Influence of Bitter Taste on Mastication Pattern

Mastication is a rhythmic activity that can be modified by peripheral information generated in the mouth. To study whether taste cognition could influence the way in which a food is broken down in the mouth, subjects masticated firm, sugar-based gelatine gels with differing concentrations of quinine, up to 1500 μmol/kg, while electromyography (EMG) of masticatory muscles was recorded. Taste intensity and composition of saliva were measured. With increasing quinine concentration, the average number of chews for nine subjects decreased from 30 to 22, and their average clearance time increased from 7 to 14 sec. Quinine concentration had no effect on chewing frequency (1.3 Hz) or on the rate of salivation (5.5 g/min). Bitterness increased, while acceptability and sweetness decreased, with increasing concentration of quinine in the gel and in saliva. Taste cognition could therefore modify food breakdown in the mouth.

Modelling post-mortem tenderisation-III: Role of calpain I in conditioning

A simple model is developed to show how proteolysis by calpain I can account for the variations in tenderness in electrically stimulated and nonstimulated beef pectoralis profundus muscles stored between 0°C and 30°C. As the pH of the muscle falls to about 6·1, calpain I is activated and causes proteolysis and tenderisation. The rate of tenderisation is then proportional to the concentration of calpain I which is autolysed slowly reducing its concentration and the rate of tenderisation. The activation energy for the inactivation (autolysis) of calpain I is slightly higher than that for its activity in tenderisation (proteolysis) and therefore, at higher temperatures, less tenderisation occurs. Proteolysis and tenderisation continue at a rate governed by the concentration of calpain I and the temperature until calpain I is depleted when tenderisation stops. Parameters for the activity and inactivation of calpain I were derived and were shown to predict 68% of the variation in toughness.

Optimisation of tenderisation, ageing and tenderness

Tenderness is an important part of meat acceptability and is affected by variations in production and processing. The tenderisation process was modelled on the activity of calpain proteinases. The extent of tenderisation is proportional to the level of calpains which accounts for the toughness of meat from β-adrenergic agonists. The rate of tenderisation increases with higher temperature and faster rigor development. These are responsible for the faster tenderisation in chicken, in meats following the use of electrical stimulation and in meats of high ultimate pH. Knowledge of these mechanisms of tenderisation afforded processes for optimisation of tenderness.

Calpain-calpastatin and toughness in M. longissimus from electrically stimulated lamb and beef carcasses

Shear strength, pH, temperature, μ-calpain, m-calpain and calpastatin levels were measured over a two-week post-slaughter period in Longissimus lumborum et thoracis (LD) from six lamb and six beef carcasses. All carcasses were subjected to high voltage electrical stimulation. The toughness of the beef LD determined by a MIRINZ tenderometer at 24 h post-slaughter showed a strong correlation (r=0.91) with pH of the LD at 3 h. Beef LD toughness at 14 days was correlated (r=0.84) with initial m-calpain levels. In both lamb and beef, LD toughness at 4 and 14 days respectively was also correlated with initial levels of calpastatin (r=0.85, 0.83, respectively). The strong correlation between calpastatin and the rate of tenderisation indicates that the calpain system is closely linked to the proteolytic breakdown of myofibrillar proteins. There is also evidence of an interaction between pH and μ-calpain activity. The μ-calpain, m-calpain, calpastatin, pH and temperature kinetic changes which occurred during the post-mortem ageing of beef and lamb LD were applied to a computer program which predicted rate of meat tenderisation by calculating in situ calpain activity. The closeness of fit between the predicted rate of meat tenderisation and the observed tenderness values of beef and lamb LD indicates that the post-mortem activity of μ-calpain is the major determinant of variations in tenderness. However, application of the meat tenderisation predictive program to LD from individual animals revealed that the program was not sufficiently robust for this use.

