Texture, composition and anatomy of spinach leaves in relation to nitrogen fertilization.
BACKGROUND
The postharvest quality and shelf life of spinach are greatly influenced by cultural practices. Reduced spinach shelf life is a common quandary in the Salinas Valley, California, where current agronomic practices depend on high nitrogen (N) rates. This study aimed to describe the postharvest fracture properties of spinach leaves in relation to N fertilization, leaf age and spinach cultivar.


RESULTS
Force-displacement curves, generated by a puncture test, showed a negative correlation between N fertilization and the toughness, stiffness and strength of spinach leaves (P > 0.05). Younger leaves (leaves 12 and 16) from all N treatments were tougher than older leaves (leaves 6 and 8) (P > 0.05). Leaves from the 50 and 75 ppm total N treatments irrespective of spinach cultivar had higher fracture properties and nutritional quality than leaves from other N treatments (P > 0.05). Total alcohol-insoluble residues (AIR) and pectins were present at higher concentrations in low-N grown plants. These plants also had smaller cells and intercellular spaces than high-N grown leaves (P > 0.05).


CONCLUSIONS
Observed changes in physicochemical and mechanical properties of spinach leaves due to excess nitrogen fertilization were significantly associated with greater postharvest leaf fragility and lower nutritional quality.
Department of Plant Sciences, University of California, Davis, CA 95616, USA. egrgutierrez@ucdavis.edu
Eduardo
E
Gutiérrez-Rodríguez
Heiner J
HJ
Lieth
Judith A
JA
Jernstedt
John M
JM
Labavitch
Trevor V
TV
Suslow
Marita I
MI
Cantwell
D002140:California; D048429:Cell Size; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D055598:Chemical Phenomena; D005110:Extracellular Space; D005308:Fertilizers / Q000009:adverse effects; D063427:Food Quality; D006801:Humans; D055595:Mechanical Phenomena; D058458:Nitrogen Cycle; D009753:Nutritive Value; D010368:Pectins / Q000032:analysis / Q000378:metabolism; D010860:Pigments, Biological / Q000032:analysis / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry* / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D013045:Species Specificity; D018724:Spinacia oleracea / Q000737:chemistry* / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism; D014867:Water / Q000032:analysis
D005308:Fertilizers; D010860:Pigments, Biological; D014867:Water; D010368:Pectins