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In Vitro Fermentation of Sheep and Cow Milk Using Infant Fecal Bacteria
(MDPI (Basel, Switzerland), 2020-06-17) Ahlborn N; Young W; Mullaney J; Samuelsson LM
While human milk is the optimal food for infants, formulas that contain ruminant milk can have an important role where breastfeeding is not possible. In this regard, cow milk is most commonly used. However, recent years have brought interest in other ruminant milk. While many similarities exist between ruminant milk, there are likely enough compositional differences to promote different effects in the infant. This may include effects on different bacteria in the large bowel, leading to different metabolites in the gut. In this study sheep and cow milk were digested using an in vitro infant digestive model, followed by fecal fermentation using cultures inoculated with fecal material from two infants of one month and five months of age. The effects of the cow and sheep milk on the fecal microbiota, short-chain fatty acids (SCFA), and other metabolites were investigated. Significant differences in microbial, SCFA, and metabolite composition were observed between fermentation of sheep and cow milk using fecal inoculum from a one-month-old infant, but comparatively minimal differences using fecal inoculum from a five-month-old infant. These results show that sheep milk and cow milk can have differential effects on the gut microbiota, while demonstrating the individuality of the gut microbiome.
Stability of the probiotic Lactobacillus paracasei CRL 431 under different environmental conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatu, New Zealand
(Massey University, 2015) Poddar, Devastotra
Probiotics are live microorganisms which provide health benefits to the host upon consumption. There is a wealth of information available on the health benefits associated with the consumption of probiotics. However, currently probiotic microorganisms are delivered mainly through refrigerated, short shelf-life products. When incorporated into ambient shelf-life products, the products generally fail to meet the regulatory criteria, which require probiotic bacteria to be viable in high numbers at the end of shelf-life. Storage temperature, oxygen and residual moisture content often result in loss of viability of probiotics during storage and distribution. A preliminary study was carried out to explore the effects of matrix composition (fat, protein and carbohydrate) on the probiotic bacterial (Lactobacillus paracasei CRL 431) viability, during fluidized bed drying and subsequent storage. The finding suggests that whole milk powder provided a superior protection to bacteria during fluidized bed drying and subsequent storage, compared to skim milk powder or milk protein isolate. Moreover, water activity of the powders during storage played a key role in determining the probiotic viability. The effects of drying techniques, moisture content and water activity on the storage stability of L. paracasei in a whole milk matrix were studied. Whole milk powder-bacteria mixtures were dried using spray drying, freeze drying or fluidized bed drying and stored at 25 ºC under controlled water activity ( 0.11 aw, 0.33 aw and 0.52 aw) for 105 days. At 0.11 aw, cell viability loss was minimal, while at 0.52 aw viability was lost in all powders within 22 days. At the intermediate 0.33 aw, there were marked differences among stored powders. Further, various analytical techniques (X-ray diffraction, FT-IR, Raman, NMR spectroscopy) were used to explore why and how structural differences in the matrix-bacteria mixtures, produced using different drying technologies, under different water activity storage conditions, influence bacterial viability. The results suggest that fluidized bed drying provided a better protection to the bacteria during storage, which was attributed to unique powder structure that reduced the absorption of water. The lower absorption of water resulted in the maintenance of a more rigid structure, which limited molecular mobility. Lactobacillus sp. is known to accumulate large amounts of inorganic manganese which apparently provides defense against oxidative damage by scavenging free radicals. The ability of L. paracasei to maintain viability during long term ambient storage may be enhanced by the ability of microorganism to accumulate manganese, which may act as free radical scavenger. To investigate this hypothesis, X-ray fluorescent microscopy (XFM) was employed to determine the changes in the elemental composition of L. paracasei during growth in MRS medium with or without manganese as a function of physiological growth state (early log vs. stationary phase). The results revealed that lower level of manganese accumulation occurred during the early log phase of bacterial growth compared with the stationary phase cells. The lower level of manganese accumulation was found to be related to the loss in bacterial viability during storage. Manganese has been known to possess pro- and anti-oxidant properties, and understanding of the changes in the manganese oxidation state was considered to provide some further insights into the bacterial death mechanisms. In view of the relatively high concentration of manganese in lactobacilli, it was of interest to better understand the oxidation state, coordination number and ligands of the manganese in the bacteria. It was possible to characterize the changes of manganese within bacteria using XANES. The results confirmed that manganese present within L. paracasei is in Mn(II) oxidation state and no changes in the manganese ligands could be observed during storage. In summary, the thesis provides a mechanistic insight into the ways to improve the stability of probiotics for application into ambient long shelf-life products. Future studies on tracking the genetic and proteomic aspects of the bacteria during storage might be useful for further understanding and process optimization.
Development and applications of a low-field portable NMR system : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University, Manawatu, New Zealand
(Massey University, 2011) Ward, Robert L
Nuclear magnetic resonance (NMR) is a phenomenon similar to MRI in which radio frequency signals are used to excite and manipulate atomic nuclei within a static magnetic field. Following excitation, the nuclei return to equilibrium, all the while offering valuable molecular level information pertaining to the sample. Within the last decade, the development of small and inexpensive NMR spectrometers and permanent magnet NMR sensors has been a significant focus within the NMR community. More recently, application scientists have sought practical applications for the new technologies. In this thesis, a prototype NMR apparatus consisting of a spectrometer and 3.2MHz permanent magnet sensor was extended to enable scientifc measurements. This involved developing radio frequency electronic circuitry for the spectrometer front-end, and electromagnetic noise shielding and temperature regulation for the magnetic sensor. Experimental results confirmed that repeatable measurements using the modified apparatus were indeed possible. The NMR apparatus was thereafter successfully used to study flow, diffusion and kiwifruit using several different experimental techniques. A significantly larger effort was then expended upon the study of T2 relaxation in pectin model systems using pH as the adjustable parameter. The fascinating experimental results were successfully interpreted and modeled across three pH zones in terms of a proton chemical exchange model and molecular conformational changes. In addition, it was found that pectin carboxyl de-protonation was significantly less than expected. Further experiments performed upon galacturonic acid monomers, dimers and trimers appeared to further illuminate the pectin results. Future experiments are planned. Also while studying pectin solutions, an unexpected pH-dependent water transverse relaxation behavior was observed at both 3.2MHz and 400MHz. The only references found in the literature were from a small publication almost 50 years ago, and a 2011 publication. Altogether, this thesis contributed to original knowledge in several ways: it showed how a low- eld apparatus and single-sided sensor could be improved and utilized for a variety of scientific measurements; it showed both experimentally and theoretically how T2 for pectin solutions change with pH; it revealed an unexpected de-protonation limit for pectin molecules; it revealed a T2 pH dependence for water.

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