Alteration of post-mortem ageing in beef by the addition of enzyme inhibitors and activators

Twenty-four hours after stunning, slices of beef M. semitendinosus were soaked in buffers at 10 °C at different pH values containing enzyme inhibitors or calcium and magnesium salts and their enzyme levels and toughness determined up to 9 days. High pH meat was tender but appeared to have the same rate of ageing as meat of normal pH. Calcium chloride accelerated ageing and produced, after completion of conditioning, more tender meat than controls. In tenderising, sodium and potassium chlorides were 43% and MgCl(2) 73% as effective as Ca salts. Cysteine proteinase inhibitors were more effective in preventing ageing than serine or aspartate inhibitors. Cysteine and aspartate inhibitors together were the most effective in preventing ageing. The inhibition of ageing by cysteine inhibitors was overcome in the presence of 30 mM CaCl(2). The results suggest a main, but not exclusive, role for calpains in meat ageing and showed a synergistic non-enzymic tenderisation by the addition of high concentrations of salts.

Modelling post-mortem tenderisation-II: Enzyme changes during storage of electrically stimulated and non-stimulated beef

Levels of calpains I and II, cathepsins B and L and β-glucuronidase were determined in extracts of electrically stimulated and control beef M. Pectoralis profundus stored at temperatures between 0 and 30°C and varied to avoid muscle shortening. The level of lysosomal enzymes remained essentially unchanged throughout storage. The levels of calpain II were largely unaffected by the early treatments and decreased slightly throughout ageing. The level of calpain I, in both stimulated and control meats, was unaffected by temperature prior to the attainment of about pH 6·2 and thereafter the loss was accelerated at higher temperatures. In the extreme case studied, that of stimulated meat held at 15°C, 73% of the activity was lost in the first 24 h. After ageing, the level was about 11% of the initial when stored at 1°C and 25% when stored at 15°C. The exponential decay constants for the decrease in the levels of calpain I were 0·01 h(-1) at 1°C and 0·06 h(-1) at 15°C, and were the same as those for the previously determined rate of tenderisation. This suggested that the rate of proteolysis by calpain I was linked to the rate of tenderisation.

Eating quality of European beef assessed at five research institutes

Loin steaks from 10 animals (five of each of two types) from each of eight European countries were assessed for eating quality at five institutes in Denmark, Ireland, England, France and the Federal Republic of Germany. All panels found wide variation in eating quality and many of the steaks were unacceptably tough. Although attempts to relate quality to production factors were often confounded, differences in post-slaughter handling, particularly between producing countries, dominated eating quality. Breed, sex, age or fatness had relatively little influence on eating quality in this trial. A common eight-category scale of tenderness/toughness was used in addition to each institute's usual descriptive scales for tenderness, flavour, juiciness and overall acceptability, employing four to eleven categories. Within panels, attribute scores were not independent and tenderness and flavour in combination were the best predictors of overall acceptability. Between panels, tenderness was highly interrelated, flavour and juiciness poorly interrelated. These findings, together with estimates of each panel's discrimination and the variation between individual assessors, are discussed in relation to standardisation and equivalence of sensory methodology.

Influence of rearing conditions on performance, behavioral, and physiological responses of pigs to preslaughter handling, carcass traits, and meat quality1

