Bio-preservation and bio-active compounds as sustainable strategies to improve quality and safety of fresh and fermented products

Abstract

Global projections reported that an increase in food demand of 35% will occur by 2030, mainly due to the population growth and economic development of emerging countries. In this perspective, a waste reduction in agro-food supply chains can be a fundamental strategy to guarantee environmental sustainability in food industry. This is possible through a valorisation of food residues, enhanced production yields and an extension of fresh food shelf-life. The increasing amount of food wastes is strongly related to the microbial spoilage, resulting in a loss of food quality and microbiological safety, especially in fresh or minimally processed products. The widespread consumers demand for natural and innovative foods directed the research towards the study of new “green” and environmentally friendly solutions, that need to be adapted to the specific characteristics of the different food products and processes. The development of sustainable approaches to assure safety, high quality and an increased shelf-life of both fresh and fermented products is a crucial aspect to pursue production efficiency and waste reduction. In particular, the attention has been focused on bio-preservation and bio-protection approaches, proposing, on the one hand, the use of natural antimicrobial compounds, and on the other, the application of microbial strains with antimicrobial properties toward pathogens and/or spoilage bacteria. In this latter case, nowadays, a limited number of commercial bio-protective and/or starter cultures are used to enhance product safety and quality. However, their application can cause product standardisation, with a loss in recognisability and peculiar features, linked to local productions. For this reason, an increased interest in traditional spontaneously fermented products as possible source of new autochthonous starter cultures or bio-protective strains for industrial purposes is emerging. Given these considerations, this PhD project, that is part of the European project BioProMedFood, financed in the frame of PRIMA – Section 2 Programme, was focused on the study of sustainable approaches to improve quality and microbiological safety of fresh or fermented meat products. With this purpose, three main strategies have been evaluated. The first concerned the valorisation of spontaneously fermented sausages microbial biodiversity, through the isolation of autochthonous microbial strains and their use as bio-protective or functional starter cultures in meat products. In particular, the work started with the characterisation of 15 traditional fermented sausages, collected in Mediterranean countries, addressed to highlight their microbial biodiversity by using metagenomic analysis. Lactic acid bacteria (LAB) and coagulase-negative cocci were the most representative microorganisms in all samples, but significant differences were observed in relation to the product characteristics and origin. More than 900 LAB strains were isolated from these traditional products and approx. 150 biotypes, mainly belonging to the species Latilactobacillus sakei, were detected. These results confirmed the high adaptation of this species to this ecological niche. These strains were studied regarding their antibiotic-resistances and amino biogenic potential and only safe strains (approx. 40) were characterised for their technological properties (growth performances at different salt concentrations and incubation temperatures) and their antimicrobial potential (inhibition of food-borne pathogens in vitro and the presence of genes related to bacteriocin production). The most promising strains were further studied for their anti-listerial activity in fresh sausages with promising results. In addition, they were used as starter cultures in the pilot plant production of fermented sausages. The results showed that the fermented sausages obtained with the selected strains were characterised by good aroma profiles and a reduced biogenic amine (BA) content. Moreover, the growth of Listeria monocytogenes during production and ripening, assessed with a challenge test, was strongly inhibited. The second aim of the work was focused on the use of natural compounds with antimicrobial potential, extracted from plant derivatives of species characterising the Mediterranean maquis. In particular, phenolic extracts and essential oils of Juniperus oxycedrus needles and Rubus fruticosus leaves were tested in vitro against a strain of List. monocytogenes and Enterococcus faecium, also by using a cytofluorimetric protocol to better evidence the effect on viability and physiological state of target cells. In the latter strain, the inhibition of tyramine production was also assessed to evaluate the plant derivatives potential in reducing the accumulation of this toxic BA. Data collected underlined relevant differences in relation to species and type of plant derivatives, but they hint at important possibilities for applications in specific foods or processes. The last topic of research of this thesis regarded the study of the effect of LAB fermentation on avocado leaves by-products. In particular, the attention was focused on the bio-availability of phenolic compounds in the plant extracts, caused by microbial metabolism. Even if the research work on this topic is still ongoing, the first data obtained are encouraging and an increase in antioxidant potential following LAB fermentation has been observed, even if in a strain-specific manner. Concluding, the work presented in this PhD thesis permitted to highlight the great potential of traditional meat products to be a reservoir of microbial biodiversity and a source of isolation of new strains with industrial importance. Moreover, the antimicrobial potential of compounds obtained from under-exploited plant matrices was also investigated to assess their possibility to serve as “green” strategies in the increase of fresh food safety. These aspects demonstrated the potential use of innovative biotechnological strategies, to pursue production efficiency and promote the sustainability of the entire production system from a circular economy perspective.