Demand for ready-to-eat products is growing steadily. With the help of a hot water treatment at 55o and for a period of 30 to 60 seconds, apples for fresh fruit salads can in future be so sanitized that consumers are offered an increased shelf life and reduced microbial load.
New washing system for fresh-cut apples
The new washing system was designed as part of the "DEKONWA" project by the Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB) in cooperation with the industrial partners Kronen GmbH and mirontell fein & frisch AG. The project was presented last week at this year's Fruit Logistica, the leading international trade fair for fruit trade in Berlin.
Healthy, fresh and especially pre-packaged snacks such as fruit salads are becoming increasingly popular in supermarkets, fast food restaurants and schools. Apples play an important role here. For the commercially available fruit salads, they are washed and cut, unpeeled.
Since the pieces of apple are more susceptible to microbial attack than whole fruits, they must be washed very intensively. Despite intensive washes in cold water, where pathogenic microorganisms on the peel indeed can be reduced, they do not completely disappear. For consumers, therefore, microbiological safety is the decisive quality criterion for fresh-cut products.
Hot water treatment against microbial contamination
If apples are sanitized using a hot water treatment at 55oCelsius for 30 to 60 seconds, this will ensure a more efficient reduction of the microflora on the shell, according to the results of the DEKONWA project. In addition, a particularly gentle product processing is guaranteed without the use of chemicals immediately before and after processing. An application is therefore also suitable for Bio-Fresh-Cut products.
In addition to a precise control of the residence time of the apples, the washing system developed in the "Hygienic Design" enables optimal cleaning and reuse of the hot water. For use in refrigerated rooms, the system is isolated and can be integrated into existing process lines and applied to similar products.
The process is not new. For example, fruit is usually treated with 45 to 55oCelsius warm water for a period of ten minutes to prevent mildew when stored for several months. For the DEKONWA project, however, the most efficient and product-friendly reduction of the total number of germs on the fruit before cutting was in the foreground.
No influence on the pulp
ATB investigated the effect of a brief hot water treatment on the microbial load and on the internal and external quality of the fruit. "The valuable ingredients within the peel should not be damaged by the treatment," explains ATB scientist Dr. med. Werner Herppich, senior scientist and deputy head of department of engineering in horticulture at ATB Potsdam.
"With the methods of chlorophyll fluorescence analysis and thermography, as well as microbiological and chemical analyzes, we could prove that the fruit properties even in relatively sensitive varieties such as 'Braeburn' by a short-term treatment 55oCelsius were not affected. On the other hand, bacteria and the risk of cross-contamination were reduced considerably by the treatment."
The cooperative project "Method development and technical support of a decontamination unit for apples using hot water "(DEKONWA) was completed in 2018, demanded by the Federal Ministry of Economics and Technology (BMWi) in the Central Innovation Program for SMEs (ZIM) and supported by the project leader research group of industrial research associations "Otto von Guericke" eV (AiF).
