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Tenderness and Colour Variation in Beef Top Sirloin Steaks

22 September 2013

Beef top sirloin steaks are one of the most popular steaks served in restaurants and sold in retail outlets across the United States.

Beef top sirloin steaks are typically marketed at lower prices compared to the other steaks from the loin and rib primals because of palatability inconsistencies, especially in cooked beef tenderness.

Even though the variation in tenderness for top sirloin steaks has been reduced research has reported similar or greater shear force values, along with lower tenderness ratings, when compared to beef top loin and/or ribeye steaks.

However, a research team from the University of Arkansas said that little is known of the shear force value of the gluteus medius muscle.

The research team also have found that there are concerns over the colour stability of the gluteus medius muscle.

The study by Jason K. Apple, James B. Machete, Ryan J. Stackhouse, Tim M. Johnson, Cari A. Keys and Janeal W.S. Yancey set out to investigate the interactive effect of USDA quality and yield grades on instrumental colour and shear force variations within the gluteus medius muscle.

Beef top sirloin butts were selected at a large commercial slaughter facility based on USDA quality grade - upper 2/3, or top, USDA Choice with “modest” and “moderate” degrees of marbling or USDA Select with a “slight” degree of marbling - and USDA yield grades 1 and 2 or 4 and 5.

A total of 48 top sirloin butts from left carcase sides were captured during fabrication, vacuum-packaged, and transported under refrigeration to the University of Arkansas Red-Meat Abattoir for further processing.

Top sirloin butts were allowed to age at 2°C for 14 days from the box date before removal from vacuum-sealed packages.

Depth of the subcutaneous fat opposite the centre of the biceps femoris (rump fat) was measured with a metal ruler prior to removal of the biceps femoris and all overlying subcutaneous fat, as well as the gluteus intermedius and gluteus profundus.

Then, beginning at the posterior end of the resulting gluteus medius, eight 2.54-cm-thick steaks were hand-cut:

  1. first and second steaks designated as posterior (POST) steaks;
  2. third steak was discarded;
  3. fourth and fifth steaks designated at middle (MID) steaks;
  4. sixth steak was discarded; and
  5. seventh and eighth steaks were designated as anterior (ANT) steaks.

One steak from each location pair was randomly chosen, identified, vacuum-packaged in a 3 mil standard barrier nylon/polyethylene pouch, and frozen approximately six weeks at − 20 °C for Warner–Bratzler shear force (WBSF) determination.

Colour and tenderness of Sirloins study

The remaining steak from each location pair was further divided into three equal length intra-steak portions, designated as lateral (LAT), central (CENT) and medial (MED) portions.

An approximately 2-g sample of gluteus medius muscle was removed from each portion for pH measurement before steak portions were placed onto polystyrene foam trays (with absorbent pads) and over-wrapped with an oxygen-permeable, PVC film.

Subsequently, individually-packaged steak portions were placed in open-topped, coffin-chest display cases, maintained at an average temperature of 2.5°C, and displayed under continuous lighting (1,600 lx of deluxe, warm-white fluorescent lighting for seven days.

Temperature was monitored with an EV2 temperature logger and steaks were rotated daily.

The other steaks were then cooked at 71°C Warner–Bratzler shear force (WBSF) determination.

The study found that the Top Choice-steaks were redder and more yellow than Select steaks during display.

Cooking losses were greatest in the medial, and least in the central, portions of gluteus medius muscle steaks.

Neither the quality grade nor the yield grade category affected the Warner–Bratzler shear force, but differences within the gluteus medius muscle were found for WBSF.

The results indicate tenderness and colour stability gradients exist within the gluteus medius muscle.

The researchers said that the variation in fresh beef colour and discolouration within the gluteus medius muscle was minimal and likely not economically important.

However, tenderness variation within the gluteus medius muscle may have some potential for economic advantage.

Large muscles, such as the gluteus medius muscle, are often cut into smaller, more appropriately-portioned steaks for food service establishments and retail sale.

The study indicated that these steaks could be further segregated according to tenderness to optimise the eating experience of consumers.

Tougher sections of the gluteus medius muscle may need further processing with a tenderising marinade or a more tenderising cookery method.

They said that further research would be needed to determine how these variations in tenderness can be overcome with further processing steps, such as moist versus. dry cookery, end-point temperature optimisation, or ingredient addition.

September 2013

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