EFFECTS OF GENETICS, CHILLING RATE AND COOKING METHODOLOGY, ON HAM QUALITY. A Thesis

Transcription

1 EFFECTS OF GENETICS, CHILLING RATE AND COOKING METHODOLOGY, ON HAM QUALITY A Thesis Presented in Partial Fulfillment of the Requirements for the Degree of Master of Science in the Graduate School of The Ohio State University By Alexandra Stengel Gress, BS Graduate Program in Animal Sciences ***** The Ohio State University 2012 Thesis Committee: Dr. Henry N. Zerby, Adviser Dr. Steven J. Moeller, Co-Adviser Dr. Francis L. Fluharty ii

2 Copyright by Alexandra Stengel Gress 2012 iii

3 ABSTRACT Two experiments, using 24 purebred Berkshires and 12 commercial crossbred pigs were conducted to evaluate the influence of fresh meat quality found in Berkshire hams with commodity hams, the influence of an early-postmortem, rapid chilling method, and the influence of cooking methodology on the processing yields, cooked color, and texture profile of cured cooked hams. The pigs were harvested at The Ohio State University Meat Science Laboratory. Experiment 1 used a 2 x 2 factorial design to evaluate chilling method and cooking method on resulting cooked ham characteristics. Left hams from the carcasses were assigned randomly to one of the two chilling methods (rapid vs. standard), and the right am was then assigned to the other chilling method. Internal ham temperature was recorded at 0, 2, 4, 8, and 12 h during the postmortem chilling process. An ultimate ph was recorded for both the Semimembranosus and the Biceps femoris muscles at approximately 24 h postmortem. Two measurements were taken in the Semimembranosus and Biceps femoris, lateral and medial, from which the Ham ph was comprised. Hams were injected (target of 125% green weight), macerated, tumbled, and netted. Then half of the hams from each of the two chill methods were assigned to each of the cooking methods (Traditional or Delta-T cooking method) balancing for equal number of left and right side across all treatments. Experiment 2 used a 2 x 2 factorial design to evaluate Berkshire hams vs. commodity hams and cooking method on resulting ii

4 cooked ham characteristics. All hams were chilled using the standard chill protocol from Experiment 1. Hams were processed and cooked following the procedures used in Experiment 1. In both experiments, pump yield ((green weight / pump weight) x 100), cook yield ((post-cook weight / netted weight) x 100), total yield ((24 h chill weight / green weight) x100) and post-cook weight and 24 h chill yields were measured. A 2.54 cm thick center slice was removed from each cooked ham to collect L*, a*, and b* values and a series of objective texture analysis measures (Warner-Bratzler shear force, hardness, cohesiveness, resilience, and springiness). There were no significant interactions between chill method and cook method in Experiment 1 or between fresh ham source (Berkshire or commodity) and cook method in Experiment 2. Therefore, results for chill method and fresh ham source were analyzed using the 48 hams within Experiment 1 and Experiment 2, respectively, and cook method was analyzed using the pooled results of from both Experiment 1 and Experiment 2. The temperature least squares means of hams subjected to the rapid chill treatment were numerically 0.65, 1.80, 3.11, and 3.09 C less than those of the normal chill at 2, 4, 8, and 12 h, respectively, however, only the difference at 4 h was significantly different (P < 0.05). The rapid chill method did not result in any differences (P > 0.05) in cooked ham characteristics. Commodity type hams from the commercial pigs had a greater (P < 0.05) trimmed green weight compared to Berkshire hams (7.9 vs. 7.3 kg, respectively). Berkshire hams had a 2.5% greater (24.7% vs. 22.3%; P < 0.05) pump yield than the commodity hams, however, there were no differences (P > 0.05) in cook yield (83.3% vs. 83.6%). Berkshire hams produced a greater (P < 0.05; 3.9%) total yield. There were no iii

5 significant differences in cooked ham slice color, however, ham slices from Berkshire pigs had a more desirable (P < 0.05) Warner-Bratzler shear force (1.71 vs kg) and significantly greater (5.6%) springiness. The hams that were cooked using the Delta-T cooking methodology had a 2.3% greater (P < 0.05) cook yield than hams cooked using the traditional method, however there was no difference (P > 0.05) between cooking methods for total yield. The results for cooked ham slices from the Delta-T method were similar to those cooked via the standard method with the exception of Delta-T Slices having a lower (P < 0.05) a* value (redness; 15.5 vs. 16.2) and greater cohesiveness (3.51 vs. 3.37). iv

6 Dedicated to my family v

7 ACKNOWLEDGEMENTS While attending graduate school here at The Ohio State University, many friendships have been formed within the department and with fellow graduate students. Thank you to all Animal Science faculty and staff, student laboratory workers, and graduate students who helped along the way collecting project data, working in the meat laboratory, or by just giving support, listening, and sharing their advice. The friendship and guidance from all has been greatly appreciated and respected. Recognition to Dr. Henry N. Zerby is owed for his encouragement towards my graduate degree and also his encouragement towards other opportunities at Ohio State. His energy and excitement for teaching helped shape my knowledge and sparked a desire to learn more about the meat industry. A special thank you is owed for his help with my research and guidance to finish my Master s degree. With great appreciation, Dr. Steven J. Moeller goes above and beyond to be helpful and was an important part of my research. Dr. Moeller helped improve my critical thinking skills, as well as, instill a strong work ethic within the meat science laboratory. Lastly, I owe a thank you to my friends and family. I would not be where I am today without their love and support. vi

