The residual nitrite (ppm) over time was similar for the nitrate and the no nitrate treatments for zero and two months, but the nitrate treatment had more nitrite at four and six months of storage. The residual nitrite was significantly affected (P<0.01) by both nitrate and storage time. The time was also significant (P<0.01).
After two months of storage, both groups decreased in the amount of residual nitrite. Woolford and Cassens (1977), Cassens et al. (1974), and Kemp et al. (1975) found decreased levels of nitrite in cured products with increased storage time. However, after four months of storage in the current study, the nitrate treated group increased in residual nitrite significantly (P<0.01) to 56 ppm. This suggests that nitrate had been reduced to nitrite by reducing microorganisms during this storage period. As would be expected, the group treated without nitrate decreased (P<0.05) in residual nitrite to 16 ppm. After six months of storage, both groups increase (P < 0.05) the residual nitrite to 129 and 27 ppm, respectively. The group treated with nitrate was expected to increase the residual nitrite level with increased storage time, since the nitrate added would continue to be reduced to nitrite as long as nitrate and the reducing microorganisms were present. The group without nitrate (containing only nitrite) had a vary slightly higher residual nitrite level at the six month sampling period. This is probably due to the trimming of the surface tissue of the hams because of mold growth. Cassens et al. (1974) reported nitrite may undergo auto-oxidation resulting in the formation of nitrate. Therefore, the interior tissue may contain more residual nitrite than the surface tissue which may had undergone more auto-oxidation.
The TBA values were not significantly affected (P>0.05) by nitrate. However, TBA values were significantly affected (P<0.01) by storage time. The interaction of nitrate x storage time was not significant.
In this research, all dry-cured hams were coated with approximately 0.4 in (l cm) lard, wrapped in a plastic bag and stored at 37±2F (3±1C) in a paperboard box. Under these conditions, most of the air would be excluded and this would help to retard oxidative rancidity. In addition, nitrite can also aid in retarding oxidation.
The TBA values in the fresh meat were 0.14. After four month of storage, TBA values had increased to 0.30; however, between four months and six months of storage, TBA values in both groups decreased. This is probably due to the trimming process of hams contaminated with molds after six months of storage. Also, the malonaldehyde already formed may break down to other compounds during the later stages of storage. The TBA values developed in the dry-cured hams during the entire storage time (6 months) were very low (less than 0.31).
The total aerobic plate counts (log 10) of the dry-cured hams were significantly (P<0.01) affected by time. However, they were not significantly affected by either nitrate nor the interaction of nitrate x storage time. Kemp et al. (1975) found that nitrate had no significant effect on the total aerobic plate counts in dry-cured sliced ham which was stored for one month at 34F (1C) and 75F (24C).
The log of the total aerobic plate counts in hams prior to processing was 4.5. The total aerobic plate counts in both groups decreased after processing. However, the microbial counts increased rapidly (P<0.01) with increased storage time up to four months. Between four and six months of storage, the total aerobic plate counts decreased in both groups. It is not clear whether the microbial growth phase has already passed the stationary phase and entered into the death phase at six months of storage under these conditions, or whether trimming of the surface tissue at six months decreased the number of microorganisms.
All hams were considered very acceptable after curing and at two months of storage; however, about one quarter of the hams analyzed were considered to be unacceptable by the taste panelists after four months of storage, due to the bacterial spoilage. All hams analyzed after six months of storage were unacceptable due primarily to mold flavor.
The elastic nets used to hang the hams during smoking were not removed before storage. The nets were not sterilized before use and may have contained some fungi spores or may have prevented smoke deposition and encouraged the accumulation of moisture adjacent to the nets during smoking and drying. Thus, the growth of molds would have been enhanced. In most cases, the molds first grew at the sides of the elastic nets. It is suggested that sterilized nets be used in future research or that they be removed before storage. Hams develop molds during aging at relative humidities above approximately 70% (Blumer, 1958). It is also suggested that the plastic film wrap be eliminated in future research to lower the relative humidity. Bullerman et al. (1969) reported that molds impart off-odor and off-flavor (malty-flavor) to the meat, and in large amounts, may produce aflatoxin. Mold growth can be greatly reduced but not completely inhibited by the use of potassium sorbate (Kemp et al. 1981).
