Daniel M. Linares’s research while affiliated with University College Cork and other places

Abstract Putrescine and cadaverine are among the most common biogenic amines (BA) in foods, but it is advisable that their accumulation be avoided. Present knowledge about their toxicity is, however, limited; further research is needed if qualitative and quantitative risk assessments for foods are to be conducted. The present work describes a real-time analysis of the cytotoxicity of putrescine and cadaverine on intestinal cell cultures. Both BA were cytotoxic at concentrations found in BA-rich foods, although the cytotoxicity threshold for cadaverine was twice that of putrescine. Their mode of cytotoxic action was similar, with both BA causing cell necrosis; they did not induce apoptosis. The present results may help in establishing legal limits for both putrescine and cadaverine in food.

The influence of the autochthonous CLA-producing Lactobacillus plantarum TAUL 1588 and Lactobacillus casei subsp. casei SS 1644 strains and the ripening time on the fatty acid (FA) content and sensory characteristics of sheep cheese were investigated. Three cheese types with different cultures and the control cheese were produced in duplicate and ripened for 8 months. 86 individual FA were determined by gas chromatography. Ripening time (2, 90, 180 and 240 days) did not have a significant effect (P >.05) on the FA content. However, the presence of both Lactobacillus CLA-producing strains led to a decrease of the saturated FA content and to 1.30, 1.19 and 1.27 times higher levels of vaccenic acid, CLA and omega-3, respectively, when compared to the control cheese. This combination allowed obtaining sheep milk cheeses with a healthier FA content, without appreciable changes on sensory characteristics. This work could be a promising approach to increase the bioactive fatty acid content of cheeses.

Spermine and spermidine are polyamines (PA) naturally present in all organisms, in which they have important physiological functions. However, an excess of PA has been associated with health risks. PA accumulates at quite high concentrations in some foods, but a quantitative assessment of the risk they pose has been lacking. In the present work, the cytotoxicity of spermine and spermidine was evaluated using an in vitro human intestinal cell model, and employing real-time cell analysis. Both spermine and spermidine showed a dose-dependent cytotoxic effect towards the cultured cells, with necrosis the mode of action of spermidine and perhaps also that of spermine. Spermine was more cytotoxic than spermidine, but for both PA the concentrations found to be toxic were above the maximum at which they have been found in food. The present results do not, therefore, support the idea that spermine or spermidine in food is harmful to healthy people.

This chapter details the production of three types of complex biomolecules by probiotic bacteria, namely vitamins, exopolysaccharides (EPS) and bacteriocins, and discusses their potential for health promotion in humans. It has been suggested that vitamin production is one of a number of functional characteristics associated with probiotic bacteria and gastrointestinal (GI) microbiota. A large number of lactic acid bacteria (LAB) have been reported to produce vitamins, such as folate (vitamin B9), cobalamin (vitamin B12), menaquinone (vitamin K2), riboflavin (vitamin B2) and thiamine (vitamin B1). A number of LAB, propionibacteria and bifidobacteria can synthesise EPS, which are excreted from the bacterial cells and which may or may not be loosely attached to the cell wall. EPS can contribute to the improved stability, rheology and texture of fermented dairy products, and may also offer protection to bacterial cells against bacteriophage attack, desiccation and osmotic stress.

The stability of probiotic cultures has been seen as an issue for dairy manufacturers and consumers and this chapter reviews the technical and scientific aspects of probiotic dairy products. Probiotic micro-organisms are shown together with their main metabolic products. This provides some information on their possible role in flavour production, but it should be noted that the traditional lactic acid bacteria (LAB) (i.e. starter cultures) are mainly responsible for much of the flavour and aroma. For probiotic products, micro-organisms are selected for their various health benefits. A wide range of fermented milk products is made in many different countries. The classical example is yoghurt. Frozen yoghurt technology may be adopted for the inclusion of probiotic cultures into ice cream and frozen desserts. The viability of probiotic bacteria in yoghurt depends on the strains used, interaction between species present, production of hydrogen peroxide due to bacterial metabolism, and the final acidity of the product.

