Antioxidant properties of liquid smoke in precooked beef patties Antioxidant properties of liquid smoke in precooked beef patties

Liquid smoke (LS) effectiveness in controlling lipid oxidation and warmed-over flavor (WOF) in beef was investigat ed. Aroma scores, " -thiobarbituri c acid (TBA) numbers, and pH values were lower (P<.05) in LS-treated beef patties than in patties wit hout LS. LS has useful antioxidativ e properties in precooked ground beef patties at the normally recommended percentage of 1.5%. That should reduce undesirabl e flavor development and product loss.


Introduction
Grou nd beef, in addition to food safety concerns, i s susceptible to developing warmedover flavor (oxidative rancidity).Although WOF can develop in fresh meat, it most commonly occurs in meats t hat are cooked or in which the cellular membranes are broken by processes such as restructuring or grinding.Antioxidant s can effectively control or retard lipid oxidation in meat products.Smokin g of food, an effective antioxidant process , contributes substantially to preservation.
Like natural smoke, liquid smoke solutions act as antioxidants, primarily because of phenol compounds.They prevent fat oxidatio n by stabilizing free radicals and are effectiv e in retarding or preventing the developmen t of oxidative off-flavors.Our objectiv e was to evaluate the antioxidative properties of liquid smoke (LS) when used at the normally recommende d level in precooked beef patties.

Experimental Procedures
Nine kg of fresh beef gooseneck round (2 weeks old), ground successiv e ly through 1/2 in., 3/16 in., and 1/8 in.plates, was formulated to yield 20% fat.One half of the meat block was treate d with 1.5% LS, and the other half was used as a control.The treatm ent and the control each were blended in a mixer for 2 min.The ground beef was made into 1/4 lb patties (1/2 in.thick), using a patty machine (Hollymatic Corp., Countryside, IL).The study was repeated three times.
Patties were coo ked according to American Meat Science Association (AMSA) Cookery Guidelines on a preheated (32 5EF) electric skillet to 16 0EF internally.To obtain uniform heat distribution, pattie s were turned every 1.5 min.After 4.5 min of cooking, patties were turned every 30 sec.Individual patties were remo ved when they reached 155 to 16 0EF, monitored by a needle probe connected to a temperatur e recorder.Patties were packaged individuall y aerobically in heat-sealed plastic bags and immediately frozen at 5EF.Patties evaluated on day 0 were not frozen.
A five-member, sensory panel from the KSU Department of Animal Sciences and Industry evaluated WOF intensity of the beef patties.Frozen precooked beef patties were thawe d at 40EF for 24 hr.Samples were reheated to an internal temperature of 16 0 EF and kept warm in an oven.Taste panel evaluations were made on 1/4 patty portions that were reheated and placed in glass petri dishes.Panelists used a 5-point scale ( 1 = no, 2 = slight, 3 = moderate, 4 = very, and 5 = extreme WOF).Five sensory sessions (0, 30, 60, 75, and 90 days) were held in individual booths with combine d red and green light and free from outside noise and odor.Patties were evaluated immediatel y following presentation and again after 15 min of cooling.Twelve samples (4 samples/ replicate) were presented at each session.TBA was determined as a measure of fat rancidity.
Measurement s of pH were taken from duplicat e thawed cooked beef patties at each time of evaluation.Ten g of sample and 40 ml of deionized distilled water were combined in a stomacher bag and blende d for 1 min before pH was measured.

Results and Discussion
Liquid smoke treated b eef patties had lower (P<.05)aro ma scores (less warmed over) compared to nontreated beef patties, both immediately after warming and after 15 min of cooling.The aroma of LS-treated beef patties evaluated immediately afte r presentation did not change (P>.05) from da y 0 to day 90 (data not shown).Aroma scores for nontreated beef patties evaluate d immediately after presentation increase d after day 0 and again after day 60.Aroma scores for beef patties after a 15-min cooling period were similar to the scores obtaine d immediately after presentation.However , aroma scores for LS-treated beef patties after the 15 min cooling increased (P<.05) b y day 90.Some panelists gave higher scores to cold samples.
The TBA numbers were lower (P<.05) from LS-tr eated beef patties than from controls on all sampling days (Figure 1) .The TBA numbers clearly demonstrated that 1.5% LS in precooke d beef patties possessed antioxidative properties.The TBA values for untreated precooke d beef patties increase d during the initial 60 days of froze n storage, then decreased by 75 days, and incre ased again at 90 days.The TBA values for treated precooked beef patties decreased (P<.05) during the first 30 days, then increased , but decreased again after 60 days.The increase and/or decrease in TBA values at different storage times could be explained by the instability of the malonaldehyde produced and/or by the oxidation and further breakdown of different lipid populations at different times.The correlation coefficient between TBA numbers and WOF intensity scores was 0.84 (P<.05).Hence, TBA and aroma results were very similar.
The pHs of precooked beef pat t ies before (0 day) and after days 30, 60, 75, and 90 are shown in F igure 2. The pH was higher (P<.05) in control than in LS-treated pattie s at all sampling days.These results were expected, because the pH of th e LS was 2.0.Higher meat pH has the disadvantage of causing longer cookin g time and/or higher final internal temperatur e required for complete protein denaturation.Thus, a high pH inhibits formation of brown cooked meat color.A l so, muscle with higher pH is more susceptible to microbial problems .Conversely, oxidation of meat pigment is favored by lower pH.