Agriculture and Food Systems - Theses
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ItemThe effect of oxygen and carbon dioxide atmospheres on the quality of packaged fresh-cut lettuce( 1999)The present study investigated the potential of using alternative storage atmospheres to maintain microbial and storage quality of fresh-cut lettuce salad mix for longer periods than those currently obtained in air and traditional low oxygen (O2): high carbon dioxide (CO2) modified atmosphere packaging (MAP). The outcome of this research was to assist the freshcut industry through improved shelf life and safe food supply. The effects of modified atmospheres containing air or 100% oxygen at pH 5.0, 6.0 and 7.0, on the growth and survival of two strains of Pseudomonas fluorescens (FSAW 3107 and ATCC 13525) were determined on an agar surface at 5C for 10 days. The aim of this preliminary study was to determine the response of this spoilage organism in a model system where the surfaces of packaged chilled fresh-cut vegetable and MAP conditions were simulated. The results demonstrated the ability of two different strains of Ps. fluorescens to survive and grow in storage atmospheres of up to 100% O2 tested at any of the pH levels, except pH 5.0. The reduction in the pH of the medium to 5.0 was sufficient to inhibit the growth of the bacteria regardless of storage atmospheres. Further studies compared the impact of 100% O2, 80% O2 : 20% CO2, passive MAP and air atmospheres on the microbial growth and storage quality of fresh-cut lettuce mix stored at 5C for 10 days, using four packaging films of differing gas permeabilities. The study also compared and evaluated the suitability of barrier, experimental, and commercial packaging films for using the 80% O2 : 20% CO2 gas mixture. A 100% O2 storage atmosphere maintained with the barrier packaging film inhibited enzymatic browning in lettuce tissue, as determined by visual assessment and colour measurements. On visual examination, the product was still acceptable for consumption after 10 days of storage at 5C, compared to all other film and atmosphere treatments. Polyphenol oxidase activity declined in lettuce stored under 80% O2 : 20% CO2 and passive MAP storage atmospheres, and was the lowest at 100% O2 treatment compared with that of air, and the atmosphere conditions that developed where high permeability experimental films were used. Accumulation of CO2 to levels above 20% in the barrier and commercial packaging films initially flushed with 80% 02 : 20% CO2 gas composition resulted in several disorders in lettuce, such as severe tissue softening and development of off-odours. The same gas mixture used with a high permeability experimental film stabilised at 20.0% O2 and 5.2 % CO2, and the product quality was poorer than in all other treatments except for lettuce stored under air. Fresh-cut lettuce stored in commercial MAP bags had a passively modified atmosphere comprising 0.9% O2 : 17.1% CO2 after 10 days at 5C. The quality of this product was not acceptable after 8 days, due to discolouration of lettuce and off-odours. In conclusion, of the modified atmospheres tested, 100% O2 retained an acceptable visual quality of fresh-cut lettuce salad mix at 5C, without a marked effect on the growth of pseudomonads, Enterobacteriaceae and the total viable count. The choice of film permeability was also demonstrated to be an important factor when using the alternative storage atmospheres. Film permeabilities that would allow development of storage atmospheres containing CO2 above 20% with high oxygen levels, should not be used since this was shown to promote physiological damage of the fresh-cut lettuce.
