Alterations on phenolic compounds and antioxidant activity during sour grape juice concentrate processing

Alterações dos compostos fenólicos e da atividade antioxidante durante o processo de concentração de sumo de uvas não amadurecidas

¹ Viticulture Research Institute, Atatürk Strt, Horozköy Ave., 45125 Yunusemre/Manisa, Turkey
² Celal Bayar University, Engineering Faculty, Department of Food Eng., 45140, Manisa, Turkey
³ Ankara University, Engineering Faculty, Department of Food Eng., Ankara, Turkey

^* Corresponding author: Tel: +902362111071, e-mail: aligguler@gmail.com

Received: 13 August 2018
Accepted: 4 October 2018

Abstract

The alterations of phenolic compounds and antioxidant capacity of sour grape juice were investigated during the concentration process stages. Phenolics and antioxidant properties of the samples changed more at the vacuum evaporation stage than that of the other stages. After evaporation, the antioxidant capacity of the samples decreased approximately between 14.2 and 17.0 % for DPPH and ABTS methods, respectively. Besides, phenolic contents also decreased approximately as 14.8%. HPLC data on phenolics of sour grape juice during concentrate processing gave 12 polyphenols, including gallic acid, (+)-catechin, (-)-epigallocatechin, vanillic acid, (-)-epigallocatechin gallate, (-)-epicatechin, caftaric acid, caffeic acid and p-coumaric acid, which were determined as 1.05-1.83 mg/100 g, 5.40-7.83 mg/100 g, 6.35-9.21 mg/100 g, 3.01-5.18 mg/100 g, 0- 1.95 mg/100 g, 2.33-3.54 mg/100 g, 12.40-37.60 mg/100 g, 1.44-2.26 mg/100 g and 0.27-0.44 mg/100 g, respectively. Ferulic, sinapic acids and quercetin were only detected at concentrate step of the sour grape juice processing and were found as 0.18 mg/100 g, 0.28 mg/100 g and 0.76 mg/100 g, respectively.

Resumo

As alterações dos compostos fenólicos e da capacidade antioxidante do sumo de uvas não amadurecidas foram investigadas durante as etapas do processo de concentração. Os compostos fenólicos e as propriedades antioxidantes das amostras sofreram maior alteração na fase de evaporação sob vácuo do que nas restantes fases. Após a evaporação, a capacidade antioxidante das amostras diminuiu aproximadamente entre 14.2 e 17.0% nas determinações efetuadas pelos métodos DPPH e ABTS, respetivamente. Por outro lado, os teores de compostos fenólicos também diminuiram aproximadamente 14.8%. Os resultados obtidos por HPLC revelaram a presença de 12 polifenóis, incluindo ácido gálhico, (+)-catequina, (-)- epigalhocatequina, ácido vanílico, (-)-epigalhocatequina galhato, (-)-epicatequina, ácido caftárico, ácido cafeico e ácido p-cumárico, com teores de 1.05-1.83 mg/100 g, 5.40-7.83 mg/100 g, 6.35-9.21 mg/100 g, 3.01-5.18 mg/100 g, 0-1.95 mg/100 g, 2.33-3.54 mg/100 g, 12.40-37.60 mg/100 g, 1.44-2.26 mg/100 g e 0.27-0.44 mg/100 g, respetivamente. Os ácidos ferúlico e sinápico e a quercetina foram detetados somente na etapa de concentração do sumo de uvas não amadurecidas, com teores de 0.18 mg/100 g, 0.28 mg/100 g e 0.76 mg/100 g, respetivamente.