Spelling suggestions: "subject:"fipids research"" "subject:"flipids research""
11 |
Lipid stabilisation and partial pre-cooking of pearl millet by thermal treatmentsNantanga, Komeine Kotokeni Mekondjo 26 July 2007 (has links)
Pearl millet is a cereal crop cultivated by subsistence farmers in semi-arid parts of Africa and Asia. In Namibia, pearl millet porridge is a staple food for over half of the population. Healthful Harvest, a cooperative of subsistence farmers in a rural area in Namibia is developing a flour product with extended shelf life and a short cooking time comprising pearl millet and cowpea. This requires the application of simple technology. The pearl millet grain is small (3-15 mg) but has a proportionally larger germ than all other cereal grains, except perhaps maize. Therefore, it tends to contain a high content of triglycerides, which are rich in unsaturated fatty acids. Pearl millet flour is susceptible to rancidity within a few days due to lipolysis and subsequent oxidation of the de-esterified unsaturated fatty acids. To try to prevent rancidity and to pre-cook, pearl millet grain was subjected to toasting, boiling and toasting then boiling before reduction to flour. The effects of these different thermal treatments on fat acidity, peroxide value (PV) and conjugated diene and triene values of pearl millet flour before and after three months storage at ambient conditions were determined. The degree of cook of starch was determined on fresh flours. The porridges made from the flour of the treated grains were evaluated by a trained panel and by consumers. Analyses of energy demands and practicality of the thermal treatments and extrusion cooking as processing technologies in manufacturing pearl millet flour in rural parts of Namibia were made. Fat acidity for the untreated flour increased significantly from 0.11 to 3.72 g KOH kg-1, whereas no significant increase observed in the flours of wet thermally-treated grains. This indicates that wet thermal treatments inhibited triglyceride hydrolysis. The PVs of the flours of the wet thermally-treated grain increased seven-fold, while the PV of the untreated flour decreased. A similar trend was observed for the conjugated diene values. The conjugated triene values increased significantly for all the samples. These results indicate autoxidation in the thermally-treated samples and that there was accumulation of hydroperoxides. The degree of cook of the wet thermally-treated grain (~40%) was twice that of the untreated and toasted grains, indicating that the wet thermal treatment partially gelatinised the grain. Porridges prepared using untreated flours were associated with rancid flavours, while those of other treatments were not, indicating that the thermal treatments can prevent rancidity. Consumers preferred the porridge prepared using flour of the boiled grain, presumably because it was fully cooked, whereas others were not. Thus, the boiling treatment can be applied to extend the shelf life of and pre-cook pearl millet flour. The energy demands for boiling and extrusion cooking were estimated to be 0.6 and 0.2 kWh kg-1, respectively. The energy demand for the boiling process can be minimised by sun-drying instead of using electricity. The cost of an extruder would be prohibitively costly for Healthful Harvest. Thus, boiling the grain is a suitable appropriate technology that can be applied in the Healthful Harvest situation by ordinary people, with no specialist skills. / Thesis (MSc(Agric) (Food Science and Technology))--University of Pretoria, 2007. / Food Science / MSc(Agric) / unrestricted
|
12 |
Lipid peroxidation and the antioxidant systems in soybean seed maturation and germination.Tyiso, Sakiwo. January 2003 (has links)
The biochemical changes taking place during soybean seed development and gennination, and some aspects of desiccation tolerance were assessed with reference to lipid peroxidation and antioxidant systems. During nonnal seed development, fresh weight and dry weight increased between 20 and 50 days after flowering (DAF), concomitant with the accumulation of triacylglycerols and sugar reserves, after which dry weight remained almost unchanged, and fresh weight decreased. Seed moisture content decreased rapidly during the last stages of development. High levels of lipid peroxidation were evident between 20 and 45 DAF, and decreased thereafter. An examination of antioxidant systems revealed that whereas total glutathione levels accumulated continuously throughout the 80 days of seed development, both dehydroascorbic acid (DHA) reductase and ascorbate free radical (AFR) reductase increased concurrently with the increase in total ascorbate content, and the overall levels did not decrease markedly during maturation drying. Ascorbate peroxidase (ASC POD) activity was high during the period ofgreatest ascorbate accumulation. Both catalase (CAn and superoxide dismutase (SOD) activities increased progressively during early seed development (20-40 DAF), but showed variable patterns of change during maturational drying, in marked contrast to ASC POD which declined from 40 DAF to undetectable levels at 70 DAF. An assessment of the relationship between the antioxidant systems and lipid peroxidation was made during imbibition and gennination, as it has been suggested that controlling free radicals was a critical event in early imbibition. Unexpectedly, lipid peroxidation increased progressively in both seeds and isolated axes, and were eight-fold higher at 48 hours of imbibition compared to dry tissues. A progressive, and co-ordinated, increase in CAT, total glutathione, total ascorbate pool, guaiacol POD, ASC POD, and SOD appeared to parallel the rise in lipid peroxidation in both whole seeds and axes. Variable responses were evident between seeds and axes for the enzymes AFR reductase and DHA reductase In order to gain a further insight into the dynamics of desiccation-tolerance and desiccationsensitivity, imbibing seeds were subjected to an unscheduled dehydration treatment, and then rehydrated for up to 24 hours. During these hydration-dehydration-rehydration (H-D-R) treatments, changes in lipid peroxidation and antioxidant systems were measured. Concurrent with the loss of viability in the axes of seeds dehydrated after 24 and 36 hours of imbibition, there were increases in both lipid peroxidation and solute leakage. Unscheduled drying was seen to be a critical stage, as intolerant axes showed four- to eightfold increases in lipid peroxidation, which were only partially reduced on subsequent rehydration. Tolerant axes, on the other hand, were able to maintain low, basal levels of lipid hydroperoxides on drying. The relationship between these observations and the antioxidant systems showed that the antioxidant enzymes CAT, ASC POD, AFR reductase, DHA reductase, guaiacol POD and SOD declined markedly during the unscheduled drying, whereas GSH and ASC declined only slightly. On rehydration, most of the enzymes, total glutathione, and total ascorbate pool increased, the only exception being the loss of ASC POD activity. ORA reductase, which was seen to decrease as a part of nonnal gennination, declined progressively also in H-D-R treatments. These results suggested that loss of viability was not attributable to a decline of the antioxidant systems but rather to the combined deleterious effects of increased lipid peroxidation, and a generalized and moderately compromised antioxidant system. These studies have indicated that the occurrence of lipid peroxidation can be seen as a nonnal part of seed development and gennination. The H-D-R studies, on the other hand, supported the concept that the balance between peroxidation reactions and the protective systems was critical to the development of desiccation tolerance. / Thesis (Ph.D.)-University of Natal, Durban, 2003.