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ItemResponses of young sheep to supplements when fed low quality roughages( 1999)The morphological components of which cereal straw is composed vary in composition and nutritive value. In a survey of relevant literature, stem materials (ST) are usually found to be consumed by ruminant animals at a slower rate than leaf material (LF) from the same crop residues when these are fed alone as separated fractions. This is attributed to the higher content of cell wall constituents (CWCs) and often lower content of N of ST. Because ST and LF can vary in proportions in the roughage fed as a basal feed, the response of animals to supplements might also be expected to be variable particularly when the basal feed is offered in excess that permits selection. In particular the response to supplemental N sources varying in ruminai degradability may vary. The objective of this thesis program was to investigate the interactions between the basal roughage and supplement measured as effects on digestion and LW responses of young sheep. The overall hypothesis was that across diets made up of different proportions of LF and ST fractions of cereal straw, the response to N supplements is dependent on CWCs concentration. The program was completed through a series of experiments conducted at the Mt Derrimut Field Satation of the University of Melbourne. In all experiments the animals were fed on a basal feed of LF or ST fractions of barley straw, with supplements including (a) Bar+USS, barley grain (Bar) fortified with urea solution prepared at a ratio of 5:1 (urea plus Na,SO4). (b) USS, urea solution alone added to the basal roughage and (c) FM, fishmeal. With each basal feed one group of lambs did not receive any supplement and served as a control group (CONT). Experiment 1 (Chapter 3) was conducted to evaluate chemical and nutritional characteristics of straw fractions of Parwon cultivar barley. Straw was separated into 4 fractions - stem (ST), leaf blade (LB), leaf sheath (LS) and broken fractions plus weeds (OT). The separated fractions were analysed chemically ( van Soest, 1974) and in vitro digestibility (Tilley and Terry 1964 ) determined. ST was the largest fraction and contained a significantly higher concentration of neutral detergent fibre (NDF; p<0.01) than LB, LS and OT (83.1, 78.6, 76.8,and 71.5 g/100g respectively). ST contained less hemicellulose (HC) than LB but more than LS and OT (37.5, 39.6, 36.3, and 35.7 respectively). N content was lower in ST than in LB, LS and OT fractions (0.4, 0.9, 0.6, and 0.7 respectively). Digestibility in vitro was significantly lower (P<0.001) for ST than for other fractions (38.5, 72.7, 60.1, and 63.0 respectively) while energy required for grinding (Chenost 1966) was much higher (P<0.001) for ST than for other fractions (121, 54.6, 64.2, 56.6 respectivly). In Experiment 2 (Chapter 4) ST and LF fractions of the same Parwon barley straw were fed as the basal feed to lambs and DM intake of ST was 15% lower than for LF (403 vs 473 g/d). When LF feed was supplemented with USS and FM, DM intake was greater by 28% and 25% respectively, while supplementation with Bar+USS resulted in 10% lower LF intake. In contrast, with animals fed ST as the basal roughage, only FM led to an increase in DM intake of only 10%. Supplementation with Bar+US and USS and FM improved overall digestibility, estimated metabolisable energy intake and N intake. Low N intakes on the basal roughages supported low ruminai ammonia-N concentrations (mg/1) immediately before feeding (ST, 20.4 ; LF 35.8), but these were improved where supplements had been fed with each of ST Bar+USS, 263.7; USS, 186.7; and FM, 151) and LF (Bar+USS, 219.5; USS, 62.5; and FM, 150). Six hours after feeding, ammonia-N concentrations (mg/l)were higher for ST (99) still low for LF(35) when fed alone, reduced below the prefeeding levels by supplements of Bar+USS (ST,167; LF 173) but raised by USS (ST, 201; LF 148) and FM (ST, 114; LF, 192). The concentrations of total volatile fatty acids (VFA) in rumen fluid (mMoUl) were not significantly different for ST and LF before feeding except where FM was the supplement, or six hours after feeding except where Bar+USS or USS were fed with LF (before feeding: ST, 51; Bar+USS, 55.7; USS,46.5; FM, 56 ; LF, 42.6; Bar+USS, 53; USS, 55.5; FM, 63.6; 6h after feeding ST, 55.5; Bar+USS, 70.2; USS, 62.1; FM, 50.4 ; LF, 55.7; Bar+USS, 69.5; USS, 60.9; FM, 60.9). Lambs on ST and LF alone lost weight (ST, -105; LF -98 g/d ). Rate of liveweight loss was less when Bar+USS (ST, -32.3; LF -2.4g/d) and USS (ST, -79.8; LF -31.2 g/d) supplements were fed, while FM promoted LW gain (ST, 37.5; LF, 72.4g/d). N retention data was consistent with these LW gains, except where Bar+USS was the supplement, in which case the animals were in positive N balance though losing weight. Wool growth was significantly improved (P<0.001) only by FM on both ST (+47%) and LF (+57%) basal roughages. In Experiments 3 and 4 (Chapter . 