Treatment of meats with ionising radiations. VIII.—pH, water‐binding capacity and proteolysis of irradiated raw beef and pork during storage, and the ATP‐ase activity of irradiated rabbit muscle

The immediate effects of 5-Mrad ionising radiation on beef and pork longissimus dorsi muscles were an increase in pH, a decrease in water-holding capacity, in increment in gel-volume for a given pH rise, and in soluble protein, and increased resistance to low- and high-speed homogenisation. the indications of cross-binding induced by irradiation were supported by studies of isolated myofibrils from rabbit psoas muscle. Irradiation markedly reduced the syneresis (18°, μ = 0.04) and the swelling (0°, μ = 0.25) induced by ATP and, to a lesser extent, over-all fibrillar ATP-ase activity (the initial fast phase being depressed more than the slower second phase of the reaction). on storage (at — 20° to + 37°), pH and water-binding capacity increased generally with increase of temperature. Changes in pH occurred earlier with pork and to a greater extent than with beef. in sterile beef longissimus dorsi (irradiated or unirradiated) there was a decrease in soluble protein during storage for 60–90 days at 37° (indicating denaturation) and increases in TCA-soluble nitrogen and tyrosine (indicating proteolysis, which was more marked in unirradiated samples). the absence of soluble hydroxyproline and the presence of clearly marked cross-striations indicated that the autolysis must have involved sarcoplasmic and not fibrillar or connective tissue protein.