|
13 |
Biophysical studies of cholesterol in unsaturated phospholipid model membranesWilliams, Justin A. January 2013 (has links)
Indiana University-Purdue University Indianapolis (IUPUI) / Cellular membranes contain a staggering diversity of lipids. The lipids are heterogeneously
distr
ibuted to create regions, or domains, whose physical properties differ from the bulk
membrane and play an essential role in modulating the function of resident proteins. Many
basic questions pertaining to the formation of these lateral assemblies remain. T
his research
employs model membranes of well
-
defined composition to focus on the potential role of
polyunsaturated fatty acids (PUFAs) and their interaction with cholesterol (chol) in restructuring
the membrane environment. Omega
-
3 (n
-
3) PUFAs are the main
bioactive components of fish
oil, whose consumption alleviates a variety of health problems by a molecular mechanism that is
unclear. We hypothesize that the incorporation of PUFAs into membrane lipids and the effect
they have on molecular organization may be, in part, responsible. Chol is a major constituent in
the plasma membrane of mammals. It determines the arrangement and collective properties of
neighboring lipids, driving the formation of domains via differential affinity for different lipids
. T
he m
olecular organization of 1
-[
2
H
31
]palmitoyl
-2-
eicosapentaenoylphosphatidylcholine (PEPC
-
d
31
) and 1
-[
2
H
31
]palmitoyl
-2-
docosahexaenoylphosphatidylcholine (PDPC
-d
31
) in membran
es with
sphingomyelin (SM) and chol (1:1:1 mol) was compared
by solid
-
state
2
H NMR spectroscopy.
Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are the two major n
-
3 PUFAs found in
fish oil, while PEPC
-d
31
and PDPC
-d
31
are phospholipids containing the respective PUFAs
at the
sn
-
2 position and a perdeuterated palmitic acid a
t the sn
-
1 position
.
Analysis of s
pectra
recorded as a function of temperature indicate
s
that in both cases, formation of PUFA
-
rich (less
ordered) and SM
-
rich (more ordered) domains occurred. A surprisingly substantial proportion of
PUFA was found to infil
trate the more ordered domain. There was almost twice as much DHA
(65%) as EPA (30%)
. The implication is
that n
-
3 PUFA
s
can incorporate
into lipid rafts, which
are
domains
enriched in SM and chol in the plasma membrane,
and
potentially
disrupt the activity of signaling proteins that reside therein. DHA, furthermore, may be the more potent component
of fish oil.
PUFA
-
chol interactions were also examined through affinity measurements. A novel method
utilizing electron paramagnetic resonance (EPR) was develope
d, to monitor
the partitioning of a
spin
-
labeled
analog
of chol
, 3β
-
doxyl
-
5α
-
cholestane (chlstn), between large unilamellar vesicles
(LUVs) and met
hyl
-
β
-
cyclodextrin (mβCD). The EPR spectra for
chlstn in the two environments
are distinguishable due to the substantial differences in tumbling rates
, allowing
the
population
distribution
ratio to
be determined by spectral simulation. Advantages of this approach include
speed of implementation and a
vo
idance of potential
artifact
s associated with
physical
separation of LUV and mβCD
. Additionally, in a check of the method, t
he relative partition
coefficients between lipids measured for the spin label analog agree with values obtained for
chol by isothermal titration calorimetry (ITC). Results from LUV with different composition
confirmed
a hierarchy of
decreased
sterol affinity for phospholipids with increasing
acyl chain
unsaturation
, PDPC possessing half the affinity of the corresponding monounsaturated
phospholipid.
Taken together, the results of
these studies
on model membranes demonstrate the potential for
PUFA
-
driven alteration of the architecture of biomembranes, a mechanism through which
human health may be impacted.
|
Page generated in 0.032 seconds