INFLUENCE OF CONTROLLED MICROBIAL CURING ON PORCINE MUSCLE

SUMMARY— A previously developed technique was adopted to study the influence of certain microbiological populations and their effects on processed meat. The technique consisted of an initial reduction of surface bacteria on conventionally handled muscle tissue via a hot water dip, followed by processing at 28° C in a sterile plastic isolator where Pediococcus cerevisiae was introduced into the curing solution. This treatment was compared to reduced initial count and conventional samples. Identification of the bacteria in the curing solution of each treatment indicated that a Lactobacillus spp. was predominant in the reduced initial count treatment. The inoculated Podiococcus cerevisiae was predominant in the reduced initial count inoculated treatment white Staphylococcus epidermidis and Flavobacterium diffusum were predominant in the conventional treatment depending upon the trial. Tenderness and bacterial load were significantly (P < .01) increased by treatment while pH was significantly (P < .01) decreased. Oxidation and muscle composition were not affected by treatment. Samples from all treatments were acceptable organoleptically.     

THE IDENTIFICATION OF CARBONYL COMPOUNDS IN BEER

Carbonyl compounds were separated from bottom-fermented lager beer by extraction with a diethylether-pentane mixture and precipitation from the extract with 2,4-dinitrophenylhydrazine. The diketones, diacetyl and 2,3-pentanedione, were identified as bishydrazones by thin-layer chromatography with benzene-petroleum ether-ethyl acetate (34:5:1) as solvent and Silica Gel HF₂₅₄ as adsorbent. For the identification of the aldehydes, the hydrazone precipitate was treated with ozone in formic acid solution and the aldehydes were determined as their corresponding carboxylic acids by iso-thermal gas chromatography on a NEGS column. Aldehydes were found in the following order of magnitude: acetaldehyde, isobutyraldehyde, isovaler- and/or opt.act.valeraldehyde (2-methylbutyraldehyde), valeraldehyde and butyraldehyde.     

EFFECTS OF FOUR SPECIES OF BACTERIA ON PORCINE MUSCLE. 1. Protein Solubility and Emulsifying Capacity

SUMMARY– A technique was used to obtain aseptic porcine muscle, portions of which were inoculated with cultures of Pediococcus cerevisiae, Micrococcus luteus, Leuconostoc mesenteroides and Pseudomonas fragi. The inoculated samples were compared with aseptic controls throughout a 20-day storage period at temperatures of 2 and 10°C. All 4 organisms grew at 10°C, but only P. fragi and L. mesenteroides grew at 2°C. The solubilities of the various protein fractions were affected by inoculation treatment. This was exemplified by correlation coefficients ranging from —.37—0.50. The coefficients indicated the interrelationships affected by storage conditions and bacterial growth. Protein solubility studies revealed a loss in the water-soluble fraction during storage of the controls and the M. luteus- and L. mesenteroides- treated samples. Samples inoculated with P. fragi evidenced an initial loss, followed by an increase. The solubility of meat proteins in a salt solution increased during the first 8 days of storage, then decreased or remained relatively constant for all samples. In comparison with controls, samples inoculated with P. fragi increased in salt-soluble protein solubility during the first 8 days, whereas those inoculated with L. mesenteroides decreased during the latter part of storage. Insoluble protein generally increased except for P. fragi- inoculated samples, which decreased. Nonprotein nitrogen (NPN) increased for all treatments and controls during the 20-day storage period. NPN extracted from the samples inoculated with P. fragi increased greatly. The pH increased with growth of M. luteus and P. fragi and decreased with growth of P. cerevisiae and L. mesenteroides. The emulsifying capacity was not influenced by the growth of M. luteus or P. cerevisiae. However, the emulsifying capacity of samples inoculated with L. mesenteroides decreased, whereas that of samples inoculated with P. fragi increased.     

EFFECTS OF FOUR SPECIES OF BACTERIA ON PORCINE MUSCLE 2. Electrophoretic Patterns of Extracts of Salt-Soluble Protein

SUMMARY– Electrophoresis of 0.6 M KCI extracts of porcine longissimus dorsi muscle revealed little change in the type or number of protein bands found either by starch-urea or disc-urea gel electrophoresis. The 0.6 M KCI extracts of muscle samples inoculated with Pediococcus cerevisiae, Leuconostoc mesenteroides and Micrococcus luteus and stored at 2 and 10°C for 20 days did not differ electrophoretically from control samples. Extracts of samples inoculated with Pseudomonas fragi showed a loss in the number of protein bands on starch-urea gel and disc-urea gel electrophoresis, indicating this organism exhibited some proteolytic effect upon the myofibrillar proteins .     

