Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Filters

1985 - 198912010 - 20122

Settings

Subject: search.filters.subject.Gastrointestinal tract

Search Results

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    In vitro gastrointestinal digestion of oil-in-water emulsions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Technology in Food Technology at Massey University, Auckland, New Zealand
    (Massey University, 2012) Li, Limin
    Oil-in-water (O/W) emulsions are widely used as a dispersion system for oil or fat or as a delivery system for lipophilic bioactive compounds in aqueous food products. There is a growing interest among food scientists in understanding the digestion behaviour of O/W emulsions when they are ingested and pass through the gastrointestinal (GI) tract. In recent years, a number of researches have been carried out to investigate the lipid digestion of emulsions using in-vitro models such as simulated gastric fluid (SGF) and simulated intestinal fluid (SIF) that mimic the biological conditions of human bodies because of the complexity of in vivo study. However, most studies have been conducted to study the effect of gastric or intestinal digestion using SGF or SIF, and the studies on the effect of sequential digestion of emulsions first in SGF and then in SIF have been very limited. The objective of this study was therefore to investigate the effect of in vitro digestion of emulsions sequentially in SGF and SIF on the physicochemical properties and lipolysis of emulsions. In this study, sodium caseinate, whey protein isolate (WPI) and Tween 20 were used as emulsifiers to prepare O/W emulsions (20% soy oil and 1% emulsifier). The mean particle size and particle size distribution, zeta potential and microstructure of freshly prepared emulsions were initially measured, and the changes in the physicochemical properties of emulsions occurring during digestion in SGF or SIF and sequentially in SGF and SIF were analysed. The hydrolysis of fatty acids from emulsified lipid core was also determined during digestion in SIF after gastric digestion. In acidic simulated gastric conditions (pH 1.6 and 3.2 mg/mL pepsin), sodium caseinate-stabilized emulsions showed extensive flocculation with some coalescence, resulting in change in the size and microstructure of the emulsions. In contrast, the emulsions stabilized with WPI or Tween 20 showed no pronounced changes over time during 2 hrs of gastric digestion. In simulated intestinal conditions (pH 7.5, bile salts and pancreatin), a massive coalescence by pancreatic lipase took place in both sodium caseinate and WPI-stabilized emulsions, leading to a pronounced increase and change in the droplet size and microstructures, whereas Tween 20- stabilized emulsions were relatively stable with much less droplet coalescence and size increase. After sequential digestion in SGF and SIF, protein-stabilized O/W emulsions showed more extensive aggregation and coalescence of droplets in comparison with their digestion in SIF only without gastric digestion, whereas Tween 20-stabilized emulsions were relatively stable with only some extent of coalescence after 2 hrs of its sequential digestion in SIF after SGF. The amounts of free fatty acids released in SIF after gastric digestion were similar between three types of emulsions and were not affected significantly by the gastric digestion prior to the intestinal digestion. The overall results indicated that the digestion behaviour of emulsions was affected by types of emulsifiers, and that the sequential digestion of emulsions in SGF and SIF resulted in more pronounced changes in the emulsion particle size and microstructure compared to the digestion in SGF or SIF. However, the rate of lipid digestion was not affected by the sequential digestion. The results of this study provide a significant insight into the effect of sequential gastric and intestinal digestion on the size and properties of emulsion systems and its effect being different depending on type of emulsifiers used to stabilise oil droplets.
  • Thumbnail Image
    Item
    Endocrine cells in the gastrointestinal tract of sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Histology at Massey University
    (Massey University, 1985) Gurnsey, Michael Peter
    Previous investigations have shown that the digestive activities of the mammalian GI tract are controlled, in part at least, by biologically active compounds released from endocrine cells in the mucosa of the GI tract itself. Despite this, comparatively few studies have been made of the endocrine cells in the GI tract of sheep. There is also a paucity of information about the suitability and reliability of histochemical and immunohistochemical methods for the identification of GI endocrine cells in sheep. The aims of this study were to: (a) establish reliable techniques for identifying endocrine cells in the GI tract of sheep, (b) use these techniques to investigate the effects of age on the distribution and densities of various GI endocrine cells, and (c) investigate possible changes in endocrine cell densities due to infection with the helminth parasite Trichostrongylus colubriformis. Initially, various histochemical and immunohistochemical staining techniques were investigated for their suitability for identifying endocrine cells in mucosal samples from reticulum, rumen, body and antral regions of the abomasum, three duodenal sites, ileum, colon and caecum, as well as the pancreas, of adult animals. As a result, the De Grandi technique was selected to estimate argyrophilic cell densities, EC cells were identified by the fast garnet technique, and ECL cells by their silver staining and morphological characteristics. The PAP immunohistochemical technique was used to identify G, S, and A cells, using antisera to gastrin, secretin, and pancreatic glucagon, respectively. No endocrine cells of any type were found in the reticulum or rumen. Argyrophilic cell densities were greatest in the abomasal body and proximal duodenum, then decreased distally. EC cell densities were highest in the duodenum, although, like argyrophilic cells, they were found throughout the abomasum and intestines. In contrast, ECL cells were confined to the abomasal body. Greatest densities of G cells occurred in the abomasal antrum and proximal duodenum; they were absent from the abomasal body, ileum and large intestine. S cells were confined in their distribution to the small intestine. Pancreatic islets of Langerhans contained A cells, as well as cells with slight argyrophilia; the identity of the latter cells was not determined. A cells were also found