8 VITA September 26, Born Ashtabula, Ohio Bachelors of Science Degree The Ohio State University Program Assistant, Animal Science Dept. The Ohio State University 2010-Present... Graduate Teaching and Research Associate The Ohio State University FIELD OF STUDY Major Field: Animal Sciences Discipline: Meat Science vii

9 TABLE OF CONTENTS Abstract... ii Dedication...v Acknowledgements... vi Vita... vii List of Tables...x List of Figures... xi Chapters: 1. Introduction Review of Literature...4 Cooked Ham...5 Meat and Non-meat Ingredients...6 Raw Material...6 Non-Meat Ingredients...12 Texture Profile Analysis...17 Chilling Methodology...19 Cooking Methodology...22 ΔT/Differential Materials and Methods...28 Experiment viii

10 Experiment Experiment Results and Discussion Conclusion...46 References...48 ix

11 LIST OF TABLES Table Page 1. Changes in Market Hog Performance Productivity Measures of U.S. Pork Industry Breed Characteristics Meat quality characteristics in different types of pig breeds Effect of different cooking methods on the physical properties of pork ham Composition of Brine Injected into Fresh Pork Legs Traditional and Delta-T Cooking Methodology Effect of chilling methodology on measurements of ham quality for hams derived from purebred Berkshire pigs Least squares means for fresh ham characteristics, ham processing yields, and cooked ham slice objective sensory measures by genetic source Least squares means for fresh ham characteristics, ham processing yields, and cooked ham slice objective sensory measures by cooking methodology Phenotypic (above diagonal) and partial (below diagonal) correlations among ham characteristics for hams derived from Berkshire pigs Phenotypic (above diagonal) and partial (below diagonal) correlations among ham characteristics for hams derived from Berkshire and commercial crossbred genetic types...45 x

12 LIST OF FIGURES Figure Page 1. A generalized texture profile analysis curve from the Instron Universal Testing Machine Heating and cooling profiles, as measured by temperature in the center of the ham, through cooking with Δ T method Post-mortem temperature decline between normal and rapid chill...40 xi

13 CHAPTER 1 INTRODUCTION According to Honeyman et al. (2006) niche products claim differentiation from commodity pork in two general ways: superior or unique product quality, and social or credence attributes. Pork quality can be defined as measures of muscle ph, water holding capacity, intramuscular fat, and tenderness. All of these parameters influence palatability where generally speaking a higher ph, higher water holding capacity, and more intramuscular fat is considered desirable. The social or credence attributes refer to aspects of the production system such as, reared without antibiotics, pasture raised, and natural. Several Heritage breeds of pigs, such as Berkshire maintain a leading role in pork quality. Berkshire pork has been known for excelling in juiciness, flavor, and tenderness. Goodwin (2004) presented data from the National Barrow Show that looked at progeny tests from purebred pigs from 1991 to Goodwin reported that Berkshire pork had a more desirable ultimate ph, color, and the lowest percentage of cooking loss; resulting in the juiciest and most tender product across all major breeds. Japanese consumers have long recognized the consistent high quality and value of Berkshire ( kurobuta ) pork which has created a niche market that allows producers to receive higher premiums for products that qualify to be labeled and marketed as Berkshire pork. The ham, or fresh leg, of a pig poses unique challenges during post-mortem processing. The recent trend in 1

14 selecting larger and heavier muscled pigs, can lead to greater ham weights which in turn leads to slower chilling within the ham muscles. This slower chilling rate can lead to lower fresh ham muscle quality and protein functionality resulting in detrimental impacts on cooked product quality. Rapid post-mortem chilling has been studied as a solution to reduce internal muscle temperature of pork carcasses with the intention of managing postmortem metabolism, mainly by slowing the rate ph decline to avoid excessive protein denaturation, thus, reducing moisture loss, and improving color in pork. Ohene- Adjei et al. (2002) reported that accelerated chill resulted in a lower (P < 0.05) percentage of drip loss in ham muscles. Maribo et al. (1998) reported that the lowering of muscle temperature early postmortem resulted in a reduced rate of ph decline and a higher ph when using cold water showering on split pork carcasses. Tenderness is consistently regarded as one of the most important palatability traits in meat products. Recently, some specialty niche products have focused on a cooking methodology know as Delta-T (Δ T) to create a product with a more desirable texture profile (including tenderness) in final product. Delta-T heats the product in stages, where the internal temperature of the product regulates the temperature of the outside cooking environment. So, the internal temperature of the product and the temperature in the cooking apparatus are within a fixed temperature range (e.g. 25 to 30 C), thus, cooking the product more slowly when compared to conventional methods. In the case of hams, this process avoids excessive heating of the ham surface. It has also been suggested that the slow heating rate forms a protein network that results in improved water binding and less jelly losses compared to traditional cooking methods (Toldra, 2007), which in turn, 2

15 leads to less cooking loss, a more tender product, and better slice cohesion (Desmond and Kenny, 2005). This research project focused on producing a brine-cured specialty cooked ham that would target up-scale niche markets. Experiment 1 focused on hams from purebred Berkshire pigs, which are known to provide flavorful, juicy pork products. Within the Berkshire sourced hams the intent was to assess both cooking methodology and the influence of postmortem chill rate on subsequent measures of ham quality. A second experiment compared Berkshire sourced hams with a standard, commodity ham sourced from ¼ Yorkshire x ¼ Landrace x ½ terminal sired pigs. Experiment 2 also evaluated the Δ-T cooking method with that of a normal cook method. The specific objectives of this study were: 1) assess the effect of a rapid chill method, when compared with a standard chill method on ultimate ph, processing yields, cooked ham slice color, and the texture profile of cooked ham slices; 2) compare fresh ham quality and textural characteristics of hams derived from purebred Berkshire pigs compared with commodity type hams from a commercial genetic source on ultimate ph, processing yields, cooked ham slice color, and the texture profile of cooked ham slices; and 3) investigate the influence of Delta-T versus that of the traditional cooking method on cooking yields, cooked ham slice color, and the texture profile of cooked ham slices. 3

