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The processing of fruits results in high amounts of waste materials such as peels, seeds, stones, and oilseed meals. A disposal of these materials usually represents a problem that is further aggravated by legal restrictions. Thus new aspects concerning the use of these wastes as by-products for further exploitation on the production of food additives or supplements with high nutritional value have gained increasing interest because these are high-value products and their recovery may be economically attractive. It is well known that by-products represent an important source of sugars, minerals, organic acid, dietary fibre and phenolics which have a wide range of action which includes antitumoral, antiviral, antibacterial, cardioprotective and antimutagenic activities. This review discusses the potential of the most important by-products of apple, grape and citrus fruits processing as a source of valuable compounds. The relevance of this topic is illustrated by a number of references.

The results of this study confirm that vitamin C and flavonoids are responsible for the antioxidant activity of rosehip tea, while only polyphenols contribute to its antiproliferative activity.

Grape seed extracts (GSEs,) obtained from Italian and Rhine Rieslings, were examined for polyphenolic composition and antioxidant activities using HPLC and ESR spectrometry. The seed extraction was carried out with ethyl acetate and ethanol. The contents of polyphenols, flavan-3-ols and antioxidant activities were found to be higher in ethyl acetate than in ethanolic extracts. IC 50 values were 0.1045 mg/mL and 0.0599 mg/mL for the stable DPPH radical in ethanolic and ethyl acetate extracts, respectively. The values for the shortlived OH radical were 0.1989 mg/mL and 0.0362 mg/mL, in the given order. The significant correlations between the antioxidant activities of GSEs and polyphenols were established (P < 0.05). Owing to their antioxidant activities, the cultivars could be used as a source to produce a GSE.

In an effort to discover new antioxidant natural compounds, wormwood (Artemisia absinthium L) an aromatic-bitter herb, was screened. The sequential extraction was realized with five solvents of different polarities (70% methanol, petroleum ether, chloroform, ethyl acetate, n-butanol). The antioxidative activity was tested by measuring their ability to scavenge stable 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical and reactive hydroxyl radical during the Fenton reaction trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), using electron spin resonance (ESR) spectroscopy. Results demonstrated that the antiradical and antioxidative activity depend on the type and concentration of applied extracts and increased in the order ethyl acetate > methanol > n-butanol > chloroform > petroleum ether > remaining water extracts. The investigation showed that the antiradical activity increased with increasing concentration of all extracts. The high contents of total phenolic compounds (25.6 mg g −1 ) and total flavonoids (13.06 mg g −1 ) indicated that these compounds contribute to the antiradical and antioxidative activity. In a model system, the formation of o-semiquinone radicals from quercetin and chlorogenic acid was obtained to prove the mechanism (hydrogen donating and/or one-electron reduction) of free-radical scavenging activity.

AbstractČanadanović-Brunet J.M., Savatović S.S., Ćetković G.S., Vulić J.J., Djilas S.M., Markov S.L., Cvetković D.D. (2011): Antioxidant and antimicrobial activities of beet root pomace extracts. Czech J. Food Sci., 29: 575-585.We described the in vitro antioxidant and antimicrobial activities of ethanol, acetone, and water extracts of beet root pomace. Total contents of phenolics (316.30-564.50 mg GAE/g of dry extract), flavonoids (316.30-564.50 mg RE/g of dry extract), betacyanins (18.78-24.18 mg/g of dry extract), and betaxanthins (11.19-22.90 mg/g of dry extract) after solid-phase extraction were determined spectrophotometrically. The antioxidant activity was determined by measuring the reducing power and DPPH scavenging activity by spectrometric metod, and hydroxyl and superoxide anion radical scavenging activity by ESR spectroscopy. In general, the reducing power of all the beet root pomace extracts increased with increasing concentrations. The DPPH-free radical scavenging activity of the extracts, expressed as EC 50 , ranged from 0.133 mg/ml to 0.275 mg/ml. Significant correlation was observed between all phytochemical components and scavenging activity. 0.5 mg/ml of ethanol extract completely eliminated hydroxyl radical, which had been generated in Fenton system, while the same concentration of this extract scavenged 75% of superoxide anion radicals. In antibacterial tests, Staphylococcus aureus and Bacillus cereus showed higher susceptibility than escherichia coli and Pseudomonas aeruginosa.

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