THE INFLUENCE OF LACTIC CULTURES ON GROUND BEEF QUALITY

SUMMARY– The effects of adding 5 and 10% lactic culture (Streptococcus lactis and Leuconostoc citrovorum) grown in skim milk; 2.5, 5, 10, and 20% lactic cultures grown in 20% milk solids; 1 and 2% frozen concentrated lactic cultures; lactic acid to pH 5.0 and 4.5; and 2.5, 5, and 10% skim milk to ground beef stored at refrigeration temperature (7°C) were studied in the 6 preliminary trials. Results obtained were used to formulate the principal investigation. The influence of 10% lactic culture and 10% lactic culture plus 450 ppm of ascorbic acid were tested in 5 replicate trials for the principal investigation. Cultures used in the replicate trials were grown in 20% milk solids. CVT (crystal violet tetrazolium) counts for gram-negative bacteria, pH, VNC (volatile nitrogen content), and organoleptic observations were evaluated. Data from the preliminary study indicated a profound inhibitory action of the lactic cultures on the growth of the inherent gram-negative bacteria in ground beef. The addition of 10% lactic culture grown in 20% milk solids was effective in preventing aerobic growth. The addition of pure lactic acid inhibited microbial growth, but caused an undesirable color and aroma. Frozen concentrated cultures required 1% lactose to inhibit the growth. The CVT count in the uncultured meat significantly increased (P < .01) as the storage time progressed. Cultured meat did not exhibit a significant increase in CVT count until 7 days of storage. The pH of the cultured meat significantly declined (P <.01) whereas the uncultured meat indicated a significant increase in pH (P < .01) during storage. VNC in the uncultured meat was significantly higher (P <.01) than in the cultured meat. Cultured meat with 450 ppm of ascorbic acid was consistently preferred for flavor, aroma, and when color was compared with the uncultured meat and the meat with culture alone.     

INFLUENCE OF FREEZE-DRYING PARAMETERS ON THE RETENTION OF FLAVOR COMPOUNDS OF COFFEE

Freeze-dried coffee powders were evaluated to determine the effect of freezing method and chamber pressure during drying on the retention of coffee flavor components. Headspace gas chromatography revealed at least 14 components of coffee aroma, but minor chromatograph peaks were re moved from consideration, and evaluation was based on the total area of the eight remaining peaks. The results showed that volatile retention was greatest when slowly frozen samples were dried at low chamber pressure. Samples that were foamed prior to slow freezing showed sizably reduced retentions. Slowly frozen samples showed gradually decreasing volatile retention as the pressure increased up to 0.7 torr, and drying at 0.8 torr resulted in a large reduction. Samples which were processed at different chamber pressures so as to give the same powder color showed significant differences in their flavor retention. Almost all the test samples had higher volatile contents than the commercial samples which were tested, though it cannot be sure that this does not reflect differences in coffee extracts.     

EFFECT OF A PORCINE PANCREATIC COLLAGENASE ON MUSCLE CONNECTIVE TISSUE

SUMMARY– Porcine and bovine pancreas as well as porcine spleen, liver and kidney were analyzed for possible collagenolytic activity. Both the porcine and bovine pancreas extracts possessed collagenolytic activity at pH 5.5 and 37°C. The ability of the pancreas extract to break down connective tissue was not due to tryptic or chymotryptic activity, but was due to a combination of collagenolytic and elastolytic activity. The collagenase was partially purified using Sephadex chromatography and was shown to degrade collagen into small soluble peptide fragments.     

INFLUENCE OF AROMA COMPOUNDS ON THE MECHANICAL PROPERTIES OF STARCH-BASED FOOD SYSTEMS

Different starches, and in particular a normal corn starch, were tested in a concentrated and complex food product. Increasing amounts of aroma compounds (limonene, ethyl vanillin or isoamyl acetate) were added at levels up to 5 mmol/mol glucose equivalent. The modifications that were induced in the gel network were characterized by penetrometry or uniaxial compression until fracture. The addition of these aroma compounds led to slightly weaker gel networks than when no flavor had been added. These effects appeared to be not related to the complexing ability of the aroma compound. The addition of isoamyl acetate slowed down the retrogradation phenomenon in corn starchbased products. It seems that the amylopectin fraction of the starch is engaged in the interactions with these aroma compounds.     

TENDERNESS OF PRERIGOR STRETCHED PORCINE LONGISSIMUS MUSCLE

Bone and connective tissues at the 14th thoracic vertebra of one randomly selected side of each of six pork carcasses were cut 90 min postmortem by the Tendercut^TMprocedure, while companion sides served as controls. Carcasses were suspended from the hock tendon and chilled for 24 h. The Longissimus muscle (LM) was removed between the 9th thoracic and 4th lumbar vertebra and divided into three equal sections (locations 1, 2, 3; anterior to posterior) to determine the effect of Tendercut on Warner-Bratzler and Lee-Kramer peak force, sarcomere length, fat and moisture content. Tendercut resulted in lower (P < 0.05) Warner-Bratzler peak force, Lee-Kramer peak force and total energy in all locations within the LM. The average decrease was 14.2% for Warner-Bratzler peak, force and 14.5% and 16.2% for Lee-Kramer peak force and total energy, respectively. The Tendercut treatment also resulted in longer (P < 0.05) sarcomere lengths in all locations within the LM, with an average increase of 19%.     

EFFECTS OF LIVE ANIMAL SAMPLING PROCEDURES AND SAMPLE STORAGE ON THE GLYCOLYTIC POTENTIAL OF PORCINE LONGISSIMUS MUSCLE SAMPLES

Eight hybrid gilts of Hampshire descent were selected at 110 kg live weight, grouped together in one pen and given a one-week adaption period prior to sampling. Longissimus samples (approximately 0.5 g) were taken using spring-loaded biopsy equipment with animals either unrestrained and free to move in the pen or, 3 h later, restrained with a nose snare for two minutes prior to sampling. There was no difference among the two handling approaches for glycolytic potential (P > 0.05). Animals were slaughtered and four longissimus samples (0.5 g) were taken from each carcass immediately following exsangination to evaluate four sample storage methods. Two viable storage methods, freezing in liquid nitrogen followed by freeze drying or immediate homogenization in perchloric acid, yielded relatively high and similar values for muscle glycolytic potential.