16 CHAPTER 2 REVIEW OF LITERATURE Annual US consumption of animal protein has steadily increased since 1960, and today, US per capita consumption of meat and poultry exceeds 230 pounds, with pork accounting for approximately 50 pounds per year (National Pork Board, 2009). According to data by the USDA Foreign Agricultural Service (2008), pork accounts for approximately 40 percent of animal protein intake worldwide, making it the world s most widely consumed meat animal protein source. Meat consumption is generally categorized as fresh or processed. Fresh products are muscle cuts sold to consumers that are cooked just before eating, while processed products can be transformed by grinding, curing, injecting, smoking, seasoning, drying, or even cooking prior to retail sale. In 2009 the National Pork Board reported that Americans consume approximately 21 percent fresh pork and 79 percent processed pork, indicating that further processed meat is a major component of the pork industry. The 79 percent of processed products consumed in-home includes products such as ham, sausage, and bacon, but does not include hot dogs. The National Pork Board also reported that ham, either as a main entrée or lunchmeat, was the overall most consumed pork product, which account for 31% of pork consumed in-home. Hams can take the form of a fresh ham, cured, cured-and-smoked, dry-cured, ready-to-eat (fully cooked hams, canned and prosciutto), luncheon and deli ham. Sebranek (2009) 4

17 reported that the curing of meat is an ancient process with evidence of cured products dating back to 3,000 B.C. Many different processes and techniques are found from region-to-region throughout the world to cure hams; including variations in the raw material, non-meat ingredients, and processing steps. Further processing of ham adds value, diversity, and convenience to the product, while enhancing product wholesomeness and helping to deliver a more satisfactory eating experience to the consumer. Factors affecting the final ham quality are focused on the raw material, type and amount of non-meat ingredients, volume of brine injected, rate and extent of tumbling, and the cooking time and temperature (Toldra, 2010). The raw material can be influenced by differences across breeds of pigs, which in turn, affects the percentage of intramuscular fat, color, ultimate ph, and water holding capacity. Fresh ham quality can also be influenced by rate and extent of postmortem metabolism which directly influences protein functionality, color, texture, ph, water holding capacity (WHC), and overall product palatability. Cooked Ham There is a broad range of types of cooked ham. In general cooked ham involves the use of a brine solution, either injected or soaked, followed by a thermal process. The most common non-meat ingredients in a brine solution are phosphate, salt, sodium nitrate/nitrites, cure color accelerators (sodium erythorbate, sodium ascorbate, and sodium citrate). These can include sugar, seasonings, and smoke flavoring (natural or liquid smoke). A cured ham that is wet cured, is either injected by needles or tumbled with the curing (brine) solution before cooking. A dry-cured ham has different 5

18 processing steps then a wet-cured ham. Dry-cured hams typically use a salt or salt and sodium nitrate mix, which is applied or rubbed onto the surface of the ham. Depending on the process, the rub may be applied multiple times during the aging process, or the hams may be packed in salt for an extended period (several months) during the aging process. The curing time is typically anywhere from 6 to 24 months depending on the process and associated traditions which vary throughout different regions of the world. Meat and Non-meat Ingredients To understand how processing and non-meat ingredients affect the functionality of proteins in a ham, it is important to have an understanding of the proteins present in meat. The majority of meat consumed in the US is derived from post-mortem skeletal muscle tissue. The three major components of meat from skeletal muscle are water (70-75%), protein (19-22%), and fat (3-9%), (Aberle et al., 2001). Skeletal muscle is the main raw material in processed meat and offers the most desirable protein-to-protein interactions. Actin and myosin are the predominant myofibrillar proteins that are capable of binding meat pieces together. Together they influence texture, stabilize fat, and chemically bind water. Differences in the raw material through breed effects, ingredients and processing techniques, have the ability to alter the solubility and functionality of actin and myosin in meat and thus impact the final texture profile of the product. Raw Material The pork industry has evolved from using traditional breeds or heritage breeds of pigs to genetically selecting for a leaner and faster growing pig. Table 1 outlines some of the differences that have taken place within market hogs when looking at productivity of a 6

19 market hog in 1950 versus Advancements in nutrition and genetics since 1950 have led to increases in average daily gain, loin muscle area, and average market weight while simultaneously resulting in decreases in days to market and back fat thickness. The commercial industry predominantly utilizes crossbred pigs to capitalize on heterosis to, combine the desirable traits from multiple breeds or genetic lines. Breeds such as Yorkshire, Landrace, and Large White are often used on the maternal side due to a greater amount of pigs per litter per sow per year. It is common to use Duroc, Hampshires, and Yorkshires as sire lines because of their excelled growth performance rate and desirable carcass characteristics. 7