5 and 6) the objective was to investigate the factors responsible for low feed intake and poor performance of lambs fed ST compred to those on LF. The DMI (g/d) of lambs fed ST and LF were similar to those achieved in experiment 2; and were significantly greater for LF (P<0.001). Likewise supplements of Bar+USS, USS and FM had similar effects to those reported for experiment 2_ Changes in DMI, MEI ruminai environment before feeding or 6 and:12 hours after feeding were consistent with those recorded during experiment 2. However concentration of total VFA was significantly elevated at 12 hours after feeding. Differences in ruminal environment were evident in terms of VFA concentrations and the distribution of rumen digesta particulate material in different size fractions; both variables were affected both by the basal diet and the supplement. For LF, the proportions of particles >2mm and of very fine particles (0.125 mm) were greater and for particles between 0.5 and 1 mm less those for ST in all cases. Further, the proportion of particles >2mm was less where FM was fed than for any other feeding regime. The mean retention times of rumen fluid, measured from CoEDTA dilution rate, and calculated for rumen particulate material was longer (24%, P<0.01) for ST than for LF but there was no significant effect of supplement on this (Experiment 4, Chapter 6). The mean percentage of very fine particles in the faeces of lambs fed on LF was higher than for lambs fed ST alone or with supplements. Rate of ruminai degradation of OM of ST and LF as measured by nylon bag technique ( Experiment 3, Chapter 5) was similar at 12 and 24 hours but greater for LF than for ST at 48 and 96 hours of incubation. Bar (cracked whole grain) was degraded more rapidly and extensiveley than FM; in LF fed sheep this difference was more marked. Rate of degradation of acid detergent fibre (ADF) was influenced by the kind of supplement and was greatest in lambs given FM , and least in lambs given ST with no supplement. Only the FM supplement resulted in LW gains, though rates of LW loss were least and LW gains with FM were greatest with LF as the basal roughage. The responses are interpreted as flowing from the greater proportion of ADF and lignin in the CWCs content and the greater digestibility of ADF in the LF fraction. The ST feed fraction with higher concentrations of cell wall constituents (CWCs) as NDF was eaten at a slower rate (Experiment 5, Chapter 7) and digesta particulate material and, in these experiments, the fluid phase are retained longer in the rumen. LF showed not only an advantage over ST in these respects but also in terms of a number of important digestion parameters supported a greater response to supplements, particularly N supplements of low degradability. Thus FM is these experiments interacted with the roughage component of the diet. It provided more consistent ruminai ammonia concentrations supporting a better environment for microbial activity and growth. Microbial protein together with undegraded dietary protein together provide a balance of nutrients that allows LW gains on otherwise submaintenance basal feeds. The greater enhancement of performance with LF compared to ST and the particle size measurements suggest that greater fragmentability of LF may be a major contributor . In terms of technical improvement of livestock feeding systems, providing the animal with opportunity for selection of more leaf and less stem may improve the likelihood of responses to supplements but this was not demonstrated in Experiment 5. FM was used as the experimental supplement to provide slowly degraded and undegraded dietary protein of high biological value to the animal. FM is expensive and other crop byproducts and local feed materials with properties of slow degradability of protein and good amino acid balance need to be identified. An alternative strategy would be to provide a maximum opportunity for the selection of most digestible parts. If refusals are then collected, quality could be further improved with alkali treatment and necessary supplementation. This would provide a strategy for the use of morphological fractions which could be an economical approach for the efficient utilization of roughages.
