October 1, 2015

International researchers look to import fresh-cut apples’ shelf life

Fresh-cut produce is in high demand. Consumers are looking for healthy snacks with increased convenience.

When it comes to fruits, apples are in demand, but shelf life is always a concern for processors and packers alike.

Researchers from around the world — Encarna Aguayo from the Postharvest and Refrigeration Group at the Technical University of Cartagena (Spain), Allan Woolf from the New Zealand Institute for Plant & Food Research (Auckland), and Roger Stanley from the University of Tasmania (Australia) — may have found a solution.

They discovered that hot water treatments in combination with cold calcium ascorbate dips help to maintain fresh-cut apple quality.

We asked Aguayo about the details.

Produce Processing: Tell me a little bit more about the study. What were you hoping to find?

Encarna Aguayo: The main problem for fresh-cut apple is oxidation caused by an enzyme named polyphenol oxidase (PPO) that exists in particularly high amounts in apples. The resulting browning makes the product unsuitable to the consumer. A range of treatments have been applied to extend the shelf life of fresh-cut apples such as dipping in solutions of a wide range of anti-browning agents (ascorbic acid, oxalic acid, oxalacetic acid, kojic acid, erythorbic acid, citric acid, and/or calcium, cysteine, 4-hexylresorcinol) at different concentrations. Among the aforementioned methods, the use of calcium ascorbate (CaAsc) has been found to be the most effective anti-browning agent and can be marketed as minimal chemical input.

In previous studies, we found that CaAsc can increase the antioxidant status and extend shelf life. Hot water treatment (HWT) is an effective physical treatment, free of chemical residues and readily applicable in the fresh-cut industry during the washing process. The use of non-chemical technologies that can improve product responses by additional interactions could improve the effectiveness of CaAsc in the fresh-cut apple industry. This study sought to determine whether HWT (48 °C or 55 °C for 2 minutes) could be recommended as a method in combination with CaAsc dips (6 percent) to help to maintain fresh-cut apple quality.

PP: After completing the study, what can you recommend to processors?

EA: We recommend the combination of CaAsc dips and HWT. CaAsc dips (6 percent) had a strong impact reducing the browning and therefore, extending the overall acceptability to 14 days. This treatment increased fivefold the antioxidant content which was further increased with the combination of HWT through an increased absorption of ascorbic acid in the apple tissue. That combination helped to maintain fresh-cut apple quality, in particular, sensory quality, extending the shelf life from 14 days to up to 21 days at 4 °C. HWT for 2 minutes at 48 °C was preferable to 55 °C. The higher temperature increases energy cost and could induce a superficial damage in the apple flesh.

PP: What is the best way for processers to use HWT and CaAsc?

EA: Firstly, apple slices should be disinfected in cold water. After that slices should be dipped into hot water (48 °C) for 2 minutes with continuous hot water recirculation to maintain the relevant temperature. After heating, apple slices are dipped for 2 minutes into 6 percent CaAsc solution and drained. This solution should be cold, around 0 °C.

The high temperature used during the HWT enhances diffusion rate of ascorbic acid and increase the solubility of ascorbic in water and apple tissue. So, the use of HWT led to a lower CaAsc doses due to a higher efficiency of ascorbic inside the apple tissue.

PP: Anything else you would like to add?

EA: The results of this study and other research were published in 2010 (“Effects of calcium ascorbate treatments and storage atmosphere on antioxidant activity and quality of fresh-cut apple slices”). In conjunction with Fresh Appeal, (http://www.fresh-appeal.com/), Plant & Food Research has a patent that combines a UV-C vortex system with the HWT and cold calcium ascorbate dip (presented here). This hurdle approach achieves high levels of food safety and product quality and is achieving significant commercial uptake in the fresh-cut apple industry in the USA.

— Courtney Culey, digital content editor