Nonenzymatic Lignification of Asparagus?

The hypothesis of nonenzymatic lignification was investigated in asparagus. Samples were stored within 2 h of harvesting at 22C, 4C and ‐ IOC and tested daily, every second day and at 30‐day intervals, respectively. Some asparagus was blanched at IOOC for 3 min prior to storage. Assays for peroxiduse and polyphenoloxidase showed no enzymatic activity in the blanched samples. Toughness, as measured by Warner‐Bratzler shear force, and crude fiber content (mechanically separated) significantly (P< 0.05) increased in both blanched and unblanched samples over the testing period at all storage conditions. Crude fiber content and shear measurements were significantly (P < 0.05) higher for the enzyme active controls. Microscopic examinations using light (LM) and scanning electron microscopy (SEM) were canied out to locate the site of lignin deposition and to quantify the extent of lignification. Sections viewed using LM techniques were stained to observe useful fluorescence (crystal violet ‐ erythrosin B) and differentiate ligniped from nonlignified cell walls fast green safranin and crystal violet ‐ ertythrosin 8). In samplesfrom each treatment and storage condition, three independent techniques indicated a significant (P < 0.05) increase in: (1) the width of the mechanical tissue layer; (2) the thickness of the cell walls of the cells comprising the mechanical tissue layer, and; (3) the thickness of the xylem vessel walls of the vascular bundles. Also, significant (P C 0.05) differences were detected between the extent of lignification of unblanched and blanched samples. These data suggest that a nonenzymatic “toughening” mechanism does occur in blanched asparagus tissue and that it may be related to lignin deposition.