The use of muscle enzymes as predictors of pork meat quality Fidel Toldra *, MoÂnicaFlores Instituto de AgroquõÂmica y TecnologõÂa de Alimentos (CSIC), Apt. 73, 46100 Burjassot, Valencia, Spain Abstract Muscle endo-protease (calpains and cathepsins) and exo-protease (dipeptidyl-peptidases and aminopeptidases) activities were assayed at 2 h post-mortem in dierent meat qualities (PSE, RSE, RFN and DFD). The sensory characteristics of the dierent pork meat qualities were also evaluated in order to correlate them to the proteolytic activity. The assay of aminopeptidase and dipepti- dylpeptidase activities (AAP, RAP, LAP, DPPI and DPPIV) at 2 h post-mortem discriminate between exudative and non-exudative classes explaining 74.6% of the variability. Also, at 24 h post-mortem 71.2% of the variability was detected by the measurement of PGAP, AAP, RAP, DPPII and DPPIV. Therefore, the exoprotease activities can constitute a novel and adequate technique to predict early post-mortem pork meat quality allowing its assay till 24 h post-mortem because of the good stability of the enzymes during this post-mortem time. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Muscle enzymes; Proteases; Exopeptidases; Pork; Meat quality 1. Introduction The prediction of pork quality on the slaughter line is not an easy task because some of the biochemical qual- ity properties have not enough time to be fully devel- oped. The evaluation of pork quality should be based on relatively inexpensive and rapid measurements taken in the slaughterline where carcass identi®cation is avail- able in order to have better use of the product for fur- ther processing and distribution. There are many techniques such as pH, colour, electrical conductivity and drip loss (DL) currently used for carcass classi®ca- tion. Although they have to be applied at speci®c post- mortem times, 2 and 24 h, or even require time, 4 days of storage in the case of DL for a correct prediction of the quality. Thus, there is a need to ®nd new biochem- ical assays, well correlated with carcass quality, in order to have a proper classi®cation in a shorter time. During the last decades many methods have been developed to detect exudative meats. Several methods have been optimised at pre-rigor state such as the mea- surements of pH 45min (Somers, Tarrant & Sherington, 1985) that is extensively used in slaughterhouse although presents certain variability. Other methods consist in the measurement of re¯ectance (Chizzolini, Novelli, Badiani, Delbomo & Rosa, 1993; Warris & Brown, 1987), elec- trical conductivity (Garrido, PedauyeÂ, BanÄoÂn, Lopez & Laencina, 1995) and impedance (Swatland, 1995). At post-rigor state, the measurement of water holding capa- city (Warris & Brown, 1987) and the measurements of luminosity (Garrido, PedauyeÂ, BanÄ o n & Laencina, 1994; Laack, Kauman, Sybesma, Smulders, Eikelenboom & Pinheiro, 1994) were developed. However, the presence of intermediate qualities among the extremes PSE and DFD increase the variability. This is the case of the high inci- dence of RSE (reddish-pink, soft and exudative) meat that has an economic impact in the pig industry (Cheah, Cheah & Just, 1998). RSE meat is characterised by an exceptionally high drip loss with normal red colour (Kauman, Cassens, Cherer & Meeker, 1992; Laack et al., 1994; Warner, Kauman & Russell, 1997). This meat might be due to a genetic disposition or also be induced by poor handling (Cheah et al., 1998). From the processor point of view, it is important to be able to predict the water holding capacity of meat (WHC) because it is responsible for weight loss in raw, cooked and processed meats. It is also responsible of poor colour in cured meat products, such as ham, and can in¯uence meat palat- ability traits. So, recent reports have been focused in the study of new techniques for a better prediction of meat quality (Boland et al., 1995; Garrido & Honikel, 1996; Kauman et al., 1993). 0308-8146/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(00)00052-2 Food Chemistry 69 (2000) 387±395 www.elsevier.com/locate/foodchem * Corresponding author. Tel.: +34-96-390-0022; fax: +34-96-363- 6301. E-mail address: ftoldra@iata.csic.es (F. ToldraÂ).