Over the last decade, a great deal of research has been done investigating how diet manipulation influences pork quality.  Most studies, regardless of dietary treatments, show that increasing the mono and polyunsaturated fatty acid ratios in carcass fat will result in decreasing pork fat quality.  In the pork industry, fat quality is generally expressed in terms of iodine value.  While not all studies calculate an iodine value, it has been demonstrated it is possible to use a variety of feed sources and feeding methods to attain similar iodine values.  Most commonly, the location of the feeding operation dictates the economics of what feed ingredients are included in the diet, meaning that iodine values will always be a source of variation.  Commercial diet manipulations will always be at the mercy of economics and least cost formulation of swine diets.  Diet manipulation/substitution has occurred off and on over the last decade because dried distillers grains with solubles have been used in diet formulations to reduce costs when they are cheaper than traditional feed stuffs.  Thus, it is a reasonable expectation that variation in iodine value and pork quality will continue to occur in the future due to the changing economics of diet formulation.

 Due to observed variation in carcass iodine values it would be beneficial to investigate ways to manage incoming fat quality.  This is especially important for belly processing as bellies contain compositionally high amounts of fat that has been shown in literature to vary in fatty acid composition.  A concept that is often forgotten in bacon quality literature is the fact that not all bacon is manufactured and stored under traditional retail vacuum storage conditions.  Bacon is inherently prone to oxidation due to its high fat content, low nitrite content, and high salt content.  These properties when combined with freezing and oxygen exposure, which are  known pro-oxidants, could potentially be a source of concern when bacon is packaged using an aerobic format such as bulk packaging schemes currently utilized for food service applications.  Food service or Hotel, Restaurant, and Institutional (HRI) bacon is typically frozen and bulk packaged under atmospheric oxygen containing systems (non-vacuum).  The management of lipid oxidation is undoubtedly much more challenging when utilizing a frozen, aerobic packaging environment compared to vacuum packaged retail bacon.  As a result, no literature exists documenting how lipid oxidation promoters such as freezing and aerobic packaging impact the shelf life of products that have different iodine values.  Therefore, the main objective of this study was to determine the shelf life characteristics of bacon slices from bellies with different iodine values that are aerobically and anaerobically packaged during extended frozen storage.  A secondary objective was to evaluate how bacon morphology differs from bellies with different iodine values.

This study was conducted in a commercial swine harvest facility, where NitFom™ technology (Near-Infrared-Transmission spectroscopy) was used to identify the iodine value of pork carcasses for Low, Intermediate, and High iodine value categories.  The iodine value sampling site was taken over the shoulder of the carcass and confirmed in plant using fat cores from the same location using a benchtop Near Infrared Reflectance (NIR) unit.  Bellies were selected from 72 carcasses with 24 carcasses representing each of three iodine value categories representing a Low, Intermediate, and High iodine value.  The Low iodine value population had an average NitFom™ iodine value of 64.9, Intermediate an average iodine value of 70.5, and High an average iodine value of 76.5.  After chilling, bellies were removed from the carcass and shipped to a commercial plant to be processed into bacon.  After slicing, bacon slices were packaged and shipped to the Kansas State University Meat Laboratory to be packaged in either vacuum or aerobic bulk food service packaging in a multiple sheet layout.  The samples were then stored at 0 ºF and evaluated at day 0, 28, 56, 70, 84, 98, 112, 126, 140, and 154 for color and lipid oxidation.
 Belly measurements were recorded for thickness, length and width.  Additionally, belly firmness was measured using the belly “bend” test.  Bacon was analyzed for pH, instrumental fat color, proximate composition, fatty acid composition, oxidative rancidity, collagen content, fat cell size and fat cell number.
 It was possible to sort carcasses into Low, Intermediate, and High iodine value categories utilizing NitFom™ technology.  However, the resulting composite iodine values for bacon samples analyzed using gas chromatography showed that the High iodine value was the only iodine value group that was shown to be statistically different when compared to the Intermediate and Low iodine value groups.  However, this did not prevent the detection of belly firmness differences between the categories.  As expected, objective firmness measurements displayed a decrease in belly firmness as the iodine value increased.  Belly dimensions (length, width, and thickness) did not differ between the iodine value categories.
 Bacon from the High, Intermediate, and Low iodine value treatments did not statistically differ in proximate composition (fat, moisture, and protein) or pH.  As expected, bacon from the High iodine value category had higher percentages of linoleic, linolenic, and total polyunsaturated fatty acids compared to the other two iodine value categories.  Also, bacon from the Low iodine value category was higher in the percentages of myristic, palmitic, stearic, and total saturated fatty acids compared to the High iodine value treatment.

Iodine value had minimal impact on fat color or lipid oxidation in both the vacuum packaged samples and the aerobically bulk packaged samples.  The one exception with regards to iodine value was that fat from the Low iodine value category was lighter in color than fat from the Intermediate and High iodine value categories regardless of storage length.  This would indicate that as iodine values increase, bacon fat becomes darker in color.  Color was most affected by packaging scheme, as aerobically bulk packaged HRI products had lighter and less red fat color. 
Lipid oxidation was significantly higher in aerobically packaged samples indicating much higher concentrations of lipid degradation by-products compared to vacuum packaged samples.  In fact, all iodine value levels packaged aerobically were much higher in lipid degradation products than vacuum packaged samples after just 28 days of frozen storage.  Additionally, most of the oxidation that occurred over the 154 day shelf life occurred in the first 28 days of frozen storage for the aerobically packaged treatments.  Bacon fat color also became more yellow with increased storage length for the aerobically packaged samples regardless of iodine value category.  Surprisingly, there was no difference in oxidation between iodine value categories within each packaging treatment.

The size of the fat cells and the total count of fat cells did not statistically differ between iodine value categories.  However, the soluble, insoluble, and total collagen contents were higher in the High iodine value category than in the Intermediate or Low iodine value categories.  The observed increase in collagen in the High iodine value group may give us insight into potential issues with bacon slice-ability as collagen is well known to be the most important component of meat tenderness.

 In summary, the NitFom™ technology was able to sort belly quality via carcass iodine value.  Iodine value did not dramatically affect quality parameters associated with vacuum packaged or aerobically, bulk packaged bacon.  Lipid oxidation dramatically increased after only 28 days of frozen storage for the aerobically packaged HRI style bacon compared to vacuum packaged bacon.  The fat histology was not significantly affected by belly iodine value.  Finally, it appears that collagen content of bacon fat increases as the iodine value increases.  This increase in collagen content may have an effect on bacon slicing yields.

 This study is the first to demonstrate that there are serious quality considerations pertaining to lipid oxidation to be considered when bulk HRI packaging systems are to be used for extended frozen storage periods.  Lipid oxidation of fat results in increased off-flavors by bacon consumers.  Therefore, it would be prudent to further study the effects of increased lipid oxidation on sensory traits of bacon packaged in aerobic packaging formats.  It may also be fruitful to determine ways to increase bacon fat stability for food service applications by either adding additional antioxidants or possibly changing manufacturing/packaging methods.  Finally, increases in collagen content due to elevated iodine values should be investigated due to their potential impact on bacon slicing yields.
For more information about the project please contact Terry A. Houser Ph.D., Associate Professor of Meat Science in the Department of Animal Sciences and Industry at Kansas State University.

Terry A. Houser Ph.D.
Associate Professor/Meat Science
224 Weber Hall
Manhattan, KS 66506
Phone 785-532-1253""
E-mail: [email protected]