the project

When fruits and vegetables are processed to manufacture food products such as wine and snacks, in most cases sulphur dioxide (SO2) has an important technical role. Sulphites are traditionally used as antioxidants and preservatives in fruit and vegetable products, dried fruits, snack products and wine. However, SO2 and sulphites strongly reduce vitamin B1 uptake, which could lead to chronic headaches and the disturbance of memory. Another risk group are asthma patients because sulphites could promote asthma attacks. Food is the main source for the intake of sulphur dioxide. With this background in mind, the SO2SAY project has developed a strategy to reduce or even replace the use of SO2 or its salts in almost all food products.


Innovation on preventing enzymatic browning

This approach aims to reduce enzyme activity of polyphenol oxidase to prevent enzymatic browning. It starts with isolation polyphenol oxidase from potatoes for biochemical characterization including their optimal pH, primary and tertiary structure and their active centre. For inactivation different peptides derived from protein hydrolysates and polyphenolic fractions from plant extracts will be tested. Also trials with enzymes for modification of phenolic substrates of the environment of the enzyme polyphenol oxidase will be undertaken. Further trials aim on the chelation of the central copper ion of polyphenol oxidase. Therefore chelating polysaccharides and chelating agents will be applied to complex the copper ion of polyphenol oxidase and, thus, inhibiting the enzyme. The different agents and polysaccharides will be tested in order to find an optimal dose/functionality ratio. Aim is to add as little chelating agent as possible. Technical approaches involve high temperature processing in combination with ultrasound treatment in order to reduce the heating time and temperature necessary for the inactivation of polyphenol oxidase. Variables to be studied are time, temperature, ultrasound wavelength and power. Because an ultrasound unit needs water as carrier, high power ultrasound will be applied for juice concentrates, homogenised products, and solid products in a water bath. Ultra filtration will be applied especially for removal of polyphenol oxidase from wine and beverages.
Development of antioxidative/ antimicrobial plant extracts

Natural compounds are screened for their ability to replace sulphur dioxide as reducing and antimicrobial agent. Starting point will be secondary plant compounds from olives and grapes. Because of the novelty of these substances the evaluation includes research on the structure-function relationship especially in the view of inhibition of enzymatic and nonenzymatic browning. Also their potentials as antimicrobiological agents will be evaluated.
Reducing properties are the primary target of this task, but antimicrobial properties are also included. Starting point will be extracts from edible plants. The main compounds will be identified and the extracts will be screened for activities. Active compounds are expected to be oleuropeins from olive residues and proanthocyanidines and stilbenols from grape residues. The extracts should be as effective as sulphur dioxide.
Extracts with similar activity as sulphur dioxide will be further fractionated in order to obtain more pure substances.
The extracts identified will be used as additives in the five model products. Antioxidant properties and influences on enzymatic and non-enzymatic browning will be investigated.
Research on other food compounds with reducing properties will also be considered. One approach is the application of peptides such as glutathione or single amino acids such as cysteine. Another field of research is the improvement of applying ascorbic acid and its derivatives. Interactions between different reducing agents will be investigated by means of statistical design of experiments.
Processing and packaging under oxygen reduced atmosphere

This approach aims on the reduction of oxygen contact. The reduced oxygen contact inhibits the activity of polyphenol oxidase and microbial growth. One way is the use of modified atmosphere in packaging and processing.
Products of interest for modified atmosphere packaging are concentrates for juices and jams, wines, vegetable products, fresh and dried fruits. The application of different gases such as nitrogen, carbon dioxide, and carbon monoxide will be tested in alone and in combination. The application of carbon monoxide will get special attention. Carbon monoxide has a reducing character and can replace sulphur dioxide also as a reducing agent. Main focus will be modified atmosphere processing. A successful modified processing has to start at the processing step where tissues are damaged such as cutting and homogenisation. Also the packaging materials will be assessed in order to improve their stability. The aim is to select packaging materials with a low permeability for oxygen and the gases used for modified atmosphere packaging. Multilayer materials that contain metal or ceramics in the layers will be tested. These materials are already used for packaging of juices. For packaging of solid fruit and vegetable products, these applications will be novel. Another promising approach is the application of dry ice saturated water bathes. By addition of dry ice oxygen is removed from the water. After dipping of solid fruit and vegetable products, these pieces are covered with a water film with low oxygen content. Throughout the process this protective water film prevents oxygen content and, thus, enzymatic browning and microbiological growth. Detailed research on the efficiency of this method on different foodstuff, especially dried fruits, including the integration into existing processes will be done in this task.

Three approaches of SO2SAY to obtain SO2-free food products

SO2SAY Objectives:

  • reduction of sulphur dioxide in food
  • development of new agents and processing techniques to replace SO2 in food products
  • prevention of enzymatic browning of food
  • improving the shelf life and appearance of food products without sulphur dioxide addition
  • Identifying alternative natural ingredients having benefits for human health through the replacement of sulphur dioxide

An important aspect of the project for food applications is the preservation of the sensory quality and shelf-life of the SO2-free products.  Reducing or replacing SO2 runs the risk of changing the sensory properties of food products, especially colour and taste. Thus, consumers may refuse such food alternatives, even though these alternative foodstuffs might be considered healthier. Therefore, all developments in the SO2SAY project will be accompanied by comprehensive sensory studies and consumer tests.