The role of food cultures and fermentates in the shelf life of soy-based burgers

Background: Food cultures and fermentates represent alternative (bio)solutions to traditional preservation approaches. Aligned with current industry and consumer trends, this study aimed at the development of an innovative plant-based meat analogue, a soy-based hamburger, incorporating two biosolutions. These biosolutions were applied with the aim of modulating the microbiome of the product and hindering the growth of pathogenic microorganisms such as Listeria monocytogenes. Methods: Three batches of soy-based burgers were produced: batch A contained a buffered vinegar (0.5%); batch B was produced with soy previously fermented with Leuconostoc carnosum; and batch C served as the control, with no preservatives. Each burger (~40 g) was inoculated (n=2) with a cocktail of seven L. monocytogenes strains and stored at 7 ºC and 10 ºC, according to the EURL Lm Technical Guidance Document to evaluate the competence of laboratories implementing challenge tests and durability studies related to Listeria monocytogenes in ready-to-eat foods (9 days + 19 days, respectively). At defined time points (days 0, 7, 13, 21 and 28), L. monocytogenes counts were determined on PALCAM agar (37 ºC, 24-48 h) according to ISO 11290-2:2017). Results: At day 0, L. monocytogenes levels in batches A, B and C were 4.3, 3.4 and 4.5 log CFU/g, respectively. With the exception of batch B, all burgers showed an increase in contamination levels throughout storage, with batch C reaching the highest value (8.5 ± 0.0 log CFU/g) after only 13 days. The maximum contamination level in batch A was observed at day 21 (7.1 ± 0.8 log CFU/g). Batch B showed the most promising results, with L. monocytogenes counts remaining below the detection limit (2.8 log CFU/g) until day 13 and only reaching 4.4 ± 0.7 log CFU/g after 28 days, which was considerably lower compared to the maximum levels observed in the other formulations. Conclusions: The tested biosolutions show potential to improve food safety and extend shelf life. Future studies should evaluate alternative formulations with a focus on their impact on sensory attributes and consumer acceptance.