Cameron Jose

This study evaluated the impact of high oxygen modified atmosphere packaging (MAP) in four different combinations, 80 % oxygen and 20 % carbon dioxide (MAP80), 40 % oxygen, 20 % carbon dioxide and 40 % nitrogen (MAP40(20CO2)), 40 % oxygen, 60 % carbon dioxide (MAP40(60CO2)), and vacuum skin packaging (VSP) under different retail display times (3 or 8 days) on the sensory scores of lamb meat. Untrained consumer sensory scores for overall liking, tenderness, juiciness and liking of flavour were assessed on the M. longissimus lumborum (loin) and M. semimembranosus (topside) of 144 lambs. In general, MAP40(20CO2) samples received higher sensory scores than MAP80 (P < 0.05). While the high carbon dioxide MAP mixture MAP40(60CO2) scored similar to MAP80 (P > 0.05). Therefore, MAP40(20CO2) minimised the detrimental effects on eating quality and is a viable alternative to the widely used MAP80. However, the highest eating quality scores were still obtained with VSP (P < 0.05).

Meat colour is an important attribute for consumer acceptance but there is an interval between colour grading and retail display. This experiment investigates the effect of time post-slaughter (5, 14 and 40 days) on colour and bloom depth (after 1 and 24 h) for beef carcasses graded AUS-MEAT colour 4 (MC 4). Sixteen carcasses were selected at grading, 8 carcasses were graded MC 4 and 8 as compliant colour (AUS-MEAT score 2 or 3). At 5 days post-slaughter, compliant loins had greater overall bloom depth and were more red than MC 4 loins. Bloom depth (24 h) increased with ageing time but reached maximum bloom at 14 days for both treatments. After ageing for 14 and 40 days, the bloom depth of MC 4 loin was no different to the 5 day aged compliant loins after 24 h on display. Colour at grading may not be a reliable measure of retail colour considering the changes post slaughter.

Hot boning (HB) is an economical processing technique often resulting in poorer meat quality and tenderness. This study tested a method of partial HB, where the short loin section was removed from the hot carcass and chilled, with the striploin remained in the skeletal system. Thirty six yearling Bos indicus steers carcasses were subjected to either low, high or no electrical stimulation and each side allocated to a cutting treatment of HB, partial HB and conventional (Achillies hung). Striploins were divided into 3 and aged for 5, 14 and 28 days. Warner Bratzler Shear force (WBSF) and sarcomere length were tested. Partial HB resulted in greater tenderization without aging compared to HB. However, optimized electrical stimulation was a requirement. Treatment did not influence sarcomere length. The study also tested the impact of Dry aging of HB striploins, which resulted in further increases in tenderness at 28 days of aging compared to wet aged product, reducing WBSF by 9 N.

This study investigated the effects of vitamin E, electrical stimulation, aging and packaging system on the colour stability of lamb meat. Eighty crossbred wether lambs, 6–8 months old were fed on either vitamin E or control pelleted diet for 31 days prior to slaughter. Half of the carcases from each group were electrically stimulated before being split longitudinally into 2. Each side was randomly allocated 1 of the 4 aging periods (5 days fresh, 10, 20 and 30 days CO2). Muscle samples were set for retail display, after the respective aging period, colour was measured over 96 h. Supplementing vitamin E nutritionally is likely to lengthen the shelf life of lamb products aged longer than 10 days. Muscle vitamin E concentrations > 3.0 mg/kg are required to increase the shelf life of lamb cuts aged for up to 30 days to 60 h. Medium voltage electrical stimulation did not have a detrimental effect on the display life of aged lamb meat.

The relationship between vitamin E supplementation rate and colour stability was investigated using 70 mixed sex 6-8 month old crossbred lambs. An initial group of 10 were slaughtered, while the remainder were fed a pellet ration containing either 30, 150, 275 or 400IU vitamin E/kg ration or on green pasture for 56days. After slaughter, carcases were halved; one side packed fresh (5days) and the other in CO2 (21days), both at 2°C. Five muscles were set for retail display for 96h. The oxy/metmyoglobin ratio was measured every 12h. Colour stability increased with increasing muscle vitamin E until an apparent maximum effect for vitamin E concentration (3.5-4.0mg α-tocopherol/kg tissue) was reached beyond which no further response was evident. This was reached within 3-4weeks (275IU treatment), and meat from these lambs should reach 60h retail display with a satisfactory surface colour. This effect was most apparent in aerobic muscle types and meat aged post slaughter.

