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Production and Characterization of Peptidases of Lactobacillus Casei Group
SOME BENEFITS OF POLYPHOSPHATES IN COOKED GROUND CHICKEN MEAT. F. Shahidi* and C. Hong, Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland AIB 3X9. The antioxidative properties of a number of polyphosphate chelating agents, with or without added sodium erythorbate, on the development of warmed-over flavour and rancidity in ground chicken meat was investigated. Sodium acid pyrophosphate was best in retarding lipid oxidation in cooked ground chicken legs and breasts. Sodium erythorbate acted as a strong synergist with the polyphosphates, in general. Soaking of chicken meats in sodium tripolyphosphate solutions, prior to cooking, had some beneficial effect on their oxidative stability. An apparent improvement in the texture and flavour of the treated chicken samples was also observed. ROLE OF METAL IONS IN AUTOXIDATION OF COOKED MEATS. F. Shahidi*, R.B. Pegg and J. Brooker, Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland AIB 3X9. The effect of myoglobin, hemin, Fe(ll), Fe(l 11), Cu(l) and Cu(ll) on the oxidative stability of cooked ground meats was studied over a 21-days storage period at 4°C. All of these compounds had prooxidant effects. The pro-oxidant activity of metal ions was more pronounced at their lower oxidation state, as determined by the 2thio barbituric acid (TBA) test. Addition of disodium salt of ethylenediamine tetraacetic acid (Na2EDTA) or polyphosphates effectively inhibited the pro-oxidant activity of the above compounds. Addition of metal ions to the meats after cooking similarly increased the rate of lipid autoxidation in the above systems, thus reflecting the importance of processing conditions on the oxidative state of cooked meat products. INFLUENCE DE CERTAINES MODIFICATIONS BIOCHIMI· QUES SUR LA TENDRETE DE LA CHAIR DE BUCCIN. J. Lavallee*, L.T. Adambounou l and F. Castaigne. Sciences et Technologie des Aliments, Universite Laval, Quebec, Quebec GIK 7P4, et IUniversite du Quebec it Rimouski, Quebec G5L 3AI. Dans ce travail portant sur la tendrete de la chair de Buccin (Buccinum undatum), nous avons etudie les modifications de la teneur en eau, du pH, de la perte en proteines ainsi qu'en hydroxyproline survenant dans des muscles soumis it differents modes de cuisson et temps d'exposition it la chaleur. Chacune de ces variables est significativement influencee, it des degres differents, par les traitements thermiques (P < 0.05). Ces changements biochimiques ont ete egalement mis en relation avec les differences de tendrete observees dans la chair lors de differents modes et temps de cuisson. SOME PROPERTIES OF PROTEASES FROM PSYCHRO· TROPHIC PSEUDOMONADS. F. Bartlett and T.R. Patel*, Biochemistry Department, Memorial University of Newfoundland, St. John's, Newfoundland AIB 3X9. The heat-stability is possibly the most outstanding feature of the extracellular proteases of psychrotrophic pseudomonads. The protease of Pseudomonas fluorescens TI6 gave D-values of I, 7.2 and 26.7 min. at 150°C, 120°C and 90°C, respectively. Circular Dichroism (CD) spectral analysis of TI6 protease at 5 and 25°C indicated that the protein was primarily a "random" coil with about a third of the molecule consisting of a -structure. No a-helix was detected. Maximum unfoldings was observed at 45-55°C. This temperature range also caused the greatest loss in the protease activity. This temperature dependent conformational change was reversed by cooling a heat-treated sample and storing it on ice. Preliminary tests suggest that proprotease (inactive form) of the enzyme may be present in the periplasmic space of the cell. An enzyme-linked immunosorbent assay (ELlSA) technique using horse-radish peroxidase conjugated to the anti-T16 protease IgG was developed for the detection of proteases in milk. QUALITY CHANGES OF "READY·TO·USE" SLICED VEGETABLES IN RETAIL PACKS. E. Hoehn, Swiss Federal Research Station, CH-8820, Wiidenswil, Switzerland. Prepared sliced vegetable salads in retail packs have become popular in recent years. These products offer convenience to the consumer but have a short shelf-life and may increase the risks of bac370 / Abstract