20 Year Performance Measures Market Weight (kg) ADG (kg) Days to 105 kg Fat Thickness (cm) Loin Muscle (cm²) Table 1. Changes in Market Hog Performance (Boggs et al., 2006) The National Pork Board (2009), outlined productivity measures of the U.S. Pork Industry from 1974 to 2008 (Table 2) demonstrating the improvement in both maternal and growth performance at the production level as well as increased red meat yield from the resulting carcasses. Litters/ Breeding Animal Pigs Marketed/ Breeding Animal Live Weight (lbs.) Dressed Weight (lbs.) Retail Meat (lbs.) Retail Meat Yield (%) Year Pigs/ Litter Dressing Percent Table 2. Productivity Measures of U.S. Pork Industry, (Adapted from National Pork Board, 2009) As, the pork industry has moved to using more efficient crossbred pigs, there has been research done comparing the quality characteristics among different breeds of purebred pigs. Research done by Goodwin (2004; Table 3.), compares quality characteristics 8

21 among common purebred pigs. Purebred Berkshire and Duroc had a greater percentage of intramuscular fat then other common purebred breeds utilized in production systems. Purebred Berkshire pigs also produced carcasses with a desirable ultimate ph, a desirable Minolta L* value combined with the lowest percentage of cooking loss when compared among other common purebred pigs. Equally important, the Berkshire carcasses produced the most tender (P < 0.05) loin chops compared to the other commercially used breeds of pigs. Warriss et al. (1996) also evaluated fresh meat quality among different genetic groups of pigs. Group I represented Traditional or Heritage breeds (Large Black, Berkshire, Tamworth, Saddleback, Gloucester Old Spots), Group II represented commercially selected breeds (Hampshire, Duroc, Large White, Landrace), and Group III represented a high-lean, heavy muscled breed (Pietrain). The traditional breeds produced product with more desirable muscle ph, muscle color, water-holding capacity, and the texture characteristics. The combined data presented in Tables 3 and 4 demonstrate the potential value to sourcing hams from purebred Berkshire pigs, as Berkshires produce fresh meat products with desirable fresh meat characteristics; this is especially important for processors or producers planning to target niche or up-scale market channels that lend themselves to branded marketing programs. 9

22 Breed IMF% Ultimate ph Minolta L* Cooking Loss % Juiciness Instron, kg Berkshire 2.51ᵇ 5.68 a 49.8ᵃ 20.8ᵃ 6.1ᵃ 5.09ᵃ Chester White 2.39ᵇc 5.70ᵃ 51.3ᵇ 22.2ᵇ 5.8ᵇ 5.58ᵇᶜ Duroc 3.07ᵃ 5.58ᵇ 51.6ᵇ 23.4ᶜ d 5.4ᶜ 5.77ᶜ d Hampshire 2.09 dc 5.58ᵇ 49.0ᵃ 22.9ᵇᶜ 5.8ᵃᵇ 5.67ᵇᶜ Landrace 1.90 c 5.47 c 54.2 d 24.0 d 5.0 d 5.43ᵇ Poland China 2.18 cd 5.61ᵇ 50.9ᵇ 22.3ᵇ 5.4ᶜ 5.86 d Spot 2.37 bc 5.55ᵇ 51.9ᵇ 22.9ᵇᶜ 5.3ᶜ d 5.75 cd Yorkshire 1.70 f 5.47 c 53.4ᶜ 23.8ᶜ d 4.9 d 5.78 cd abcd Means within a column with the same superscript are not statistically different (P > 0.05) Table 3. Breed Characteristics, Goodwin (2004) In addition to breed differences, there are known genetic mutations within breeds that can influence fresh and cooked pork quality. Warriss (2000) reported that some of the major defects in fresh pork quality include the presence of pale, soft and exudative (PSE) or dark, firm and dry (DFD), abnormally low ultimate ph, and a low percentage of intramuscular fat. Two genetic mutations of concern in the pork industry, in regards to pork quality, are the halothane (Hal n ) gene and the RN - gene. Both gene mutations have been shown to have detrimental impacts on water holding capacity and further processing yields of pork products. 10

23 Breed Type a Group I Group II Group III ph 45 in LD muscle Muscle Colorᵇ Water-holding capacityᶜ Graininess of muscle d a Breed Type: Group I = Large Black, Berkshire, Tamworth, Saddleback, Gloucester Old Spots; Group II = Hampshire, Duroc, Large White, Landrace; Group III = Pietrain b Measured as reflectance (EEL units); higher values indicate paler muscle. c Measured as the percentage loss of exudate from stored meat. d Subjective score based on a scale of 1=fine, 4= coarse Table 4. Meat quality characteristics in different types of pig breeds (Warriss et al., 1996) The halothane gene is associated with stress-susceptible breeds of pigs. Pigs showing halothane-positive characteristics have difficulty in coping with stressful situations, which can result in high mortality during transport, or carcasses that exhibit PSE meat. The Redement Napole (RN-) mutation has often been referred as the Hampshire effect because of the high occurrence of the mutation with the Hampshire breed. The RNmutant allele demonstrates increased glycogen content within the muscle. The increased amount of glycogen leads to a lower than normal ultimate ph in meat. A rapid decline in ph is observed in carcasses that produce PSE meat due to a rapid build-up of lactic acid during postmortem muscle metabolism. The PSE conditions results muscle tissue that is exposed to a low ph and an elevated temperature prior to the complete formation of the actin-myosin crossbridges. This combination of events subjects both actin and myosin to a greater level of protein degradation, which ultimately, decreases water-holding capacity of the muscle, resulting in pale color, increased exudate, and soft muscle. In contrast, RN - mutation follows a similar slope to normal 11

