Evaluation of objective beef juiciness measurments techniques and their relationship to subjective taste panel juiciness ratings

Abstract

The objectives of this study were to develop an objective juiciness measurement technique that could be used simultaneously with current objective tenderness evaluation procedures and evaluate juiciness differences in varying treatments of beef strip loins. To accomplish this, treatments were selected to maximize variation in juiciness and included: USDA Prime, upper 2/3 Choice (Top Choice), lower 1/3 Choice (Low Choice), Select, and Standard as well as two enhanced USDA Select treatments [injected to 112% (Select High Enhanced) and 107% (Select Low Enhanced) of raw weight with a water, salt, and alkaline phosphate solution]. After aging (21 d), strip loins were cut into 2.5-cm thick steaks and frozen (-20°C) prior to subsequent analyses. Steaks for sensory and cooked analyses were cooked to three degrees of doneness (DOD) [rare (60°C), medium (71°C), and well-done (77°C)] to create additional juiciness variation. Several objective measures of juiciness were evaluated on both raw and cooked samples. Instrumental techniques evaluated on raw samples included: marbling, pH, L*, a*, and b* values, percent fat, moisture, and protein, drip loss, expressible moisture, water holding capacity, Carver press compression values, water activity, and water binding ability or protein swelling. Cooked techniques evaluated included: cook loss, drip loss, expressible moisture, Carver press compression values, pressed juice percentage (PJP), and fat percentage in expressed PJP fluid (FE). The PJP method was a compression-based juiciness evaluation method developed to allow for juiciness testing from the steak portion remaining after slice shear force (SSF) sample removal. For subjective juiciness ratings, steaks were evaluated by a seven member trained sensory panel for initial juiciness (TI) and sustained juiciness (TS). Moreover, consumers (n = 252) evaluated samples of their preferred DOD from each treatment for juiciness (CJ) and juiciness acceptability. Correlation analyses were used to identify and quantify relationships among instrumental measurements and CJ, TI, and TS. Of the objective measures evaluated, aside from cook loss, the strongest correlation (P < 0.05) with sensory ratings occurred between PJP and CJ (r = 0.45), TI (r = 0.69) and TS (r = 0.67). Also, FE was positively correlated (P < 0.05) with CJ (r = 0.39), TI (r = 0.34) and TS (r = 0.37). Cook loss had the highest correlation (P < 0.05) with CJ (r = -0.51), TI (r = -0.75) and TS (r = -0.73). However, cook loss was measured on the steaks evaluated by sensory panelists, whereas PJP and FE were measured on a steak cooked at a different time and used only for cooked objective measurements. Regression analysis indicated TI was explained (P < 0.05) by the equation: TI = -11.46 + 2.91 × PJP (R2 = 0.48). The equation TS = -18.10 + 2.94 × PJP explained 45% of the variation in TS (P < 0.05) and CJ was predicted by the equation CJ = 31.21 + 1.50 × PJP (R2 = 0.20).