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ItemSeed dormancy in vetch (Vicia species)( 1999)The aims of this study were to develop appropriate methods for screening Vicia species for dormancy and dormancy mechanisms and determine factors responsible for the development of seed impermeability and how impermeability can be overcome. The materials recommended by the International Seed Testing Association (ISTA 1993 and 1996) for the germination of seeds were evaluated. Loamy sand, paper towel and Petri dishes were all suitable for germination of Vicia seeds. The three types of material have their advantages and disadvantages but the advantages outweighed the disadvantages in the different type of media. The towel method was chosen for this study because it was easier to germinate many seeds (100 seeds per towel) at a time and the towels could be reused until the end of the study. Also, there was no need for regular watering during the tests because towels held enough water for two weeks. The optimum temperature for Vicia seed germination was identified to be between constant 15 and 20C. These results agree with recommendations by ISTA of germinating most Vicia seeds at 20C. A fluctuating temperature of 22/11C also had good germination but the germination rate was reduced. Ten Vicia species and subspecies were assessed for dormancy. Vicia sativa, V. benghalensis, V. ervilia and V. articulata had no impermeable seeds. Almost all the V. villosa accessions had a high level of impermeable seeds ranging from as low as 10% to a high of 60%. Breeding against this trait has been successfully achieved by SEEDCO, a seed company based in South Australia and cultivars with reduced levels of impermeable seeds have been released. The remaining species; V. sativa ssp nigra, V. sativa ssp sativa, V. serratifolia, V. amphicarpa and V. lutea all had higher levels of impermeable seeds ranging from 50 to 95%. These studies concentrated on overcoming impermeable seed coat by mechanical and chemical scarification. Scratching the seed coat with a pin was enough to enhance germination. Commercial scarifier was not as effective as scratching the seed coat with a pin. This could partly explain the need to penetrate the seed coat as achieved by a pin as compared to rubbing off part of the seed coat with sand-paper. The use of sulphuric acid was effective in enhancing germination in Vicia seeds with high proportion of impermeable seeds. Exposure of the seeds to the acid for 30 minutes was effective. Low temperature storage (5C) reduced the level of impermeable seeds in most species. The seed moisture was increased under low temperature storage and this resulted in higher germination. This type of storage is not suitable for long term storage but can be used if the relative humidity is reduced to about 0%. High temperature storage reduced seed moisture and encouraged seed impermeability. Fluctuating temperature of 22/11C reduced the proportion of impermeable seeds. Storage environment also played an important role in the development of impermeable seeds in Vicia. Dry conditions imitated by desiccator reduced seed moisture and resulted in higher levels of impermeable seeds. Seed storage under laboratory conditions had no effect on the proportion of impermeable seed.
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ItemNutritional modification of muscle long-chain omega-3 fatty acids in lambs : effects on growth, and composition and quality of meat( 1999)Three experiments were conducted to investigate the effects of dietary supplements rich in omega-3 fatty acid on muscle omega-3 fatty acid deposition. The consequential effects on growth performance of lambs, colour and lipid oxidative stability of muscle over refrigerated display, and the sensory properties of cooked meat were also examined. A mixture of lucerne chaff : oaten chaff was used as basal diet, offered in different proportions were fed to lambs ad libitum (Expt. 1) or at 90% ad libitum (Expts. 2 and 3). Such mixtures of roughage diet support slow growth and provide a feed quality pattern similar to late spring to late summer pasture. In Expt. 1, fish meal (7%), canola meal (8%) and soymeal (7%) as natural feed supplements were compared in lambs fed low quality roughage diet. In Expt. 2, fish meal (9%) and oilseed supplements either in unprotected form (rapeseed - 7%) or in protected form (ground canola seed - 6%) were examined in lambs on medium quality roughage diet. Lipids and the proteins in the ground canola seed were treated (RUMENTEK) with aldehyde to protect them from the rumen microbial activity. Fish meal (9%), fish oil (1.5%), fish oil (1.5%) with sunflower meal protein (9%),' and sunflower meal protein alone (10.5%) (a commercial product of a protein supplement from RUMENTEK) were compared in lambs fed medium quality roughage diet in Expt. 