Massey Documents by Type

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

Browse

Has files: YesSubject: search.filters.subject.Lipolysis

Search Results

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Effect of Gel Structure on the In Vitro Gastrointestinal Digestion Behaviour of Whey Protein Emulsion Gels and the Bioaccessibility of Capsaicinoids
    (MDPI (Basel, Switzerland), 2021-03-04) Luo N; Ye A; Wolber FM; Singh H; Kontominas MG
    This study investigated the effect of gel structure on the digestion of heat-set whey protein emulsion gels containing capsaicinoids (CAP), including the bioaccessibility of CAP. Upon heat treatment at 90 °C, whey protein emulsion gels containing CAP (10 wt% whey protein isolate, 20 wt% soybean oil, 0.02 wt% CAP) with different structures and gel mechanical strengths were formed by varying ionic strength. The hard gel (i.e., oil droplet size d4,3 ~ 0.5 μm, 200 mM NaCl), with compact particulate gel structure, led to slower disintegration of the gel particles and slower hydrolysis of the whey proteins during gastric digestion compared with the soft gel (i.e., d4,3 ~ 0.5 μm, 10 mM NaCl). The oil droplets started to coalesce after 60 min of gastric digestion in the soft gel, whereas minor oil droplet coalescence was observed for the hard gel at the end of the gastric digestion. In general, during intestinal digestion, the gastric digesta from the hard gel was disintegrated more slowly than that from the soft gel. A power-law fit between the bioaccessibility of CAP (Y) and the extent of lipid digestion (X) was established: Y = 49.2 × (X - 305.3)0.104, with R2 = 0.84. A greater extent of lipid digestion would lead to greater release of CAP from the food matrix; also, more lipolytic products would be produced and would participate in micelle formation, which would help to solubilize the released CAP and therefore result in their higher bioaccessibility.
  • Thumbnail Image
    Item
    Studying the relationship between emulsion structure and lipid digestibility for infant milk : a thesis was present in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology, at Massey University, Palmerston North, New Zealand
    (Massey University, 2020) Deng, Le
    Milk, whether maternal or formulated, provides the sole source of nutrition to infants in the early stages of life, providing critical micronutrients, support for the immune function and primary dietary macronutrients including lipids. In healthy adults, lipids are primarily digested in the small intestine. However, for infants, the neonatal small intestine is not fully developed after birth, so the gastric environment plays a more significant role in milk fat digestion. Clinical studies have shown that maternal milk fat is digested more efficiently than lipids in infant formulae in infants under infant gastric conditions. Compositional differences, the structure of the oil droplets, and especially the interfacial composition may all play a crucial role in influencing lipid digestibility in the infant's stomach. In this thesis, the simulated gastric digestion of model emulsions and commercial infant formula was studied. The model emulsions comprised either a phospholipid or complexed protein-phospholipid interface while keeping all other facets of emulsion properties equivalent. Gastric digestion of these emulsions was carried out across variable pH conditions using an analogue gastric lipase, alone and in combination with pepsin with findings providing insights into the role of each enzyme and their combined effect on gastric lipolysis. The rate and extent of lipolysis were characterised, along with morphological changes to the structure of the oil droplets. Results showed that gastric lipolysis might be influenced by pH conditions in the gastric environment when lipase was present alone in the simulated gastric fluid. The inclusion of pepsin resulted in significant structural changes when emulsions were stabilised with protein, in terms of droplet aggregation, size and morphology. However, no significant differences in the extent of lipolysis were determined. Thus, while the protein interface of both model and formulated emulsions was not observed to be a barrier for gastric lipolysis. Proteolysis of protein stabilised emulsions may lead to very different structural outcomes during gastric digestion when compared to phospholipid stabilised emulsions. While the research within this thesis demonstrates how the gastric environment influences emulsion structure as a consequence of interfacial composition, any specific relationship between structure and relative rate of gastric lipolysis currently remains undetermined. This research also highlights some of the ongoing challenges in the use of in vitro models to provide mechanistic understanding and interpretation of findings from clinical studies.
  • Thumbnail Image
    Item
    Interfacial aspects of in vitro lipolysis using tensiometry and SAXS : a thesis presented in partial fulfilment of the requirements for the degree of Master of Food Technology at Massey University, Manawatu, New Zealand
    (Massey University, 2019) Wang, Xuerun
