The main hydrophilic antioxidant compounds (3-, 4-and 5-monocaffeoylquinic and 3,4-, 3,5-and 4,5-dicaffeoylquinic acids, caffeine and browned compounds, including melanoidins) and the antioxidant capacity (Folin-Ciocalteau, ABTS, DPPH, Fremy´s salt and TEMPO) were evaluated in Arabica and Robusta spent coffee obtained from the preparation of coffee brews with the most common coffeemakers (filter, espresso, plunger and mocha). All spent coffee grounds, with the exception of those from mocha coffeemaker, had relevant amounts of total caffeoylquinic acids (6.22-13.24 mg/g of spent coffee), mainly dicaffeoyquinic acids (3.31-5.79 mg/g of spent coffee) which were 4-7 fold higher than in their respective coffee brews. Caffeine was ranged from 3.59 to 8.09 mg/g of spent coffee. The antioxidant capacity of the aqueous spent coffee extracts was 46.0-102.3% (filter), 59.2-85.6% (espresso), and less than 42% (plunger) in comparison to their respective coffee brews. This study allowed us to obtain spent coffee extracts with antioxidant properties that can be used as a good source of hydrophilic bioactive compounds.

22The impact of cooking heat treatments (frying in olive oil, frying in sunflower oil and

Spent coffee that is produced in tons by restaurants and cafeterias, and consumers at domestic levels, could be a good opportunity to have an important source of natural antioxidants. The main aim of this work was to study the influence of several process factors on the antioxidant capacity extraction from spent coffee. Total phenolic compounds, radical scavenging activity (ABTS and DPPH) and browned compounds (Abs 420nm) of spent coffee extracts obtained with continuous (soxhlet 1h and 3h) and discontinuous methods (solid-liquid extraction and filter coffeemaker), several solvents (water, ethanol, methanol and their mixtures), successive extractions, and water with different pHs (4.5, 7.0 and 9.5) were carried out. Spent coffee extracts with the highest antioxidant capacity were obtained after one extraction with neutral water (pH 7.0) in a filter coffeemaker (24 g spent coffee per 400mL water). Furthermore, spent coffee defatting and extracts lyophilization allowed us to obtain spent coffee extracts powder with high antioxidant capacity that can be used as an ingredient or additive in food industry with potential preservation and functional properties.

A total of 21 (poly)phenolic compounds (free and bound) were quantified in raw, olive oil fried, sunflower oil fried and griddled green pepper before and after a simulated gastrointestinal digestion. Flavonoids, particularly quercetin rhamnoside, were the main compounds. The bioaccessibility of (poly)phenolic compounds after gastrointestinal digestion was higher in cooked (>82%) than in raw (48%) samples, showing a positive effect of heat treatment on the release of (poly)phenols from the vegetal matrix. Additionally, a fecal fermentation was carried out for 24h. A time-dependent microbial metabolic activity was observed, which resulted firstly (<5h) in the hydrolysis of flavonoid glycosides and then in the formation of 3 catabolites, namely 3,4-dihydroxybenzoic acid, dihydrocaffeic acid and 3-(3'-hydroxyphenyl)propionic acid, this being by far the most abundant. Catabolic pathways for colonic microbial degradation of flavonoids and hydroxycinnamic acids have been proposed. Griddled pepper showed the highest amount of (poly)phenols both after gastrointestinal digestion and colonic fermentation.

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