Abstract
Meat has been consumed widely around the world as a staple food and its consumption is essential for an optimal human growth and development. Tenderness is considered to be the most important attribute in meat and it is one of the parameters that are used to categorise different meat cuts into different quality levels. Many conventional methods have been developed to improve the tenderisation of meat. However, these methods often produce side effects such as severe excessive oxidation and in some cases mushiness, altering the quality. Pulsed electric field is a technology that has the potential in improving the tenderisation of meat without severely damaging the muscle structure of the meat. Moreover, pulsed electric field has the ability to deliver different intensity treatment conditions to different muscles in order to optimise the product quality accordingly. The present work aimed to investigate the effects of pulsed electric field (PEF) on several quality attributes of cold-boned and hot-boned beef Longissimus lumborum and M. Semimembranosus muscles.
Six loins (Longissimus lumborum) and six topsides (M. semimembranosus) were removed from 6 carcasses at 24 h post-mortem (cold-boned) or 4 h post-mortem (hot-boned) and processed within 6 h (cold-boned) or 2 h (hot-boned). Each muscle was subjected to six different PEF treatments (combination of 5 or 10 kV, with frequencies of 20, 50 or 90 Hz at 20 µs) or repeated (1x, 2x or 3x) PEF treatments (10 kV, 90 Hz and 20 µs) and a non-treated control sample and aged for 3, 7, 14 and 21 days post-treatment.
There was an average of 19% reduction in the shear force of PEF treated cold-boned LL and SM muscles. An average of 2.5 N reduction in the shear force was found in cold-boned LL muscles for every extra application of PEF treatment (10 kV and 90 Hz) while no effect of repeated PEF treatment was found in cold-boned SM muscles. Different effect was observed in hot-boned beef muscle where there was a 21.6% reduction in the shear force due to PEF treatment in hot-boned beef SM muscle and an increased shear force with the increasing of PEF frequency in hot-boned LL muscle. The shear force of 1x PEF treated (10 kV and 90 HZ) hot-boned beef LL muscle was lower than the non-treated control samples. However, the shear force increased with every extra application of PEF treatment and it was found that 2x and 3x PEF treatments resulted in a higher shear force compared to the non-treated control samples. PEF also showed to be beneficial for the tenderisation of cold-boned LL beef muscle with a low pH (5.5 – 5.8) compared to higher pH level ranges (5.8 – 6.1 and > 6.1).
Myofibrillar protein profile, troponin-T and desmin degradation was also investigated in treated and non-treated cold-boned and hot-boned beef LL muscles. Some of the cold-boned PEF treated sample showed an increased proteolysis as indicated by the increased in troponin-T and desmin degradation which indicated that biochemical mechanism/s were responsible for the increased tenderisation in low intensity PEF treatment. However, high intensity PEF treated sample also resulted in tenderizing action but without sufficient evidence of proteolysis and may be attributed to physical mechanisms. Similar trends were observed in hot-boned PEF treated samples. Low intensity (5 kV- 20 Hz, 10 kV- 20 Hz, and 1x PEF treatment of 10 kV and 90 Hz) exhibited the most prominent troponin-T and desmin degradations whereas the high intensity PEF treatments did not show the same effect. This suggested that high temperature generated during the PEF treatment may have caused cellular changes interfered with proteolysis, hence less proteolysis was observed in high intensity PEF treated samples.
PEF appeared to have differential effect towards the total moisture loss (purge loss and cooking loss) of each muscle (LL and SM), some muscles was not affected while some are affected as indicated by an increase or decrease in the purge loss or the cooking loss. Colour stability of cold-boned beef was negatively affected by repeat PEF treatment, which was indicated by the increase in hue values for every extra application of PEF treatment and a lower colour difference (630 nm – 580 nm) in 1x PEF treated (10 kV and 90 Hz) cold-boned LL muscle. Lipid oxidation was not affected by PEF treatments.