USE OF A RAPID MUSCLE PROTEIN SOLUBILITY TECHNIQUE TO PREDICT BEEF MUSCLE YIELD AS A FUNCTION OF TIME, TEMPERATURE, SALT AND PHOSPHATE

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Abstract
An improved muscle protein solubility method has been developed which has two distinct advantages over the traditional method: it requires much less time and may be conducted at room temperature. The pre‐ or post‐rigor sample is homogenized in a Brinkman Polytron in 25 ml buffer and is centrifuged. The supernatant is decanted and soluble protein determined as in the traditional method (biuret). Comparable results were obtained for old vs new method for samples of porcine longissimus muscle which encompassed a wide range of sarcoplasmic and myofibrillar protein solubilities. The new method can also be applied with accuracy equivalent to the traditional method for the determination of solubility in cooked meat samples. A four‐factor response surface experimental design (central composite) was utilized to evaluate the role of process variables and product ingredients on the cooking losses of USDA Utility grade biceps femoris muscle. The factors were cooking time (0.5–12.0 hr), temperature (55–85°C), NaCl (0–4%), and Na tripolyphosphate (0–0.5%):Shrink was determined on ground 25‐g samples by calculating the free moisture lost (as a percentage of total moisture) after centrifugation in Wierbicki tubes. Sarcoplasmic and myofibrillar protein solubility were determined on the same samples by the rapid solubility technique. Stepwise regression was used to tit a multiple polynomial equation to shrink loss and protein solubility (P < 0.001). The results indicated that cooking temperature was decisively the most important factor controlling yield and protein solubility. Shrink and protein solubility were nearly independent of time in the center point regions of the experiment which are, based on the type of design (central composite), the most accurate areas for prediction. Previous studies have demonstrated that the major tenderization reactions in beef are dependent both on time and temperature. Therefore, these findings suggest that improved yield in commercial thermal processes is possible by selecting long‐time, low‐temperature treatments since protein solubility and, therefore, yield are primarily functions of temperature and are relatively independent of time at a given temperature.