    Backgrounds/Aims: Lipolysis is an interfacial process in the conversion of dietary triglycerides to free fatty acids, and is affected by the interfacial compositions of the oil droplet. The aim of the study was to analyze any effects of co-dependency of lipase and protease enzymes on the hydrolysis of oil droplets stabilized by interfacial protein, and to determine the transitions in the internal structure of oil droplets during in vitro lipolytic digestion. Methods: The changes of interfacial tension and dilatational rheology at the oil interface during gastric digestion was measured by pendent drop tensiometer, in which a droplet of olive oil was expressed in a 0.1% WPI solution at various pH levels (pH 3.5 and pH 4.5). Additionally, small angle x-ray spectrometry (SAXS) was used for identifying the differences of the self-assembled structure formed during gastrointestinal lipolysis of three different types of oils (coconut oil, olive oil and palm stearin). Results: The interfacial tension of oil droplets at pH 3.5 was found to be higher than at pH 4.5 which indicated the interface was destabilized by acids. The emulsifier acted as a barrier at the oil interface and protected it from lipolysis by gastric lipase. The extent of pepsinolysis was enhanced with low pH because of the protein degradation by acids. At pH 3.5, the interfacial tension of WPI coated oil droplet was raised 35% whereas only 19% increased at pH 4.5. In the presence of both pepsin and gastric lipase, the protein layer was first weaken by pepsin and then lipase acted at the oil interface. From the SAXS data, there was no liquid crystals formed at the oil droplet during gastric digestion. The results showed the transitions of internal structure of oil droplets after intestinal digestion depended on the pre-digestion under gastric condition and the source of oil phase. After gastric digestion, lamellar phase was the dominate structure whereas various sub phases were formed after the intestinal digestion without the pretreatment, including bicontinuous cubic and hexagonal phase. Conclusion: In vitro, the stability of oil droplet interface was affected by pH, emulsifier and interactions between enzymes. The study has proved gastric lipolysis and pepsionolysis were co-dependent at the oil interface. Gastric lipolysis was important for the following intestinal digestion as the self-assembled structure was weaken by gastric condition.
  • Thumbnail Image
    Item
    An investigation of lipolysis in the bovine rumen : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science.
    (Massey University, 1969) Clarke, David Graeme
    1.1. Lipases 1.1.1. Terminology Lipolytic enzymes may be considered as a special class of carboxyl esterases, as they catalyse the hydrolysis of ester link-ages in lipids with the formation of alcohol and fatty acid moieties. In mammalian systems lipolytic enzymes are generally subdivided into three classes; those acting on fats (lipases); those acting on fats in the form of lipoprotein (lipoprotein lipases); and those acting on the ester bonds in phospholipids (phospholipases). However this classification based on substrate specifity is of limited value only, as many of the enzymes that hydrolyse carboxyl esters, exhibit a very wide substrate specificity. Consequently a review of lipases is complicated by the general confusion centred around the exact meaning of the term 'lipase'. With a natural triglyceride, e.g. triolein, specificity of the enzyme may be referred to the alcohol glycerol, so that enzymes hydrolyzing fatty acids from glycerol are lipases. Alternatively specificity may be referred to the long chain fatty acid, and enzymes hydrolysing long-chain fatty acids from esters of several different alcohols may be regarded as lipases (Balls and Matlack, 1938). [FROM INTRODUCTION]
  • Thumbnail Image
    Item
    Preparation, characterisation and application of naturally derived polar lipids through lipolysis : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 2016) Sofian-Seng, Noor-Soffalina
    Monoglycerides are lipid based emulsifiers extensively used for their broad technical function in the food industry. Commercial monoglycerides are generally manufactured through chemical synthesis; however, lipolysis of triglycerides by lipase enzyme provides a biochemical pathway by which monoglycerides may be produced. This is particularly appealing for consumers for whom all natural and clean labelled food products are a particular driver. Accordingly, rather than replacing monoglycerides from formulations with other types of emulsifiers (and that may lack the requisite functionality), an alternative approach may be to develop a non-chemical and more natural pathway to produce the emulsifier, thereby allowing the particular monoglyceride functionality to be retained within products. Therefore, this study was conducted to investigate the feasibility of using lipase enzyme as a processing tool to synthesise polar lipids, namely monoglycerides, in situ of the manufacture of whippable food emulsions, such as cream and ice cream. This concept idea was initially proven viable through interfacial tension (IFT) measurements obtained using a straight-forward surface characterisation technique. R. miehei lipase was found to competitively bind at the interface of vegetable oils-water and that the adsorbed protein (sodium caseinate and whey protein isolate) or surfactant layer (lecithin and Tween 80) did not act as a barrier to lipase adsorption at the oil-water interface. IFT measurements were also able to demonstrate the progressive accumulation of polar lipids at the oil-water interface arising from lipolysis, and were additionally used to indicate how thermal treatment of the enzyme could be used to terminate activity. In considering how the requisite functionality could be achieved for whippable emulsion formulations, emulsion droplet size, type of emulsifiers used as well as lipase concentration were shown to be key variables by which the extent and rate of lipolysis could be manipulated and controlled. The results showed that formulation (emulsifier types and oil content) and processing conditions (Microfluidizer® pressure and number of passes) had significant effects on the emulsion droplet size. As part of controlling the extent of lipolysis, the conditions by which the reaction could be terminated were investigated by measuring the viability of R. miehei lipase against thermal treatment. Results showed that the R. miehei lipase was thermostable up to temperatures of 70 °C. Above this temperature, substantial reduction of the residual activity occurred. However, even elevated temperature of between 90 and 100 oC did not immediately inactivate the lipase, with heating for ~ 2 min required before activity was no longer detected. In terms of emulsion stability, the palm oil