NITROGEN FERTILISER RATE AFFECTS THE N-FRACTIONS OF CELERY PETIOLES FOR THE FRESH PROCESSING INDUSTRY

Abstract

The objective of this research was to study the effect of two N fertiliser rates on the protein, nitrate and ammonia contents of celery stalks used as raw material for the minimal fresh processing industry. Green celery plants ('Istar') were grown on an inert substrate in a plastic greenhouse where, after the first month, two treatments were applied: a control (NC) with the commonly applied N concentration and a 25% reduction in N concentration (RN). Remaining nutrients were kept at the same level for RN and CN. Plants were hand harvested and the following fractions were prepared: leaves, petioles, internal stalks and basal disc. Total-N, N-protein, N-nitrate and N-ammonia contents were analysed. The protein content of the petioles (fraction used by the industry for producing celery sticks) was not affected by the level of fertiliser. However, a positive correlation was found between the rate of N fertiliser and the nitrate and ammonia concentration. Since the ingestion of excessive amounts of nitrate can cause adverse effects on health, celery grown under 25% lower N supply could be considered safer from the nutritional point of view and, at the same time, with an adequate level of proteins. Organoleptic properties were not affected by the rate of fertiliser. No undesirable changes in quality factors (firmness, visual appearance, flavour) of interest for minimal fresh processing due to low N supply were found.