Two widely applied spectrophotometric assays based on aluminium complex formation used for determination of total flavonoid content in food or medicinal plant samples were examined for several compounds from different classes of flavonoid family. The method which involves the measurement at 410–430 nm after addition of AlCl₃ solution is selective only for flavonols and flavones luteolin. The procedure in the presence of NaNO₂ in alkaline medium seems to be specific for rutin, luteolin and catechins, but also phenolic acids exhibit considerable absorbance at 510 nm. Application of both procedures to natural samples gave different order in terms of their flavonoid content. Thus, the expression “total flavonoid” content is not adequate as the results of both methods are dependent on the structure of the individual flavonoids present.

Hesperidin is a bioflavonoid occurring in high concentrations in citrus fruits. Its use has been associated with a great number of health benefits, including antioxidant, antibacterial, antimicrobial, anti-inflammatory and anticarcinogenic properties. The food industry uses large quantities of citrus fruit, especially for the production of juice. It results in the accumulation of huge amounts of by-products such as peels, seeds, cell and membrane residues, which are also a good source of hesperidin. Thus, its extraction from these by-products has attracted considerable scientific interest with aim to use as natural antioxidants. In this review, the extraction and determination methods for quantification of hesperidin in fruits and by-products are presented and discussed as well as its stability and biological activities.

The 2,2-diphenylpicrylhydrazyl (DPPH) assay is widely used in plant biochemistry to evaluate the properties of plant constituents for scavenging free radicals. The method is based on the spectrophotometric measurement of the DPPH concentration change resulting from the reaction with an antioxidant. Several protocols have been followed for this assay using different conditions such as different reaction times, solvents, pH and different compounds used as antioxidant standards. This review shows to what extent the mentioned parameters have the influence on the presented results.

Chlorogenic acids and caffeine are important for flavor formation as well as the health effect of green coffee brews and its extracts. The content of these compounds was determined by HPLC–DAD analysis in twelve samples of coffee from Robusta and Arabica types of different geographical origin including steamed and decaffeinated coffees. Generally, Robusta coffee extracts contain twice as much caffeine as Arabica, and its content varies from 3.41 % per dry mass in Arabica type from Laos or Rwanda to 8.16 % in Robusta coffee from Indonesia. The highest concentration of 5-O-caffeoylquinic acid (5-CQA) was obtained for both coffees from Uganda. Decaffeination process does not affect the concentration of this main chlorogenic acid, but steaming of the coffee beans with hot water produced a significant decrease in the level of 5-CQA. Antioxidant activity of coffee extracts was measured by CUPRAC and F–C assays, which really measure the reducing power of the sample components. Extracts of green coffee beans from Vietnam possessed the highest antioxidant activity in both assays.