The effect of ft on the eting qulity of pork Ensuring the best eting qulity Ensuring the best flvours The effect of cooking ft on the eting qulity of pork How to get the best eting qulity of pork
The cooking of pork Ensuring tenderness nd juiciness Cooking met correctly is essentil to ensure the best possible result. But wht ctully hppens to met during cooking? And how cn this explin the differences in eting qulity? These questions hve been ddressed in number of studies t the Dnish Met Reserch Institute. In this rticle, you cn lern how - nd why - the right cooking method ensures the best eting qulity. By Mrgit D. Aslyng nd Cmill Bejerholm, Dnish Met Reserch Institute Chnges during cooking Over 7% of met is ctully wter, with proteins ccounting for nerly 5% nd ft round 3%. Most of these proteins re structured round myofibrils or long threds running prllel to one nother. Myofibrils minly consist of two different types of proteins - myosin nd ctin. They re surrounded by connective tissue, which lso consists of proteins. When met is heted, the proteins strt to denture, chnging their structure. They shrink nd lose the wter tht ws previously bound in the cvities round the myo-fibrils. Different proteins denture t different tempertures. Myosin strts to denture t temperture of round C (see Figure 1), which mens tht the met strts to become tougher thn when rw. As the temperture rises, the met strts to shrink - first trnsversely, reducing the dimeter of the met nd then longitudinlly, mking the cut of met shorter. During this process, the open structures in the met lso strt to close s the entire cut of met shrinks. As the temperture reches 5 C, wter is forced out of the met. This cooking loss increses lmost linerly with the incresing core temperture until round 7 C, t which point the rte of increse strts to decline. The connective tissue proteins strt to denture t round C. Initilly, the connective tissue hrdens, but then it becomes soft in contrst to the myofibrillr proteins. This mens tht muscles rich in connective tissue nd muscles with little connective tissue rect differently to the cooking temperture. Seling the met Brown the met in frying pn nd sel in the juices before cooking hs been the trditionl dvice in cooking met. But, is it ctully possible to sel the met in this mnner? In study, pork loin steks were browned in frying pn t three different tempertures: 15 C, 15 C, nd 5 C nd were com-pred with steks tht hd not been browned. The cooking of the met ws then finished in n oven, nd the steks were weighed t core tempertures of C, 7 C, nd C (see text box 1). The results showed tht browning hd no effect on the cooking loss. Wter, which cn no longer be bound in the met due to the protein denturtion, is forced out. It is therefore not necessry to brown the met to void cooking loss, though it does help enhnce met flvour. Toughness Cooking loss 3 5 7 9 C Denturtion Myosin Connective tissue Actin Shrinkge Trnsverse Longitudinl Srcomere length Seling of pores Figure 1. Chnges in the met during cooking. Note how the chnges in toughness correlte with denturtion of myosin nd connective tissue nd with shrinkge of the met. Pn-frying temperture: 15 C - modertely hot 1 C - hot 5 C - very hot. Core temperture: C - red 7 C - light- just chnged from rose C - well-done - grey Text box 1.This text box describes the different pn frying tempertures nd the colour of pork t the core tempertures mentioned in the prgrph Seling the met
% Cooking loss C % Cooking loss 7 C % Cooking loss C 3 3 1 1 1 Stndrd low ph high ph high met% Stndrd low ph high ph high met% Stndrd high ph low ph high met% Oven 19 C Oven 9 C Frying pn 155 C Figure. Reltionship between cooking loss (pork loin) nd rw met qulity, cooking method nd core temperture. Core temperture is importnt for cooking loss nd juiciness Cooking loss ws mesured for the different rw met qulities t different core tempertures. Pork loin without ft ws cooked in n oven t high nd low tempertures, nd pork loin steks were fried in pn (see Figure ). At core temperture of C, the cooking loss ws highest when cooking in n oven t high tempertures. This ws possible becuse it ws ctully the core temperture tht ws being mesured. It must be ssumed tht the temperture close to the edge of the rost ws higher t the high oven temperture thn t the low oven temperture. The proteins in this prt of the met will therefore hve dentured to greter extent nd will hve forced more wter out of the met. It cn lso be seen tht met with low ph t this temperture hs higher cooking loss thn other kinds of met. This is becuse met with low ph contins more loosely bound wter tht leves the met more rpidly in the form of cooking loss. The longer the met is cooked, the greter the cooking loss. At the sme time, the differences in cooking loss re reduced, being ffected by both the cooking method nd the qulity of the rw met. At C, the cooking loss is high, irrespective of the rw met qulity nd the cooking method used, since both the myofibrillr proteins nd the connective tissue hve prcticlly finished chnging their structure t this temperture. Any wter tht cn ctully leve the met hs effectively disppered t core temperture of C. For tht reson, the core temperture is the most importnt prmeter in determining cooking loss. How-ever, if the core temperture is not too high, gentle cooking t low oven tempertures will lso result in lower cooking loss thn cooking t high oven tempertures. Intensity of tenderness 1 1 1 b b b b 5 75 Pork loin - rost, 9 C oven temperture. Pork loin - pork loin stek fried in frying pn. Outside hm muscle - rost, 9 C oven temperture. Pork esclope - schnitzel fried in frying pn. Core temperture C Figure 3. Reltionship between tenderness nd core temperture ccording to cooking method nd muscle. Different letters indicte tht there ws significnt difference in the tenderness of the sme met type/cooking dependent on the core tempertures.
