P.A. Koolmees

Determinants of tenderisation in beef Longissimus dorsi and Triceps brachii muscles

Tenderisation of bovine Mm. longissimus dorsi and triceps brachii and factors impacting tenderisation were studied. Mm. longissimus dorsi and triceps brachii of 12 Friesian-Holstein cows (age 3-11 years; 212-349 kg carcass weight) were sampled at various times post mortem (p.m.) for determination of pH, temperature, fibre type and morphology, connective tissue distribution, SDS-PAGE of myofibrillar proteins, Warner-Bratzler shear force, sarcomere length and osmolality. The stretched position of the M. triceps brachii (sarcomere length 2.35 ± 0.24 μm) resulted in a relatively low shear force at 1 day p.m. (6.2 ± 0.9 kg/cm(2)) with further storage having little additional effect. M. longissimus dorsi entered rigor in a more contracted state (sarcomere length 1.65 ± 0.11 μm), resulting in a relatively high shear force at 1 day p.m. (10.3 ± 2.3). Stepwise linear regression was used to calculate the best 1- to 3-variable equations for shear force of M. longissimus dorsi at 1, 7 and 14 days p.m. and the decrease in shear force between 7 and 14 days p.m. Shear force at 1 day p.m. appeared to be determined mainly by the speed of pH- and temperature-decline. Proteolysis of myofibrillar proteins and animal age appeared to be the main determinants for shear force at 1 and 14 days p.m. The average surface area of type I fibres could explain part of the variation in the decrease in shear force between 1 and 14 days p.m.

Immunohistochemical detection of brain tissue in heated meat products

Immunohistochemical methods were used to determine whether brain tissue could be detected in test batches of meat products prepared with known levels of this tissue (0, 1, 5, 10, or 20% bovine brain tissue or 5% porcine brain tissue). Four different, commercially-available antibodies were examined: anti-Neurofilament (anti-NF), anti-MyelinBasicProtein (anti-MBP), anti-NeuronSpecificEnolase (anti-NSE) and anti-GlialFibrillaryAcidicProtein (anti-GFAP). Results obtained with the four antibodies differed with the heat treatment applied to the products (pasteurisation or sterilisation). The amount of immunoreaction product in the raw meat product varied with the antibody, even when the sample contained the same amount of brain tissue. The staining pattern also varied with the antibody. Overall, the anti-MBP antibody proved to be most useful in detecting brain tissue in finely comminuted heated meat products.

Effect of initial mild curing, with additives, of hog and sheep sausage casings on their microbial quality and mechanical properties after storage at difference temperatures

Sausage containers, derived from animal intestines, are usually preserved by salting and/or drying. Adequately salted final products are microbiologically fully acceptable. However casings, even those packed in dry salt, sometimes deteriorate in quality. Experiments were performed to improve salting procedures by adding food-grade additives to the salt to improve the microbiological and mechanical properties of the casings. Before storage, casings were cured by slush- or dry-salting with or without additives for 3 weeks, and after that the rinsed and re-salted (dry- or slush-salting) casings were stored for 6 months at different temperatures (10, 20, and 40°C). During storage, growth of halophylic bacteria was observed in control casings (salted, no additives) but not in casings cured with citric or lactic acid and their relative sodium salts. The casings cured with citric acid/Na(3)-citrate had good mechanical properties and filling characteristics when assessed after prolonged storage at 10°C.

Mechanical and microstructural characteristics of meat doughs, either heated by a continuous process in a radio-frequency field or conventionally in a waterbath.