24 postmortem ph decline, but due to the greater glycogen stores in the muscle, continues to a lower ph as anaerobic metabolism continues for a longer duration. As the muscle approaches its isoelectric point, this, in turn, decreases the space available for capillary activity to hold water within the muscle. The low ultimate ph has shown to result in greater drip losses (lower water-holding capacity; Bidner et al. 2004). The incidence and severity of these quality traits can have detrimental impacts on processing yields and sensory attributes of fresh and processed pork products and ultimately consumer acceptability. Non-Meat Ingredients Water Numerous non-meat ingredients are used in the further processing of hams. Water is the predominant non-meat ingredient used in a cured ham. It adds weight (value) and juiciness to the ham, while also capable of influencing other sensory attributes. Water is capable of solubilizing other non-meat ingredients in a brine solution. The interactions of meat proteins with the non-meat ingredients of a brine solution and their influence on ham are greatly facilitated by the use of water to dissolve and disperse the brine ingredients evenly throughout the ham. This is especially critical for dispersion of sodium nitrite because of the low amount that is allowed in meat products. Water, along with salt, plays a very important role in the solubilization of meat proteins. Once solubilization of proteins has occurred a critical gelation occurs during the heating process. The heat-set gelation is responsible for trapping the present water and fat within the product, which also affects the product yields (Sebranek, 2009). Also, the formation 12

25 of the gel structure affects the product tenderness, juiciness, and mouth feel of the final product. The USDA (2011) has set limitations for meat ingredients in order to maintain the expected product properties and to prevent the excessive addition of water to meat product formulations. Ham product water content is limited on a protein-fat-free (PFF) basis. The PFF labeling requirement serves to restrict the amount of water that can be added to these products. Examples for ham include: Ham (20.5% PFF), Ham with natural juices (18.5%-20.5% PFF), Ham-water added ( % PFF), or Ham and water product (<17.0% PFF) (USDA, 2011). Phosphates and Water Holding Capacity Phosphates are available in many forms for the food industry, but typically alkaline phosphates are used in meat products, such as sodium tripolyphosphate, sodium hexmetaphosphate, sodium pyrophosphate, and monosodium phosphate (Sebranek, 2009). Phosphates have many functions in food products. Phosphates are able to sequester metal ions, increase water binding, buffer or adjust ph, form ionic bridges, and interact with proteins (Aberle, 2001). In the meat industry, the addition of phosphates plays an important role in enhancing protein binding of reformed meat, increasing moisture retention, stabilizing color, and retarding lipid oxidation. The most important function of phosphates in the production of a cured ham is the ability to increase water-holding capacity (WHC). When the isoelectric point of a protein represents the ph in which the protein has equal negative and positive charges (net charge of zero), actin and myosin are in close proximity to one another within the sarcomere (Aberle, 2001). Phosphates have the ability to break the actin-myosin 13

26 crossbridges, relaxing the muscle fiber and increasing space between the filaments. The increase in ph, due to phosphates, moves ph further from the isoelectric point, which increases the space between actin and myosin and allows for increased WHC. The increased space between the myofibrillar proteins allows for capillary retention of freeand loosely-bound water (Claus et al., 1994). Including phosphates in the brine solution increases the ph of the meat block and thus, increase the WHC which often leads to increased processing yields and overall value or profit potential of the product. Increased WHC also results in increased moisture retention or less purge loss in packaged products, thus leading retail products with greater consumer appeal. Phosphate and salt present in a brine solution are able to work together synergistically and effectively extract myofibrillar proteins and improve WHC. Phosphates capability to dissociate the actomyosin crossbridge enhances salt s ability to solubilize myosin, which leads to the improvement of WHC (Claus et al., 1994). The extraction of actomyosin also improves the binding of reformed meat products during cooking. Claus et al. (1994) suggested that phosphates are able to chelate divalent cations away from protein crossbridges, allowing the myofibrillar proteins to open up and hold more water. However, some researchers believe that phosphates may only affect free cations and not cations already bound to muscle proteins. The chelation by phosphates protects cooked meats from off flavors and is able to stabilize cured color. By increasing the ph with the addition of phosphate the oxidation of natural meat pigments is slowed, leading to a more stable color that is appealing to consumers. The ability to chelate metal ions also 14

27 helps prevents lipid oxidation and increases product shelf-life. Phosphates in processed meat products are limited to 5,000 ppm (USDA, 2011) Sodium and Salt-soluble Proteins Salt is the most widely used ingredient in curing meat, most commonly sodium chloride (NaCL). Salt is highly water soluble and forms sodium (Na + ) and chloride (Cl - ) in solution, and the functions that salt provides are largely determined by the dissociated ions. The three basic functions of salt are to add or enhance flavor, extract salt-soluble proteins, and extend the shelf-life of a product. Apart from having sensory functions and extending the shelf-life, the most important function of salt in a ham product is to extract myofibrillar proteins to create effective binding. The ionic strength of the salt solution makes it necessary for the extraction of proteins. Ionic strength causes myofibrils to swell, disintegrate, and solubilize the myofibrillar proteins (Claus et al., 1994). The Cl - ion will interact with proteins to increase the negative electrical charges on the proteins and increase water binding properties. The swelling allows more weakly bound water within and between proteins to be retained (Claus et al., 1994). This step is facilitated by tumbling and massaging actions and assists in creating a tacky exudate. The exudate creates pliable meat pieces that are able to be pressed together. The addition of heat to the reformed ham product coagulates the proteins and forms stable bonds. The amount of extracted proteins will depend upon salt present and tumbling and massaging actions. Myosin is the major protein that is extracted and actin and other myofibrillar proteins have been shown to have some binding effect. The sarcoplasmic proteins (water soluble proteins, such as myoglobin) from the muscle play a minor role on binding the meat. It 15