The reltionship between cooking loss nd the juiciness of the met Reducing cooking loss is importnt since it directly ffects the juiciness of the met. Advnced mesurements hve shown tht the degree of juiciness in the met cn lrgely be explined by the distribution of the wter in the met. The lrger the pores in the cooked met, the juicier the met will be. When the met shrinks nd forces out the wter, the size of the pores chnges, nd the met seems less juicy during chewing, even though there is lot of wter left in the met. The higher the cooking loss, the less juicy the met will be. Core temperture nd tenderness Results vry s to the extent to which the tenderness of pork chnges with incresed core tempertures. The results in Figure 3 show tht the tenderness will not chnge substntilly with n incresed degree of cooking in the cse of pork loin, muscle contining reltively little connective tissue, when it is cooked gently in n oven (9 C). However, if pork loin steks re cooked in frying pn, they become less tender, though only t very high core tempertures. For pork esclope, which is reltively rich in connective tissue, the tenderness strts to decrese t even lower levels between 5 C nd 75 C, mening tht the connective tissue hrdens during this temperture rnge. This tkes plce both when the met is cooked s rost in n oven or s slices in frying pn. When the temperture is incresed to C, the connective tissue will strt to become softer, nd the met will gin strt to become more tender. Slow cooking results in lower cooking loss Although the core temperture is very importnt, the cooking time is lso importnt. At fixed core tem-perture ( C), the cooking loss is significntly lower t low oven temperture thn t high oven temperture (see Figure ). This is lso reflected in the fct tht the met is more juicy nd tender t the low oven temperture. The protein denturtion does not hrden the myofibrils or expel s much wter during longer cooking process t lower temperture. Slow cooking nd low core temperture In order to minimise cooking loss nd obtin the mximum juiciness nd tenderness in the met, the core temperture is criticl. If the core temperture is kept low, this will result in juicy piece of met. How-ever, the cooking time is lso importnt. When cooking in n oven, low oven temperture (9-1 C) is recommended s this will increse both the tenderness nd juiciness of the met. Sensory intensity % cooking loss 1 1 35 3 5 15 1 5 Juiciness Tenderness Cooking loss. 19 C 9 C Figure. Juiciness, tenderness nd cooking loss of pork loin cooked in n oven to core temperture of C t high nd low oven temperture (19 C nd 9 C), respectively.