terial infection if preparation and handling are not adequate. The effect of preparation steps, packaging and storage temperature on quality changes, microbial spoilage and shelf-life were evaluated. The initial viable count of vegetables ranged from IOE5 to IOE8/g. Commercial preparation practices reduce the microbial counts by 90070. Shelf-life depends mainly on storage temperature, as well as packaging and, under refrigeration, is up to five days. SENSORY AND INSTRUMENTAL ANALYSES OF COTTAGE CHEESE FIRMNESS. D. Froehlich*, D. Emmons, J. Elsaesser, D. Beckett and L. Hutt, Food Research Centre, Building #55, Central Experimental Farm, Ottawa, Ontario KIA OC6. The firmness of four commercially available 2070 b.f. creamed cottage cheeses were evaluated by sensory and instrumental analyses. A computerised curd firmness meter was used for instrumental firmness measurement. A ten-member trained panel perceived one cottage cheese as being firmer than the other three, which corresponded to a difference in instrumentally measured firmness of approximately 100 g force. A 41-member consumer-type panel found no significant difference among three of the cottage cheeses in either texture or overall acceptability, but did rate one sample lower overall than the others. Extrapolating from instrumental firmness measurements, the sensory results seem to suggest that the mid-range in firmness of cottage cheese was liked best by the panel. PRODUCTION AND CHARACTERIZATION OF PEPTIDASES OF LACTOBACILLUS CASEI GROUP. G. Arora* and B.H. Lee, Department of Food Science and Agricultural Chemistry, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec H9X lCO; and Agriculture Canada, Food Research Centre, St. Hyacinthe, Quebec. Proteolytic system of lactobacilli, especially the Lactobacillus casei group has gained much attention recently due to their strong peptidase and esterase activity, which has great importance in accelerated maturation and enzyme modification of cheese. However, their utilities and specificities have not been studied. In the present work, cell free extracts of twenty strains of Lactobacillus casei were screened for their extra, intra and membrane bound enzymes through API ZYM (microenzyme) technique, under standardized parameters of growth and disintegration. Four strains selected from the above experiments were further studied for their peptidase production behaviour in relation to growth phases. Specificity of peptidases were determined by chromogenic substrates and polyacrylamide gel electrophoresis. DEVELOPMENT OF A GAS CHROMATOGRAPHIC SYSTEM FOR TRAPPING AND ANALYZING VOLATlLES FROM CANNED WHOLE TUNA. R. Przybylski* and N.A.M. Eskin, Department of Foods and Nutrition, University of Manitoba, Winnipeg, Manitoba R3T 2N2. A sensitive method for trapping and separating volatiles from canned whole tuna is reported. The method involves mixing the contents from the can with sodium suI fate and refluxing at 70°C. The volatiles elicited are trapped on a column immersed in liquid nitrogen which is attached to a capillary column. Part of these volatiles are introduced onto the capillary column using a unique pneumatic system containing a splitting device. Samples analyzed for volatiles by programmed temperature include freshly canned tuna as well as canned tuna samples evaluated by inspectors from the Department of Fisheries and Oceans. THE EFFECT OF CRYOPROTECTANTS ON THE RHEOLOG· ICAL AND STRUCTURAL PROPERTIES OF FRESHW ATER SURIMI. T. Pawtinsky* and M.A.H.lsmond, Food Science Department, University of Manitoba, Winnipeg, Manitoba R3T 2N2. The effects of various cryoprotectants on the texture of surimi produced from three underutilized freshwater fish were examined. Firmness was evaluated using the Ottawa texture measuring system; viscoelasticity was determined with the Bohlin VOR rheometer, set in an oscillatory mode. The storage modulus, G', and the loss modulus, G", were monitored over a frequency of 0.1 to 20.0 Hz; the resultant loss tangent, tan i5 was subsequently calculated. Finally, thin sections, of each fish gel were evaluated microscopically to assess the formation of protein networks. Differences were observed in the firmness, viscoelasticity, and protein networks of the three species depending upon the type of cryoprotectant incorporated. J. Inst. Can. Sci. Techno/. Aliment. Vel. 21, No. 4,1988
