Phenolics, potatoes chlorogenic acid

Phenolic compounds in grains, fruits and vegetables act as antioxidants and may have health benefits. Total free phenolics, primarily chlorogenic acid, decreased significantly due to extrusion in potato peels produced by steam or abrasion peeling (unpublished data). We suspect that the lost phenolics react with themselves or with other compounds to form larger insoluble materials. 

Table 6.6 lists the phenolic acid content of 25 potato powders prepared by lyophilization of commercial potatoes with unknown history. For the dry lyophilized powders, the data show that chlorogenic acid levels (in mg/lOOg wt) ranged from 3.28 for Kenebec potatoes to 637 for... 

Polyphenol Oxidases. Plant trichomes and their exudates confer resistance to a variety of insects (54-56). In solanaceous plants, such as the tomato and potato, trichomes contain polyphenol oxidases and catecholic phenolics (e.g., caffeic and chlorogenic acids), which contribute to resistance to a variety of insect pests. In the potato plant, the polyphenol oxidases and phenolics are separated in different trichomes. When insects, such as aphids or leaf hoppers, walk across the surface of the plant they break the two types of trichomes. Trichomal fluids are liberated and, upon mixing, polymerize as a result of polyphenol oxidase activity on catechols, forming an often lethal adhesive trap for the insects (52,58) In tomato plants, the polyphenol oxidase and chlorogenic acid are separated by intracellular compartments, but upon breakage of trichomes by insects, polymerization and physical entrapment occurs (54). 

An HPLC study of the individual phenolic acid derivatives showed chlorogenic acid to be the predominant compound in potato (22-71 mg/kg). Cryptochlorogenic acid (11 mg/kg), neochlorogenic acid (7 mg/kg) and isochlorogenic acid (4,5-dicaffeoyl quinic acid) (Fig. 4) (3 mg/kg) were also present in smaller amounts [80]. It was also demonstrated that caffeic acid compounds are not distributed uniformly in the tuber, but occur in strongly decreasing concentrations from the outer to the inner section. About 50% of the compounds as a whole are located in the potato peel and adjoining tissue. 

Both constitutive phenolic acids and phytoalexins may be involved in the resistance of potatoes to Envinia sp. [94]. This resistance could result from the increase of calFeic, chlorogenic, and ferulic acids and the formation of suberized barriers after wound injury or pathogen attacks [11,63,94]. Both polyester-forming HCAs and Ugninlike monolignols of potato suberin constitute a dense... 

Phenolic Acids acid chlorogenic Grapefruit, potato... 

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