The cooking of pork Ensuring the best flvour Idelly, pork should hve plesnt fried met flvour, with no ftertste. In its rw stte, met hs n insipid rom, nd it is only during cooking tht molecules re formed to deliver its unique flvour nd tste. This rticle exmines how cooking ffects the flvour of met nd how to obtin delicious-tsting product every time. By Mrgit D. Aslyng nd Cmill Bejerholm, Dnish Met Reserch Institute Flvour is delivered by tste molecules tht bind to the tongue nd by rom compounds tht re trnsported from the orl cvity nd up into the nose s we et. The voltile rom compounds re essentil for our bility to perceive the flvour of met. Tht is why food is tsteless when we hve cold nd our sense of smell is dulled. It hs been shown tht if we et met without these voltile rom compounds entering the nose, the primry tste senstions re sourness followed by slt tste. It is vitl to understnd how these voltile compounds re relesed when working to improve the flvour of pork. Finlly, the orl cvity s perception of temperture (for exmple, cold,wrm or burning), vi the trigeminl nerve, is lso crucil to understnding our pprecition of flvour. The complex chemistry of flvour When met is heted, cscde of chemicl rections is set in motion. Amino cids rect with crbohydrtes, resulting in fried or rosted met flvour. The rection is known s the Millrd rection, nmed fter Louis Cmille Millrd, who discovered it in 191. It is the sme bsic rection tht occurs in coffee during rosting nd in bred during bking. The initil rection does not produce mrked flvour, due to the smll number of compounds formed t this erly stge. However, s cooking progresses, compounds such s py- rzines, thiophenes nd furnones re formed (see Figure 1). The resulting compounds nd the mounts formed depend both on the kind of mino cids nd crbohydrtes present nd on other conditions, such s the ph of the met nd, more importntly, the temperture of the het source. While Millrd rections cn tke plce t low tempertures, it is only when the temperture exceeds level of round 1 C tht the rection rte influences flvour formtion. The higher the temperture, the greter the number of different voltile compounds influencing the flvour. Ftty cids in the met re nother importnt source of flvour compounds. The unsturted ftty cids re degrded by oxidtion during cooking. The kind of compounds formed depends to lrge extent on the kind of ftty cids present in the met. Mny of the unsturted ftty cids re present in the membrnes - the so-clled phospholipids - nd these re considered to be the most importnt cids for flvour formtion. In cses where the Millrd rections require high tempertures to contribute to flvour formtion, the degrdtion of ftty cids will strt t very low tempertures. The degrdtion of other compounds in the met, for exmple thimine, cn lso contribute to the overll tste senstion, l-though more reserch is needed to understnd this process more fully Group of compounds Generl rom Approx. threshold vlue Pyrzines Rosted, nutty ppb-ppm Thiophenes Rosted. If the sulphur tom (S) is ppb in the 3rd position, they hve met rom. Otherwise n onion rom Furnes/furnones Rosted, crmel, burnt ppb-ppm Aldehydes (from lipid degrdtion) Green, ftty, fruity pb-ppm Figure 1. Exmples of groups of compounds formed during heting of met
Cooking longer t the sme temperture It doesn t tste of nything so let s fry it bit longer. This is tempting thought perhps, but ctully prolonged cooking of met t the sme pn temperture does not hve much of n effect. As shown in Figure, the intensity of the fried met flvour of pork loin steks does not increse significntly from core temperture of 5 C until it reches C. This is becuse the voltile flvour compounds formed re the sme t the sme pn temperture. Prolonged cooking of the met t the sme temperture results in the formtion of more of the sme kind of compounds rther thn other compounds which con-tribute more to fried met flvour. Temperture is the most importnt fctor when frying The met rom nd flvour, which re chieved slowly t moderte pn tempertures, re chieved fster when the pn temperture is incresed. As shown in Figure 3, the met will hve n identicl fried met flvour when fried t high pn temperture ( C) to core temperture of 5 C s when it is fried in modertely hot pn (155 C) to core temperture of 5 C. However, the met will rpidly cquire burnt flvour if it is fried too long t the high temperture. There re two resons for this. Firstly, the hot frying pn cuses the formtion of other voltile compounds, nd secondly, some of the compounds formed t low tempertures become degrded t high tempertures. 1 1 Intensity Met flvour 5 75 Figure. Fried met flvour of pork loin without ft cooked s pork loin steks in frying pn (155 C) or s rost in n oven (9 C) to three different core tempertures. Different letters indicte significnt difference in cooking loss within the sme cooking method. The rte of the Millrd rections depends on both temperture nd wter. The higher the wter ctivity, the less the met will brown. It is therefore recommended tht met is dried off before frying. Studies hve shown tht it is very importnt tht the pn is hot when the met is plced in it. Any wter on the surfce of the met will evporte, llowing the Millrd rections to tke plce. The temperture in the oven is lso importnt Oven temperture lso hs significnt effect on met flvour. At n oven temperture of 9 C, the surfce of the met never reches the tempertures t which the Millrd rection strts to influence flvour formtion. The met is not browned, nd the met flvour is not s intense. At 1 C, some browning cn be chieved nd tsted (see Figure ). If met is cooked t low oven temperture, it is good ide b Core temperture b b Frying pn Oven Fried met rom Burnt rom Intensity 7 5 C b 5 C 7 5 3 1 15 C C Intensity 9 7 5 3 1 c b b 15 C C 5 C 5 C Pn temperture Pn temperture Figure 3. Fried met rom nd burnt rom dependent on frying pn nd core tempertures. Flvour nd rom followed the sme pttern. Different letters indicte significnt difference between the four smples in the sme figure.
