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    The effect of milk processing on protein digestion and amino acid absorption in the gastrointestinal tract of pigs as a model human : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Nutritional Sciences at Massey University, Manawatū, New Zealand
    (Massey University, 2024-06-19) Ahlborn, Natalie Gisela Marlis
    Globally, milk is processed using heat and homogenisation to improve food safety and extend shelf life. These common processing techniques can alter the native structures present in milk, including protein structures. However, the impact of these processing-induced changes on the digestion of milk protein and subsequent absorption of amino acids in the human body is not yet fully understood. The overall objective of this research was to understand how heat treatment and homogenisation affect milk protein coagulation and digestion in the stomach, and to investigate how changes to gastric coagulation (curd formation) influence amino acid (AA) absorption in the small intestine and AA concentrations in blood circulation. Due to the limited accessibility of the human gastrointestinal tract, pigs were used as a model of the human. An initial study using raw bovine (cow), caprine (goat), and ovine (sheep) milk established the role of gastric curd formation in small intestinal AA absorption in piglets at a single postprandial time point. Specifically, differences in the retention of AA in the gastric curd were responsible for differences in the small intestinal AA absorption across milk of different species. A separate study using bovine milk as a milk model was then conducted to determine the effect of heat treatment and homogenisation on the kinetics of milk protein digestion and small intestinal AA absorption. The selected processing treatments were pasteurisation, ultra-high temperature treatment (UHT), and homogenisation. Raw milk was included as a comparator. In the stomach, heat treatment and homogenisation altered the strength and structure of the curd formed during gastric digestion, which in turn affected both milk protein hydrolysis and the rate of AA entering the small intestine. Differences in the release of digested protein and AA into the small intestine were reflected in the kinetics of AA absorption of the processed milk types. For example, UHT milk had both a faster rate of AA entering the small intestine and a faster rate of AA absorption. Processing also altered the appearance of some AA in blood circulation; however, these differences were not directly reflective of the differences observed in their small intestinal absorption kinetics. In conclusion, this PhD research demonstrated that the rate of small intestinal AA absorption was modulated by gastric curd formation, indicating that milk processing could be used as a strategy to modulate protein digestion and AA absorption in the gastrointestinal tract.
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    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 H
    Despite 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.
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    Metabolizable energy and standardized ileal amino acid digestibility of full-fat soybeans for broilers are influenced by wet-heating, expansion temperature, and autoclaving time
    (Elsevier Inc. on behalf of Poultry Science Association Inc, 2022-09) Abdollahi MR; Wiltafsky-Martin M; Zaefarian F; Ravindran V
    The influence of wet-heating (WH) and expansion temperature (ET), and autoclaving time (AT) on the nitrogen-corrected apparent metabolizable energy (AMEn) and standardized ileal digestibility (SID) of AA in full-fat soybeans (FFSB) for broilers was examined in 2 experiments. The AMEn and SID AA of FFSB were determined by the difference and direct methods, respectively. In Experiment 1, raw FFSB (K0) were either treated by WH at 80°C for 1 min and expanded at 115°C (K1-115) or 125°C (K1-125), WH at 100°C for 6 min and expanded at 115°C (K2-115) or 125°C (K2-125), or WH at 100°C for 16 min and expanded at 115°C (K3-115) or 125°C (K3-125). Wet-heating and ET significantly (P < 0.001) increased the AMEn in FFSB. Among heat-treated FFSB, K1-115 and K1-125 resulted in the lowest and highest AMEn values, respectively, with all samples wet-heated at 100°C being intermediate. The K3-125 had AMEn values similar (P > 0.05) to K1-125. Among heat-treated FFSB, the highest average SID AA was recorded for K3-125. In Experiment 2, K3-125 from experiment 1 was divided into 9 batches and autoclaved at 110°C for 15 (Z1), 30 (Z2), 45 (Z3), 60 (Z4), 120 (Z5), 180 (Z6), 240 (Z7), 300 (Z8), and 360 (Z9) min. A quadratic (P < 0.01) pattern was observed for the effects of AT on AMEn. The AMEn was unaffected until 300 min AT and then declined at 360 min. The AT quadratically (P < 0.001) affected the average SID AA where the SID increased from K3-125 to Z1, plateaued to Z5, and then declined to Z9. In conclusion, the results demonstrated that WH at 100°C for 16 min followed by expansion at 125°C as the most optimal wet-heating and expansion processing, associated with the highest SID AA. Autoclaving at 110°C for 30 min enhanced energy utilization and AA digestibility in FFSB, suggesting that further advantages may be achieved by short-time autoclaving of previously wet-heated and expanded FFSB samples.