Characteristics of Ham Knuckles and Bacon Cured Using Different Brine and Meat Temperatures

Experimental design.

Two experiments were conducted to test the effect of 1) brine temperature and 2) brine and meat temperature, on processing yields and cured ham knuckle quality. In the first Experiment, 2 replicate blocks of 51 and 60 pork knuckles (North American Meat Processors Association [NAMP], 2010; #403H Pork Leg, Tip) were used in a randomized complete block design, to test the effect of brine temperature on processing yields and quality of cured knuckles tempered to 4°C. In the first block knuckles were collected from pigs slaughtered and fabricated at the University of Illinois Meat Science Laboratory. Following fabrication, all knuckles were sealed in vacuum bags and stored in boxes at –29°C for approximately 70 d. Two days before processing, knuckles were removed from frozen storage and allowed to thaw at 4°C. Knuckles were assigned identification numbers, netted individually, weighed, and randomly allotted to 1 of 3 brine temperature treatments: 1) –1°C (Cold), 2) 7.2°C (Medium), or 3) 15°C (Warm), such that the mean weight of each treatment group was 1.28 kg. Procedures for the second block of experiment were the same as in first block, except that knuckles were sourced from a commercial abattoir, were not held in frozen storage, and were processed fresh. Between the 2 blocks, there were 37 replications per each of the 3 treatments (N_total = 111).

In the second experiment, 59 fresh pork knuckles (20 replicates for Cold/Cold and Medium/Medium treatments, 19 replicates for Warm/Warm treatment) were used in a completely randomized design experiment to test the effects of brine in conjunction with meat temperature on processing yields and cured knuckle quality. Frozen knuckles were removed from storage and allowed to thaw at 4°C for 48 h, after which knuckles were assigned identification numbers, netted, then individually weighed, and allotted to 1 of 3 brine temperature/meat temperature treatments using the same temperatures in the first experiment; 1) Cold/Cold, 2) Medium/Medium, and 3) Warm/Warm, such that the mean weights of each treatment were not statistically different.

After allotment to treatments, knuckles used in both experiments were allowed to equilibrate to a temperature equal to the targeted brine temperature associated with their respective treatment.

Cured knuckle processing.

For both ham knuckle experiments, a master batch of curing solution was formulated to deliver 1.81% sodium chloride, 0.40% sodium tripolyphosphate, 0.13% sugar (sucrose), 0.06% sodium erythorbate, 0.04% spices, and 0.018% sodium nitrite at a 30% pump-uptake. Knuckles were then allowed to drain for 30 min. Cure ingredients, not including nitrite, were mixed approximately 13 h prior to injection. The master batch was then divided into 3 equal aliquots of cure solution and allowed to equilibrate to their respective temperature treatments (–1°C, 7.2°C, and 15°C) for approximately 13 h and then the temperature was adjusted accordingly by either placing the brine in freezer (–29°C) or, by placing into the brine solution, a sealed plastic bag containing 82°C water. Brines were thoroughly agitated during temperature manipulation to ensure representative and accurate temperatures. Brine temperatures were verified using a hand-held digital thermometer (Big Red Water Resistant In-Line Pocket Thermometer; Bunzl Distribution USA, Inc; St. Louis, MO). Immediately before injection, sodium nitrite, in the form of Prague powder Powder (Sure Cure, Excalibur Seasoning Co. Ltd., Pekin, IL), was mixed into each aliquot.

For Experiment 1, knuckles were allowed to equilibrate to an internal temperature equal to processing facility ambient temperature (4°C) following the 48-h thawing period. In Experiment 2, knuckles were allowed to thaw at 4°C for 48-h, after which Cold/Cold knuckles (initial temperature = 4°C) were stored in a freezer (–29°C) for approximately 3-h, until mean internal temperature had reached –1°C; Medium/Medium knuckles remained at processing facility ambient temperature (4°C) for 3-h, and Warm/Warm knuckles were stored for 12-h at 15°C, until mean internal temperature had reached 15°C. All temperatures were verified using a hand-held digital probe thermometer (Big Red Water Resistant In-Line Pocket Thermometer; Bunzl Distribution USA, Inc; St. Louis, MO).

Prior to injection for both experiments, knuckles were weighed for an initial weight to account for purge loss, and individual knuckle temperature for Experiment 2 was recorded. Knuckles were then pumped with a multi-needle brine injector (Schroder Injector/Marinator model N50, Wolf-Tec Inc., Kingston, NY) to a targeted pump uptake of 30% of initial weight at a pressure of 2.2 Bar and 32 strokes per min using 3 mm needles. In both experiments, the Medium-brine treatment was injected first. All knuckles were passed through the injector twice, with a targeted brine uptake of 15% of initial green weight per pass through the injector, weighed immediately after injection and allowed to drain for 30 min. Cold and then Warm-brine treatments were injected following the Medium-brine treatment, using the same protocol. After the 30 min drain period, knuckles were weighed again to determine final cure pumped weight and pump uptake percentage was calculated: [(pumped weight – initial weight) / initial weight] × 100. After draining, knuckles were hung randomly on a smokehouse cart, and placed in the smokehouse for thermal processing (Table 1). Knuckles were cooked and smoked for 6 h and 30 min in an Alkar smokehouse (Model 1000; Alkar; Lodi, WI) to reach an internal temperature of 66.6°C. After thermal processing, knuckles were showered with cold water for 15 min then immediately weighed to determine hot cooked weight. Knuckles were then placed in a cooler and chilled at 2.2°C. When internal temperature reached approximately 7.2°C they were weighed to determine cooked and chilled weight. Evaporative chilling loss was calculated using the following equation: [(hot cooked wt – netted chilled wt) / (hot cooked wt)] × 100. Overall yield was calculated (with netting removed) using the following equation: (chilled wt / initial wt) × 100.

