The significance of cheese sampling in the determination of histamine concentration: Distribution pattern of histamine in ripened cheeses

Cheeses are becoming a major safety and public health concern: cheeses available in supermarkets occasionally contain high histamine concentrations that can have negative effects on consumer health. In this study, we have attempted to assess the histamine distribution pattern in ripened cheeses, with the purpose of establishing a correct cheese sampling strategy for the quantification of histamine. To this aim, histamine was determined in four distinct areas of twelve long-ripened hard cheeses: the external and internal rind, along with the outer and inner core of the wedge. The concentrations measured were remarkably different: histamine accumulated in the central core, whereas the lowest amount was found in the peripheral rind. To explain this heterogenous distribution, histamine producers were determined in the four areas by identifying the hdc sequences obtained from cheese samples. Non-starter bacteria were identified as main histamine producers; however, these microbiota were homogeneously distributed throughout the wedge. Nevertheless, the analysis of psychochemical properties of the different areas revealed an observable trend: histamine tended to accumulate in the saltier, more humid, and less oxidized areas in a wedge. Overall, this study highlights the significance of a correct sampling strategy when histamine is quantified in cheese

A Novel NAD(+)-dependent Aldehyde Dehydrogenase Encoded by the puuC Gene of Klebsiella pneumoniae DSM 2026 that Utilizes 3-Hydroxypropionaldehyde as a Substrate

3-Hydroxypropionic acid (3-HP), a versatile and valuable platform chemical, has diverse industrial applications; but its biological production from glycerol is often limited by the capability of the enzyme aldehyde dehydrogenase (ALDH) to convert an intermediary compound, 3-hydroxypropionaldehyde (3-HPA), to 3-HP. In this study, we report a new ALDH, PuuC, from Klebsiella pneumoniae DSM 2026, that efficiently converts 3-HPA to 3-HP. The identified gene puuC was cloned, expressed in Escherichia coli, purified, and characterized for its properties. The recombinant enzyme with a molecular weight of 53.8 kDa exhibited broad substrate specificity for various aliphatic aldehydes, especially C-2-C-5 aldehydes. NAD(+) was the preferred coenzyme for the oxidation of most aliphatic and aromatic aldehydes tested. The optimum pH and temperature for PuuC activity were pH 8.0 and 45 degrees C. The K-m values for 3-HPA and NAD(+) were 0.48 and 0.09 mM, respectively. The activity of PuuC was enhanced in the presence of reducing agents such as 2-mercaptoethanol or dithiothreitol, while several metal ions, particularly Hg2+, Ag+, and Cu2+ inhibited its activity. The predicted structure of PuuC indicated the presence of K191 and E194 in close proximity to the glycine motif, suggesting that PuuC belongs to class 2 ALDHs