Proteomic analysis of temperature-dependent changes in stored UHT milk

Molecular changes in milk proteins during storage of UHT-treated milk have been investigated using two-dimensional electrophoresis (2-DE) coupled to MALDI-TOF mass spectrometry. UHT-treated samples were stored at three different temperatures, 4 °C, 28 °C, and 40 °C, for two months. Three main changes could be observed on 2-DE gels following storage. They were (1) the appearance of diffuse staining regions above the position of the monomeric caseins caused by nondisulfide cross-linking of α and β-caseins; (2) the appearance of additional acidic forms of proteins, predominantly of α(S1)-casein, caused by deamidation; and (3) the appearance of "stacked spots" caused by lactosylation of whey proteins. The extent of the changes increased with increased storage temperature. Mass spectrometric analysis of in-gel tryptic digests showed that the cross-linked proteins were dominated by α(S1)-casein, but a heterogeneous population of cross-linked forms with α(S2)-casein and β-casein was also observed. Tandem MS analysis was used to confirm deamidation of N(129) in α(S1)-casein. MS analysis of the stacked spots revealed lactosylation of 9/15 lysines in β-lactoglobulin and 8/12 lysines in α-lactalbumin. More extensive analysis will be required to confirm the nature of the cross-links and additional deamidation sites in α(S1)-casein as the highly phosphorylated nature of the caseins makes them challenging prospects for MS analysis.     

Adoption of sustainable irrigation management practices by stone and pome fruit growers in the Goulburn/Murray Valleys, Australia

The management of water resources by orchards in the south-eastern region of Australia is an increasingly important policy issue, especially given the low water allocations and concerns about salinity in recent years. Optimal management for economic and environmental sustainability can be described as best management practice (BMP). A project was developed to run an extension program, which aimed to achieve behavioural change among orchardists through the adoption of irrigation BMPs and benchmarks. The effectiveness of the extension program was evaluated and the drivers for adoption assessed. In the first stage of the project both BMPs and benchmarks were determined for irrigation management. A survey of 200 growers showed no relationship between yield and irrigation system or irrigation volume suggesting that increased yields were not a key driver for adoption of sustainable irrigation practices. Stage two of the project involved undertaking an extension program aimed to facilitate the adoption of BMPs and benchmarks and incorporated a suite of activities to meet the learning needs of a diversity of participants (40 growers). The program was effective in establishing behavioural change for many of the growers involved; however, it was resource intensive requiring significant one-on-one input. Stage three aimed to analyse the key drivers for adoption of sustainable irrigation practices for the whole of the stone and pome fruit industry in south-eastern Australia using market research. The study determined that water use efficiency was not a key driver for adoption of sustainable irrigation practices (micro irrigation and soil moisture monitoring) and adoption was generally not limited by lack of knowledge. Groups of growers were identified where extension programs could be effective by focussing on specific information e.g. redevelopment of orchard. Other groups had no need and/or ability to change unless the external operating environment was to change e.g. regulation, access to pressurised water. The voluntary adoption of more sustainable irrigation practices will probably require extensive resources using one-on-one methodology. The extension program should not focus on the broader social objective of improved water use efficiency but promote other potential benefits (e.g. labour saving, redevelopment of production systems, management flexibility) with targeted messages for specific groups.     

Dietary carbohydrate and growth,body composition and heat increment in rainbow trout (Salmo gairdneri)

A study was conducted to determine growth, body composition and heat increment (HI) of rainbow trout reared on isonitrogenous high digestible carbohydrate (HC) and high fat (HL) diets at 15°C. Trout reared on the HC diet had a significantly lower final body weight and carcass lipid content and a significantly higher feed:gain ratio and carcass protein content than trout reared on the HL diet after 12 weeks on the test diets. The lower carcass lipid composition indicates that trout do not readily convert dietary carbohydrates into fat. HI of trout reared on the HC diet was significantly higher than that of fish reared on the HL diet. Considering the poor utilization of dietary carbohydrates as an energy source and the apparently low conversion of dietary glucose into fat, the cause of the higher HI associated with the HC diet is not completely understood. However, it is possible the elimination of excess dietary glucose is an energy dependent process resulting in an increased heat production which would partly account for the increased HI. Furthermore, if the HC diet is a low net energy diet, then the metabolism and utilization of dietary and tissue proteins (amino acids) for energy by the trout may also be partly responsible for the increased HI of the trout reared on the HC diet.     

