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Extraction of bioactive compounds from blackberry (Rubus spp.) bagasse using pressurized liquids

Author: Ana Paula Fonseca Machado (2014)

Abstract: Blackberry is a fruit rich in phenolic compounds, especially in anthocyanins. Besides its consumption as fresh fruit, blackberry is used industrially in the manufacture of juices and derivatives. However, this process generates about 10 % of solid residue, which still contains a large amount of phytochemicals. In order to add value to these wastes, the aim of this study was to obtain extracts rich in blackberry’s major bioactive compounds, such as polyphenols, by employing the clean technique of pressurized liquid extraction (PLE). First, bagasse pulp of blackberry was characterized with respect to total phenolic content (PC), monomeric anthocyanins (MA), antioxidant activity (AA), pH, total soluble solids (SS) and chemical composition. Then, PLEs were carried out using three temperatures (60, 80 and 100 °C) and 4 different solvents (water, acidified water with pH 2.5, ethanol and a mixture of ethanol and water 50%), resulting in 12 different assays. In the extraction processes by PLE some parameters were fixed: pressure (75 bar), ratio S/F (18.0 g solvent/g fresh residue), running time (30 min) and mass of raw material (5.0 g). Subsequently, the major and minor anthocyanins were identified in subcritical extracts by Ultra performance liquid chromatography (UPLC-QTOF-MS). Besides PLE, classical Soxhlet extraction technique and maceration were performed in order to compare the results with those obtained in the best condition of PLE. Also, at the best conditions of PLE, extraction kinetics were determined at three different flow rates (1.67, 3.35 and 6.70 mL/min). The extracts obtained by the different techniques were evaluated in terms of global yield (X0), PC, MA and AA. The characterization of the raw material showed that it is highly rich in protein, carbohydrates, fiber and bioactive compounds (polyphenols). Thus, blackberry is a good and caloric food source, which enables its potential application in the food industry. In general, it was observed that the increase of temperature from 60 to 100 °C resulted in better values for the response variables, except for the MA, in which a slight decrease was observed. The analysis by UPLC-QToF-MS showed that cyanidin-3- glucoside and cyanidin-3-rutinoside are the major anthocyanins present in blackberry residues. Cyanidin-3-glucoside and cyanidin-malonyl-3-dioxalil-glucoside are the anthocyanins present in lower levels. The condition that was considered the best of all tested in the present work was the one that used hydroethanolic mixture as the extraction solvent, at a temperature of 100 ºC. The values of the response variables in this condition were: PC = 7.36 EAG/g fresh residue (FR), MA = 1.02 EC3G/g (RF), DPPH = 76.03 TE/g FR, ABTS = 68.28 TE/g FR and X0 = 6.33 %. Comparing these values with those obtained by conventional techniques (Soxhlet and maceration), they were generally higher. Studies of the kinetic parameters indicated that is more interesting to work with low flow rates when employing hydroethanolic mixture at high temperatures (100 °C) via PLE procedure. Therefore, the PLE technique may be a promising alternative for the extraction of antioxidants from food matrices.