Meat doughs, all having the same chemical composition, were pasteurised to a comparable heat intensity (calculated as Cook values: target level of 5 min at 100°C): (i) while flowing through a glass tube (inner diameter 50 mm) mounted in a special radio-frequency (27 MHz) heating section; (ii) after flowing unheated through the glass tube at the same rate and heated in a waterbath; and (iii) after sampling immediately after the pump and heated in a waterbath. The cooked products were sampled in the core and at the rim of the product for rheological (oscillation and uniaxial compression tests at small strain), fracture measurements (uniaxial compression tests at high strain) and microstructural evaluation (light microscopy and video image analysis). Additional core samples were used for a sensory evaluation (triangle tests) of the texture of the differently processed doughs. The fast heating rate (25-30 K/min) at a mass flow of the dough of 100 kg/h (mean velocity 0.014 m/s) during dielectrical pasteurisation affected the mechanical character, the microstructure and the triangle test results of core samples from the sausages, compared to heating in a waterbath. Flow of the unheated dough through the tube of the continuous processing equipment, followed by heating in a waterbath, had little effect on the results of the mechanical tests, the microscopical evaluation and the triangle tests. The radio-frequency heated products had both higher storage and loss moduli (were more firm), fractured at higher stress values and were considered more firm in the sensory evaluation. The microstructure of dielectrically heated versus other samples displayed a more open structure of the protein matrix with larger irregularly shaped fat particles that were surrounded by relatively thin and compact protein bridges. The effects of flow and heating method on the behaviour of rim samples were very similar to their effects on the core of the products. A comparison of the mechanical behaviour of core and rim samples only was significant for radio-frequency heated doughs. The rim samples had lower storage and loss moduli and fractured at lower stress values than the core samples. Micrographs of the dielectrically heated rim versus core samples displayed more orientation of connective tissue particles in the direction of flow and of elongated, larger and irregularly shaped fat particles. Probably, shear at the wall of the tube affected the characteristics of the rim samples. All heated doughs displayed hardly and cooking losses. The radio-frequency heated products always displayed a thin layer of moisture on their surface and occasionally a little fat separation.

Participation of breast and leg muscles in shivering thermogenesis in young turkeys and guinea fowl

Abstract Turkey (Meleagris gallopavo) and guinea fowl (Numida meleagris) chicks (0–27 days posthatch) were exposed to decreasing or increasing ambient temperatures. Root mean square electromyographic activity of musculus pectoralis (m. pect.) and musculus iliotibialis (m. iliot.) was recorded simultaneously with O2 consumption and CO2 production. From both muscles, relative mass, water fraction and fibre type were determined. M. iliot. participated in shivering from hatching onwards. The relationship between its root mean square electromyographic activity and ambient temperature resembled that of metabolic rate and ambient temperature, and the shivering threshold temperature was indistinguishable from the lower critical temperature. This suggests that the leg muscles are major contributors to shivering thermogenesis. M. pect. participated in shivering only at days 6–20 in turkeys and at days 6–10 in guinea fowl. Both water fraction and histological analysis indicated that m. pect. was less developed than m. iliot. at hatching. We hypothesize that a minimal level of maturity is required before a muscle can participate in shivering, which is probably represented by a water fraction of about 0.85. Both species recruited the aerobic leg muscles first; the anaerobic breast muscle was recruited only when the rate of mass-specific heat loss was high.

Comparative histological studies of mechanically versus manually processed sheep intestines used to make natural sausage casings.

The natural sausage casings industry is large and worldwide, and casings prepared from the small intestine of sheep form a large part of it. Food safety authorities in several countries have been concerned about the risk to consumers from the bovine spongiform encephalopathy (BSE) agent. Although this agent could enter the European small ruminant population via infected feed, there is no evidence that it has. Because the BSE agent introduced experimentally into sheep and goats has a tissue distribution very similar to that found in animals with natural cases of scrapie, the agent would likely be found in the intestine and lymph nodes of some infected sheep from an early age. When natural casings are prepared from the intestine, the ileum (known to be infected in animals with natural cases of scrapie) is removed and the intestine is cleaned such that the inner (tunica mucosa) and outer (tunica serosa and tunica muscularis) layers are removed, leaving only the submucosa. There are two main methods for cleaning the intestine: manual and mechanical. The cleaning efficiency of these two methods was examined in the commercial environment as practiced on healthy sheep considered fit for human consumption in Turkey and Great Britain. The investigation involved a qualitative and quantitative histological approach. There was no significant difference in cleaning efficiency between the two methods, although there was some variation. No Peyers patches or residues of them were found in any part of the cleaned casings. This finding is important because in sheep infected with transmissible spongiform encephalopathies (TSEs) Peyers patches are likely to contain a major part of the intestinal infectivity. No serosa was found in any casing, but some residual mucosa and muscularis was retained, with more of the former than the latter. The results indicate that the cleaning efficiency of the two methods was broadly equivalent, that there was significant removal of tissue that could promote TSE infection, and that TSE risk reduction likely would be achieved by both methods, although this probability could not be quantified by the methods used in this study.

