Agriculture and Food Systems - Theses

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    The effect of temperature on the timing of grapevine phenology
    Cameron, Wendy ( 2021)
    Climate change and associated temperature increase is having a profound impact on the timing of grapevine phenology. The expectation that this will continue necessitates grape growers to adapt to climate change. Part of adaption will be understanding what cultivars to plant in existing and new vineyard sites, specific knowledge of which is currently lacking. This thesis aimed to increase our knowledge of the phenological response of grape cultivars to temperature, with the longer-term goal of assisting future selection of cultivars. Using historical data from four commercial vineyards in climatically different regions in Victoria, Australia, and using advanced statistical modelling techniques, the study showed that the phenological stages maturity, veraison and flowering had advanced as related to springtime maximum temperature and there are significant differences between cultivars and their rate of advancement. Later ripening cultivars advanced maturity at a greater rate than earlier ripening cultivars at the same vineyard. Yet, the same cultivar at different vineyards, advanced maturity at a greater rate in the cooler vineyard. A significant delay in the timing of maturity was also demonstrated for one cultivar. These findings provide explanations for the observation of time compression of the harvest period and noted that as temperature further increases, vines will move beyond their optimal growth temperature range for growth and show the impact of heat stress with delayed rates of phenological advancement. Comparisons of the rates of advancement for a given phenological stage across different vineyard regions showed that the response of cultivar to temperature was nonlinear and differed according to the vineyard grouping and the temperature. The intervals between the four major phenological stages, budburst, flowering, veraison and maturity were also investigated. It was found that the budburst to flowering interval was more highly correlated to temperature than intervals between other phenological stages and had shortened at a significantly greater rate than the flowering to veraison and veraison to maturity intervals, as related to springtime maximum temperature. The relationship between temperature and budburst to flowering interval was best described by a curve, indicating that as the average daily maximum temperature during this interval increases, the decrease in interval length will slow and plateau. By extension, this also indicates that the observed advancement in maturity timing, as related to springtime maximum temperature, is expected to slow and plateau with future increases in temperature. These results will inform future management decisions as the wine industry responds to the challenges of a changing climate and show that cultivar diversity will be an important tool in these adaptation strategies.
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    Structural determinants of the quality of cooked meat
    Spirovska Vaskoska, Rozita ( 2020)
    The quality of cooked meat is valuable for consumers and meat industry. The aim of this research was to identify structural determinants of the quality of cooked meat. Muscle type (bovine semitendinosus, psoas major, biceps femoris), cooking temperature (45 C to 85 C), ageing time (14 vs 0 days in beef; prolonged 15 vs conventional 3 days in pork), enzyme inhibition (with/without cathepsin inhibitor) and fibre type (bovine masseter 100 percent type I; cutaneous trunci 93 percent type II) were investigated factors affecting meat quality. Methods for measuring quality (cooking loss and Warner- Bratzler shear force (WBSF)), structural changes (shrinkage) and protein denaturation [Differential Scanning Calorimetry (DSC) and Fourier Transform Infrared (FTIR) microspectroscopy] were used. Cooking loss was higher in semitendinosus compared to biceps femoris and psoas major; and it increased with temperature in beef and pork. Cooking loss increased with ageing of beef independent of temperature and muscle type; and decreased with prolonged ageing compared to conventional ageing, of pork (cooked at 70 C and 80 C). The denaturation enthalpy of masseter and cutaneous trunci explained 58 and 59 percent of the variation in cooking loss, respectively. Reduction of WBSF in bovine muscles rich in collagen (all but psoas major) with cooking at 60 C to 65 C was attributed to collagen denaturation. The increase in WBSF in unaged beef with cooking at 70 C and 80 C was attributed to intact titin denaturation. In relation to shrinkage, 3D laser scanning was compared to caliper measurements, and was found inferior in measuring volume and predicting cooking loss. Cuboids` transverse and longitudinal shrinkage were higher in muscles with higher collagen content and sarcomere length, respectively. Transverse shrinkage started 5 C higher in psoas major fibre fragments, compared to semitendinosus and biceps femoris, likely due to predominant type I fibres. It was proven that transverse and longitudinal shrinkage of fibre fragments is caused by myosin and actin/titin denaturation, respectively. Since ageing reduced the longitudinal shrinkage of cooked beef (biceps femoris and psoas major cuboids at 80 C, semitendinosus and biceps femoris fibre fragments at temperatures greater or equal to 75 C) and pork, an important role of titin in longitudinal shrinkage was hypothesized. Cathepsin inhibition reduced the longitudinal shrinkage (semitendinosus, biceps femoris, psoas major cooked at temperatures greater than 75 C), and increased the transverse shrinkage (semitendinosus at temperatures greater or equal to 60 C) of fibre fragments. Longitudinal and transverse shrinkage were major contributors to cooking loss (beef and pork) and WBSF (beef), respectively. Cutaneous trunci had higher cooking loss (at temperatures lower or equal to 75 C), higher transverse (at temperatures lower or equal to 60 C), longitudinal (at temperatures lower or equal to 80 C) and volume shrinkage of fibre fragments (at temperatures lower or equal to 65 C); as well as lower transition temperature of myosin, higher reduction in alpha-helix and beta-sheet, and higher, compared to masseter, formation of beta-aggregated strands, random coil and aromatic side chains (at temperatures lower or equal to 60 C). The differences in protein denaturation and shrinkage between masseter and cutaneous trunci cooked at 55 C were attributed to the myosin isoform, while the differences in muscle fibre and connective tissue proteins’ denaturation at 60 C and 65 C were pH dependent. Myosin (isoform, denaturation), actin (denaturation), titin (degradation, denaturation), collagen (content, denaturation) and sarcomere length were proven or postulated, as structural determinants of the quality of cooked meat.