Eect of Muscle Condition Before Freezing and Simulated Chemical Changes During Frozen Storage on Protein Functionality in Beef M. M. Farouk* & J. E. Swan Mirinz Food Technology and Research Ltd., PO Box 617, Hamilton, New Zealand (Received 29 July 1997; revised version received 20 February 1998; accepted 22 March 1998) ABSTRACT The eect of rigor temperature (RT, 35 versus 10  C), increased ionic concentration (MS: 0 versus 0 . 2% mixed salts), oxidized lipids (OL, 0 versus 1% added oxidized fat), increased free amino acids (FAA, 0 versus 0 . 3% added mixture of amino acids), fat con- tent (FC, 0 versus 15% added fat) and excluding atmospheric gases (V, 0 versus 99 . 9% vacuum) on protein functionality in mince stored 1 month at 20  C was studied using a complete 2 6 factorial design. All factors studied aected the functional properties of beef. Fresh 24 hr samples that entered rigor at 35  C had lower total (TPS), myo®brillar (MPS) and sarcoplasmic (SPS) protein solubilities than samples entering rigor at 10  C (p<0 . 01). During frozen storage, RT, MS and OL alone did not aect protein solubi- lities, FAA increased TPS but did not aect MPS and SPS, increasing the meat's fat content raised TPS and SPS but did not aect MPS, applying a vacuum increased TPS and MPS but lowered SPS (p<0 . 05). Cook yield of frozen stored mince increased with higher FAA but decreased with higher fat content, and the peak force of patties made from frozen stored mince was lowered by increased MS and low FC during storage. Various signi®cant interactions are tabulated and discussed. # 1998 Elsevier Science Ltd. All rights reserved INTRODUCTION Protein functionality in frozen meat may be aected by factors such as ice crystal forma- tion, dehydration, increased solute concentration, fat hydrolysis and/or oxidation, pre- sence of atmospheric gases (particularly oxygen), protein oxidation and proteolysis, and rigor temperature (Roubal and Tappel, 1966; Awad et al., 1968; Butkus, 1970; Penny, 1977; Matsumoto, 1979; Shenouda, 1980; Davies, 1987; Smith, 1987; Srinivasan and Hultin, 1995; Zotos et al., 1995, Farouk and Swan, 1997a). Most studies on the eect of frozen storage on protein functionality have been done on ®sh muscles and have usually involved only one, or a few, of the factors listed. Because of the processing and energy Meat Science, Vol. 50, No. 2, 235±243, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain PII:S0309-1740(98)00035-7 0309-1740/98/$19.00+0.00 235 *To whom correspondence should be addressed. Fax: 00 64 7 854 8560; E-mail m.farouk@mirinz.org.nz