Natural sources with high antioxidant capacity represent an interesting potential to prevent or minimize the oxidative stress that causes many chronic diseases. The antioxidant capacity of red fruits (strawberry and cherry) was evaluated by miniaturized spectrophotometric methods 2,2’-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and nitroblue tetrazolium (NBT). ABTS and DPPH colorimetric methods are based on the ability of antioxidants to scavenge synthetic free radicals produced in vitro, which have a different chemical structure from the natural reactive oxygen species generated in the human body. In this respect, the NBT method stands up because it is based on O2•– scavenging which is generated in vitro by enzymatic reaction systems. The spectrophotometric assays adapted on microtiter plates allowed a rapid, inexpensive and simultaneous analysis. Larger amounts of lipophilic and hydrophilic antioxidants were obtained from strawberry fruit, which showed the lowest 50% signal inhibition concentration (IC50) values. The fruit analyzed showed promising sources of bioactive compounds with high antioxidant properties.

Resumo A composição bromatológica, o conteúdo mineral e a capacidade antioxidante de 7 frutos nativos da Amazônia foram avaliados. Os frutos mostraram, em sua maioria, alto conteúdo de umidade (> 63,02%) e teores de cinzas, proteína bruta total e carboidratos totais na faixa de 0,22-2,07%, 0,17-2,44% e 7,17-41,71%, respectivamente. Os maiores teores em lipídios foram obtidos nos frutos de uxi (23,25%) e monguba (18,67%). Uma ampla variedade de minerais foi detectada, sendo as maiores concentrações obtidas nas amostras de sementes de monguba (Ca, Cu, Mg e Zn), polpas de uxi (Fe e Mn) e pajurá (Na). Todos os frutos mostraram atividade antioxidante, em que a polpa de pajurá revelou o maior potencial, semelhante estatisticamente à acerola (p < 0,05). Maiores teores em vitamina C foram obtidos nos frutos de bacuri e cupuaçu, fenólicos totais na monguba e pajurá, enquanto flavonóides foram determinados somente nos frutos de pajurá. Uma correlação positiva entre o teor de Na e a capacidade antioxidante também foi observada. Baseado nos resultados obtidos, os frutos analisados são adequados para uso na dieta humana, nas indústrias de alimentos e cosméticos, bem como em composições farmacêuticas.

Abstract The proximate compositions, mineral contents, antioxidant capacity and bioactive compounds of 7 native Amazon fruits were chemically evaluated. The majority of the fruits showed high moisture contents (> 63.02%), and ash, total crude protein and total carbohydrate contents in the ranges of 0.22–2.07%, 0.17–2.44% and 7.17–41.71%, respectively. High levels of total lipids were found in uxi (23.25%) and monguba (18.67%). A wide range of mineral contents was detected and the highest levels were found in the samples of monguba seeds (Ca, Cu, Mg, and Zn), uxi pulp (Fe, and Mn) and pajurá pulp (Na). All the fruits showed antioxidant capacity, but the pajurá revealed the highest potential, statistically similar to that of acerola (p < 0.05). The highest vitamin C contents were found in bacuri and cupuaçu and the highest phenolic compound contents in monguba and pajurá fruits, but flavonoids were only detected in pajurá. A statistical correlation between the Na content and antioxidant capacity was also observed. Based on the results obtained, the fruits analyzed are suitable for use in the human diet, in the food and cosmetics industries as well as in pharmaceutical compositions.

Initially, all major factors that affect the rate of the AldH-catalyzed reaction (enzyme concentration, substrate concentration, temperature and pH) were investigated. Optimal activity was observed between pH values of 7.5 and 9.5 in the temperature range of 25 to 50 ºC. Kinetic parameters, such as Km (2.92 µmol L-1) and Vmax (1.33 10-2 µmol min-1) demonstrate a strong enzyme-substrate affinity. The sensors were based on screen-printed electrodes modified with the Meldola Blue-Reinecke salt (MBRS) combination. Operational conditions (NAD+ and substrate contents, enzyme loading and response time) were optimized. Also, two enzyme immobilization procedures were tested: entrapment in poly(vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ) and crosslinking with glutaraldehyde. Chronoamperometry was employed to observe the biosensor responses during enzymatic hydrolysis of propionaldehyde and also to construct inhibition curves with maneb and zineb fungicides. Best results were found with the following conditions: [NAD+] = 0.25 mmol L-1; [propionaldehyde] = 80 µmol L-1; enzyme loading = 0.8 U per electrode; response time = 10 min, and inhibition time = 10 min. Current intensities around 103 ± 13 nA with the sensors and good stability was obtained for both immobilization procedures. Detection limits, calculated using 10% inhibition were 31.5 µg L-1 and 35 µg L-1 for maneb and zineb, respectively. Results obtained with other MBRS-modified electrodes consisting of mono and bi-enzymic sensors were compared. The ability to catalyze NADH oxidation by MB was also highlighted.