Influence of Brewing Method and Acidity Regulators on the Antioxidant Capacity of Coffee Brews

Abstract

Antioxidant capacity of the coffee brews prepared with different coffeemakers (filter, plunger, mocha and espresso) was measured by colorimetric (Total Phenolic compounds and ABTS) and Electro Spin Resonance (ESR) spectroscopy techniques (Fremy's salt and TEMPO). Mocha coffeemaker had the highest yield in coffee antioxidant extraction per g of ground roasted coffee, but espresso coffee was the richest in terms of antioxidant intake (per mL of coffee brew) followed by mocha, plunger and filter. Both Folin-Ciocalteau (Total Phenolic compounds) and ABTS assays reacted with standard solutions of chlorogenic acids (CGA) and melanoidins (MO-Ala and MO-Gly). However, Fremy's salt was mainly scavenged by chlorogenic acids, whereas the stabilized radical TEMPO was effectively scavenged by melanoidins, but not by chlorogenic acids. Thus, electron spin resonance (ESR) spectroscopy allows distinguishing between phenolic and nonphenolic antioxidants.Moreover, the addition of pH-regulator agents to coffee, such as sodium carbonate (75ppm) and bicarbonate (75ppm), to extend its shelf-life, slightly increases the pH, modifying the antioxidant capacity in those coffee brews with the highest capacity (mocha and espresso).

Evaluation of Spent Coffee Obtained from the Most Common Coffeemakers as a Source of Hydrophilic Bioactive Compounds

“…12,28 As it is shown in Figure 2, ESR antioxidant capacity of Arabica spent coffee from espresso coffeemaker was lower than that from filter one, whereas for Robusta spent coffee these results were reversed. The behaviour of the results of antioxidant capacity measured by Fremy's salt technique (Figure 2a) was similar to those obtained by the colorimetric assays, but rather different to that of the amounts of caffeoylquinic acids in spent coffee.…”

“…Moreover, although Fremy's salt is mainly scavenged by chlorogenic acids, other antioxidants, including melanoidins, can scavenge this stabilized radical in a nonspecific manner and in a very low proportion. 12,47 On the other hand, TEMPO scavenging capacity (Figure 2b) was at least 10 fold lower than Fremy's salt, showing that the contribution of roasting-induced antioxidants is rather limited in spent coffee. Similar behaviour was also observed in coffee brews by other authors.…”

“…This higher result might be explained by the slightly higher browning index (Abs 420nm 0.165), but also because melanoidins have different antioxidant capacities, depending on the structure, their composition and the phenolics bound in their skeleton. 12,[47][48][49] In conclusion, spent coffee obtained from the most common coffeemakers used at domestic and cafeterias level (filter and espresso), and in less proportion from plunger ones, could be considered as a good potential source of hydrophilic bioactive compounds. These compounds are easily extracted with water to obtain extracts with antioxidant properties that might be used in food and pharmaceutical industries to increase food nutritional values, product stability or to develop new healthy products.…”

“…Similar behaviour was also observed in coffee brews by other authors. 12,32,47 For that reason, all TEMPO results should be considered as very low, including the significantly higher TEMPO antioxidant capacity of the aqueous extracts obtained from Arabica spent coffee grounds from filter coffeemaker. This higher result might be explained by the slightly higher browning index (Abs 420nm 0.165), but also because melanoidins have different antioxidant capacities, depending on the structure, their composition and the phenolics bound in their skeleton.…”

“…8,10 Similarly, the spent coffee grounds originated by the preparation of a cup of coffee might also contain relevant amounts of bioactive compounds. However, a direct transfer of the results of industry soluble coffee extraction to coffee brew preparation is not possible because, despite the type of coffee, there is a clear influence of (i) different coffee brewing procedures, including different coffeemakers, 11,12 but also (ii) technological factors, such as water temperature and pressure, coffee/water ratio, grinding, etc. on the extraction of coffee compounds.…”