Quantitative histological analysis of bovine small intestines before and after processing into natural sausage casings

A histological study was undertaken to determine the efficiency in the removal of the mucosa and Peyers patches by standard processing of bovine intestines into natural sausage casings. The second objective was to calculate the quantity of lymphoid and nervous tissue per consumable sausage. For the histological analysis, intestinal samples were collected from 80 beef cattle during the slaughter process. Fresh and cleaned intestines were compared in analyzing the thickness of the intestinal wall, weight reduction during cleaning, removal of the mucosal layer, and the presence of lymphoid and neural tissue after cleaning. The obtained data indicate a weight reduction of about 50% during standard cleaning procedures, as 90% of the mucosa and 48% of the lymphoid tissue are removed. Based on the quantitative histological image analysis, it was calculated that 1 m of cleaned casings, weighing on average 64 g, contains about 2.8 g of mucosa, 0.3 g of lymphoid tissue, and 0.1 g of neural tissue. Assuming, in a worst-case scenario, that the sausage casing is ingested when consuming 200 g of sausage at one meal, this consumption includes 0.09 g of lymphoid tissue and 0.02 g of neural tissue as part of the sausage casing. These data can be included in a risk assessment on the potentialexposure of consumers to bovine spongiform encephalopathy infectivity after eating sausages in beef casings.

Quantitative histo-morphometric analysis of heat-stress-related damage in the small intestines of broiler chickens

The aim of the current research was to present a methodological approach allowing reproducible morphometric and morphological (Chiu/Park scale) analyses of the alterations in the intestines of broilers exposed to heat stress. Ross broilers were exposed over four consecutive days to a high-temperature regime in controlled climate rooms, with a day temperature of 39°C (±1°C) and a night temperature of 25°C (±1°C), respectively. A control group was kept at an ambient temperature of 25°C (±1°C) during the entire experimental period. At the end of the exposure period, the birds were sacrificed and specimens were taken of the duodenum, jejunum and ileum for histology. Blood was collected for oxidative stress analysis. Histo-morphological and morphometric analyses of the intestines indicated that the duodenum and jejunum showed more damage than the ileum. The major alterations in the control intestines were limited to the villus tips, while heat stress led to villus denudation and crypt damage. When compared with morphologically normal villi, heat-stress-associated alterations were also observed in villus height (decreased), villus breadth at base (increased) and epithelial cell area (decreased). Birds exposed to heat stress presented with an increase in glutathione peroxidase activity and a decreased antioxidant capacity. It can be concluded that the chosen model allows a reproducible quantification of heat stress effects, which is suitable for the evaluation of dietary intervention strategies to combat heat stress conditions.

Changes in lightness of porcine lean meat batters during processing

The pattern of changes of lightness (L(∗)) for porcine lean meat batters (PLMBs) with time was divided in two phases: chopping process (Phase 1) resulting in a sharp increase of L(∗), and the subsequent storage of the batters for 24 h at 15°C (Phase 2). During Phase 2, L(∗)-values decreased with time approximating a plateau. The subjects of study were effects on the course of L(∗) of: (1) added sodium chloride and phosphate in Phase 2, (2) the fate of air bubbles embedded in the batters in Phases 1 and 2, and (3) changes in light absorption by the pigment myoglobin in Phase 2. (1) Sodium chloride and phosphate appeared to have very little impact on the changes in L(∗) during storage of the PLMBs at 15°C, although microstructural changes were distinct. (2) Continuous entrapment of air during the chopping process had a major effect on the increase of L(∗) in Phase 1, air bubbles being scattering elements in the PLMB. Disproportionation caused a decrease in the number of small air bubbles, resulting in a decrease of L(∗) during the early stage of Phase 2 (about 35 min), immediately after the chopping stage was finished. (3) Strong evidence was obtained that shifts in the absorption traits of pigments (red nitric oxide myoglobin was formed at the cost of grey met-myoglobin) during the period from 1 to 5 h, caused a marked decrease in the pattern of L(∗) during Phase 2.

Tissue composition of mechanically deboned pork (MDP).

The tissue composition of the mechanically deboned pork produced by a discontinuous pressure system was investigated. By means of quantitative microscopy volume ratios (in terms of volume in volume fractions) of striated muscle, collagenous and elastic connective tissue, bone and cartilage in homogenized samples from eight different producers were determined. Crude protein, fat, calcium and the hard bone residue were determined chemically. In addition, we measured the size of the hard bone particles. The muscle/connective tissue ratio varied from 0·3 to 6·9. The hard bone residue, determined by means of the KOH-method, varied from 0·05 to 0·62%. 0·6% of the bone particles were larger than 3 mm. In addition to chemical analysis we regard quantitative microscopy for the determination of the tissue composition of mechanically deboned pork as imperative for quality control.