A 4 × 3 factorial experiment (n= 8 pigs per treatment combination) was conducted with 96 female Landrace × Large White pigs to examine the required level of dietary vitamin E and optimum feeding duration before slaughter to maximise muscle vitamin E content in the Longissimus thoracis et lumborum (LTL) muscle. The respective factors were four dietary levels of vitamin E (supplemented as dl-α-tocopheryl acetate; 35, 300, 500, and 700 IU/kg) and three feeding durations (14, 28 and 42 days before slaughter). Vitamin E concentration in the LTL was maximised at 6 mg/kg, which was achieved by feeding a 700 IU vitamin E diet for 28 days before slaughter (P < 0.001). There was no further increase in the vitamin E content of the LTL by feeding the high vitamin E diet more than 28 days before slaughter.

Dark cutting is detrimental to meat quality and therefore is the major cause of carcass downgrades under the Meat Standards Australia grading system. This study quantified the variation between months in the incidence of dark cutting, in southern Australia. Four years of Meat Standards Australia grading data, from nine individual beef processors in Western Australia, South Australia, Victoria and Tasmania, was utilised for the analysis. The dataset contained 42162 slaughter groups, of 10 or more grass-fed cattle, which allowed for the percentage of dark cutters per slaughter group to be analysed. The interaction between month, year and state was significant (P < 0.001). The lowest risk of dark cutting for South Australia and Western Australia was in October (1.53% ± 0.75 and 6.96% ± 0.76) and November in Tasmania and Victoria (7.34% ± 0.9 and 5.27% ± 0.81) potentially when feed availability and quality is highest. The incidence of dark cutting was highest for all states during the period from February to June. Lower pasture availability and quality in combination with higher levels of stress due to extreme high or low temperatures during this time could all contribute to the higher incidences. The findings of this study show that procurement and management decisions made by cattle buyers, producers and processors need to change throughout the year to help mitigate the incidence of dark cutting carcasses and reduce financial loss.

Current iron (Fe) levels in fresh pork are below requirements to claim for a source of Fe (Anonymous, 2013). Dietary studies to increase muscle Fe in pork have generally failed, although an increase in muscle redness, associated with increased haem Fe, was observed (Apple et.al 2007). Under normal feeding conditions about 10% of dietary Fe is absorbed, however this value increases markedly under Fe deficiency (West and Oates 2008). This study tested the hypothesis that feeding lower levels of dietary Fe (depletion) followed by feeding higher levels of dietary Fe (repletion) to pigs will increase muscle Fe levels.

Variation in pork quality has been proposed to be mostly due to different rates of post-mortem muscle pH decline (Ryu and Kim, 2006) and its influence on tenderness (Pomponio et al. 2010), which is an important eating quality discriminator. The variable nature and inconsistency of meat quality attributes, such as meat colour and pH, in outdoor bred pigs in Western Australia, and the related quantity of stored muscle glycogen at slaughter, led to this investigation. High levels of muscle glycogen pre-slaughter increases potential lactic acid production, the extent of pH decline, and the lightness of pork. The effect of high glycogen levels on the rate of pH decline is controversial (Scheffler and Gerrard, 2007) and has never been examined in outdoor bred pigs in Australia. The aim of this experiment was to investigate the influence of loin glycogen stores pre-slaughter on post-slaughter pH decline in outdoor bred pigs in Western Australia.

The iron content of pork meat is low in relation to lamb and beef even though it can vary considerably according to muscle type, with the ‘redder’ (more aerobic) muscles generally possessing higher iron levels. Australian pork currently does not meet the Australian Food Standards Code requirements of being a food that is “a good source” of iron, for to achieve such a rating the food must contain no less than 25% of the recommended daily intake (RDI) for that mineral. Furthermore, it appears that the iron content of Australian pork may be lower than that reported by other major pig-producing countries such as Canada and the USA. Evidence to date indicates that various nutritional strategies (e.g., adding more iron to the diet) to elevate the iron content in pork been largely unsuccessful suggesting that muscle iron storage is refractory to dietary iron content, the amount of which can vary in the diet according to the age and feeding phase of the pig. In this context, muscle-specific manipulation of iron levels by examination of the effects housing systems or dietary formulation may be possible assuming any increased iron absorption directly relates to a deposition in the muscle in redder/more aerobic fibre types. Three experiments were conducted to test the general propositions that (i) pigs raised in deep-litter/eco-shelter systems will have more iron and myoglobin than their counterparts that are raised indoors (“conventional”); (ii) feeding diets lower in iron (to induce mild iron depletion) followed by feeding diets higher in iron (to induce iron repletion) will increase circulating serum iron levels and will increase levels of iron in a redder muscle type; and (iii) there will be differential expression of candidate genes implicated in muscle iron metabolism in relation to feeding different iron concentrations throughout the grower finisher stages of growth.