Tenderness increased (P < 0.01) with storage time but was not effected by nitrate. The interaction of nitrate x storage time was also significant (P < 0.01).
Color scores were significantly affected (P < 0.01) by nitrate only. At zero time, the color scores of the group treated with nitrate were significantly darker (P < 0.01) than that of the group treated without nitrate, but at two, four and six months of storage, these groups were not significantly different in color. However, it is important to point out in this research the semimembranosus muscle was only used, and in a small size ham it is easy to distribute the curing ingredients evenly without aging.
Flavor, saltiness, and overall acceptability scores were not significantly affected by nitrate but were significantly (P < 0.01) affected by storage time. This suggested that aging may not have occurred as desired for the dry-cured hams in this experiment. After six months of storage, the dry-cured hams were not sensory acceptable. It is speculated that the plastic film prevented moisture loss, appropriate aging, lack of flavor development, and encouraged mold growth which produced the undesirable flavor. Kemp et al. (1979) reported no significant differences in general appearance and yield due to the presence or absence of nitrate indicating that nitrite alone is capable of producing a desired boneless dry-cured ham. Simon et al. (1973) also indicated that nitrate has no effect in cured flavor development in all meat frankfurters.
The percentage of water and fat were significantly affected (P < 0.05) by storage time (particularly after four months of storage), but not by either nitrate nor the interaction of nitrate x storage time. Protein and salt were not significantly affected by nitrate or storage time. In this research, the hams had the highest moisture content after six months of storage. This probably resulted from the trimming of the surface tissue of the hams which contain drier tissue than the interior.
Fat percentage was inversely related to water content. This is in agreement with the works of Ockerman (1985). Percentage of salt was inversely related to the percentage of water and this was probably also caused by trimming late in storage.
The pH of these two groups (with and without nitrate) slightly increased during two months of storage. The pH values of both groups significantly decreased (P < 0.01) after four months of storage. This decrease was probably due to lactic acid producing bacteria fermenting sucrose to lactic acid. Lactobacilli has been found to be one of the natural flora of dry-cured hams (Kemp et al., 1975). After six months of storage, the pH values of both groups (with and without nitrate) increased (P < 0.01) to 6.50 and 6.41, respectively. This is probably due to the decomposition of dead microbial cells to amines and ammonia which would cause an increase in pH values. These high pH values also indicated the off condition of the dry-cured hams. Butz et al. (1974) reported the pH of the dry-cured hams was 5.80 to 6.20. Graham and Blumer (1971b) cited that an average pH of 5.90 was reported in dry-cured hams aged between one and six months, but no significant changes in pH resulted during this period.
Residual nitrite was negatively correlated (P < 0.01) to fat as would be expected. Ockerman and Dowiercial (1980) reported high amounts of residual nitrite were found with higher lean content. The TBA values were positively correlated (P < 0.01) with fat content. This also would be expected, since fat is more apt to produce oxidative rancidity. Total plate counts (log 10) were positively correlated with water content (P < 0.01) and negatively correlated with salt content (P < 0.01), color (P < 0.01), flavor (P < 0.05) and overall acceptability (P < 0.01) Bartholomew and Blumer (1980b) reported hams with the fewest number of microorganis developed the best flavor. Water content is negatively correlated with fat content (P < 0.01) and salt content (P < 0.01) and positively correlated with tenderness (P < 0.01). Salt content was positively correlated with flavor (P < 0.05) and overall acceptability (P < 0.01). Bartholomew and Blumer (1980a) indicated the aged flavor of dry-cured hams was enhanced by increased salt levels. Overall acceptability was positively correlated with color (P < 0.05), flavor (P < 0.01), and saltiness (P < 0.01).