Effects of curcumin-based photodynamic treatment on the storage quality of fresh-cut apples

Highlights

• Curcumin-based PDT reduced browning and water loss of fresh-cut apples.

• Curcumin-based PDT inactivated E. coli on the surface of fresh-cut apples.

• The nutritional and antioxidant properties were not negatively affected by PDT.

• Activities of PPO and POD were inhibited after photodynamic treatment.

Abstract

Photodynamic treatment (PDT) is an innovative technology with non-thermal and environmentally sound merits, but the evaluation on the storage qualities of fresh produce was scarce. In this study, the effects of curcumin-based PDT on the quality of fresh-cut ‘Fuji’ apple slices during storage at 4 °C were investigated. The impacts on the survival of Escherichia coli, color and weight loss were examined under different curcumin concentrations, illumination time or incubation time. Curcumin-based photodynamic inactivation of E. coli on the surface of apple slices reached 0.95 log. Curcumin-based PDT was proven to prevent browning and weight loss. Additionally, PDT significantly reduced the activity of polyphenol oxidase and peroxidases to 48% and 51%, respectively. Moreover, there were few negative changes in total phenolic, ascorbic acid content and anti-oxidant activity of the treated apples. These results indicated that curcumin-based PDT was a viable and promising non-thermal technology to preserve the quality of fresh produce.

Introduction

In the past decades, fresh-cut fruit and vegetables have seen tremendous growth with changes in lifestyles, especially consumers' demand for fresh, healthy and convenient foods (Rico, Martín-Diana, Barat, & Barry-Ryan, 2007). A great diversity of these products has been marketed for both retail and foodservice distribution (Gorny, Cifuentes, Hess-Pierce, & Kader, 2000).

However, mechanical injury after the cutting process on fruit and vegetables generates a series of physiological and biochemical changes such as moisture loss, enzymatic browning, nutrient content deterioration and microbial contamination, which limit the shelf-life of products (Oms-Oliu et al., 2010, Albanese et al., 2007). Particularly, color is related to the consumer perception of appearance. Browning on the cut surface of fresh-cut products is mainly caused by the oxidation of phenols involving polyphenol oxidase (PPO) and peroxidase (POD) (Jang & Moon, 2011). More seriously, outbreaks of food-borne disease associated with fresh-cut fruit and vegetables have increased dramatically since the 1970s (Abadias, Usall, Anguera, Solsona, & Vinas, 2008). Moreover, because of the loss of protective epidermal and sub-epidermal tissues after fresh-cut processing, the exposure of nutrient-rich internal tissue supports pathogen attachment and growth (Luo, Lu, Zhou, & Feng, 2011). In this respect, it is important to develop processing technologies that not only preserve the sensory and nutritional quality but also guarantee the food safety of fresh-cut fruit and vegetables.

During the last few decades, to meet consumers’ demands for more natural and healthier food, the emphasis in the postharvest technology of fruit and vegetables has shifted from conventional chemical sanitizers that were suspected to be environmentally unsound toward novel non-thermal preservation techniques (Luksiene & Brovko, 2013). PDT is a novel non-thermal and environmental treatment to inactive bacteria via cytotoxic reactive oxygen species (ROS) produced by the photoactive compound (photosensitizer) after visible light irradiation (Jiang, Leung, Wang, Zhang, & Xu, 2013). Compared with other anti-bacterial tools, one of the most crucial advantages of PDT is the absence of any bacteria resistance (Nitzan & Ashkenazi, 2001). Curcumin is a food additive (E100) and a naturally occurring plant pigment, well-known for its various biological activities, including anti-proliferative, anti-microbial, and anti-oxidant activities (Rai, Singh, Roy, & Panda, 2008). Previous studies have shown that PDT can be successfully applied for the decontamination of fungal spores (Al-Asmari, Mereddy, & Sultanbawa, 2017), Gram-positive and Gram-negative bacteria such as Staphylococcus aureus, E. coli, Salmonella typhimurium (Penha et al., 2017), Listeria monocytogene (Ghate et al., 2013) and Vibrio parahaemolyticus (Wu et al., 2016) in vitro. In the case of food systems, a recent study by Oliveira, Tosati, Tikekar, Monteiro, and Nitin (2018) demonstrated that the combination of UV-A light and curcumin can significantly reduce bacterial cross-contamination of fresh produce. Despite its great anti-microbial efficiency, it is unknown whether PDT will keep or damage the storage quality of fresh-cut fruit. Thus, it was necessary to evaluate the effects of PDT on the qualities of fresh-cut fruit during storage.

Consequently, the aim of the present work was to evaluate the effects of the PDT on the major quality parameters of fresh-cut ‘Fuji’ apples during storage, under a range of experimental conditions (such as, different concentrations of curcumin, time of light exposure and incubation). The results of this study could provide a meaningful reference to explore the potential application of curcumin-based PDT in fresh-cut fruit and vegetable processing and develop an alternative novel non-thermal technology.