Consumer concern about the relationship between food and health has generated a growing interest in functional foods. Conjugated linoleic acid (CLA) has been associated with several beneficial health properties. Therefore, this study reports the design of co-cultures containing CLA-producing strains and their performance in MRS and in skim milk. The four designed co-cultures were tested under different conditions. In MRS, co-culture 2 (containing autochthonous Lactococcus lactis strains and Lactobacillus plantarum TAUL 1588) was the highest CLA-producer (98.01 µg/mL) after 48 h incubation. In milk, the highest total CLA production (56.51 µg/mL) was reached with co-culture 4 (containing autochthonous Lactococcus lactis, Lactobacillus plantarum TAUL 1588 and Lactobacillus casei SS 1644) after 72 h. These results open the way for the use of co-cultures containing CLA-producing strains to manufacture cheese and obtain functional dairy products rich in bioactive fatty acids.

In this study, 85 strains of lactic acid bacteria isolated from artisanal cheeses were screened to determine their capacity to synthesise bioactive compounds. Four Lactobacillus plantarum and two Lactobacillus casei subsp. casei strains were capable of synthesizing conjugated linoleic acid (CLA). The highest level of CLA formed in MRS after 48 h incubation was 19.26 µg/mL. Six Lactobacillus brevis and four Lactococcus lactis subp. lactis strains produced gamma-aminobutyric acid (GABA) and the highest concentration (2524.05 µg/mL) was found after 72 h incubation. The detection of genes encoding linoleate isomerase or glutamate decarboxylase system could be suitable for use as screening method of CLA or GABA-producer strains, although this should be studied in a larger number of strains. Our findings suggest that the above strains are potential candidates for the design of starter cultures with the capacity to generate bioactive compounds, offering new possibilities for the manufacture of functional dairy products.

Consumer interest in healthy lifestyle and health-promoting natural products is a major driving force for the increasing global demand of biofunctional dairy foods. A number of commercial sources sell synthetic formulations of bioactive substances for use as dietary supplements. However, the bioactive-enrichment of health-oriented foods by naturally occurring microorganisms during dairy fermentation is in increased demand. While participating in milk fermentation, lactic acid bacteria can be exploited in situ as microbial sources for naturally enriching dairy products with a broad range of bioactive components that may cover different health aspects. Several of these bioactive metabolites are industrially and economically important, as they are claimed to exert diverse health-promoting activities on the consumer, such as anti-hypertensive, anti-inflammatory, and anti-diabetic, anti-oxidative, immune-modulatory, anti-cholesterolemic, or microbiome modulation. This review aims at discussing the potential of these health-supporting bacteria as starter or adjunct cultures for the elaboration of dairy foods with a broad spectrum of new functional properties and added value.

Here is presented the whole-genome sequence of Streptococcus thermophilus APC151, isolated from a marine fish. This bacterium produces gamma-aminobutyric acid (GABA) in high yields and is biotechnologically suitable to produce naturally GABA-enriched biofunctional yogurt. Its complete genome comprises 2,097 genes and 1,839,134 nucleotides, with an average G+C content of 39.1%.

Biogenic amines (BAs) are low molecular weight, nitrogenous, basic, organic compounds mainly synthesised via the decarboxylation of amino acids. BAs can be found in many types of food and beverage, albeit in very different concentrations. The most important BAs in dairy products are histamine, tyramine, putrescine, cadaverine and β-phenylethylamine. This chapter describes the biochemistry of BAs, the micro-organisms and genes responsible for the production of the main BAs found in dairy products, the toxicity of BAs and the intoxication symptoms associated with their ingestion. A detailed analysis of the factors affecting the accumulation of BAs in dairy products is also reviewed from the perspective of their nature as toxins produced in situ in foods as a result of microbial activities. The pH, temperature and salt concentration have an impact on BAs accumulation since they can influence the growth of BAs-producing bacteria, their gene expression, and the activity of their enzymes and transporters.