28 has also been reported that chloride ions from salt play a role in cured color because Cl - has can accelerate cured color formation by increasing the rate of nitric oxide formation from nitrite (Claus et al., 1994). Salt is considered a generally recognized as safe (GRAS) substance by the USDA. Salt is considered a self-limiting ingredient, as high levels of salt concentration in a product would lead to an unpalatable product. Nitrites/Nitrates and Color Nitrate and Nitrite are essential ingredients for cured meats because these compounds are responsible for stabilizing color, producing the characteristic cured meat flavor, and inhibiting growth of bacteria, particularly Clostridium botulinum. Either nitrate or nitrite may be used in cured products; however, nitrate is only effective in curing if it is reduced to nitrite. For this reason, nitrite is the compound that is typically used. To be able to produce the pink pigment that is typical of cured products, nitrites must produce nitric oxide. Adding nitrite to water creates nitrite ions (NO - ) to react with H+ ions in the weak acid conditions of the meat mixture. These conditions form nitrous acid (HNO 2 ). Nitrous acid is in equilibrium with N 2 O 3, which dissociates to form NO (nitric oxide) and NO 2 (nitrogen dioxide); (Claus et al., 1994). The nitric oxide reacts with myoglobin in the raw product to produce a red or brown color, which is converted to pink nitrosylhemocrome upon cooking. The cured meat flavor is the least understood function of nitrite. The cured flavor may be due to the reduced lipid oxidation by nitrite. In addition to stabilizing color and contributing flavor, nitrite is an important antimicrobial agent. Nitrite is an important inhibitor to anaerobic bacteria such as Clostridium botulinum and is also helpful in controlling microorganisms such as Listeria 16

29 monocytogenes. Again, it is unclear how nitrite is able to achieve these antimicrobial properties, but much of the effectiveness is tied in to the production of nitric oxide and changes in the ph of the product. Nitrites and nitrates are used in small amounts in meat products due to their toxicity. USDA regulations vary between cured products. The objective of the regulation is to provide sufficient nitrite to achieve bacterial inhibition and still maintain a product that is safe for consumption. The limitations on nitrite in a cured ham is 200 ppm present in the final product (USDA, 2011) Texture Profile Analysis The principle of the Texture Profile Analysis (TPA) test is illustrated in Figure 1. TPA was designed to compress a bite-size piece of food two times in a reciprocating motion that imitates the action of chewing (Bourne, 2002). From the resulting force time curves, a number of textural parameters that correlate with sensory evaluation are calculated. Bourne s (1968) procedure has been the basis for practically all General Food Texture Profile Analysis (GF TPA) using the Instron Texture Analyzer. The definitions of the various textural parameters are based on those of Szczesniak (1969), Bourne (1968), Breene (1974), and Friedman et al. (1963). 17

30 Figure 1. A generalized texture profile analysis curve from the Instron Universal Testing Machine. A1, area 1; A2, area 2; A3, area 3. The dotted lines indicate the times at which hardness is measured. According to Szczesniak (1962), the classification of textural characteristics can be grouped into three main classes: 1) Mechanical characteristics, 2) Geometrical characteristics, and 3) Other characteristics (referring to moisture and fat content of the food). Mechanical characteristics are derived by how the food reacts to stress and is the most important in determining how the food handles and behaves in the mouth (Szczesniak, 1962), whereas, Geometrical characteristics refer to the size and shape of the food product and Other characteristics relate to mouthfeel qualities of the food. The five basic parameters of mechanical characteristics are: hardness, cohesiveness, viscosity, elasticity, and adhesiveness. Three additional secondary parameters that are derived from the basic mechanical characteristics are: fracturability, chewiness, and gumminess. 18

31 Descriptions for mechanical characteristics that are important in TPA of ham are listed below. Mechanical Characteristics Hardness: Peak force required for the first compression, (Figure 1: Max peak of A 1 ) Cohesiveness: Ratio of the positive force area during the second compression to that in the first compression, (Figure 1; A 2 /A 1 ). The extent to which the sample can be deformed prior to rupture. Springiness (Elasticity): Defined as the rate at which a deformed material goes back to its undeformed condition after the deforming force is removed. The distance that the sample recovers after the first compression is measured from the initial sample contact to the contact on the second chew. Resilience: A measurement of how the sample recovers from deformation. Resilience is the ratio of the first decompression stroke to the first compression stroke. Chilling Methodology In conventional chilling systems, carcasses are placed into a chill room and held at about 1 C as soon as the carcass has been dressed, washed, and inspected. Because of the amount of carcasses placed into the chill room, the heat that dissipates from these carcasses will often increase the temperature of the chill room to above 1 C and decreases the rate at which the carcasses chill. There are numerous studies that have looked at the effects of rapid carcass chilling on overall pork carcass quality characteristics. Rapid chilling systems can range from an initial 30 min to 2 h period of carcasses being 19

