Phenolic profile and antioxidant activity in apple juice and pomace: effects of different storage conditions

Abstract

Introduction. Apples have been part of the human diet since ancient times and are one of the most commonly consumed fruit worldwide, rich in phenolic compounds. Phenolics are naturally occurring non-nutritive plant compounds, possessing several health benefits. The effect of storage conditions on phenolics concentrations and on the antioxidant activity of apple juice and pomace was studied. Materials and Methods. Experiments were carried out with two apple varieties, an ancient Tuscan variety, Panaia-red, and a commercial variety, Golden Delicious. The antioxidant activity was assessed by means of two different in vitro tests: scavenging of DPPH• radical, and inhibition of tyrosine nitration mediated by peroxynitrite (ONOO− ). Analyses of juices were carried out immediately after production and after 2 weeks storage in 3 different temperature conditions: 4 °C, –20 °C and room temperature after pasteurisation. Results and discussion. Highly significant differences were recorded between the two varieties, the Panaia-red juice having a higher concentration of phenolic compounds and a higher antioxidant activity. During apple juice storage, phenolic compound concentrations and antioxidant capacity remained quite stable. A correlation between antioxidant activity and phenolic concentration was observed (0.69 ≤ r ≤ 0.97). Conclusion. The effects of a short storage time and different conditions of storage on the phenolic concentration and antioxidant activity seem to be less relevant than variety effects. The apple pomace revealed an amount of phenolic compounds, ranging from 6.8 to 15.5 mg GAE 100 g-1 DM of total polyphenols, which paves the way for their use as ingredients in foods lacking in polyphenols.