to brown the met to chieve the fried met flvour on the surfce. This cn be done by browning the rost in frying pn - either before or fter it is plced in the oven. The effect on flvour is gretest when finishing the cooking process by browning the rost. Other met ttributes, such s juiciness nd tenderness, re not ffected by the browning of the met. Cooking method is importnt for met colour The brown colour is dependent on the extent to which Millrd rection hs tken plce nd lso on the content of flvour precursors in the met nd the frying pn temperture. Another importnt chnge in met colour occurs when the rw red colour turns into well-done greyish colour. This is cused by denturtion of the myoglobin nd by the relese of iron from the protein. Denturtion strts round C, with most of the trnsformtion tking plce between C nd 7 C. If the met is cooked to core temperture within this rnge, smll temperture vritions will determine how well-done the met ppers. Different muscles cn lso differ in well-done ppernce t the sme temperture. If the met is cooked t low oven temperture, its temperture will be very similr both t the core nd close to the surfce. This will therefore result in uniform red or rose-pink colour cross the entire met when it is sliced. However, t high oven temperture, the difference in temperture throughout the rost will be greter, nd the met will pper browner close to the surfce thn t the core. 3,5 1,5 1,5 Met flvour 9 C 1 C Figure. Met flvour of pork loin rosted t oven tempertures of 9 C nd 1 C, respectively. Key cooking tips So how do you produce both juicy nd gret tsting met? Above ll, it is importnt to stop cooking t the right time. If the core temperture reches too high level, the met becomes dry. It is lso importnt to het the frying pn well before cooking. When cooking in n oven, low tempertures re recommended, but the rost should lso be browned to relese the met flvours. The effect on flvour is gretest if the rost is browned fter cooking hs been completed.
Ft or len The effect of cooking ft on the qulity of pork 1 Opinions vry s to the extent to which the level of ft ffects the eting qulity of pork. The flvour is in the ft, nd it is vitl contributor to the juiciness nd flvour of pork, which would be dry nd tsteless without it. Cn consumers relly enjoy pork s prt of low-ft diet? Here re some views from some experts t the Dnish Met Reserch Institute. By Mrgit D. Aslyng nd Cmill Bejerholm, Dnish Met Reserch Institute Ft is present in met in severl plces. There is intrmusculr ft, which is embedded in the met it-self. It consists of two min frctions - membrne ft (phospholipids) locted in the membrnes of the muscle cells nd mrbled ft (triglycerides), which consists of strnds of ft between the muscle cells. Then there is intermusculr ft between the muscles, nd subcutneous ft, which is locted between the muscles nd the outer rind. The ltter two types constitute by fr the lrgest proportion of ft in met, though they re lso the fts tht cn be most esily removed by those wishing to reduce their intke of ft. Intrmusculr ft provides the met with tenderness nd flvour In pork loin, the ft content in the muscle is between 1% nd %. The mount of ft in pork fillet or tenderloin corresponds to the mount of ft in glss of.5% skimmed milk. Although this is reltively low mount, the mrbled ft ensures plesnt eting experience. Mrbled ft improves the tenderness of pork loin steks, regrdless of whether they re cooked to moderte core temperture of 5 C or to higher level of C (see Figure 1). Irrespective of their 1 T enderness Juiciness 5 C Juiciness C Low (,-1,3% ) M edium (1,-,% ) High (,3-,1% ) Figure 1. The effect of ft mrbling (IMF) on the eting qulity of pork loin steks fried in frying pn (core temperture 5 C or C respectively, frying pn temperture 155 C, repetitions). ft content, pork loin steks re juicy when cooked to 5 C. However, if the core temperture reches C, the intrmusculr ft will increse the juiciness of the met. This effect occurs in met contining resonble level of mrbled ft (1.