Preparation of Samples and Experimental Design
Thirty-two hams (16 carcasses) were collected from pigs slaughtered at The Ohio State University Meat Laboratory. Samples (2.2 to 3.3 lb; 1 to 1.5 kg) were taken from the semimembranosus (SM) muscle of the hams, approximately three days after slaughter. All separable fat and visible connective tissue were removed from the SM muscle samples, which were then stored frozen at -9F (-32C) for seven days and thawed at 37 ± 2F (3 ± 1C) for forty-eight hours prior to use. Four pairs of SM muscle were randomly assigned to two groups (with nitrate and without nitrate). Group I was dry-cured with 1 oz/lb (62 g/kg) from meat of a mixture consisting of a ratio of 78.8% salt, 19.7% brown sugar, 1.2% sodium nitrate (resulting in 750 ppm of the meat block) and 0.3% sodium nitrite (resulting in 180 ppm of the meat block). Group 2 was cured with the same ingredients except no sodium nitrate was used. The curing mixture was evenly rubbed on the surface of the sample and the product was then tumbled at a speed of 12 revolutions per minute for a five hour continuous cycle. The samples were held in a cooler (37 ± 2F; 3 ± 1C) for seven days following tumbling. Before further processing the samples were again tumbled for one hour. The hams were pressed (348 lbs/sq in: 24.5 kg/sq cm) and shaped in a rectangular mold by using a Carver Laboratory Press, Model B (Fred S. Carver, Inc.), in order to produce a uniform, compact finished product. Samples were then cooked within the molds in a 350F (177C) oven to an internal temperature of 145F (63C).
The samples were stored in a cooler (37 ± 2F; 3 ± 1C) overnight and removed from the molds, placed in elastic nets, smoked, and dried (140F; 60C dry bulb, 32F; OC wet bulb) for six hours. Then, the samples were chilled in a cooler and coated with approximately 1 cm of lard. When the liquid lard was applied to the cold surface of the samples, it solidified gradually. The finished samples were wrapped in a plastic freezer bag (low gas permeability) and placed in a paperboard box and stored at 37 ± 2F (3 ± 1C) for zero, two, four, and six months, then evaluated.
Analytical Methods
The coating fat was removed by scraping with a knife and one quarter of each sample was ground through an 1/8 in. (3.17 mm) plate twice at 37 ± 2F (3 ± 1C) and analyzed for total aerobic plate counts, moisture, fat, protein, salt, residual nitrite, TBA values and pH. The grinder was washed with soapy water and wiped with 70% ethyl alcohol before use for each sample. The remaining sample () was cooked for taste panel evaluation. Moisture, crude fat, protein, salt, pH, and residual nitrite of the finished product were determined according to Ockerman (1985). After only six months of storage, the hams were trimmed to remove the mold growth before grinding for analysis.
The TBA values were determined according to Ockerman (1985). A "K" value of 7.29 was experimentally obtained and results were expressed as mg of malonaldehyde per kg of sample.
The pH of the hams was determined with a Beckman Expandomatic SS-2 pH meter after blending 10 g of meat with 100 ml distilled water for 1 min. (Ockerman, 1985).
Microbiological Counts
A 20 g meat sample was removed and mixed in a Stomacher (Model # 400, Dyratech Laboratory) with 180 ml of distilled water for two minutes. Total aerobic plate counts were made by using Tryptone Glucose Extract Agar (Difco). All plates were incubated at 37C for forty-eight hours.
Sensory Panel Evaluation
Samples were cooked in a 300F (149C) oven (General Hotel Supply Co.) to an internal temperature of 150F (66C). Samples (0.5 cm thick) were served warm to each of the eight trained members of the descriptive attribute panel. Panelists evaluated each sample for tenderness, color, dry-cured ham flavor, saltiness and overall acceptability, using a 10-point structured scale with 10 = extremely tender, dark, intense dry-cured ham flavor, salty, and likely acceptable.
Statistical Analysis
Data were analyzed by analysis of variance procedures of the Statistical Analysis System (SAS, 1979) and Maximum Likelihood General Purpose Program of Harvey (1977). Individual F-tests were used to determine the significance of nitrate, storage time and the interaction effects. Means were separated by the Duncan (1955) technique.