Skip to main content

Replacement of sulphur dioxide (SO2) in food keeping the SAme qualitY and shelf-life of the products

Periodic Report Summary 1 - SO2SAY (Replacement of sulphur dioxide (SO2) in food keeping the same quality and shelf-life of the products)

Project context and objectives:

The SO2SAY project has been initiated to develop a strategy to replace the application of sulphur dioxide or its releasing salts for the most relevant food products. During the development of respective food applications, maintenance of sensory quality and product shelf-life were key targets for products manufactured without sulphur dioxide treatment. Hence, other mechanisms for the prevention of enzymatic browning in foods (especially fruit and vegetable products) than the inhibition of Polyphenol oxidase (PPO) and the prevention of quinones oxidation by sulphur dioxide were investigated along with suitable preservation against microbial spoilage.

Three approaches were followed to enable an effective reduction of sulphur dioxide use:

1. inactivation of the PPO enzyme to prevent enzymatic browning;
2. development of plant extracts containing secondary plant metabolites with a high antioxidative capacity (e.g. plant polyphenols) and antimicrobial activity;
3. processing and packaging under an oxygen reduced atmosphere.

These strategies were initially planned to be successful as stand-alone technologies whereas production environments verified the need to adapt combinations of two or three technologies in a tailored process to meet the requirements of fluid and solid food products. After a thorough review of permitted and industrially performed application of sulphur dioxide treatments:

- fruits and vegetables;
- wine and beverages;
- snack and convenience products

have been identified as most relevant food stuffs. In order to develop suitable alternative processing regimes to replace sulphur dioxide in food, the SO2SAY approach was designed to make use of fundamental scientific data and a complete understanding of molecular mechanism behind the novel technological applications. An analytical work package has been set out to verify quality characteristics in sensorial analysis and to prove an acceptable shelf-life of the newly developed products.

Project results:

Upon the kick-off meeting the framework for the future work including e.g. the selection of model products, the establishment of a legal framework as well as the compilation of a database with potential stakeholders was elaborated.

Each approach to replace sulphur dioxide was investigated firstly stand alone: In order to reduce oxygen exposure, several packaging materials such as plastic foils in combination with metal or ceramic layers were evaluated in-depth and in combination with different mixtures of cover gases. An innovative approach lay with the total processing including packaging under e.g. a total nitrogen or carbon dioxide atmosphere. For fresh cut apples and potatoes the application of edible coatings, based on proteins and carbohydrates, was assessed. Finally the ability of dip bathes with carbon dioxide saturated water was tested to inhibit browning of fresh cut fruits and vegetables.

Within the approaches to reduce enzyme activity high temperature processing in combination with ultrasound was tested for apples, grapes and potatoes. Vast ultrafiltration trials were performed for grape must, either for wine or for grape juice in order to separate the PPO enzyme by its molecular weight fraction. Basic research approaches covered the investigation of inhibition mechanisms based on purified mushroom-derived PPO. In cooperation with the University of Groningen remarkable contribution to solve the crystal structure was made. Furthermore, numerous copper chelating agents were tested towards their ability to inactivate the enzyme PPO by chelation of its central copper ions.

To cope with the reducing and antimicrobial properties of sulphur dioxide more than 60 plant extracts were screened as alternative. The 16 most effective were further fractionated to identify exactly the functional groups that cause these effects. Finally, several extracts and fractions were tested in in vivo trials on the model food systems. For two selected compounds the structure-function relationships as well as their metabolism pathways were revealed.

Even if some approaches delivered promising results none of them was able to cope with all properties of sulphur dioxide. Therefore the most effective ones were combined to find a solution for each relevant food. The best results from these combination trials were obtained for red wine and fresh cut potatoes. Thus these combinations were selected for up-scaling. Thereby different extract combinations were tested for red wine at the participating winery Biurko Gorri. The combination of an extract treatment with modified atmosphere packaging was tested at Gemüse Meyer. Both scale-ups were performed under realistic conditions at the corresponding beneficiary facilities.

Consumer acceptance testing was performed in Germany, Spain and the United Kingdom for red wine and peeled and cut potatoes. The results were centrally evaluated and summarised by ttz who performed an in-depth Optimised descriptive profile (OPD) analysis for sensorial characterisation of these products. In order to evaluate the safety of the novel treatments and shelf-life of the products in comparison to sulphite treated products a vast shelf life study with dried apple rings and fresh cut potatoes was performed including sensorial, microbiological and chemical analysis. According to the results of the consumer tests the developed red wine was a success. Only the ODP study panel was able to identify a slightly different colour of the novel wine. However this deviation was not rated negatively.

Towards the end of the project three publications in peer reviewed journals were published. Furthermore a video about the SO2SAY activities was produced in cooperation with two large German broadcasting services.

Potential impact:

The SO2SAY project has been set out to establish procedures for a significant reduction and towards a waiver of sulphur dioxide and its releasing salts in food processing. Thereby a lower intake of sulphites for the European consumers and thus a significant contribution towards improved food and beverage safety was expected whilst safeguarding microbial and sensorial shelf-life. A major approach within the project was the development of plant extracts with antimicrobial property to meet the high quality standards of food producers and consumers. Further results were expected to be derived from novel physical procedures such as oxygen exclusion in processing and packaging, ultrafiltration, high power ultrasound treatment, and novel chemical solution such as compounds from plant extract with reducing and antimicrobial activity, and novel biological alternatives such as targeted enzyme inhibition by copper chelation and biological available inhibitors of PPO. Bearing in mind a very broad application of the novel technologies, the SO2SAY project delivered relevant data and information on different combinations of novel technologies in correlation to the diverse nature, the form and the physical and chemical properties of the different foodstuffs tested. Hence, it is expected that the SO2SAY project will not only directly impact on the fruit and vegetable processing industry, but that its technological developments can be easily transferred to other products, as well. Applications which no longer bore relevance on the market, such as sulphur dioxide treatment of seafood, were not included into the project activities or exploitation planning.

For instance, the exclusion of oxygen from working environments has been forecasted for further application in the pharmaceutical industry to prevent oxidation of active ingredients. The enzyme inhibition approach might also be applied for different undesired enzymatic procedures in food such as pectinase activity during fruit softening or even as medicinal approach for the treatment enzymatically mediated disorders. Reducing or antimicrobial active plant extracts will have potential for various food applications, but also in pharmaceutical and cosmetic products. Suitable extracts will be able to replace synthetic food additives, which will increase the trust of the consumers in the whole food industry and will contribute to improved sustainability in the food production chain. These novel reducing and antimicrobial plant extracts can further be obtained from by-products of food processing in contrary to inorganic additives such as sulphur and, therefore, contribute to the ambitious way of total valorisation of food by-products. Novel eco-efficient packaging technologies were tested for the packaging of fruit and vegetable products which directly impacts on re-evaluating strategies to avoid food and resource wastage by smart packaging processes. A heavily benefiting sector from SO2SAY processing steps has been identified in the traditional food processing where currently many traditional fruit and vegetable products contain considerable amounts of sulphites to prevent enzymatic browning. In summary, the SO2SAY proposal will seriously contribute to improve the knowledge based bio-economy and, thus, strengthen the position of the European food industry on its way to establish competitive sustainable production processes and improve their position against competing economies from overseas. In order to assure the envisaged impact, the organoleptic properties and shelf-life of SO2SAY treated products in comparison to untreated or sulphur dioxide treated products represented the key argument for industrial up-take and consumer acceptance. The strong interest and positive consumer opinion was also mirrored in the great media interest in the SO2SAY project.

Project website: http://www.so2say.eu