5 cm) were prepared, sanitized in 50 ppm NaOCl, and stored in air at 5, 7.5 and 10°C during 9 days. L*a*b* color measurements were determined with a reflectance colorimeter and chroma values were calculated. Samples were taken daily for analysis of PAL (Phenylalanine ammonia lyase) and PPO (Polyphenol oxidase) activities in crude extracts, using phenylalanine and coumaric acid as substrates. Phenolic compounds were extracted with 80% ethanol and determined colorimetrically.

RESULTS: Concentrations of total phenolic compounds increased during storage and were highly correlated in time with changes in chroma at the 3 storage temperatures. Color changes were greater at higher storage temperature. Wound-induced PPO activities reached similar maximal levels within 1 day of cutting regardless of temperature, and declined after day 3. Wound-induced PAL activities were temperature dependent with maxima occurring at 4 and 6 days at 10 and 7.5°C, respectively. PAL activity was barely detectable at 5°C and no discoloration or increase in phenolics was observed until day 9. PAL activities were about 10% those observed in cut lettuce.

SIGNIFICANCE: Color changes in fresh-cut jicama were associated with increased concentrations of phenolic compounds. Changes in PAL and PPO activities did not fully explain the increase in discoloration of the pieces, indicating that other mechanisms are probably also associated with color change in fresh-cut jicama.