Cured ham knuckle color evaluation.

Knuckles were placed in numerical order and sliced in half for instrumental color evaluation using a Konica Minolta CR-400 Chroma Meter (Minolta Camera Company, Osaka, Japan; D65 light source, 0° observer, 8 mm aperture, white tile for calibration). The knuckles were placed cut surface side up and 4 measurements were collected working in a clockwise direction starting in the upper left of the knuckles cut surface, and the mean of the 4 readings were reported as cured L*, a*, and b*. Then, two 2.54-cm steaks for Experiment 1 were collected from the center of each knuckle. The first 2.54-cm steak was used for texture analysis and proximate composition, and the second 2.54-cm steak was used for sensory evaluation (for Experiment 1 only). Sensory evaluation was conducted only on ham knuckle steaks from Experiment 1, as the 15°C treatment from Experiment 2 may have posed a food safety risk.

One 2.54-cm steak for Experiment 2 was collected and used for texture analysis and proximate composition. Each sample was individually vacuum sealed, retaining identification, and stored at –40°C until further analyses.

Cured ham knuckle texture profile analysis.

Cured ham knuckle steaks were removed from refrigeration (4°C) and four 2.54-cm cores (representing 4 quadrants of the steak surface) were removed from each sample and compressed using a Texture Analyzer TA.HD Plus (Texture Technologies Corp., Scarsdale, NY/Stable Microsystems, Godalming, UK). A 5.08-cm diameter plate compressed each core in 2 consecutive cycles to 75% of the samples original height with 2 s intervals between cycles. Cycles are labeled as area of work 1 and area of work 2. The cross-head moved at a constant speed of 5 mm/s. A force-time curve was plotted. Hardness is the absolute peak force on the first down stroke, fracturability is the force at the first peak, springiness is a ratio of the area of work 2 by the area of work 1, cohesiveness is the ratio of the products original height, gumminess is calculated by multiplying hardness by cohesiveness, chewiness is calculated by multiplying gumminess by springiness, and finally resilience is measured on the withdrawal of the first compression. The values for the 4 cores were averaged and reported as hardness, fracturability, adhesiveness, springiness, cohesiveness, gumminess, chewiness, and resilience of each cured knuckle sample.

Cured ham knuckle proximate composition.

Proximate composition was determined by homogenizing cured knuckle samples, collected from steaks used for texture analysis, in a food processor (Cuisinart model CUI DFP-7BC, Cuisinart, East Windsor, NJ). Duplicate samples (10 g) of the homogenate were oven dried at 110°C for at least 24 h to determine moisture content. Extractable lipid content was determined by washing the dried sample multiple times in an azeotropic mixture of warm chloroform: methanol (4:1) using the protocol described by Novakofski et al. (1989). Initial weight, cooked weight, as well as cured knuckle moisture and extractable lipid did not differ among treatments, so protein fat-free was not determined.

Cured ham knuckle sensory evaluation.

Exempt status from the University of Illinois Institutional Review Board was not sought. However, sensory work for this experiment followed the World Medical Association Declaration of Helsinki (2013). Participation in the panels was voluntary. Panelists consented to participate in the research. The study involved minimal or no risk to the panelists as they consumed bacon samples that were inspected and deemed wholesome by the USDA-Food Safety and Inspection Service. Each panelist was informed that they were not obligated to consume any of the samples, should they choose. All panelist personal information was kept confidential.

Sensory evaluation was conducted on only Experiment 1 knuckles. Samples were thawed for at least 12 h at 4°C. Eleven panelists participated in training sessions for orientation to scale attributes prior to evaluation. Panelists rated attributes on a 15-cm line scale with anchors at 0, 7.5, and 15 cm, where 0 cm indicated not salty, not juicy, and rubbery texture and where 15 cm indicated very salty, very juicy, and mealy texture. Panelists were presented ham and hot dogs with various attributes prior to evaluation for training. A low sodium ham and a regular sodium ham were used to anchor for saltiness. A ham with natural juices and ham, water added, was used to anchor for juiciness. Low sodium hot dogs and beef hot dogs were assessed for mouthfeel. Panelists sampled the products, discussed their sensory attributes, and then established anchors based on the discussion.

