Journal Articles
Permanent URI for this collectionhttps://mro.massey.ac.nz/handle/10179/7915
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Item The relationship between pH, pigments production, and citrinin synthesis by Monascus purpureus during red fermented rice fermentation(Elsevier Ltd, 2025-09-01) Farawahida AH; Palmer J; Flint SRed fermented rice (RFR) is consumed as a traditional medicine in many countries. Consumption of food contaminated with citrinin (CIT) has adverse effects on the liver cells and the kidneys. This study aimed to understand the relationship between pH, pigments, and CIT levels during the fermentation of RFR. The rice underwent soaking, steaming, and autoclaving before being inoculated with Monascus purpureus isolates (MF1 or MS1) and fermented at 30 °C for 30 days. The difference between these isolates was that MF1 and MS1 required 4 days and 7 days, respectively, to produce light blue fluorescence on Coconut Cream Agar (CCA), an indicator of the presence of CIT. The pH, pigments, and CIT levels were recorded during fermentation using a pH meter, spectrophotometer, and Ultra-High-Performance Liquid Chromatography with a Fluorescence Detector (UHPLC-FLD), respectively. The pH dropped from 6.8 to 5.3 after 9 days of fermentation. The CIT levels increased from day 4 until day 5 and then decreased during the fermentation period. The pigments increased after 5 days of fermentation, suggesting a relationship between pigments production and CIT reduction. Mixing the CIT standards and pigments extracted from MF1 and MS1 (a mixture of yellow, orange, and red pigments) showed that there was a reduction in CIT of 26–68 % and 16−45 %, respectively. It is suggested that future work should determine which pigments are responsible for CIT reduction. The optimization of pigments production with the control of pH at 5.5 may help to control CIT levels during the fermentation of RFR.Item The effect of three different preservatives on the numbers and types of bacteria, Brix percentage, pH and nutritional composition of bovine colostrum sourced from New Zealand dairy farms(Taylor and Francis Group, 2024-09-02) Cuttance EL; Mason WA; Cranefield S; Laven RAAIMS: To investigate the effect of preservation by addition of yoghurt starter, potassium sorbate and citric acid on counts of aerobic bacteria, Lactobacillus spp., Streptococcus thermophilus and coliforms, Brix percentage, pH, protein, fat and anhydrous lactose concentrations at 0, 7 and 14 days after collection for colostrum stored at ambient temperature. METHOD: Approximately 2 L of first milking colostrum was collected from 10 farms in the Waikato region. Following mixing, it was split into five 400-mL sub-samples and allocated randomly to a control (two sub-samples), or treatment with yoghurt, potassium sorbate, or citric acid preservative. Throughout the trial samples remained in the laboratory at ambient temperature with the lids slightly ajar, and were stirred daily for 15-30 seconds using a sterile spatula. Sub-samples were tested on Days 0, 7 and 14. On Days 0 and 14 aerobic bacteria (by aerobic plate count (APC)), Lactobacillus spp., coliforms and Streptococcus thermophilus counts, pH, Brix percentage, protein, fat and anhydrous lactose were measured. On Day 7 only bacterial counts were completed.The data were analysed using non-parametric clustered bootstrap sampling to estimate the effect of treatment, time, and their interaction on the outcome variables. RESULTS: Compared to control samples, on Day 7 the APC for potassium sorbate (1.0 (90% CI = 0.6-1.6) × 108 cfu/mL) was approximately seven-fold lower than for yoghurt (7.3 (90% CI = 4.1-11) × 108 cfu/mL), and approximately three-fold lower than citric acid (3.2 (90% CI = 0.2-4.3) × 108 cfu/mL) remaining low to Day 14. All preservatives reduced coliform growth compared to control samples at Day 7 but growth was lower for potassium sorbate than the other preservatives. For Lactobacillus spp., at Day 7, samples with yoghurt preservative had greater counts than the other two preservatives. Potassium sorbate reduced growth of S. thermophilus compared to the other treatments, especially at Day 7, with 7-10 times fewer S. thermophilus per mL compared to the other three groups. All groups showed an obvious acidification over time, with very little variation within days and treatment groups. There was no evidence for change in fat or protein percentage over time regardless of treatment. CONCLUSION AND CLINICAL RELEVANCE: Aerobic and coliform bacteria proliferate extensively in unpreserved colostrum. All preservatives decreased coliform counts compared to un-preserved colostrum, but potassium sorbate was more effective at decreasing both coliforms and aerobic bacteria than either yoghurt or citric acid.Item Emulsification Properties of Garlic Aqueous Extract: Effect of Heat Treatment and pH Modification(MDPI, Basel, Switzerland, 2023-10-10) Bravo-Núñez Á; Golding M; Gómez M; Matia-Merino L; Dai HDespite the broad research available in the literature dealing with