Investigation of the nutritional requirements of Australian snapper Pagrus auratus (Bloch & Schneider, 1801): effects of digestible energy content on utilization of digestible protein

This study used a curvilinear model to investigate the effects of different digestible energy (DE) levels on the digestible protein (DP) requirements of juvenile snapper Pagrus auratus. For each DE level (15, 18 or 21 MJ kg⁻¹), DP content was increased from about 210–560 g kg⁻¹ in seven evenly spaced increments by formulating a summit diet (highest DP content) and a diluent diet (lowest DP content) at the desired DE level and combining the summit and diluent diets in various ratios to achieve the desired DP content. This ensured the DE level remained relatively stable. Each of the 21 dietary treatments was fed to three replicate groups of snapper twice daily to apparent satiation for 57 days. At the completion of the trial, fish were weighed and killed for chemical analysis. Results indicated that the rapid growth of snapper weighing 30–90 g was highly dependent on the ratio of DP to DE and that optimum protein deposition did not occur until snapper were offered feeds with at least 350 g DPkg⁻¹, irrespective of DE level. According to the fitted models, diets formulated for snapper reared at temperatures from 20–25°C should contain approximately 23 g DP MJ DE⁻¹ to promote optimal weight gain and protein deposition. Based on the feeding regime used in this study, this could be achieved with practical diets containing a DP:DE ratio of 460:20, 420:18 or 350:15.     

Effects of thyroid hormone supplementation of canola meal-based diets on growth,and interrenal and thyroid gland physiology of rainbow trout (Salmo gairdneri)

Rainbow trout fed a 26% canola meal-based (CM) diet for 12 weeks at 15°C exhibited reduced growth, lower feed conversion, enlarged thyroid glands and lower plasma thyroid hormone (TH) levels than comparable fish fed equinitrogenous, equicaloric soybean meal-based (SB) diets. Supplementation of the SB diets with either T₄ (20 mg/kg) or T₃ (10 or 20 mg/kg) had no effect on the growth rate, feed conversion and thyroid histology of the trout. However, plasma T₄ levels weredepressed in trout fed the T₄- and high T₃-supplemented SB diets. In trout fed T₄- and T3-supplemented CM diets the growth rates and feed conversion were not significantly different from those of the SB-fed groups. Moreover, in the T₄-supplemented group, plasma T₄ levels were in the normal range. However, thyroid enlargement was evident in all the CM-fed fish, and plasma T₃ levels were markedly elevated in groups fed the T₃-supplemented CM diets. The data suggest that antithyroid components in the CM diets inhibited TH synthesis (but not their release), and impaired TH clearance from the circulation. There were no significant differences in plasma cortisol levels in the 8 treatment groups, nor were there differences in the histological appearance of the interrenal gland. However, when the data from SB- and CM-fed fish were pooled, plasma cortisol levels in the SB-fed fish were significantly lower than in the CM-fed animals. Glucosinolates at a level of 164 mg/kg diet were toxic to young trout, but the effect was ameliorated by dietary TH supplementation.     

Physical characteristics,and proximate composition of oocytes,liver and muscle of wild caught and tank-reared Macquarie perch

Macquarie perch (Macquaria australasica) is a freshwater percichthyid endemic to south-eastern Australia. In view of its conservation status (indeterminate), and its importance as a sport fish, natural stocks are replenished through a breeding programme using mature stock taken from the wild each year.This paper is the first of a series of investigations instigated to understand the underlying causes of the lack of response of Macquarie perch, caught from the wild and spawned and then tankreared for a year, to hypophysation techniques. In this paper, results of physical characteristics, proximate composition and ovarian histology of wild-caught and tank-reared fish (injected with salmon GnRHa and non-injected) are presented. Oocyte diameter distribution patterns indicate that Macquarie perch spawn once each year, and that in tank-reared fish oocyte maturation is incomplete with only a small proportion of oocytes reaching maturation. The mean (sd) gonadosomatic and hepatosomatic indices of wild fish were 11.25 (2.38) and 0.59 (0.10) and that of tank-reared fish were 4.84 (0.70) and 1.44 (0.09) respectively. These two parameters differed significantly (p<0.05) in the two groups of fish.Major differences also existed in the proximate composition of the liver and the way the liver components responded to GnRHa injection. The percent (sd) protein, lipid and ash by dry weight in the liver of wild injected fish were 57.02 (0.66), 30.63 (1.22) and 8.24 (0.05) respectively while in the liver of tank-reared uninjected fish these values were 30.87 (1.36), 24.59 (1.18) and 6.43 (0.13) respectively. When expressed as an absolute amount or an amount kg^–1 body weight, all of moisture, protein, lipid, ash and nitrogen free extract were greater in tank-reared than wild fish. No significant differences were observed between wild and tank-reared fish in the composition of the body musculature or the oocytes.