For each sensory session, 6 of the 11 trained panelists were randomly selected to participate in sensory evaluations. Panelists were separated in individual booths with ambient temperature (21°C) and humidity, and red lighting. Panelists were provided apple juice and unsalted crackers as palate cleansers. Vacuum packaged ham knuckle steaks were heated in hot water (Hamilton Beach 4 Quart Slow Cooker, Hamilton Beach Brands, Inc., Model 33040Y) for 30 min. Samples were removed at random and cut into 1.75 cm × 2.54 cm pieces, placed on paper plates and served to panelists 1 at a time. There were 19 sensory sessions with at least 6 samples per session and treatments were balanced within each session. Panelist data was averaged for each sample.

Experimental design.

In Experiment 3, a randomized complete block design was used to test the effects of brine temperature on processing yields and sensory attributes of bacon. Sixty pork bellies (NAMP #409 Pork Belly, Skinless, left sides) were procured from a commercial abattoir, individually weighed and allotted to 1 of 3 brine temperature treatments: 1) –1°C (Cold), 2) 7.2°C (Medium), 3) 15°C (Warm) such that the mean initial belly weight of each treatment were not statistically different. Within treatment group, bellies were randomly allotted into 2 blocks. Block was defined as smokehouse cycle.

Bacon processing.

A master batch of curing solution was formulated to deliver 1.70% sodium chloride, 0.38% sodium tripolyphosphate, 0.13% sucrose, 0.055% sodium erythorbate, 0.04% spices, and 0.015% sodium nitrite at a targeted 10% pump uptake. Cure ingredients, not including nitrite, were mixed approximately 13 h prior to injection. The master batch was divided into 3 equal aliquots of cure solution similar to Experiments 1 and 2.

Bellies were weighed to determine initial weight, and pumped with a multi-needle brine injector (Schroder Injector/Marinator model N50, Wolf-Tec Inc., Kingston, NY) at a pressure of 2.2 Bar and 51 strokes per min using 3-mm needles. The Medium-brine treatment bellies were injected first. Bellies were weighed immediately after injection to determine pump weight and to calculate pump uptake: [(pumped weight – initial weight) / initial weight] × 100. Bellies were then hung randomly on a smoke cart using stainless steel belly combs. The Cold/Cold and then the Warm/Warm treatments were injected following the Medium/Medium treatment, using the same protocol as was used for the previously injected treatment. The injector was flushed with water (4°C) between treatments. Bellies were then placed in an Alkar smokehouse (Model 1000; Alkar; Lodi, WI) and cooked and smoked for 6 h and 17 min until the bacon had reached an internal temperature of 52.2°C (Table 2). After thermal processing, bellies were showered with cold water, then placed in a cooler and chilled at 2.2°C. When bellies had chilled for at least 24 h they were weighed to determine final cooked weight. Overall yield was calculated using the following equation: (chilled wt / initial wt) × 100.

Bacon slabs were sliced using a push-feed style Treif Puma slicer (Treif model 700 F, Oberlahr, Germany) and sliced to 4 mm thickness. Bacon was removed from the slicer and divided into 3 equal zones representing the blade end, center, and flank end. Two slices from the middle of each zone were collected and stored –4°C for proximate composition determination. An additional 3 slices were collected from the middle of each zone, vacuumed packaged, and stored at –4°C for sensory evaluation at a later date.

Bacon proximate composition.

Proximate composition was determined by first homogenizing 2 slices from each of the 3 zones in a food processor (Cuisinart model CUI DFP-7BC, Cuisinart, East Windsor, NJ). Duplicate 5-g samples of the homogenate were oven dried at 110°C for at least 24 h to determine moisture content. Extractable lipid content was determined by washing the dried sample multiple times in an azeotropic mixture of warm chloroform: methanol (4:1) using the protocol described by Novakofski et al. (1989).

Bacon sensory evaluation.

As with sensory evaluation of knuckles, exempt status was not sought from the University of Illinois Institutional Review Board. Administration of sensory evaluation protocols followed the World Medical Association Declaration of Helsinki (2013).

Prior to sensory evaluation, bacon samples were thawed for at least 12 h at 4°C. Eleven panelists participated in training sessions for orientation to scale attributes prior to evaluation. Panelists rated attributes on a 15-cm line scale with anchors at 0, 7.5, and 15 cm, where 0 cm indicated no saltiness, no flavor intensity, or no off-odor associated with lipid oxidation and 15 cm indicated very salty, very oxidized odor, or very oxidized flavor. During training, panelists were presented with low sodium ham to assess saltiness and oxidized vegetable oil to assess oxidized flavor intensity and odor intensity prior to evaluation.

For each session, 6 of the 11 trained panelists were randomly selected from the pool of available panelists. Panelists were separated in individual booths under ambient temperature, humidity, and under red light. Panelists were provided apple juice and unsalted crackers for palate cleansers and coffee grounds for olfactory cleanser. Eighteen bacon slices (3 from each sample) were placed on baking sheets and cooked at 177°C for 15 min in a convection oven (Southbend Model V-15, Fuquay-varina, NC). Cooked slices were allowed to cool for approximately 5 min and then cut into 2.54 cm pieces. Each panelist received 3 pieces in a plastic cup covered with a plastic lid. Samples were labeled with a sample code. There were 10 sensory sessions with at least 5 samples per session and treatments were balanced within each session.