32 subjected to -10 to -20 C temperatures and some also include high velocity air to extenuate the chilling process. Rapid chilling reduces weight loss from the carcass during chilling, reduces the incidence of PSE (pale, soft, exudative) pork, and improves water-holding capacity (WHC) and lean color (Warriss, 2000). Springer et al. (2003) investigated the effects of conventional chilling (2 C) and accelerated chill (-32 C) for 60, 90, 120, or 150 min, immediately postmortem to determine an optimal chilling scenario to improve pork quality. Carcasses in their study were randomly assigned to treatment groups of conventionally chilled (CC, 2 C, air movement 1.2 m 3 /s) or accelerated chilled (AC, -32 C, air movement of 2 m 3 /s) for 60, 90, 120, or 150 min. After AC, all carcasses were chilled at 2 C for the remainder of the 24 hour chilling time. Temperature measurements were collected at 0.5 h postmortem, immediately before the carcass exited the harvest floor, and at 1.5, 2.5, 3.5, 4.5, 5.5, and 24 h postmortem. Temperature and ph reading were taken in the Longissimus muscle between the 5 th and 6 th lumbar vertebrae and at the center of the hams in the Semimembranosus muscle. After colorimeter and quality attribute evaluations, the hams and loins were individually vacuum packaged and chilled to 4 C. Hams and loins were stored at 2 C for 14 d after harvest and then evaluated for purge loss. Loins were cut into chops and cooked for Warner Bratzler shear force (WBSF), sensory panel, and cooking loss evaluations. Hams were pumped to 130% of green weight with a brine solution; vacuum tumbled, stuffed into casings and cooked to an internal temperature of 65 C. Differences in loin ph were not detected (P > 0.05) at 24 h. However, at 3.5 h, carcasses 20

33 that spent either 90 or 120 min in the freezer showed greater (P < 0.05) ph values, and at 4.5 and 5.5 h post-treatment, the 90-, 120-, and 150-min loins produced greater (P < 0.05) ph values. In hams, ph differences were only detected at 1.5 h postmortem, when hams from the conventional chill had higher (P < 0.05) ph values than hams from the accelerated chill treatment. Accelerated chilling at any time showed improved (P < 0.05) loin muscle color when compared to CC carcasses. Loin texture and firmness were improved (P < 0.05) by AC, except at 120 minutes when no significant difference was shown between AC and CC. Accelerated chill carcasses had lower (P < 0.05) L* values (darker) for loins, but did not affect (P > 0.05) loin a* values and lowered (P < 0.05) b* values. Ham color, texture, firmness, and L*, a*, and b* values were not affected (P > 0.05) by accelerated chilling treatments. Cooking loss and WBSF values for processed hams were not (P > 0.05) affected by chilling treatment of the carcasses. Cured ham color, uniformity of color, L*, a*, and b* values, and sliceability were not affected by any chilling treatment (P > 0.05). This study concluded that 90 minutes of accelerated chilling improved scores over conventional chilling and is the recommended chilling method to be used by processors to improve pork quality and reduce the incidence of PSE pork. Ohene-Adjei et al. (2002) evaluated the effects of chilling rate and location within the muscle on the quality of ham and loin muscles. Three chilling treatments were used: accelerated chill (AC: held at -30 C for 2 h, with air circulation, followed by equilibration at 4 C for h), conventional chill (CC: held at 4 C for h with water sprayed every 2 h until 12 h postmortem), and slow chill (SC: held at 10 C-12 C for 12 h, 21

34 followed by equilibration at 4 C for h). Temperature decline was measured starting at approximately 40 min postmortem. A temperature probe was inserted into the Semimembranosus, approximately 1 cm posterior to the symphysis pubis and another probe was inserted into the center of the Longissimus thoracis at the10th rib. Temperatures were recorded every 30 min for 22 h. Samples for color, ph, and drip loss were taken from three sites of both the Semimembranosus (SM) and Biceps Femoris (BF). The locations were identified by their anatomical position relative to the femur: The inner (I) site was closest to the femur, the outer (O) site was a minimum of 5 cm from the femur, and the mid (M) site was located medially between the O and I sites. The Longissimus thoracis (LT) at the 10th rib and the Longissimus lumborum (LL) at the 3rd lumbar were also evaluated. Ultimate ph and color were determined 48 h postmortem. Loin and ham temperatures were the lowest for AC, when compared to CC and SC after 1.5 h of chilling. In general, temperature declined at a greater rate in the Longissimus and ham muscles for AC compared with SC between 1-5 h postmortem; however at 1.25 h postmortem the Longissimus showed no significant difference between chilling treatments. Minolta L* a* and b* color measurements were not significantly different between the different muscles or between the chilling treatments. Cooking Methodology The cooking methodology and the degree of doneness play an important role in different types of meat products and their resulting palatability characteristics. Meat cookery and the effect of heat on specific muscle components is one of the most important yet least understood aspects of meats research (Seideman and Durland, 1984). In hams, there are 22

35 several techniques to developing the final product. Hams may be fresh, cured, or curedand-smoked (USDA, 2011). The most popular cooking methodology in the United States is the cured and smoked ham. As noted by Toldra (2010), cooking has the following effects of meat products: 1) destroys considerable numbers of organisms and improves the storage life of meat products if not contaminated post processing, 2) improves meat palatability by intensifying the flavor and altering the texture, 3) develops color, 4) decreases water content of raw meat, which lowers the water activity and extends the shelf life of a meat product, 5) modifies the texture or tenderness of meat, 6) coagulates and denatures meat proteins, while altering their solubility and stabilizing the cured meat color, and 7) inactivates endogenous proteolytic enzymes and prevents development of off-flavors due to proteolysis. The destruction of bacteria and the improvement of product stability is the most important function of cooking. The eating quality of pork is a combination of flavor, tenderness, and juiciness. Tenderness is often considered one of the major attributes of importance, in regards to pork eating quality (Aaslyng et. al, 2002). Davey and Neiderer (1977) suggested that heat tenderizes meat in three distinct stages. The first stage, up to 65 C, was from increased proteolytic breakdown of myofibrillar elements; the second stage, between 70 C and 100 C, was through the destruction or solubilization of collagen with little loss of myofibrillar strength; and the third stage, beyond 100 C, was from a combination of collagen and myofibril breakdown. Their research concluded that cooking in the range of 70 C to 100 C halved shear forces values and was as effective as aging in increasing tenderness. 23

