The antioxidant properties of green and roasted coffee, in relation to species (Coffea arabica and Coffea robusta) and degree of roasting (light, medium, dark), were investigated. These properties were evaluated by determining the reducing substances (RS) of coffee and its antioxidant activity (AA) in vitro (model system beta-carotene-linoleic acid) and ex vivo as protective activity (PA) against rat liver cell microsome lipid peroxidation measured as TBA-reacting substances. RS of C. robustasamples were found to be significantly higher when compared to those of C. arabica samples (p < 0.001). AA for green coffee samples were slightly higher than for the corresponding roasted samples while PA was significantly lower in green coffee compared to that of all roasted samples (p < 0.001). Extraction with three different organic solvents (ethyl acetate, ethyl ether, and dichloromethane) showed that the most protective compounds are extracted from acidified dark roasted coffee solutions with ethyl acetate. The analysis of acidic extract by gel filtration chromatography (GFC) gave five fractions. Higher molecular mass fractions were found to possess antioxidant activity while the lower molecular mass fractions showed protective activity. The small amounts of these acidic, low molecular mass protective fractions isolated indicate that they contain very strong protective agents.

The antiradical properties of water-soluble components of both natural and roasted barley were determined in vitro, by means of DPPH* assay and the linoleic acid-beta-carotene system, and ex vivo, in rat liver hepatocyte microsomes against lipid peroxidation induced by CCl4. The results show the occurrence in natural barley of weak antioxidant components. These are able to react against low reactive peroxyl radicals, but offer little protection against stable DPPH radicals deriving from peroxidation in microsomal lipids. Conversely, roasted barley yielded strong antioxidant components that are able to efficiently scavenge free radicals in any system used. The results show that the barley grain roasting process induces the formation of soluble Maillard reaction products with powerful antiradical activity. From roasted barley solution (barley coffee) was isolated a brown high molecular mass melanoidinic component, resistant to acidic hydrolysis, that is responsible for most of the barley coffee antioxidant activity in the biosystem.

The water soluble antioxidant properties of carrot, cauliflower, celery, eggplant, mushroom, garlic, onion, white cabbage, white potato, tomato, yellow bell pepper, and zucchini were investigated. Vegetable juices were obtained by centrifugation, and each antioxidant property was determined in terms of the protective activity (PA%) against rat liver microsome lipid peroxidation induced by CCl 4 and measured by malondialdehyde release. All juices were found to be active. PA was very high (90-100%) and constant (relative standard deviation (RSD) ) 4-7) for mushroom, garlic, cauliflower, and potato. For white cabbage, zucchini, and eggplant the PA reached similar values (80%) but was less constant (RSD ) 12-15). Onion and yellow bell pepper showed high PA (75%) which was more variable (RSD ) 20-24), and the PA for tomato and celery was less high (50%) and very variable (RSD ) 25), especially in the case of carrot juice (6%) (RSD ) 50). The juices were also analyzed after different technological treatments (boiling, freezing, and freeze-drying). In general, boiling and freezing juices resulted in a slightly decreased PA while freeze-drying slightly increased their PA values. Cluster analysis was carried out considering the PA values of the variously treated juices and their relative RSD values and permitted us to subdivide the vegetables according to their behavior. Juice components were separated according to their polarity on a Baker C 18 cartridge. Bound and unbound fractions obtained from each vegetable juice were shown to be protective against lipid peroxidation with the exception of the bound yellow bell pepper fraction. The results pointed out different interactions between the vegetable juice components.

One of the most extensively studied and best-established properties of coffee is its antioxidant activity. We have shown that coffee brew has the ability to inhibit lipid peroxidation completely in a rat liver microsome biological system. The inhibitory activity was mainly due to the high molecular weight (HMW) fraction; this consisted of five components that were isolated, purified, and seen to occur in different amounts in the brew. Each component had different spectra and element compositions, although they all contained nitrogen. HMW, nitrogen content, and brown color enabled three components to be attributed to the melanoidin family; the two nonbrown components could not be considered as melanoidins. Each melanoidin and nonmelanoidin component contributes to a different extent to the protective action exerted by coffee brew. None of the isolated components completely inhibited microsomal lipid peroxidation alone, suggesting that each acts at different sites and/or possesses different mechanisms of action. The protective activity of coffee brew is thus underpinned by the antiradical properties, reducing power, and metal chelating ability of the individual components, each contributing to a different extent.

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