terial infection if preparation and handling are not adequate. The effect of preparation steps, packaging and storage temperature on quality changes, microbial spoilage and shelf-life were evaluated. The initial viable count of vegetables ranged from IOE5 to IOE8/g. Commercial preparation practices reduce the microbial counts by 90070. Shelf-life depends mainly on storage temperature, as well as packaging and, under refrigeration, is up to five days. SENSORY AND INSTRUMENTAL ANALYSES OF COTTAGE CHEESE FIRMNESS. D. Froehlich*, D. Emmons, J. Elsaesser, D. Beckett and L. Hutt, Food Research Centre, Building #55, Central Experimental Farm, Ottawa, Ontario KIA OC6. The firmness of four commercially available 2070 b.f. creamed cottage cheeses were evaluated by sensory and instrumental analyses. A computerised curd firmness meter was used for instrumental firmness measurement. A ten-member trained panel perceived one cottage cheese as being firmer than the other three, which corresponded to a difference in instrumentally measured firmness of approximately 100 g force. A 41-member consumer-type panel found no significant difference among three of the cottage cheeses in either texture or overall acceptability, but did rate one sample lower overall than the others. Extrapolating from instrumental firmness measurements, the sensory results seem to suggest that the mid-range in firmness of cottage cheese was liked best by the panel. PRODUCTION AND CHARACTERIZATION OF PEPTIDASES OF LACTOBACILLUS CASEI GROUP. G. Arora* and B.H. Lee, Department of Food Science and Agricultural Chemistry, Macdonald College of McGill University, Ste. Anne de Bellevue, Quebec H9X lCO; and Agriculture Canada, Food Research Centre, St. Hyacinthe, Quebec. Proteolytic system of lactobacilli, especially the Lactobacillus casei group has gained much attention recently due to their strong peptidase and esterase activity, which has great importance in accelerated maturation and enzyme modification of cheese. However, their utilities and specificities have not been studied. In the present work, cell free extracts of twenty strains of Lactobacillus casei were screened for their extra, intra and membrane bound enzymes through API ZYM (microenzyme) technique, under standardized parameters of growth and disintegration. Four strains selected from the above experiments were further studied for their peptidase production behaviour in relation to growth phases. Specificity of peptidases were determined by chromogenic substrates and polyacrylamide gel electrophoresis. DEVELOPMENT OF A GAS CHROMATOGRAPHIC SYSTEM FOR TRAPPING AND ANALYZING VOLATlLES FROM CANNED WHOLE TUNA. R. Przybylski* and N.A.M. Eskin, Department of Foods and Nutrition, University of Manitoba, Winnipeg, Manitoba R3T 2N2. A sensitive method for trapping and separating volatiles from canned whole tuna is reported. The method involves mixing the contents from the can with sodium suI fate and refluxing at 70°C. The volatiles elicited are trapped on a column immersed in liquid nitrogen which is attached to a capillary column. Part of these volatiles are introduced onto the capillary column using a unique pneumatic system containing a splitting device. Samples analyzed for volatiles by programmed temperature include freshly canned tuna as well as canned tuna samples evaluated by inspectors from the Department of Fisheries and Oceans. THE EFFECT OF CRYOPROTECTANTS ON THE RHEOLOG· ICAL AND STRUCTURAL PROPERTIES OF FRESHW ATER SURIMI. T. Pawtinsky* and M.A.H.lsmond, Food Science Department, University of Manitoba, Winnipeg, Manitoba R3T 2N2. The effects of various cryoprotectants on the texture of surimi produced from three underutilized freshwater fish were examined. Firmness was evaluated using the Ottawa texture measuring system; viscoelasticity was determined with the Bohlin VOR rheometer, set in an oscillatory mode. The storage modulus, G', and the loss modulus, G", were monitored over a frequency of 0.1 to 20.0 Hz; the resultant loss tangent, tan i5 was subsequently calculated. Finally, thin sections, of each fish gel were evaluated microscopically to assess the formation of protein networks. Differences were observed in the firmness, viscoelasticity, and protein networks of the three species depending upon the type of cryoprotectant incorporated. J. Inst. Can. Sci. Techno/. Aliment. Vel. 21, No. 4,1988