Effect of storage duration on phenolics stability in ready-to-drink coffee beverage

Abstract

Ready-to-drink (RTD) coffee is one of the innovations in coffee beverages that is widely circulated in the market and is quite popular among various groups of people. This study aimed to partially validate the Folin-Ciocalteu method for phenolic compounds analysis in ready-to-drink (RTD) coffee and determine the effect of storage time on the stability of phenolic compounds in RTD coffee. Coffee drinks were made from Robusta coffee extract added with other ingredients (sugar and potassium sorbate), pasteurized, hot filled into plastic cups, and stored at room temperature (25 – 28 oC) for 0, 2, 4, 6, and 8 weeks. Two proposed methods (Folin-Ciocalteu methods) for routine phenolic analysis (Total phenolic content (TPC) and total tannin content (TTC)) in RTD coffee were partially validated. In general, partial validation parameters of TPC gave more satisfying results, such as linearity (R2 = 0.9991); precision (RDS < 2/3 RSDHorwitz); recovery (109%) and sensitivity (LOD = 14.20 mg L-1). Phenolic stability in RTD coffee was evaluated using the Folin-Ciocalteu method (TPC and TTC) and HPLC method (individual caffeoylquinic acids (CQAs) (3-CQA, 4-CQA, and 5-CQA)). In general, TTC values in all storage time were higher than TPC values because the TTC method had higher recovery (132%). Furthermore, the three parameters observed (TPC, TTC and CQAs) experienced significant degradation during storage. The decrease percentage of TPC and TTC during 8 weeks of storage was 11% (from 63 to 55 mg/100 mL) and 10% (160 to 143 mg/100 mL), respectively. Meanwhile, 5-CQA was the most sensitive CQAs and its degradation for 8 weeks of storage reached 19% (from 28 to 23 mg/100mL ). TPC is recommended for monitoring the effect of storage duration on phenolic compound stability in RTD coffee and analysis of 5-CQA as the most unstable individual phenolic may support the monitoring.