A total of 120 crossbred [synthetic line x (Large White x Landrace)] pigs (castrated males and females) were used to evaluate the influence of rearing conditions for growing-finishing pigs on growth performance, carcass, stress reactions at slaughter, and meat eating quality. At approximately 35 kg of live weight (LW), littermates were allocated to either a conventional (fully slatted floor, 0.65 m2/pig, considered as control, CON) or an alternative (sawdust bedding with free access to an outdoor area, 2.4 m2/pig, OUT) system, until slaughter at approximately 110 kg of LW. Pigs had free access to standard growing and finishing diets. The trials were conducted in spring, summer, and winter, with each season involving 2 pens of 10 pigs in each system. Compared with the CON, the OUT pigs exhibited a greater growth rate (+10%, P < 0.001) due to their greater feed intake (+0.23 kg/d, P < 0.01), resulting in a greater body weight at slaughter (+7 kg, P < 0.001). The OUT pigs had thicker backfat (+2.4 mm, P < 0.01) and lower lean meat content (- 2.0% points, P < 0.001) than the CON pigs. The OUT system did not (P > 0.10) influence the behavioral activities of pigs during lairage at the slaughterhouse, or the urinary levels of catecholamines and cortisol, and plasma levels of ACTH, cortisol, lactate, creatine kinase, and FFA immediately after slaughter. The OUT pigs had similar (P > 0.10) pH values 30 min postmortem (pH1) in the LM, biceps femoris (BF), and semimembranosus (SM) muscles, similar ultimate pH (pHu) in LM, but lower pHu in SM (- 0.07 unit, P < 0.001) and in BF (- 0.03 unit, P = 0.029). Despite nonsignificant effects of production system on stress reactions at slaughter, assessed by urine and plasma indicators and muscle metabolism at 30 min postmortem, meat from OUT pigs had more LM drip loss after 2 (+1.0%, P = 0.003) and 4 (+1.1%, P = 0.010) d than did meat from the CON pigs. The OUT system slightly increased meat yellowness (b* value) in the LM (+0.7 unit, P = 0.001), BF (+0.5 unit, P = 0.014), and SM (+0.5, unit P = 0.041), whereas redness (a*) and lightness (L*) of the 3 muscles were unaffected (P > 0.07). Intramuscular fat content was greater in the LM (+17%, P = 0.001), BF (+14%, P = 0.004), and SM (+17%, P = 0.003) of the OUT pigs. Outdoor rearing during summer and winter improved meat juiciness, whereas odor, flavor, and tenderness were unaffected (P > 0.10). Influence of rearing conditions on all the other traits studied did not depend on the season.

Modified-atmosphere storage under subatmospheric pressure and beef quality: II. Color, drip, cooking loss, sarcomere length, and tenderness1,2

Beef has a requirement for refrigerated storage up to 14 d to achieve adequate aging and a tender product. To achieve this aging with little spoilage and no surface drying, vacuum packaging is attractive, because it is inherently simple and offers a clear indication to the packer when the process has failed or there is risk of spoilage. However, there is increasing pressure on the meat industry to limit the use of packaging materials in view of their cost and the cost involved in their recovery and recycling. The purpose of this report was to evaluate an alternative storage system in containers using modified atmospheres at reduced pressure (approximately 25 kPa). The quality of the meat for both container- and vacuum-packed treatments was measured during chilled storage for up to 3 wk. Storage time had the most significant effect on quality characteristics, irrespective of the packaging method. Storage in containers under a 70%N2:30%CO2 gas mixture gave characteristics similar to beef stored under vacuum. Storage in containers under 100% CO2 produced less drip loss than under 70%N2:30%CO2, but generally container storage produced 3 times as much drip loss as vacuum packaging. Shear force of the LM was unaffected by the type of packaging, and at d 2 after slaughter (i.e., before the storage trial was begun), sarcomere lengths of muscles intended for container storage were similar to those destined for vacuum storage. During the packaging treatment, the comparison between the storage systems was always done within 1 animal using one carcass-half for container storage and the other half for vacuum packaging; all bulls were shackled from the left hindleg during bleeding. The majority of the muscles from the left sides had lower shear force values than those from the right sides at the earlier storage times (2 and 9 d after slaughter) but had similar values after longer storage (16 and 23 d after slaughter). This is the first report that shackling beef carcasses from the left side can result in more tender meat in the LM from that side. The increased tenderness in the LM from the shackled side probably resulted from an early decrease in pH and an increase in calpain activity after mechanical strain of the muscles on the shackled side. This effect of shackling should be taken into account when designing systematic comparisons of tenderness in beef.

