WP 3 had a dual focus, investigating the role of microbes on the shelf-life one side and on the enzymes on reduced colour stability on the other side. Surrogate strains for EHEC and Salmonella were successfully identified and could be used in WP5 as model organisms. Kinetics of pathogens and suitable surrogates were determined in different juices. The impact of different thermal and non-thermal treatments on the global gene expression of selected strains was investigated. The matrix impact on thermal resistance of bacteria was analyzed.
The overall progress of WP4 (ESRs 3, 4, 5, 7, 11)was exceptionally high, almost overfulfilling the expectations. The ESRs analysed a large spectrum of different fruit quality aspects, as well as harvesting and processing regimes. This included an initial screening of more than 100 strawberry varieties for colour stability during processing identified two promising candidates of potential commercial interest and resulted in a colour stability prediction value (ESR5). The main outcome was that cultivar has a strong impact, more than harvest time which is more important than ripening stage. In addition, proanthocyanidin contents and the presence of epiafzelechin in proanthocyanidins correlated with low colour stability in nectars. In contrast, a low pectin's arabinan to galactan ratio correlated with high colour stability in nectars (ESR11). Of course, not all of the identified colour stable cultivars would be of agronomic relevance (poor performance with respect to yield, fruit size and abiotic and biotic stress tolerance), but we identified several promising breeding lines in the pipeline, which will probably become available to the market in the next years. Thus, specific cultivation of colour stable cultivars for processing and the use of overripe strawberries harvested late in the season would significantly increase the shelf-life of strawberry nectars.
In WP5, multivitamin analysis methods using HPLC-MS/MS were developed for the water-soluble B and C vitamins (ESR10). The work concentrated on defined and prepared raw materials (strawberry nectar, raspberry juice, sour cherry juice) and managed a number of challenges in establishing the logistics for large-scale fruit purchasing, processing, and sample distribution to ensure uniformity and traceability of samples, with analytical tasks distributed according to ESSR’s laboratory specialization. Microbial inactivation kinetics using surrogate microorganisms for all preservation technologies was conducted. Specific kinetic and validation studies for PEF, ohmic, and HPP technologies were performed and standardized processing parameters for all treatments were established and applied. This systematic approach ensures that the comparison of conventional and non-conventional preservation treatments is scientifically rigorous, reproducible, and relevant for both food safety and product quality objective.
