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    Magnesium enrichment of skim milk : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Auckland, New Zealand
    (Massey University, 2019) Begum, Noorzahan
    Effective magnesium enrichment of dairy products depends on the amount of magnesium salt added and the nature of its distribution between the serum and micellar phases. Thus, this study firstly aimed to profile the magnesium distribution in skim milk as a function of pH (pH 5.50 to 7.20), preheating temperatures (20 to 80 ± 1 °C) and concentration of added magnesium chloride (0 to 40 mmol L-1). The second aim was to investigate the rheological properties of magnesium-induced skim milk gels as a function of different concentrations of magnesium chloride (0 to 20 mmol L-1) added to heated skim milk. The total concentration of magnesium in skim milk and serum was determined using a complexometric titration (EDTA titration) and the EDTA results were validated by atomic absorption spectroscopy (AAS). The measurement of ionic magnesium (Mg2+) in milk is of importance for understanding the bioavailability of magnesium-enriched dairy products. Hence, the concentration of ionic magnesium (Mg2+) in the serum phase was measured using a novel magnesium fluorescence dye (Magnesium 510 probe). In all the samples, a reduction in the pH increased the total soluble magnesium and ionic magnesium (Mg2+) concentrations in the serum phase, regardless of whether magnesium chloride (15 mmol L-1) was added or not to skim milk at 20 ± 1 °C. At pH 5.50, more than 92% magnesium was found in the serum phase for both added (15 mmol L-1) and no added magnesium chloride samples. The concentration of magnesium in the serum phase remained unchanged as the preheating temperature was increased from 20 to 80 ± 1 °C. The addition of magnesium chloride to skim milk reduced the milk pH and increased the ionic magnesium (Mg2+) and total soluble magnesium concentration in the serum phase at 20 ± 1 °C. The pH values are important for new magnesium-enriched dairy products as the distribution of added magnesium chloride in the serum phase was different dependent on pH adjustment between the pH 6.50 and natural pH 6.70. Rheological measurements using cone and plate geometry at constant strain showed that the addition of 5 mmol L-1 magnesium chloride induced the gelation of skim milk after 22 min of heating at 80 °C in the rheometer. The time and temperature for reaching the gelation in skim milk depended on preheating and concentration of added magnesium chloride. A higher concentration of added magnesium chloride achieved gelation at a lower temperature in the rheometer. With the magnesium-induced gels, G’ values obtained were found to increase with increasing concentrations of added magnesium chloride (0 to 20 mmol L-1), increasing holding times (10 to 60 min) and increasing heating temperatures (70 to 80 °C). Compared with samples with 5 mmol L-1 magnesium chloride, those with 15 mmol L-1 magnesium chloride showed a more rapid increase in G’. The G’ value obtained with 15 mmol L-1 magnesium chloride was 15.01 Pa at 80 °C during 10 min of holding and cooling to 20 °C rapidly increased the final G’ value to 81.44 Pa. In contrast, the addition of 5 mmol L-1 magnesium chloride resulted in the formation of a weak gel with a final G’ value of 6.87 Pa after cooling to 20 °C. The oscillation stress of milk gels also increased with increasing magnesium chloride concentration, heating temperatures and holding times in the rheometer. Preheating significantly (P < 0.05) affected the strength of magnesium-induced skim milk gels. The addition of 20 mmol L-1 magnesium chloride to preheated skim milk followed by heating at 85 °C then cooling to 20 °C formed strong skim milk gels. In parallel, samples with no added magnesium chloride did not undergo gelation. In conclusion, the distribution of magnesium was influenced by pH and magnesium concentration added and the strength of magnesium-induced gels was influenced by magnesium concentration added, preheating and the heating time and temperature in the rheometer. The technology of making magnesium-induced skim milk gels can be exploited commercially for the formation of non-fermented dairy products supplemented with magnesium.