36 Cheng et al. (2005) investigated the feasibility of water cooking compared with two popular traditional cooking methods of dry air cooking and wet air cooking for processing hams. Fresh pork legs were deboned and trimmed of extra fat and connective tissue. A brine solution was injected to 20% of the green weight; legs were tumbled, and netted. Hams undergoing the wet air cooking (WAC) and water cooking (WC) were packaged into cooking bags; hams subjected to dry air cooking (DAC) where not packaged. Dry air cooking at 120 C and WAC at 82 C took place in a preheated steam convection oven and water cooking at 82 C was performed in a water bath. All samples were cooked to an internal temperature of 72 C. After the completion of cooking, all samples were chilled using traditional air blast cooling (1± 1 C) to cool samples to 4 C. Cooking efficiency, yield, texture, nutritional, sensory and microbiological attributes from cooked hams were evaluated. The DAC and WC method took 292 and 297 min, respectively, to finish cooking, which was significantly shorter than WAC (363 min) (P < 0.05). The DAC and WC method were shown to have a very similar cooking efficiency (min/ C) when compared to the WAC method. No significant difference was observed among the treatments for cooling time (min) and cooling efficiency (min/ C) (P > 0.05). Weight loss of the ham was observed in both the cooking look and cooling loss of the hams. Dry air cooking had the highest cooking loss (22.25%) compared with WC (9.73%) and WAC (12.74%), which shows that the greater cooking temperature would lead to a greater percentage of cooking loss. Evaporative cooling loss was effected by cooking methods in this study. Dry air cooking had the lowest cooling loss, while WAC had the highest cooling loss. Physical properties were evaluated (Table 5) and showed 24

37 that cooking treatment affected the quality attributes of the hams. The results of color (L*, a*, and b*), Warner Bratzler Shear, springiness, and water holding capacity showed no difference (P > 0.05) amongst the cooking treatments. Hardness, chewiness and cohesion were all significantly affected by the cooking methods (P < 0.05). Water cooking had the same value in hardness, chewiness, and cohesion with WAC, which was significantly different from DAC (P < 0.05). Wet cooking method was shown to be a possible method for creating a high quality ham. Cooking Methodᵃ L* a* b* WBS (N) H (N) S (%) Ch (Nmm) Co WHC (%) DAC b b 5.17 b b b b b 0.44 b b (120 C) WAC b 9.80 b 4.80 b b bc b bc 0.41 bc b (82 C) WC (82 C) b 9.86 b 5.25 b b c b c 0.39 c b a Cooking Method: DAC=dry air cooking, WAC=wet air cooking, WC=water cooking Physical attributes: WBS = Warner-Bratzler shear, H = Hardness, S = Springiness, Ch = Chewiness, Co = Cohesion, WHC = water holding capacity bc Means in the same column with different superscripts are different (P < 0.05) Table 5. Effect of different cooking methods on the physical properties of pork ham, Cheng et al. (2005). ΔT/differential Heat Treatment Reichert (1995) demonstrated that temperature influences protein binding ability in a direct manner. A slow heating rate, using 65 C cooker temperature, forms a protein network with better binding ability and less jelly loss than 75 C. Therefore, a low 25

38 starting temperature and slow heating rate is recommended to achieve a good texture with high binding ability. One method that can be used to achieve a low steady temperature combined with a slow heating rate is Delta- T. Delta- T cooking consists of an increase in the internal temperature of the product through steps of gradual heating, not exceeding a set temperature differential between the product and cooking apparatus. This process avoids excessive heating of the surface of the ham. An example of the heating profile is shown in Figure 2. Figure 2. Heating and cooling profiles, as measured by temperature in the center of the ham, through cooking with Δ T method. The influence of Δ T cooking methodology was shown when Desmond and Kenny (2005) tested the effects of two hanging methods (Achilles and aitch-bone suspension) and two cooking methods (normal and Delta-T (ΔT)) on the quality of cooked hams produced from two muscles. Left and right sides of split pig carcasses were equally divided 26

39 amongst the hanging methods and allowed to chill for 24 h at 0-2 C before the Semimembranosus and Biceps femoris were removed from the leg. The Semimembranosus and Biceps femoris were pumped to 120% of their green weight with a brine solution, tumbled, stuffed into an elastic netting, and vacuum packed in a heat shrinkable cooking bag. Hams in this study were either steam cooked using a normal one-stage cooking cycle (cooked at 85 C to a core temperature of 72 C) or a ΔT cycle (maintain a constant temperature difference of 35 C, between oven and core temperatures until the oven reached 85 C, and the internal temperature of the ham was allowed to reach 72 C). Texture analysis was carried out using the Kramer shear cell and also Texture Profile Analysis (TPA). Hardness, cohesiveness, springiness, gumminess, and chewiness were measured using TPA on 10 cores (diam. 2.5cm x ht. 2cm) per ham. Instrumental color of the ham was represented by five measurements to represent the whole ham slice. Delta-T cooking was shown to significantly reduce cooking losses by 2 to 3% in the different ham muscles and hanging methods. Also, hardness and chewiness measurements from the texture analysis were shown to be significantly different (P < 0.05, P < 0.01 respectively) when comparing ΔT cooking methodology with the normal cooking method, showing that ΔT cooking produced a more tender product. 27