3. Long-chain omega-3 fatty acids (eicosapentaenoic acid + docosahexaenoic acid) in muscle longissimus thoracis was increased modestly and markedly with fish meal and fish oil alone or with sunflower meal protein diet, respectively. These long-chain fatty acids were deposited in the muscle structural phospholipid rather than in storage triglycerides. All the diets mentioned above also significantly reduced omega-6:omega-3 fatty acid ratio in meat which is another beneficial effect, as the dietary recommendation in many countries has been to reduce the ratio of omega-6:omega-3 in human diet. Soymeal diet increased modestly both the omega-3 and omega-6 fatty acid content of muscle longissimus thoracis resulting in no differences in the omega-6:omega-3 ratio of the meat. A supplement of protected canola seed significantly increased the precursors of omega-6 (linoleic) and omega-3 (linolenic) but not the long-chain analogues such as arachidonic acid (omega-6) and eicosapentaenoic, docosahexaenoic acid (omega-3), respectively. The marked increase in linoleic acid content was in both triglyceride and phospholipid fractions of muscle longissimus thoracis but the modest increase in linolenic acid content was only in triglyceride fraction of meat. Supplements of canola meal used in Expt. 1, unprotected rapeseed used in Expt. 2 and protected sunflower meal protein used in Expt. 3 did not alter the fatty acid composition of muscle longissimus thoracis compared with lambs fed the control diet in that particular experiment. The increased level of long-chain omega-3 fatty acid and/or omega-6 fatty acid with the lipid supplements discussed above did not significantly affect the meat colour stability and lipid oxidative stability of fresh and vacuum packaged meat over the storage at refrigerated display. This suggests that the conditions under which the animals are grown (grazing vs grain fed or feedlot) and the species of animal are important in determining the oxidative stabilities of meat by altering the levels of muscle vitamin E concentrations at slaughter. The level of inclusion of lucerne chaff in the basal diet is an important factor in improving the redness of meat indicated by the a*-value; a higher level of lucerne chaff intake is more likely to be associated with increased intake of vitamin E. Thus colour and lipid oxidative stabilities of meat can be improved in red meat animals that are on poor quality diets by the inclusion of lucerne chaff in their diet. The sensory properties of cooked meat evaluated in the present study were not affected by the significant increase in muscle long-chain omega-3 fatty acid or omega-6 fatty acid content with fish oil and protected canola seed supplements, respectively. Addition of protected sunflower meal as a protein supplement together with fish oil significantly lowered the ratings of flavour and overall acceptability of meat compared with the control lambs. The results demonstrate that the common `lamby' and `muttony' flavour and aroma attributes were not hidden by any of the dietary treatments. These two characters associated with the species flavour and aroma were recognised by the panellists as a distinct attribute. Dry matter intake was not adversely affected by any of the lipid supplements used in the present study. Feed conversion efficiency was highest with fish meal diet on both low and medium quality roughage diets. At medium quality roughage-based diet, Feed conversion efficiency was modestly improved by protected canola seed diet but other supplements providing either natural (unprotected rapeseed) or protected protein (protected sunflower meal) did not support significant differences compared with basal diet. The significant increase in liveweight gain with fish meal diet reflected a significant increase in hot carcass weight compared with all other supplemented lambs either on low or on medium quality roughage diet. Protected lipid and protein offered by protected canola seed diet significantly and moderately increased liveweight gain and hot carcass weight from control diet but not different from unprotected rapeseed diet. The greatest muscle deposition was with the fish meal diet and is attributed mainly to the increased amount of protein and energy absorbed from the small intestine of those lambs. In addition to energy and protein absorption, the alteration of omega-3 polyunsaturated fatty acids in muscle membranes may have a further influence in lean meat production. In terms of carcass gain and intramuscular fat deposition of fishmeal and fish oil fed lambs, the results also lead to a hypothesis that modifying omega-3 polyunsaturated fatty acid of muscle membrane phospholipids may have an influence in improved muscle deposition in lambs by improving the insulin action at skeletal muscle site.
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