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    Some factors affecting magnesium uptake by citrus leaves : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1971) Thapa, Shaligram Kumar
    Pineapple sweet orange seedlings and rooted leaf bud cuttings of Meyer lemons were used to investigate the effects of some of the factors affecting magnesium uptake by leaves. Magnesium was determined by thiazole yellow method of Drosdoff and Nearpass (1948) and uptake was usually measured 24 hours after spray treatment. It was shown that the addition of wetting agents to magnesium nitrate sprays significantly increased the uptake of magnesium by leaves. The nonionic wetter (Terric GN9) at the very low (0.01% a.i.) and high (0.08 - 0.1% a.i.) concentrations did. not affect magnesium uptake, whereas at intermediate concentrations, magnesium uptake was increased. Use of the humectant glycerine at 1 or 2 percent significantly increased the uptake of magnesium by leaves, compared with sprays to which no glycerine was added, but had no beneficial effect over sprays which contained a nonionic wetter (Terric GN9). Magnesium uptake by leaves grown in 100% relative humidity for two weeks was greater than the uptake by leaves grown in average relative humidity of 71% Both morning and the evening sprays resulted in greater uptake of magnesium by leaves, compared with afternoon sprays. A significant increase in leaf magnesium concentration occurred after 2 hours of a magnesium nitrate spray application. Leaf magnesium concentration rose steeply for 24 hours after spraying, thereafter remaining constant. (Because it was not possible to measure the degree of magnesium transport out of the leaf, it is not clear whether magnesium uptake, in fact, stopped after 24 hours). Of the three magnesium salts used, magnesium nitrate and magnesium chloride sprays resulted in greater magnesium uptake by leaves, compared with magnesium sulphate sprays. Uptake varied with the concentration of magnesium in. the leaves. The lower the concentration of magnesium in the leaves, the loss the uptake of magnesium by leaves, and the higher the concentration of magnesium, the higher the uptake of magnesium. Leaf nitrogen also affected uptake of magnesium by leaves. High leaf nitrogen (2.92% of dry weight) resulted in greater uptake of magnesium than the low leaf nitrogen (2.08% of dry weight). The average increase in the concentration of magnesium in the leaves of low nitrogen plants was 0.09% of dry weight, while in leaves of high nitrogen plants the increase was 0.19%. Thus the increase in the % leaf concentration of magnesium in the high nitrogen plants was double that of the low nitrogen plants. This may be a direct effect of the low leaf nitrogen or an indirect one due to the induced low leaf magnesium in those plants.
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    The relationship between nutritional adequacy and 24-month fracture occurence in Māori and non-Māori of advanced age : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Science in Nutrition and Dietetics, Massey University, Albany, New Zealand
    (Massey University, 2015) Towgood, Alice
    Abstract Background The life expectancy of both Māori and non-Māori is continually increasing with more New Zealanders expected to live into advanced age. Adults over the age of 80 experience greater health loss than any other age group, with chronic disease and associated disability increasing substantially with age. Osteoporosis and the morbidity associated with fractures, particularly hip fracture, are of critical concern for an ageing population and may diminish quality of life and independence for older people, thus placing an increased burden on health and disability support services. The role of nutrition in the maintenance of bone mineral density (BMD), bone integrity, and subsequent fracture prevention, particularly in octogenarians is unclear. The ability to meet adequate energy requirements decrease with increasing age and may compromise intake of nutrients related to bone health. Nutrients necessary for bone health including: protein, calcium, vitamin D, phosphorous, magnesium and potassium are modifiable factors. Achieving optimal bone nutrient intakes may influence potential for maintenance of good bone health in adults of advanced age. This study aims firstly to investigate food and nutrient intakes of Māori and Non-Māori octogenarians to establish an understanding of nutrient adequacy. Secondly, to investigate the energy and nutrient intakes of participants who experience a fracture compared with those non-fractured to identify nutrient specific risk factors for fracture in adults of advanced age. Method Comprehensive nutritional parameters were collected using two separate 24-hour multi-pass recalls. FOOD files were used to analyse food sources and nutrient intake. Face to face interviews were conducted to ascertain specific social, demographic, health and fracture information. Fracture occurrence was measured over a 24 month period following the 2 x 24-hour Multi Pass Recall’s and included self-reported and hospitalised fracture occurrences. Hospitalisation data was obtained with permission from the participants. National Health Index New Zealand (NHI) numbers were used to identify fractures. Results There were 317 participants (113 Māori and 204 non-Māori), aged 80-90 