Combined effects of aging and low temperature, long time heating on pork toughness
Introduction
Meat tenderness is the most important quality attribute that affects consumer's eating satisfaction and repeat buying (Li, Xu, & Zhou, 2012). Although different methods and techniques have been used to improve meat tenderness, such as pre-slaughter management (Küchenmeister, Kuhn, & Ender, 2005), tenderstretch hanging (Sørheim et al., 2001), electrical stimulation (Contreras-Castillo, Lomiwes, Wu, Frost, & Farouk, 2016), traditional aging (Lepper-Blilie, Berg, Buchanan, & Berg, 2016), injection of calcium or enzymes (Bekhit, Hopkins, Geesink, Bekhit, & Franks, 2014; Colle et al., 2018),Variations in tenderness still remains to be a big quality control problem for the meat industry. More recently, more advanced techniques, such as high hydrostatic pressure processing (Morton et al., 2017), shockwave (Bolumar, Enneking, Toepfl, & Heinz, 2013), and pulsed electric field (Suwandy, Carne, van de Ven, Bekhit, & Hopkins, 2015), have also been tested for their potential in improving tenderness, with various successes.
Sous-vide cooking is a method of low temperature (below 60 °C) and long time heating (prolonged times up to 30 h), which is increasingly used in food sector, for example, the catering industry (Baldwin, 2012; Creed, 1995; Dominguez-Hernandez, Salaseviciene, & Ertbjerg, 2018). Prolonged cooking at relatively low temperature improves meat tenderness and juiciness, and generates a more uniform color (Christensen, Bertram, Aaslyng, & Christensen, 2011). Low temperature and long time (LTLT) cooking has shown considerable effects on meat tenderization in different meat species, such as pork (Christensen, Ertbjerg, Aaslyng, & Christensen, 2011), beef (Christensen et al., 2013), and lamb (Roldán, Antequera, Martín, Mayoral, & Ruiz, 2013). The tenderization effect of LTLT cooking is mainly attributed to its weakening of connective tissue through collagen solubilization and gelatinization (Becker, Boulaaba, Pingen, Krischek, & Klein, 2016). To a less extent, increased tenderness of sous-vide cooked meat could be caused by weakening of myofibrils due to the action of proteolytic enzymes, such as cathepsin (Christensen, Ertbjerg, et al., 2011).
In meat industry, whole carcasses or the primal cuts are generally held in a cooler chamber (2–5 °C) and aged for designated times to obtain premium tenderness. Depending on the animal species, age, or meat cuts, a period between 7 and 21 days may be required to achieve tenderization (Bolumar et al., 2013). During the aging period, proteolysis of myofibrillar proteins occurs and leads to the disruption of muscle fiber, which ultimately contributes to the improvement of meat tenderness. However, this process is time- and energy-consuming, and requires the accumulation of high stock of meat and large refrigerated space for storage, all of which significantly increase the processing cost (Bolumar et al., 2013). To the best of our knowledge, most documented studies on sous-vide cooking focused on the effects of cooking temperature and time on meat tenderness alone, without taking into account the aging effects. It remains unknown whether meat with various aging periods would respond differently to LTLT cooking in relation with tenderness, namely, whether it is it possible to replace prolonged aging process with appropriate LTLT temperature-time regime to obtain equivalent meat tenderness.
Therefore, the aim of the present study was to study the combination effects of aging and LTLT cooking on meat toughness of Longissimus dorsi aged for 1 or 10 days. The solubility of collagen, proteolysis of myofibrillar proteins, and microstructure of connective tissue were studied after different LTLT treatments.
Section snippets
Raw material and sample preparation
Four commercial crossbreed pigs (carcass weight 71–80 kg) were obtained from a local slaughterhouse 24 h post mortem. Both pork loins of each pig (between 6th thoracic vertebrae and 6th lumbal vertebrae) were removed, and the pH was determined at the cranial end using a portable pH meter (Testo 205, Testo, Lenzkirch, Germany). Only loins with a pH in the range 5.5–5.8 were used in this study, and eight loins from four carcasses were used in total. All loins were trimmed off the fat and
Shear force
Both LTLT and aging time affected meat shear force (P < .05), with no interaction effects (P > .05, Table 1). Shear force values decreased with increasing temperature and time. The highest shear force was observed in meat cooked at 53 °C for 10 h, while the lowest shear force was measured in meat cooked at 58 °C for 20 h. Meat cooked at 53 °C for 20 h had similar shear force values to meat cooked at 58 °C for 10 h. Irrespective of LTLT treatments, meat aged for 10 days showed lower shear force
Discussion
Low temperature and long time cooking (LTLT) has become popular among the catering industry to produce tender meat. Meanwhile, the aging process as a commonly used tenderization method is costive due to the need of large refrigerated rooms for storage. The question also arises whether it is possible to replace prolonged aging process with appropriate LTLT temperature-time regime while obtaining desirable meat tenderness. The present study aimed to elucidate whether LTLT cooking could reduce the
Conclusion
The present study showed that LTLT cooking and aging independently affected meat toughness, as indicated by the shear force values. As cooking temperature and time increased, meat toughness decreased, meanwhile, irrespective of LTLT treatments, 10-day aged pork had lower shear force values than that aged for one day. It was further revealed that higher temperature or longer times were required to reduce toughness of one-day aged meat to the same level as in 10-day aged meat. Furthermore, under
Acknowledgements
The authors acknowledge the financial supports from National Natural Science Foundation of China, China (31701671) and Liaoning Provincial Education Department, China (2017J034).
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