Orientadora: Profa. Dra. Angélica Marquetotti Salcedo Vieira

Data da Defesa: 28/02/2012



 INTRODUCTION. The oxidative stress originated by reactive oxygen species (ROS) is fundamentally linked to the manifestation of numerous chronic and degenerative diseases. Fortunately, studies have strongly demonstrated that a diet rich in antioxidants can protect from health harms caused by the oxidation process. Guava (Psidium guajava L.) is a popular tropical fruit characterized by excellent nutritional and sensory properties, besides an extraordinary content of carotenoids, especially lycopene. Because fruits constitute the major dietary source of phenolic compounds, it has been suggested that fruit juices have potential to be used as functional ingredients in food industry. As grapes are rich sources of potent antioxidants with proven cardio protective properties, concentrated grape juice could be applied as a potential functional ingredient in food formulations. In this context, guava and concentrated grape juice could figure as great raw materials in jam formulations, thus originating potential functional products with a high sensory appeal.
AIMS. The present study aimed to develop production technology of guava jam with addition of concentrated grape juice, prioritizing the antioxidants profile and rheological characterization of this new product.
MATERIALS AND METHODS. The following elements were used in the jams processing: pink guava fruits, Paluma cultivar; commercial sucrose; mineral water; high methoxyl pectin; citric acid and potassium sorbate. The concentrated grape juice was obtained by reverse osmosis process from the natural juice of Isabel cultivar grapes. One standard formulation (GP) and one enriched formulation (GS), in which concentrated grape juice was added in the proportion of 29.70%, were elaborated. Guava jams were therefore prepared using different concentrations of sugar (39.52 % and 19.80%) and pectin (0.69 %, and 0.99 %). For the physicochemical characterization of the jams, the following analyses were performed: total soluble solids (°Brix), acidity (% citric acid), moisture and total sugar. In order to investigate the antioxidant potential of the guava jams, fresh samples were subjected to sequential extractions with methanol and acetone, and in the end of the process the two extracts were combined. The amount of phenolic compounds in the extracts was determined by the Folin-Ciocalteu colorimetric method and gallic acid were used as standard. The results were expressed as gallic acid equivalents (GAE). Extracts of the guava jams and the concentrated grape juice used as a enriching ingredient were analysed by High-performance liquid chromatography (HPLC) to quantify different phenolic compounds. Standards of gallic acid, catechin, caffeic acid, p-coumaric acid, ferulic acid, resveratrol, quercetin and kaempferol were used to obtain the standard curve. Two antioxidant systems, which act by distinct mechanisms, were used to evaluate the antioxidant activity of the guava jams. That were the β-carotene-linoleic acid coupled oxidation system and the 1,1- Diphenyl-2-picrylhydrazyl radical (DPPH•) method. The stability of the phenolic compounds and the antioxidant activity of the jams were evaluated through 90-day storage at room temperature (on average 25°C). The rheological behaviour of the samples were assessed at temperatures of 25°C, 35°C, 45°C and 55°C using a Brookfield rheometer model DVIII with a SC4-34 spindle. The data of deformation rate and shear stress were adjusted by the Power Law model, while the effect of temperature on apparent viscosity was described by an equation analogous to Arrhenius.
RESULTS AND DISCUSSION. The results showed all jam formulations had total soluble solids content compatible with the requirements of the Brazilian legislation, which establishes a minimum of 65 °Brix for total soluble solids in jam. The values obtained for the moisture content in GP and GS, which were 36.34% and 37.16% (wet basis), respectively, were also in accordance with the legislation. The total sugar content found for both guava jam formulations are close to the values related in other references. The acidity (% citric acid) found for GS formulation was higher than the value found for GP formulation, which indicates that the addition of grape juice promoted a increasing in the jam acidity, though GS acidity value still is in accordance to legislation parameters. As expected, was found a greater concentration of phenolic compounds (PC) in the GS formulation than in the GP formulation, and most important,  the enriched jam showed a PC content of more than two times the standard formulation content. Moreover, the data obtained over the monitoring period showed a decreasing on the PC content with the days, for both GP and GS formulations. The pair of guava