years in this study. For men and women respectively the median energy intakes were 6,943kJ vs. 5,603kJ for Māori; and 8,203kJ vs. 6,225kJ for non-Māori; protein as a percentage of energy was 15.5% vs. 15.9% for Māori and 15.7% vs. 15.5% for non-Māori. The top foods contributing to energy were bread, butter and margarine for all Maori and non-Maori with beef and veal contributed the most protein for Māori men, bread for Māori women and milk for non-Māori, men and women. Compared to the Estimated Average Requirement (EAR) intakes of calcium, vitamin D, magnesium and potassium were inadequate for all participants. Compared to an EAR of 1100mg for men and women, median calcium intakes were low, 559mg vs. 539mg for Māori and 748mg vs. 672mg for non-Māori, men and women respectively. The primary food groups contributing to calcium were milk, cheese and bread. Compared to the EAR (15 μg/day in men and women) and vitamin D intake from food was low (≤ 4 μg) for all participants. Compared to the EAR (350mg/day men and 265mg/day women), median magnesium intakes were 259 mg/day vs. 204mg/day for Māori and 271 mg/day vs. 238 mg/day for non-Māori, men and women respectively. The primary food groups contributing to magnesium were bread, breakfast cereals and fruit. A total of 18.6% of Māori and 20.6% of non-Māori sustained a fracture over a 24 month period. One in five Māori and non-Māori women sustained fractures. Among non-Māori women those who fractured were 1.1 times more likely to be financially insecure than non-fractured women (p=0.033). For Māori women who were fractured, inability to afford to eat properly was 3.3 times more likely (p=0.012), and previous fractures were 1.5 times (p=0.015) more likely than for non-fractured women. Fractured Māori women consumed significantly less vitamin D (2.0μg vs 3.0μg) (P=0.01) and magnesium (143.0mg vs 211mg) (P=0.033) compared to non-fractured Māori women. Conclusion Energy intakes were low for all participants and may have manifested the suboptimal intakes of calcium, vitamin D, potassium and magnesium prevalent in Māori and non-Māori, men and women. Fractures were more frequent in women than men, and both Māori and non-Māori sustained similar rates of fracture over the 24 month period. Magnesium and vitamin D intakes were significantly related to fracture occurrence in Māori women; this relationship diminished with further regression analysis. Increased intake of energy in adults of advanced age, with a focus on protein rich and nutrient dense foods, particularly calcium and magnesium, should be encouraged through consuming a variety of foods from the major food groups. Greater intakes of calcium can be achieved through higher consumption of milk and dairy products including yoghurt and cheese; and magnesium through increased green leafy vegetables, seafood, dairy, mushrooms, avocado, beans and bananas. Vitamin D intakes were minimal from food; however it is possible participants were receiving supplementary vitamin D and further investigation is warranted. For fractured Māori women, magnesium intake was significantly lower than those with no fractures. Promoting increased intakes of culturally acceptable foods such as vegetables and seafood may be advantageous to increase magnesium intakes.
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    Single-molecule folding mechanisms of the apo- and Mg(2+)-bound states of human neuronal calcium sensor-1
    (Biophysical Society, 7/07/2015) Naqvi MM; Heidarsson PO; Rodriguez Otazo M; Mossa A; Kragelund BB; Cecconi C
    Neuronal calcium sensor-1 (NCS-1) is the primordial member of a family of proteins responsible primarily for sensing changes in neuronal Ca(2+) concentration. NCS-1 is a multispecific protein interacting with a number of binding partners in both calcium-dependent and independent manners, and acting in a variety of cellular processes in which it has been linked to a number of disorders such as schizophrenia and autism. Despite extensive studies on the Ca(2+)-activated state of NCS proteins, little is known about the conformational dynamics of the Mg(2+)-bound and apo states, both of which are populated, at least transiently, at resting Ca(2+) conditions. Here, we used optical tweezers to study the folding behavior of individual NCS-1 molecules in the presence of Mg(2+) and in the absence of divalent ions. Under tension, the Mg(2+)-bound state of NCS-1 unfolds and refolds in a three-state process by populating one intermediate state consisting of a folded C-domain and an unfolded N-domain. The interconversion at equilibrium between the different molecular states populated by NCS-1 was monitored in real time through constant-force measurements and the energy landscapes underlying the observed transitions were reconstructed through hidden Markov model analysis. Unlike what has been observed with the Ca(2+)-bound state, the presence of Mg(2+) allows both the N- and C-domain to fold through all-or-none transitions with similar refolding rates. In the absence of divalent ions, NCS-1 unfolds and refolds reversibly in a two-state reaction involving only the C-domain, whereas the N-domain has no detectable transitions. Overall, the results allowed us to trace the progression of NCS-1 folding along its energy landscapes and provided a solid platform for understanding the conformational dynamics of similar EF-hand proteins.