Polyphenol in grape juices : stability during processing and storage / Polifenois em suco de uva : investigaçao sobre a estabilidade durante o processo e armazenamento

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Epidemiological studies have demonstrated that polyphenol-rich foods and beverages exert beneficial physiological effects. Grape juices are relevant sources of flavonoids, particularly flavan-3-ols, mostly in the monomeric forms of catechins [(+)-catechin and (-)-epicatechin]. The objectives of this work were to characterize and quantify phenols (TP), catechin monomers (CAT+EPI), radical scavenging activity (RSA) and specific sensory attributes during processing and storage of commercial grape juices. Concentrated Concord (CCJ) and Isabel (CIJ) grapes juices (68° Brix) were sampled during processing an d after concentration and stored at 5°C. Pasteurized ready-to-drink juices (1 4 to 19° Brix) of the same grape cultivars (PCJ and PIJ) were kept at room temperature under indirect lighting for 10 months, both simulating industrial/commercial storage conditions. TP were determined using the Folin-Ciocalteu method; CAT+EPI by HPLC with fluorescence detection and RSA by the DPPH assay. For the sensory analysis, the quantitative descriptive analysis (QDA) was used with a pre-determined list of attributes: colour, astringency, bitterness, sweetness and characteristic grape juice flavour. The major components of juices were investigated by direct infusion and electrospray ionization mass spectrometry (ESI-MS) both in the negative ion mode. During processing, CCJ showed higher RSA and TP contents than CIJ with slight variations at each step. Although CCJ showed 50% higher TP contents, RSA was on average 25% higher. During storage, TP retention ranged from 93% (CCJ) to 84% (PCJ) and RSA from 87% (PIJ) to 85% (CCJ and PCJ). (+)-Catechin retention during storage ranged between 63% (PCJ) and 52% (PIJ) and (-)-epicatechin between 32% (CCJ) and 15% (CIJ). Concentrated juices of both cultivars showed notably higher catechin amounts and CCJ presented the greatest phenolic contents. Despite the marked differences in TP and CAT+EPI contents, similar RSA values were observed for all the juices. PIJ yielded the highest RSA ?per phenolic unit?, with the lowest TP content. In the concentrated juices, peonidin and peonidin-3-O-glucoside gave way to malvidin and dimethoxy-flavylium as significant components during processing; malvidin and piceatanol-O-glucoside decreased after 8-month storage whereas dimethoxy-flavylium was maintained. Regarding the sensory aspects, concentrated juices stored under refrigeration received higher ratings for desirable attributes such as colour, sweetness and flavour than juices aged in bottles at room temperature. CCJ was more stable during storage with sensory characteristics of astringency, bitterness and higher colour intensity while CIJ was characterized by sweetness and juice flavour. Thus, processing and storage conditions applied to commercial concentrated grape juices are capable of maintaining antioxidant capacity and sensory quality

ASSUNTO(S)

flavonoids espectrometria de massa catechins sensory analysis flavonoides mass spectrometry catequinas uva grape analise sensorial

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