garlic health benefits, little information is found regarding the functional properties of garlic components. The aim of this study was to evaluate the emulsification properties of garlic water-soluble compounds (GWSC), encompassing proteins, saponins, and carbohydrates, after heat treatment (10 min at 95 °C) or pH adjustments (2.5, 3.5, and 7.8). After the various treatments, the extracts were used as such or filtrated (0.45 µm), and 10% soybean oil-in-water emulsions were prepared using low (0.48%) or high (6.55% wt/wt) extract concentrations. Results showed that whereas at low GWSC concentrations, both heating and acidifying resulted in the formation of bigger oil droplet sizes (i.e., from d32 = 0.36 µm using unmodified extract to d32 = 7-22 µm at pH 2.5 with or without extract filtration), the effects were opposite at the highest GWSC concentration. In the latter, heat treatment clearly reduced the droplet size as observed from the micrographs as well as the degree of creaming, though the occurrence of depletion and/or bridging flocculation was still strong. The acidification of the extract at this high GWSC concentration significantly reduced the droplet size, as observed from the micrographs; however, a strong flocculation was observed. Removal of protein aggregates, and possibly also saponin micelles, from the extract resulted in an obvious increase in emulsion droplet size. This research brings valuable insights on this study and utilisation of novel natural food emulsifiers from plant sources.Item The Role of Gastric Lipase and Pepsin in Lipid Digestion of a Powder Infant Formula Using a Simulated Neonatal Gastric System(Springer Nature, 2024-02-08) Deng L; Golding M; Lentle R; MacGibbon A; Matia-Merino LThis study has sought to determine the impact of interfacial dynamics on the in vitro lipid digestion of a commercial infant formula; in particular, the specific role of interfacial proteolysis on the subsequent rates of reaction of droplet lipolysis. A powder infant formula was used as the as a protein-stabilised emulsion substrate during simulated infant gastric digestion at different pH level 3.5, 4.5 and 5.5. The digestate was treated with a fungal lipase and porcine pepsin (used to analogue human gastric lipase and pepsin) respectively and in a combined action. The study found that for fungal lipase treated digestate, the rate and extent of lipolysis were observed to be maxim at pH 5.5, in accordance with the optimal pH activity of the lipase. Findings also indicated that the proteinaceous interface did not appear to act as a barrier to lipolysis, since treatment with lipase and pepsin did not result in any significant increase in extent of lipolysis. However, it was observed that surface proteolysis did lead to alteration of the structural fate of the enzyme during digestion when compared to when the emulsion was digested solely by lipase. Findings suggest that lipolysis under these conditions may be independent of the structural dynamics of the emulsion during digestion, as observed within the context of this study design.Item Integrating pH into the metabolic theory of ecology to predict bacterial diversity in soil(National Academy of Sciences, 2023-01-17) Luan L; Jiang Y; Dini-Andreote F; Crowther TW; Li P; Bahram M; Zheng J; Xu Q; Zhang X-X; Sun B; Brown JMicroorganisms play essential roles in soil ecosystem functioning and maintenance, but methods are currently lacking for quantitative assessments of the mechanisms underlying microbial diversity patterns observed across disparate systems and scales. Here we established a quantitative model to incorporate pH into metabolic theory to capture and explain some of the unexplained variation in the relationship between temperature and soil bacterial diversity. We then tested and validated our newly developed models across multiple scales of ecological organization. At the species level, we modeled the diversification rate of the model bacterium Pseudomonas fluorescens evolving under laboratory media gradients varying in temperature and pH. At the community level, we modeled patterns of bacterial communities in paddy soils across a continental scale, which included natural gradients of pH and temperature. Last, we further extended our model at a global scale by integrating a meta-analysis comprising 870 soils collected worldwide from a wide range of ecosystems. Our results were robust in consistently predicting the distributional patterns of bacterial diversity across soil temperature and pH gradients-with model variation explaining from 7 to 66% of the variation in bacterial diversity, depending on the scale and system complexity. Together, our study represents a nexus point for the integration of soil bacterial diversity and quantitative models with the potential to be used at distinct spatiotemporal scales. By mechanistically representing pH into metabolic theory, our study enhances our capacity to explain and predict the patterns of bacterial diversity and functioning under current or future climate change scenarios.