emulsion tested in this study was found to be thermostable up to 100 oC, thus allowing development of a thermalisation step that was able to inactivate the enzyme without compromising the stability of the emulsion. The shear stability analyses on lipolysed O/W emulsion showed the lipolysed emulsions were susceptible to shear-induced aggregation, and that the degree of aggregation could be manipulated as a consequence of controlling the extent of lipolysis through either enzyme concentration or holding time. The drastic increase in the viscosity curve between the nonlipolysed and lipolysed emulsion suggested that the shear–induced partial coalescence was primarily due to the lipolysis reaction and was not as a result of the high fat content (30 %). The findings elucidate the ability of the generated polar lipids in the emulsion to displace the existing sodium caseinate adsorbed layer, thus compromising emulsion stability upon shearing. The quantification of synthesised polar lipids from the triglyceride component of fat droplets by the lipolysis reaction showed a mixture of fatty acids, di- and mono-glycerides being produced. Palmitic acid was observed to be the main liberated fatty acids. While, monoolein and monopalmitin were the most prominent monoglycerides, with measured concentrations of 3.755 ± 0.895 and 1.660 ± 0.657 mg / g fat respectively after 15 min with lipase concentration of 50 mg /g fat. The relative concentration of polar lipids produced was found to be dependent on the lipase concentration as well as time of lipolysis. Furthermore, up to 30 min of lipolysis (concentration 50 mg /g fat) were seen to have no observable effect on the droplet size distribution of the emulsion suggesting that quiescently stable emulsions could be produced. The results show the importance of controlling reaction conditions (both enzyme concentration and reaction time) in order to provide requisite functionality without excessively destabilising emulsions such that droplet structuring can occur under quiescent conditions. The generation of monoglycerides at quantum satis levels able to impart critical functionality was demonstrated in whipped cream and ice cream. The addition of R. miehei lipase at very low concentration of 5 mg /g fat was able to produce a rigid and stable whipped cream with overrun exceeding 100 %. However, good stability of the whipped cream over time was achievable with concentration above 10 mg /g fat. Similarly, ice cream made with the addition of 5 mg /g fat exhibited good melt stability and firmness. The findings proved the feasibility of in situ production of polar lipids, namely monoglycerides and fatty acids, in replicating the functionality imparted by commercial monoglycerides in whippable emulsions. Thus, the findings in this thesis offer an alternative biochemical pathway for the generation of polar lipids to that of commercially available monoglycerides, which are currently produced synthetically. The potential for using this approach as part of the processing step for food emulsion manufacture has also been demonstrated. The concept can be tailored for various emulsion based food products.
  • Thumbnail Image
    Item
    Aspects of lipolysis in sheep : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Animal Science at Massey University
    (Massey University, 1983) Peterson, Samuel Walter
    Treatments which might be expected to produce lipolytic responses were applied to ewes. These treatments included fasting and the administration of ACTH, noradrenaline and BGH. Twelve experiments are reported, 3 of which involved indirect calorimetry and 9 which involved measuring the responses of blood hormones and metabolites including GH, insulin, FFA's and glucose. 2. Two groups of ewes were used. The first group consisted of 2 Romneys and 2 Southdowns. Each breed pair comprised a short, fat and a long, lean phenotype which may have been qenotypically different in their propensity to be overfat. The second group of ewes comprised 4, 5 year cull Romney ewes. 3. Calorimetry showed that there were no differences in the normal fed metabolic rate of the first group of sheep sufficient to explain their differences in fatness. 4. Fasting (2-3 days) resulted in significantly elevated mean afternoon plasma FFA levels in the long, lean ewes. 5. The fat ewes had steeper regressions of RQ on time when fasted than the lean ewes, which probably indicated a greater rate of lipolysis. 6. The injection of ACTH into ewes produced inconclusive results in terms of plasma hormones and metabolites. 7. Injection of the catecholamine, Bronkephrine into the cull Romney ewes, did not produce any significant effects on blood hormones and metabolites in one study. In a second study N.A. resulted in transitory peaks in GH insulin and FFA's. These results were confused with concurrent responses to feeding. 8. Fasting cull Romney ewes resulted in higher mean afternoon levels of GH and FFA. Insulin levels were lower than in fed sheep but differences were not statistically significant. 9. Administration of ACTH and N.A. did not produce detectable changes in heat production or respiratory exchange ratios. However these studies were complicated by ruminal CO2 production following feeding. 10. Both BGH and PBS infusions produced marked declines in plasma insulin and increases in FFA levels. 11. It is concluded that the prime control of lipolysis in sheep is probably the autonomic nervous system through the release of N.A. at sympathetic nerve endings. GH and insulin secretion are neurally mediated and these hormones have important roles in directing the transfer and utilisation of metabolites between tissues. GH potentiates lipolysis, defends tissue protein stores and promotes the transfer to and utilization of FFA in productive tissues such as muscle and mammary gland. Insulin is primarily anabolic and antilipolytic in adipose tissue. It antagonises GH action in adipose tissue yet supports the anabolic role of GH in the productive tissues.