% -.%) compred with lower levels (< 1.3%). The incresed juiciness occurs, even though there is no difference between these products with regrd to cooking loss. There is lso smll effect on the fried met flvour. The intensity is higher in the products with higher level of mrbled ft. However, there is no difference recorded in products with higher levels of intrmusculr ft. As regrds tenderness, it is importnt to hve s high level of mrbled ft s possible, wheres juiciness nd flvour re reduced in met with lower levels of mrbled ft. Does the level of visible ft contribute to the flvour nd juiciness of pork No - the eting qulity of met is not ffected by cooking with or without the visible ft edge. In tests, steks were tken from the sme cut of pork loin, nd comprison showed no difference in flvour or juiciness, regrdless of whether they were cooked with or without the covering ft. However, cooking of stndrd rib rosts with the ft lyer remining between the muscles, compred with muscles cut nd cooked with the ft removed, produced more rost flvour. In this cse, the ft bove simply melts down over the met nd deposits flvours on the surfce of the met below. Ft content in minced pork or pork burgers Minced met with high ft content is often cheper thn the lener lterntive. Mny of us like to et len met, nd yet there is lso view tht met tstes better if it contins ft. Is this correct nd how should this guide our choice of met? A comprison between pork burgers mde with minced pork with vrying ft contents, from either the shoulder (which is often used for minced met) or from pork loin (with its lower ft content) showed tht the level of ft prticulrly ffects the juiciness, softness nd crumbliness of these products fter cooking. The higher the ft content of the pork mince,
1 1 Juiciness % 5% 1% 15% % 5% 1 1 Softness % 5% 1% 15% % Pork loin L Pork loin H Shoulder L Shoulder H Figure. Juiciness nd softness of pork burgers with ft content of between % nd % prepred from minced pork loin nd shoulder, cooked to core temperture of 75 C (L) or 5 C (H) (3 repetitions). the juicier nd softer the resulting pork burgers. However, by lowering the core temperture, you cn chieve the sme level of juiciness s by using mince with higher ft content (see Figure ). In terms of flvour, it is minly the ftty flvour, smell nd ftertste which re intensified in met with higher ft content.the effect is lmost liner: the higher the ft content, the fttier the flvour. At the sme time, sourish flvours re reduced, while sweeter nd porkier flvours re intensified. However, the differences re not prticulrly significnt. The difference ws most pronounced when the ft content ws higher, in the rnge of % to 1%, but there ws no significnt chnge when the level ws incresed still further. Len nd low-ft It is possible to et pork s prt of blnced or even low-ft diet if the visible ft, or the outer lyer nd the ft between the muscles, is removed. Alterntively, it cn be n dvntge to choose met with lrger mount of mrbled ft. The mount of ft consumed through eting pork is still reltively limited, nd the level of mrbled ft substntilly improves its eting qulity. Eting qulity is not ffected by the visible ft being removed before or fter cooking.
