Use of Weibull distribution for describing kinetics of antioxidant potential changes in fresh-cut watermelon

Abstract

Changes in antioxidant capacity, vitamin C, lycopene and total phenolic compound retention of fresh-cut watermelon stored at selected temperatures (5–20 °C) for 14 days storage were accurately described by a Weibull distribution function. The temperature dependency of the Weibull kinetic rate constants was studied through an Arrhenius-type relationship. The degradation kinetic constants of Weibull model increased with temperature. Therefore, initial antioxidant potential of fresh-cut watermelon was best maintained at storage temperature of 5 °C for 14 days. The activation energies for lycopene, vitamin C, antioxidant capacity and total phenolic compounds were 56.5 kJ mol⁻¹, 55.9 kJ mol⁻¹, 34.5 kJ mol⁻¹ and 26.9 kJ mol⁻¹, respectively. Thus, a high temperature sensitivity of lycopene, vitamin C and antioxidant capacity related reactions were observed compared to that of total phenolic compounds.

Introduction

Fresh-cut produce meets the expressed consumer desire for convenience appearance and health. Minimally processed products are one of the major growing segments in food retail establishments (Soliva-Fortuny and Martín-Belloso, 2003). In fact, a considerable number of fresh-cut commodities are already on the market playing an important role on the nutrient intake of an increasing number of consumers. Watermelon contains significant amounts of lycopene, a compound responsible for its red colour (Perkins-Veazie and Collins, 2006) as well as small amounts of phenolics and vitamin C (Gil et al., 2006). In recent years, lycopene has aroused considerable attention as a health-promoting antioxidant, associated with lowered risk of coronary heart disease and certain types of cancer (Giovannucci, 2002, Giovannucci et al., 2002, Fraser and Bramley, 2004).

An intelligent selection of preservation techniques is expected to have significant potential for extending the shelf-life of fresh-cut products, keeping the organoleptic characteristics and nutritional value of the original fresh product. However, maintaining the correct product temperatures throughout the chill chain is often the most important factor in ensuring the quality and safety of fresh-cut fruits and vegetables (Artés-Hernández et al., 2007). Storage temperature may have a substantial impact on the stability of health-related compounds. For instance, the rates of vitamin C oxidation are substantially increased when temperature rise (Davey et al., 2000). Temperature also plays an important role in the synthesis of carotenoids in watermelon, which is enhanced under high temperature (Perkins-Veazie and Collins, 2006). Storage temperature significantly affected to lycopene, phenolic and vitamin C content of tomato slices stored under modified atmosphere packaging. The changes were related to an excessive amount of CO₂ inside the trays as a consequence of microbial growth at abusive temperatures (over 10 °C) (Odriozola-Serrano et al., 2008).

Weibull distribution function has an interesting potential for describing microbial, enzymatic and chemical degradation kinetics (Cunha et al., 1998). Traditionally, the degradation of nutrients in foods during their thermal processing and storage has been described in terms of zero, first or higher order kinetics (Taoukis et al., 1997). However, some authors have proposed a model for non-isothermal degradation of nutrients, pigments and enzymes in foods, considering that the disappearance of a given population of molecules is characterized by a Weibull distribution (Manso et al., 2001, Corradini and Peleg, 2004). The Weibull model is extremely flexible owning to the inclusion of a shape constant in addition to the rate constant. In this way, Manso et al. (2001) used the Weibull distribution functions to describe the thermal degradation of ascorbic acid in orange juice at 20–45 °C. Odriozola-Serrano et al. (2009) also used the Weibull distribution function to fit variations of anthocyanins and antioxidant capacity of fresh-cut strawberries stored at different temperatures.

Therefore, the objective of this study was not only to study the effect of the storage temperatures (5, 10, 15 and 20 °C) on the antioxidant potential of fresh-cut watermelon but also to propose a kinetic approach to properly describe changes in the antioxidant properties of fresh-cut watermelon stored at different temperatures.