Monitoring beef quality attributes as affected by high pressure processing

High pressure processing (HPP) is becoming of increasing importance in the food industry as it offers the opportunity to obtain minimally processed food products with increased safety and extended shelf-life. A sound knowledge of the effects of high pressure on meat attributes is necessary for a successful implementation of HPP in the meat industry. The aim of this work was to determine the effects of combined pressure and temperature treatments on meat. Beef M. pectoralis profundus samples were pressurized at 200, 300 and 400 MPa at 20oC and 40oC. Both the degree of pressure and temperature applied had a significant effect on cook loss, oxidation and colour measurements. Cook loss increased at higher levels of pressure. Under pressure conditions, lower cook loss was observed at 40oC compared to 20oC. An increase of TBARS values was observed at the higher pressure levels (300, 400 MPa). Pressurization at 200 MPa produced a lower impact on colour parameters than higher pressurization levels. These results show that mild pressure treatments would minimally affect meat quality parameters, suggesting that HP technology could be applied to raw meat as a pre-treatment for obtaining prepared meals, allowing a reduction of cooking process. Introduction In recent years there has been a growing demand among consumers for ready to eat meat products of high sensory and nutritional quality, microbiologically safe and with an extended shelf life (Crehan et al., 2000). This has encouraged research into technologies that provide an alternative to conventional heat processing. One such technology is high pressure processing which improves microbiological quality of food (Cheftel & Culioli, 1997). A sound knowledge of the effects of high pressure on meat attributes is necessary for a successful implementation of HPP in the meat industry. The effect of high pressure treatment on appearance must also be considered. Previous studies have suggested that high pressure treatment of meat may result in colour changes (Serra et al., 2007). Lipid oxidation is a major cause of deterioration in the quality of meat, especially of processed meat products. Several studies have been carried out on various muscle foods to determine critical pressure levels (Ma et al., 2007, Cheah and Ledward., 1996, Beltran et al., 2003, Cruz-Romero et al., 2008). This work investigates the effects of high pressure processing at 20 and 40 C on meat quality with particular attention to fat oxidation. Materials and methods Meat sampling and high pressure treatment: Post rigor beef M. pectoralis profundus muscles were obtained from a local meat plant. Muscles were cut into steaks 2.5cm in thickness. After vacuum packaging, samples were treated with a combination of different levels of pressure and temperature. 200, 300 and 400 MPa of pressure applied at 20C and 40C for 20 min using a 1L Stansted high pressure unit (Stansted Fluid Power Ltd., Stansted, UK). Three samples for each pressure / temperature combination were treated. Non treated samples were kept as a control. pH measurement: pH values were measured using a glass probe (Orion pH meter 250A, Orion Research Inc.) by direct insertion into the meat. Six measurements were made for each sample. Colour measurements: Internal colour of samples was using the CIE L*a*b* system with a dual beam xenon flash spectrophotometer (Ultra Scan XE, Hunter lab). Three measurements for each treatment were taken for each sample. Cook loss: Steaks were cooked in a water bath at 72C, until an internal temperature of 70C was achieved. Weight was recorded before and after cooking. Cook loss was expressed as the percentage of the weight difference. Microbiological analysis: Ten g of meat sample were added to 90 ml of maximum recovery diluent and homogenised. After appropriate dilutions Total Viable Counts (TVC) were enumerated by plating on PCA agar (Merck, Darmstadt, Germany) at 30C for 72 h. Lactic Acid Bacteria (LAB) were enumerated by plating on MRS agar (Oxoid, Basingstoke, Hampshire, England) incubated at 37C for 24 h; Enterobacteriaceae were enumerated by plating on Violet Red Bile Glucose agar (Merck) at 30C for 24 h. The presence / absence of Listeria, Salmonella and Campylobacter was analysed according to ISO 11290-