Whole, concentrated and reconstituted grape juice: Impact of processes on phenolic composition, "foxy" aromas, organic acids, sugars and antioxidant capacity.

The concentration and reconstitution processes of grape juices can result in losing compounds associated with beverage quality. In this context, three tanks containing 50,000 L of grape juice were individually concentrated up to 68 °Brix using a triple vacuum concentrator. The concentrated juice was reconstituted up to the original °Brix of the whole juice (18.4). Phenolic compounds, sugars and organic acids were quantified by high-performance-liquid-chromatography. "Foxy" aromatic compounds were also quantified by gas-chromatography/mass-spectrometry. The concentration and reconstitution process resulted in significant losses (Tukey test, p < 0.01) of trans-caftaric acid, decreasing from 397.08 to 159.14 mg/L, chlorogenic-acid from 34.97 to 8.44 mg/L, aromatic furaneol compound from 9.06 to 1.93 mg/L, as well as total losses for gallic-acid, caffeic-acid, p-coumaric-acid, syringic-acid, hesperidin, pelargonidin-3-glucoside and epicatechin compounds. The concentration and reconstitution of grape juice preserved the antioxidant capacity and most of the quantified compounds, with the reconstituted juice having good nutritional quality.

Processing methods with heat increases bioactive phenolic compounds and antioxidant activity in grape juices.

In this work, the influence of the method of processing on phenolic composition and the in vitro antioxidant activity (AOX) of grape juices was studied. The classic methods of producing "Hot Press" (HP), "Hot Break" (HB), and "Cold Press" (CP), and an artisanal method using steam were compared. Among the methods of elaboration of evaluated grape juices, those that heated the grape showed higher content of bioactive phenolics and AOX. The artisanal method using steam presented acceptable bioactive content and could be simple alternative for grape juice production. The main bioactive compounds quantified in the studied juices were procyanidin B1, quercetin-3-pyranoside, chlorogenic acid, malvidin-3-glucoside, cyanidin-3-glucoside, and petunidin-3-glucoside. These were correlated by principal component analysis (PCA) with the antioxidant activity. The characteristics obtained from the different juice elaboration methods demonstrate that the HB method was responsible for the greatest extraction of bioactive compounds from the grapes. PRACTICAL APPLICATIONS: Worldwide consumption of grape juice has been increasing. The factors that have contributed to this growth include the good sensory acceptance and the nutritional appeal related to bioactive compounds. The bioactive compounds of grape juice are mainly flavonoids and phenolic acids, and several factors exert influence on the phenolic composition of this beverage, among them, the method of elaboration. The present work presents new information on the influence of grape juice processing methods on the profile of bioactive compounds of nutritional interest and contributes to improvements in the production processes of this beverage.

Integrated analyses of phenolic compounds and minerals of Brazilian organic and conventional grape juices and wines: Validation of a method for determination of Cu, Fe and Mn.

The phenolic profile and antioxidant activity (AOX) of "organic vs. conventional" Brazilian wines and grape juices were analyzed. A simple method for the determination of minerals Cu, Fe and Mn by F-AAS was validated and used to characterize the samples studied. In the validation of the Cu, Fe and Mn determination method, the protocol for samples preparation by hot digestion with HNO3 + H2O2 proved to be more suitable for the grape juice and wine matrices. The validation parameters were considered satisfactory. Conventional products presented higher anthocyanins content, and no significant differences were observed on other phenolic compounds, AOX and Cu, Fe and Mn minerals. All the evaluated samples presented similar results between the same cultivars and in products from grapes of the two cultivation systems. The AOX of juices and wines, organic and conventional, was high, and correlated with procyanidin B1, petunidin-3-glucoside and cyanidin-3,5-diglucoside.