in exocrine acini, but these were the only cells in the exocrine portion of the pancreas that were stained by any of the histochemical or immunohistochemical techniques used. No A cells were identified in the mucosa of the GI tract. These studies also clearly established that ovine G cells are not argyrophilic. This finding is in contrast to those reported for most mammalian species with a simpler form of stomach. The effects of age on endocrine cell densities were studied using the tissues from 100 - 110 day old foetuses, 2 week and 24 week old lambs, and adult sheep. All endocrine cell types identified in adult sheep were also present at the other ages. However, in the foetuses, endocrine cell densities were lower than in other age groups. The most notable age-related trend was that antral G cell densities increased with increasing age. In contrast, from 2 weeks of age, there was a decrease in intestinal G cell densities with increasing age. It was also clear that D cell densities were much higher in 2 week old lambs than for any other age group. Possible explanations for these age-related changes in endocrine cell densities are discussed. D (somatostatin containing) cells were located throughout the abomasum and intestines of all nonadult animals and in pancreatic islets of 2 and 24 week old lambs. The effects on endocrine cell densities of an experimental infection with 40,000 T. colubriformis larvae was investigated in 40 week old lambs. Although the resultant infestation was mild, there was a significant (P<0.001) increase in argyrophilic cell densities in the proximal small intestine. Specific identification of the argyrophilic cell type(s) which had increased was not possible, however, the most likely candidates were D1, X and K cells. It was concluded from these studies that endocrine cells, similar in morphology and staining characteristics to those of other mammalian species, occur within the mucosa of the abomasum, small and large intestine of sheep. Greatest densities of endocrine cells occur in the abomasum and proximal duodenum. Cell types identified in the GI tract included EC, ECL, G, S and D cells, while D and A cells were identified in pancreatic islets. It was demonstrated that endocrine cell densities change with age and that significant changes in cell densities can occur in mild trichostrongylosis.
  • Thumbnail Image
    Item
    An immobilised cell system for the delivery of functional Lactobacillus reuteri DPC16 cells to their target site in a simulated gastrointestinal tract : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Science at Massey University, Albany, New Zealand
    (Massey University, 2012) Zhao, Qian
    The objective of this study was to design and produce calcium alginate beads that can deliver immobilised cells of Lactobacillus reuteri DPC16 to a target site of the colon in the gastrointestinal (GI) tract, without any diminution of their important physiological characteristics. Several factors that might affect the effectiveness of calcium alginate beads for the cell delivery were investigated, using an in vitro GI tract model to simulate the conditions within the tract. Firstly, by varying the concentration of alginate at a constant concentration of CaCl2, and combining the system with gelatin, chitosan or skim milk, the survival of immobilised DPC16 cells in simulated gastric fluid (SGF) was observed. Secondly, the physical stability of calcium alginate beads containing skim milk was observed during sequential incubation in the GI fluids using optimal concentrations of alginate. Finally, the survival of DPC16 cells immobilised within alginate beads containing skim milk was monitored when the beads were incubated for different times during sequential exposure to the simulated fluids. The results demonstrated that non-encapsulated DPC16 cells were sensitive to an acidic environment, and no viable cells were detected after 90 min exposure in SGF (pH 1.2). After appropriate experimentation, an alginate concentration of 3% (w/v) was deemed to be the optimum value and was used in subsequent investigations. When skim milk (8% (w/v)) was added to the alginate solution, the cell survival in SGF was improved markedly. The optimal concentration of calcium chloride was 0.3 M, based on the beads maintaining their integrity in SGF and simulated intestinal fluid (SIF) while disintegrating in simulated colonic fluid (SCF) to release viable cells. Hence, the beads made from 3% alginate, 8% skim milk and 0.3 M CaCl2 proved to be an effective delivery and release system for DPC16 cells. L. reuteri DPC16 has strong antimicrobial activities against pathogens, due mainly to its ability to produce reuterin. Hence this and other functional properties of the bacterial cells were studied before and after passage through the GI tract. The cells that were recovered after release from the alginate beads in the SCF showed no diminution in functional properties, including their growth kinetics, ability to adhere to epithelial cells and ability to inhibit the adhesion of E. coli to epithelial cells. However, the bacteriostatic and bactericidal properties of the recovered cells against some pathogens were significantly greater (P<0.05) than those of the original cells. Production of reuterin by the recovered cells was significantly greater (P<0.05) than that of the original cells when cultured in MRS medium in the absence of its metabolic precursor, glycerol. The results demonstrate significant (P<0.05) consequences for the application of the encapsulation technique to protect and/or enhance the functional properties of the probiotic cells. Subsequently, an investigation was carried out to find the reason for the antimicrobial activity enhancement. By recovering cells from different stages of the immobilisation and delivery process and examining them for their antimicrobial properties, it was found that it was the immobilisation process per se, rather than passage through the simulated gastrointestinal fluids, that caused the enhancement of antimicrobial activity, and that this was related to increased activity of the enzyme (diol dehydratase) that is responsible for reuterin production from glycerol. Finally, it was demonstrated that freeze-drying of the alginate beads was not an appropriate storage technique as it resulted in a significant (P<0.05) diminution of the antimicrobial activities. Based on these findings it is confirmed that the alginate-skim milk-CaCl2 immobilisation system is an effective and efficient method, not only for protecting the viability of DPC16 cells, but also for maintaining the physiological characteristics.