Influence of an adjunct culture of Lactobacillus on the free amino acids and volatile compounds in a Roncal-type ewe’s-milk cheese

Free amino acids and volatile compounds were analysed in a Roncal-type cheese made from pasteurized ovine milk with and without an added adjunct culture (Lactobacillus paracasei + Lactobacillus plantarum). In both batches, the total free amino acid concentration increased 11–12-fold with ripening time, the main amino acids being Leu, Glu, Lys, Phe, Val, and Ile. At the end of ripening, significant differences were recorded for Leu, Ile, Gaba, Phe, Pser, Ser, Gin, Ala, and Orn.     

Microbiological, physicochemical, and sensory characteristics of kefir during storage

Changes in certain microbiological, physicochemical, and sensory parameters of kefir were studied during refrigerated storage. Kefir batches were prepared using 1% and 5% added kefir grains, and samples for analysis were taken 24 h after inoculation and then after 2, 7, 14, 21, and 28 days of storage at 5 ± 1 °C. After fermentation for 24 h after inoculation, lactobacilli and lactococci were present at levels of 10⁸ cfu/ml, and yeasts and acetic acid bacteria were present at levels of 10⁵ and 10⁶ cfu/ml, respectively. The lactic acid flora decreased by about 1.5 log units between days 7 and 14 and then stabilized at that level. Yeast and acetic acid bacterial counts, lactose, and pH all remained constant over the storage period, while the total fat content and dry matter decreased. The percentage inoculate did exert an influence, and the sample batches made using 1% added kefir grains had higher lactic acid bacterial counts, lactose, and pH, while the sample batches made using 5% added kefir grains had higher yeast and acetic acid bacterial counts and viscosity. The total fat and dry matter contents were similar in both sample batches. Sensory analysis of the kefir samples revealed maximum acceptability levels in the first 2 days of storage.     

Sources of enterococci in Idiazábal-type cheese

Enterococci are a ubiquitous group and are natural constituents of the intestinal flora of nearly all animals and humans and can reach high levels in a variety of farmhouse cheeses. The purpose of this study was to determine the origin of the different enterococcal strains present in cheeses at different stages of ripening by typing the enterococci isolated from the raw milk, the cheeses, the cheesemaking environment, and from the faecal matter of the ewes and humans associated with cheese production. The potential presence of vancomycin-resistant enterococci (VRE) at all stages of the process and in the cheeses was also considered. The study was carried out at two separate cheesemaking dairy plants, and samples of the ewes' faeces, the shepherds' and cheesemakers' stools, teat cups, vat, brine, holding tank milk, vat milk, and the cheeses after brining and after 1, 15, and 60 days of ripening were collected. Cheesemaking procedures at the two plants were similar, yet the enterococcal levels and species observed differed at all the sample collection points, though E. faecalis predominated in all the milk and cheese samples. The traceability study performed for the species E. faecalis present at all the sample collection points suggested that the cheesemaker and the cheesemaking equipment were the source of the enterococci in the cheeses, though other possible non-faecal sources remain to be determined. VanC1 and vanC2/C3 enterococcal strains were isolated from the ovine faeces, teat cup, brine, and vat samples at cheesemaking dairy plant A, while only two vanC2/C3 strains were isolated from ovine faeces samples at dairy plant B. No VRE strains were detected in any of the milk or cheese samples.     

Polymers beyond standard optical fibres – fabrication of microstructured polymer optical fibres

This paper reports the overall fabrication process of microstructured polymer optical fibres (mPOFs). mPOF fabrication involves a two‐step process: on the one hand, the design and creation of a preform containing a large‐scale version of the desired fibre and, on the other, the precise heating and drawing of the preform to the final fibre. The preforms are produced either by an improved drilling technique or by capillary stacking. For a correct and accurate drawing of the fibre, a controlled and precise heating unit has to be designed, an issue that will be explained in detail in this work. The quality and optical performance of the final mPOF depends strongly on key factors such as the preform annealing, the accuracy of the technique selected for the creation of the preform structure, the heating stage, as well as on the drawing parameters. All of them are analysed in detail and some drawn mPOFs of interest are reported as well. © 2018 Society of Chemical Industry     

Cover Image,Volume 67, Issue 9

The cover image, by Eneko Arrospide et al., is based on the Review Polymers beyond standard optical fibres ‐ fabrication of microstructured polymer optical fibres, DOI: 10.1002/pi.5602 .

     

Effect of lactobacillus adjunct cultures on the microbiological and physicochemical characteristics of Roncal-type ewes'-milk cheese

The effect of two different experimental adjunct cultures composed of native facultatively heterofermentative lactobacilli (FHL) on the development of various groups of micro-organisms in Roncal-type ewes' milk cheese was studied. Four cheese batches were manufactured from raw milk (C), pasteurized milk (P), pasteurized milk and an adjunct culture of Lactobacillus paracasei (PP); and pasteurized milk and adjunct culture of Lactobacillus paracasei plus Lactobacillus plantarum (PPP). Retention of the two adjunct cultures in the cheeses was good, and population levels remained constant at around 10(7) cfu g(-1) of cheese throughout ripening. Levels of Enterobacteriaceae and enterococci fell off more abruptly in the batches made with the Lactobacillus adjunct cultures, suggesting competition between the added lactobacilli and those groups of micro-organisms. The inhibitory effect was greater for the adjunct culture composed of L. paracasei plus L. plantarum. Lactococcal levels were higher in the batches made with added FHL, which may be indicative of a synergistic effect between these two groups.     

A million-channel reformer on a fingertip: Moving down the scale in hydrogen production

The present contribution reports the design, manufacture and experimental proof of concept of an ethanol micro-reformer for portable-fuel cell feeding. Through photo-assisted electrochemical etching, a silicon micromonolithic substrate with perfectly parallel cylindrical channels of 3.3 μm diameter was achieved (density of channels of ca. 4 × 10⁴ channels mm⁻²). The channel walls were coated with a cobalt-based catalyst. The resultant functionalized micromonoliths were implemented in a stainless steel microreactor including feed evaporation facilities and electrical heating. The unit was successfully tested for ethanol steam reforming under non-diluted feed conditions at 773 K, achieving high hydrogen specific production rates, high ethanol conversions (>80%) and adequate selectivity profiles, with H₂:CO₂ molar ratios of ∼3 and low CO outlet concentrations. A performance comparison was performed with two other reforming substrates with the same catalyst formulation, namely, a conventional cordierite monolith and a conventional stainless steel microreactor. Results show for the Si-micromonolithic reactor a remarkable improvement of the specific hydrogen production rate (per unit reactor volume and feed flowrate), operating at considerably reduced residence times, due to the increase in contact area per unit volume.