Ft or len The effect of cooking ft on the qulity of pork Opinions vry s to the extent to which cooking ft ffects the eting qulity of pork. Some people think tht met bsorbs cooking ft during the frying process, nd there re those who think tht it is best to fry in butter. However, wht re the fcts? And is it possible to et pork s prt of low-ft diet? These questions hve been ddressed in number of studies t the Dnish Met Reserch Institute. By Mrgit D. Aslyng nd Cmill Bejerholm, Dnish Met Reserch Institute Although pork itself contins certin mount of ft, different types of cooking ft re often used for frying. The choice of ft helps determine the flvour of the met, though it is common misconception tht met bsorbs ft during the cooking process. Does met bsorb cooking ft or does the ft melt wy during the cooking process? With the ft sizzling, the met is plced in the pn. When the met is cooked through, the ft hs ll but disppered. It is only nturl to think tht it hs been bsorbed by the met. However, chemicl nlyses of the ft content in met before nd fter cooking show tht the ft content in pork schnitzel increses by round.5 g per 1 g rw met, even when lrge mount of cooking ft is used. The percentge increse in the ft content is somewht greter, due to the cooking loss, which mostly comprises wter. Most of the cooking ft tht is bsorbed by the met forms thin lyer on the surfce of the met. When ftty met (for exmple, high-ft minced pork or ftty cuts such s bcon) is cooked, distinct ft-melting process tkes plce. For minced pork ptties contining 1% ft, round.5 g ft per 1 g rw met melts wy, irrespective of how much cooking ft is used, while for bcon, which cn hve cooking loss of up to 7%, 15 g ft per 1 g bcon melts wy. The ft tht melts wy is the intermusculr nd subcutneous ft, i.e. the ft tht is not present in the muscle. The intrmusculr ft does not melt wy, no mtter how thoroughly the met is fried. There is perfectly logicl explntion for this. Wter ccounts for round 7% of the weight of the met muscle. Since wter nd ft do not redily mix, why would the ft be bsorbed by the hydrophilic met? In fct, the ft relly does dispper from the pn much of it cn be wiped wy from the cooking top, or it ends up in the cooker hood. Ftty cid composition chnges only in ftty cuts The melting point of the ftty cids is dependent on their degree of unsturtion. The more unsturted the ftty cids re, the lower their melting point will be. There is therefore tendency to believe tht the helthy unsturted ftty cids will be the first to melt wy from the met. Fortuntely, however, this is not the cse. Anlyses hve shown tht the ftty cid composition of minced pork ptties contining 1% ft remins prcticlly unchnged before nd fter frying, irrespective of the pn temperture. Only the mount of one ftty cid, C1: (linoleic cid), chnged. However, in pn-fried pork belly, which is very ftty cut with high cooking loss, the polyunsturted ftty cids melt to greter extent thn the monounsturted ftty cids, while the sturted ftty cids do not chnge. Choosing the right type of cooking ft While some would opt for butter, others would recommend mixture of butter nd oil. A lrge number of consumers use oil or mrgrine. But wht difference does it ctully mke? 1
Cooking ft 1 Cooking ft Difference Butter-olive oil Olive oil Yes Butter Mrgrine Yes Rpeseed oil (hot-pressed) Rpeseed oil (cold-pressed) Yes* Rpeseed oil (cold-pressed) Olive oil (cold-pressed) No Rpeseed oil (hot-pressed) Grpeseed oil (hot-pressed) No *P=. Tble 1. Comprison of pork chops fried in two different types of cooking ft. The comprison ws mde by mens of difference test (tringle test). A comprison of pork chops fried in different types of cooking ft showed tht there ws significnt difference in the flvour of pork chops fried in butter compred with mrgrine or mixture of oil nd butter. There ws lso slight difference in the flvour of pork chops fried in hot-pressed rpeseed oil compred with cold-pressed rpeseed oil, wheres there ws no difference in the flvour of pork chops fried in cold-pressed rpeseed oil compred with olive oil or pork chops fried in hot-pressed rpeseed oil compred with grpeseed oil (see Tble 1). Eting pork s prt of low-ft diet You cn et pork s prt of low-ft diet. Choose your preferred cooking ft nd do not be frid to use whtever quntity you think is pproprite very little of it will be bsorbed by the met. Just remember to discrd the ft in the pn fter frying. These differences were subsequently described in sensory profile nlysis. The butter primrily imprts butter flvour, though the met flvour is lso more intense thn for the other types of cooking ft. When butter nd olive oil re mixed, the butter flvour is reduced, while the met flvour remins intense. Hot-pressed grpeseed oil imprts n oily flvour, described s deep-ft fried flvour. Furthermore, the pork chops cquire more sourish flvour. Mrgrine imprts the most neutrl flvour, since ll the flvour ttributes re less intense thn for the other fts. Since met does not bsorb cooking ft, it is not necessry to choose the helthiest type of ft. The type of ft you choose to fry your met in should depend on wht you like best, nd, in prticulr, on whether or not you like butter flvour, since tht is the most intense flvour. If you wish to void n oily flvour nd yet still wish to use oil to cook with, it is recommended to choose cold-pressed oil. 11
Dnish Met Reserch Institute Mglegrdsvej DK- Roskilde Tlf: +5 7 dmri@dti.dk www.dti.dk Mde in co-opertion with DANISH AGRICULTURE AND FOOD COUNCIL 1