jams presented similar stability over the storage time, since the PC content of GP formulation dropped 32.18% while the PC content of GS formulation dropped 36.21%. The major compound identified in the samples was the flavonoid catechin, followed by gallic acid and quercetin in very minor concentrations. The GS formulation presented greater contents of galic acid, caffeic acid, p-coumaric acid and ferrulic acid than the GP formulation, and even presented superior contents of these compounds than the  concentrated grape juice that was added to its formulation. In this last, was found an extraordinary content of catechin in addition to less representative contents of the other compounds, reason why the addition of concentrated grape juice in guava jam  formulation provided a significant contribution in terms of phenolic compounds, especially in terms of catechin. Among the phenolic compounds quantified in the guava jams, catechin represented 99.93% and 52.58%, respectively, of the total value of compounds found for GS and GP. In the guava jams extracts were also found low contents of quercetin and kaempferol. The GS formulation showed a content of quercetin 2-fold higher than the GP formulation, while both formulations showed equivalent contents of kaempferol. At the 45th day of storage, the results obtained for the measure of antioxidant activity of the jams by the β-carotene-linoleic acid system were: among the positive controls used in this test, Trolox showed the highest value of antioxidant activity, which were 58.28 ± 2.78% at 100 ppm; GS presented an antioxidant activity of 53.862 ± 0.388%, that were 18.5% higher than the value found for GP; and the antioxidant activity of the positive controls BHT, Trolox and Propyl gallate were not significantly different (p < 0.05).The data of the antioxidant activity monitoring of the guava jams based on the β-carotene method, during 90-day storage, surprisingly revealed a increasing in antioxidant activity with time, for both jams and for the positive controls. So the antioxidant activity of GP at the end of the 90-day  storage was 1.7-fold higher than the value found for the 1st day, and GS showed a corresponding increase of 1.5-fold the original value. This results could be explained by a possible transformation in the phenolic compounds with time, where the originated polyphenols presented lower antioxidant activity in the hydrophilic DPPH• system and greater activity in the lipophilic β-carotene system. On the results of the DPPH• assay at the 45th day of storage, the antioxidant activity ranged from 95.86 ± 0.15 % (Propyl gallate) to 63.94 ± 1.03 % (GP). GS extract showed better antioxidant efficiency value than GP extract, with an antioxidant capacity of 67.93 ± 0.81 %. The EC50 values, inversely proportional to the antioxidant activity values, were of 25.45 ± 1.03 μg/mL for GP and 20.40 ± 0.22 μg/mL for GS,  which indicates that the enriched jam provided higher protection against oxidation than the standard guava jam. In the rheological behaviour study of both guava jams, the values of consistency coefficient, K, and the flow behaviour index, n, were obtained by curve fitting using least square method. The satisfactory regression coefficients, R2, all superior to 0.984, showed the effectiveness in fitting. The n values, found for the pair of samples, showed that GP and GS exhibited exhibited a non-Newtonian shear-thinning behaviour (n < 1) at all evaluated  temperatures. The increasing of temperature showed no significant influence on the pseudoplasticity of both guava jams. Also the phenomena of decreasing on consistence coefficient, K, with temperature, was observed. There were a decreasing in the GP and GS values of apparent viscosity with increasing shear rate and temperature. A close observation on the apparent viscosity results showed that the GS formulation suffered  higher drop in its viscosity than the GP formulation, with the temperature increasing. GP and GS values of apparent viscosity dropped 26.78% and 34.67%, respectively, when the temperature increased from 25°C to 55°C. The GS formulation presented  higher apparent viscosity values than GP formulation, for all evaluated temperatures. The values of activation energy found for GP and GS were of 8.16 kJ.mol-1 and 12.47 kJ.mol-1, respectively, which indicate that the GP was more sensitive to temperature changes than GS, thus, the enriched formulation presented higher stability than the standard formulation when exposed to temperature variation.

CONCLUSIONS. The incorporation of concentrated grape juice in the jam formulation  promoted an increase of more than 2-fold in its phenolic compounds content, with catechin representing 99.93% of the total value of compounds found for GS, furthermore, provided an increase in the antioxidant activity of the product in almost  20%. This way, the consumption of the enriched guava jam could potentially deliver health benefits by the supply of natural antioxidants, especially the flavonoid catechin. The enriched guava jam exhibited a non-Newtonian behaviour and behaved as a shear thinning fluid for all evaluated temperatures. The Power Law model described appropriately the rheological behaviour of the elaborated jam. This study revealed that the guava jam enriched through the addition of concentrated grape juice constitute a new product with a notable antioxidant potential, even greater than the potential presented by the standard guava jam, worldwide appreciated delicacy.


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