Meat texture of lambs from different European production systems

Measurements of meat texture (Warner-Bratzler shear force, WBSF), compression stress at 20% (S20) and 80% (S80) of initial sample thickness, sarcomere length, pH, and sensory tenderness score were determined on the longissimus muscle from lambs from 22 diverse European lamb types from 6 countries. Carcasses chilled to minimise cold shortening. The types ranged from 1-month-old milk-fed lambs to 1-year-old heavy wether lambs reared on the transhumance system (extensive system based on moving animals from valleys to high mountains in search of seasonal resources). Overall, it seems that breed was more important in influencing meat toughness than age or gender. Within breed, there was some evidence of an age effect (the older the animal the tougher the meat), and nutritional handling was, in some cases, significant. The lowest WBSF values were for meat from 16-kg carcasses of pasture-fed animals of the Icelandic breed (average 1.7 kg) and the highest were for meat from 19–20 kg carcasses of the Bergamasca breed (average 4.1 kg). The two youngest types had the highest values for S20 (10.5 and 11.8 N/cm2), the compression value related to myofibrillar component. There was a very good agreement between panels from the different countries in the ranking of tenderness; meat from the Icelandic breed was the most tender and that from the Bergamasca breed the least, in concurrence with the WBSF results, with a significant relationship between tenderness and WBSF values in all the lamb types studied.

Variability of the masticatory process during chewing of elastic model foods

Many studies show a consistent individual chewing pattern; chewing being governed by a pattern generator and regulated by sensory feedback. The aim of this study was to determine the variation in chewing between sessions, replicates and subjects using elastic model foods. Fifteen young male subjects were selected to chew four food products differing in hardness. Four sessions were performed at 1-wk intervals for each subject and, within each session, the four model foods were presented 3 times each. Jaw movement was recorded simultaneously with masseter and anterior temporalis electromyographic activities. Several chewing characteristics increased progressively from one session to the next; the largest increase occurred from the 1st to the 2nd session, with little difference between the last two sessions. No differences were observed between the samples of the same food product within a session. As mastication progressed, the amplitude and speed of the cycles and the muscular work decreased progressively. The first cycle appeared to be very different from the subsequent for all parameters except for occlusal duration. Thus, under our experimental conditions, the origin and amount of variation in chewing patterns were identified and provide information to improve the accuracy and comparability of results in studies of mastication.

Relationship between muscle growth and poultry meat quality

For a number of years, poultry selection has concentrated on growth velocity in meat lines, producing improvements in growth that have not been without consequence for muscle structure, metabolism, and meat quality. Higher growth rates may induce morphological abnormalities, induce larger fiber diameters and a higher proportion of glycolytic fibers, and a lower proteolytic potential in the muscles. After death, the faster development of rigor mortis increases the likelihood of paler color and reduced water holding capacity and poorer quality of further processed products. Reduced proteolytic potential is likely to increase toughness of poultry meats.

The urinary excretion of orally administered pteroyl-L-glutamic acid by the rat

1. The urinary excretion of folates after oral administration of [2-(14)C]pteroyl-l-glutamic acid was studied by assaying the radioactivity in the urine and in materials purified and characterized by t.l.c. 2. Radioactivity excreted was 6.8, 5.9 and 30.7% of the oral dose in the first 24h after doses of 3.1, 32 and 320mug/kg respectively. 3. Extensive decomposition of urinary folates to pteroyl-l-glutamic acid was prevented by antioxidants or collection of urine frozen. 4. At the three dosages, two major and one minor radioactive compounds were isolated. One of the major metabolites was 5-methyltetrahydropteroylglutamic acid. The others were unidentified but were not pteroylglutamic acid, 7,8-dihydro-, 5,6,7,8-tetrahydro-, 5- or 10-formyl-tetrahydro-, 5,10-methylidyne-tetrahydro-, 5-formimidoyl-tetrahydro-, 5,10-methylene-tetrahydro-, 5-methyltetrahydro-pteroylglutamic acid, nor any decomposition products of these compounds formed during isolation. Labelled unconjugated pteridines were absent. 5. Labelled pteroyl-l-glutamic acid was displaced by oral administration of unlabelled pteroyl-l-glutamic acid (1.6mg/kg) when given 3.5h after, but not when given 24h after the labelled dose. 6. The results show that orally administered [2-(14)C]pteroyl-l-glutamic acid is absorbed without metabolism and is then metabolized into naturally occurring tetrahydro-folates. 7. These findings are discussed with reference to previous work.