Effect of freezing and ageing time on shear force and sensory quality in beef meat

The eating satisfaction of beef meat is the result from the interaction between tenderness, juiciness and flavor, with tenderness as the most important trait (Koohmaraie, 2002). It has been found that freezing causes several physico-chemical changes in meat that lead to a worsening in organoleptic quality (Ngapo et al., 1999). This deterioration is one reason for the reduced acceptability of frozen meat by consumers (Farouk et al., 2003).

In this study nine young bulls of the Swedish Holstein breed were used. Both Longissimus dorsi (LD) from each animal were analyzed. Both LD muscles were cut in four pieces, vacuum packed and stored at 4° C for 2, 7, 14 days, day 0 being the day of slaughter. At each time one sample from each animal was split into two parts and one was cooked to measure water holding capacity and shear force, and the other one was frozen at -20° C to be analyzed later. Shear force was measured with a Warner-Bratzler shear force method. Sensory analyses were performed either with a trained panel and with a consumer panel.

Instrumental measurements indicate that both freezing and ageing time influenced meat Warner Bratzler Shear Force (WBSF) values and Water Holding Capacity (WHC).
The frozen samples had significantly lower WBSF values (P<0.01) than the chilled samples for beef LD aged 2 and 7 days post mortem. Samples frozen and thawed before cooking had higher water loss (P<0.001) at 2 and 7 days post mortem.
In samples with different ageing time WBSF values declined over time (P<0.01) indicating a higher tenderness with longer storage. Water loss was the highest in meat aged for 7 days.
According to the sensory panel, the chilled meat obtained higher sensory score for all of the tree parameters judged; tenderness (P<0.05) juiciness (P<0.01) and meat taste (P<0.01). The consumer test showed that the chilled and frozen meat did not differ significantly (P=0.25).
Results show that meat that was frozen and then thawed is more tender according to shear force measurements but is not perceived as more tender by sensory panel.