Greek Coffee Quality Loss During Home Storage: Modeling the Effect of Temperature and Water Activity

Abstract

The aim of this study was to monitor and characterize Greek coffee staling during home storage (secondary shelf life, SSL) using sensory evaluation techniques. Storage temperature (T) and product water activity (a_w ) are considered as the major factors affecting SSL. Water sorption isotherms fitted to Guggenheim Anderson-de Boer model were used to predict product stability; coffee samples were stable at a_w < 0.52. Coffee samples equilibrated at a_w = 0.15 (the fresh sample), 0.22, 0.33, and 0.52 were stored at T = 25 °C, 35 °C, and 45 °C under simulated home storage conditions. Samples were obtained at appropriate times for each T and a_w condition and sensorially evaluated. Greek coffee brews were prepared and freshly served during sensory evaluation. The use of Weibull hazard analysis provided an effective approach to SSL determination as a function of T and a_w . SSL values ranged from 20 (Τ = 45 °C, a_w = 0.52) to 104 days (Τ = 25 °C, a_w = 0.15). Quality loss based on coffee aroma changes (aroma quality, aroma intensity, aftertaste, off-flavor) was also studied (S_i , sensory scoring using 9-point magnitude scale) and kinetically modeled. Quality loss rates (k_i ) were calculated and used to predict SSL values. Based on the results of both Weibull hazard analysis and sensory scoring of individual aroma characteristics, it was concluded that the lowest SSL was calculated for a_w = 0.52 at T = 35 °C to 45 °C. The temperature dependence of aftertaste, aroma quality loss, and off-flavor production was not statistically significant for 0.15 < a_w < 0.33 (P > 0.05); the aroma intensity was the most sensitive parameter. PRACTICAL APPLICATIONS: Secondary shelf life (SSL) represents the time after pack opening during which a food maintains an acceptable quality level. During home/catering usage, coffee is not consumed immediately after pack opening. During consumption, quality degradation reactions proceed with higher rates due to variable storage conditions mainly related to atmosphere changes in the pack, leading to the entrance of oxygen/moisture and temperature. Therefore, SSL is important, and can be used as a tool for product management during consumption reducing food waste. There is a lack of studies dealing with SSL prediction of coffee, while no studies have been carried out on Greek coffee.

Keywords: Weibull analysis; roasted ground coffee; secondary shelf life; sensory evaluation; water activity.