New Techniques in the Analysis ofFoods

New Techniques in the Analysis of Foods New Techniques in the Analysis of Foods Edited by Michael H. Tunick Samuel A. Palumbo Pina M. Fratamico and USDA-Agricultural Research Service Wyndmoor, Pennsylvania Springer Science+ Business Media, LLC Ltbrary of Congress Catalogtng-tn-Publlcatlon Data New techniques in the analysis of foods 1 edited by Mic hae l H. Tunick, Samuel A. Palu mbo and Pina M. Fr a t amic o. p. crn . Proceedlngs of an American Chem i cal Society Sy~posl um an New Techniques in th e Analysis of Foods, held Septernber 7-11, 1997, in Las Vegas, Nevada. Includes blbliographlcal refere nce s and Index. ISBN 978- 1-4419-3307-2 ISBN 978- 1-4757-5995-2 (eBook) DOI 10.1007/978-1-4757-5995-2 1. Food --Analysis. I. Tunick, Mi chael. II. Palu mbo, Samuel A. III. Frataoico, Pina M. IV. Amer i can Chemical Society Sym posium an New Techniques in the Analysis of Foods t1997 Las Vegas , Nev adal TX541 . N53 1999 664' .07--dc21 98-48207 CIP Proceedings of an American Chemica1 Society Symposium on New Techniques in the Analysis of Foods, he1d September 7- 11, 1997, in Las Vegas, Nevada ISBN 978-1-4419-3307-2 © 1998 Springer Science+Business Media New York Originally published by Kluwer Academic 1 Plenum Publishers, New York in 1998 10987654321 A C.l.P. record for this book is avai1able from the Library of Congress. Ali rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher PREFACE The contributions in this volume were first presented at a symposium organized by the editors and held at the 214th National Meeting of the American Chemical Society in Las Vegas in September, 1997. The symposium was sponsored by the ACS Division of Agricultural and Food Chemistry and covered recent developments of interest in food analysis. Many changes have occurred since the standard textbooks on food analysis were published: E. coli 0 157:H7 has leaped into prominence, requiring new and rapid methods of detection; MALDI-MS was developed and used in food analysis for the first time; electron microscopy, fluorescence spectroscopy, and electrorheology have been applied to cheese, bread, meat, and chocolate, new methods for monitoring and predicting shelf life have been introduced; new techniques for determining the composition of food have evolved. This book includes many emerging approaches which food scientists may find useful and probably will not find in a textbook. The editors thank the authors whose work is presented in these chapters, the Division of Agricultural and Food Chemistry for agreeing to hold the symposium, and our editors at Kluwer Academic I Plenum Publishers whose assistance made our task easier. Michael H. Tunick Samuel A. Palumbo Pina M. Fratamico v CONTENTS Physical Properties I. Transmission Electron Microscopic Imaging of Casein Submicelle Distribution in Mozzarella Cheese .... . . ....... . . ... . . . . ... . . . . . . . ........ . . Michael H. Tunick, Peter H. Cooke, Edyth L. Malin, Philip W. Smith, and V. H. Holsinger 2. Confocal Microscopy of Bread ....... . ............. . . . .... .... ..... .. . Yael Vodovotz and Pavinee Chinachoti 3. Dimensional Analysis of the Electrorheological Behavior of Milk Chocolate Christopher R. Daubert and James F. Steffe 9 19 4. Extracting Useful Information from Irregular and Irreproducible Mechanical and Other Signatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Micha Peleg 37 5. DSC Analysis of Starch Thermal Properties Related to Functionality in Low-Moisture Baked Goods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Louise Slade, Harry Levine, Martha Wang, and James Ievolella 53 6. Phase Transitions of Soy Globulins and the Development of State Diagrams Alfredo Morales and Jozef L. Kokini 7. A Novel Fluorescent Method for Rapid Screening of Compounds for Antioxidant Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Arti Arora and Gale M. Strasburg 69 79 Microbiological Analyses 8. An Overview ofMethods for Identification of E. coli 0157:H7 . . . . . . . . . . . . . . Mary Lou Tortorello and Diana Stewart 91 vii Contents viii 9. A Surface Plasmon Resonance Biosensor for Real-Time Immunologic Detection of Escherichia coli 0 157:H7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pina M. Fratamico, Terence P. Strobaugh, Marjorie B. Medina, and Andrew G. Gehring I 0. Bioluminescence: Shedding New Light on Old Problems . . . . . . . . . . . . . . . . . . . Mansel W. Griffiths II. Use of the Submerged-Coil Heating Apparatus in the Study of Thermal Resistance of Foodbome Pathogens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vijay K. Juneja and Arthur J. Miller I 03 113 131 12. A Rapid Method for Predicting the Potential Shelf-Life of Fresh Chicken . . . . . . Scott M. Russell 143 13. Rapid Impediometric Method to Determine Crustacean Food Freshness LoriN. Cotton and Douglas L. Marshall 147 Compositional Analyses 14. Rapid Methods for Compositional Analyses of Meat and Meat Products . . . . . . . Joseph G. Sebranek 15. A New Mass Spectrometric Method for the Regiospecific Analysis of Triacylglycerols in Edible Oils and Fats . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hazel R. Mottram and Richard P. Evershed 16. MALDI-MS for Food Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peter Spoms and Darcy C. Abell 17. Analysis of Food Carbohydrates: Sugars, Starches, and Dietary Fiber Polysaccharides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Betty W. Li 18. Determination of Nitrate and Nitrite in Meat and Dairy Products...... ... .... Daniel C. Siu, Alan Henshall, and Walter A. Ausserer Index 161 171 181 193 201 211 1 TRANSMISSION ELECTRON MICROSCOPIC IMAGING OF CASEIN SUBMICELLE DISTRIBUTION IN MOZZARELLA CHEESE Michael H. Tunick, Peter H. Cooke, Edyth L. Malin, Philip W. Smith, and V. H. Holsinger U.S. Department of Agriculture Agricultural Research Service, Eastern Regional Research Center Wyndmoor, Pennsylvania 19038 1. INTRODUCTION The increased demand for reduced-fat dairy products has spurred research into low fat (LF) cheeses, including Mozzarella. The LF Mozzarella procedure developed in our laboratory has been scaled up and tested in schools 1 and is now being served on pizzas in the National School Lunch Program 2 . We have conducted studies with different cooking temperatures and homogenization pressures to determine the effects on casein breakdown, rheological properties, and microstructure in LF Mozzarella 3 •4 , and are using these results to improve the quality of this cheese. The effects of coagulant type on composition, proteolysis, and physical properties of full fat Mozzarella have been reported recently. Berg et a/. made Mozzarellas by the direct acid method using calf chymosin, bovine pepsin, porcine pepsin, and Rhizomucor miehei (formerly Mucor miehei) as coagulants'. The calf chymosin cheese had the greatest melt and smallest stretch, the porcine pepsin cheese had the least melt and largest stretch, and the other two cheeses were similar to each other. Coagulant type did not affect pH, moisture, or browning. Yun , Barbano, and Kindstedt prepared full-fat Mozzarellas with Cryphonectria parasitica (formerly Endothia parasitica), R. miehei, and chymosin derived by fermentation, and found no differences in pH, moisture, fat, and protein 6 . The C. parasitica cheese underwent more proteolysis of a, 1-casein than the others and was the only one in which P-casein was broken down. There were no significant rheological differences among the cheeses, however 7 • Electron microscopic imaging can be performed on cheese to examine its structure. Previous studies in this laboratory have shown that the microstructure of Mozzarella changes during refrigerated storage 8•9 • Rearrangement of casein submicelles was observed, and a technique for examining their spacing and distribution was developed . The rearNew Techniques in the Analysis of Foods. edited by Tunick era/. Kluwer Academic I Plenum Press, New York, 1998. M. H. Tunick eta/. 2 Table I. Coagulants used in preparation of Mozzarella cheeses Coagulant Strength Chr. Hansen's calf rennet Marschall Marzyme Supreme® Pfizer Surecurd® single double triple Enzyme chymosin Rhizomucor miehei (formerly Mucor miehei) protease Cryphonectria parasitica(fOrmer/y Endothia parasitica) protease rangement may have been related to proteolytic breakdown of casein. The purpose of this study was to investigate the effect of coagulant type on rheology and microstructure of LF Mozzarella. Electron microscopic imaging was performed to determine if the coagulant type influenced the arrangement of casein submicelles. 2. MATERIALS AND METHODS 2.1. Cheese Preparation LF Mozzarella cheeses were prepared using the method of Tunick et al. 8 Two batches were prepared each week on different days and three replicates were made from each coagulant shown in Table l. 2.2. Compositional Analyses Percentage of moisture was determined by the forced-draft oven method 10 and percentage of fat was measured by the modified Babcock method 11• Fat in dry matter (FDM) was calculated as(% fat)/(100-% moisture). Moisture in nonfat substance (MNFS) was calculated as(% moisture)/(100-% fat). Three replicates of each sample were analyzed after I wk of storage. 2.3. Rheological Analyses Hardness and springiness were determined by texture profile analyses performed at 22-24oC on an Instron model 4201 Universal Testing Machine (Instron, Inc., Canton, MA) 3 ' 12 • Elastic modulus (G ' ) and viscous modulus (G") were measured at 22- 24°C at a frequency of 100 rad/s by a Rheometries Dynamic Analyzer model RDA-700 (Rheometries, Inc., Piscataway, NJ)3' 12 • Meltability, which is unitless, was determined by the Schreiber tese·' 2, in which the increase in diameter of a cheese disk is measured on a target graph of concentric circles after 5 min of heating at 232 °C. All tests were performed in triplicate at l and 6 wk. 2.4. Microscopy The microstructure of cheese samples after I d and 6 wk of storage was examined by scanning electron microscopy (SEM) 3 • Cubes measuring approximately 5 mm on a side were removed from the interior of the cheese with a razor and fix ed in a solution of I% glutaraldehyde in 0.1 M sodium cacodylate at pH 7.2. The samples were washed in 0.1 M sodium cacodylate buffer, soaked in 2.0 mL of 2% osmium tetroxide-0.1 M sodium cacodylate buffer for 2 h, and rinsed with distilled water. The samples were dehydrated in a graded ethanol series containing 50, 80, 90, and 100% ethanol. After extraction with three 3 Transmission Electron Microscopic Imaging in Mozzarella Cheese A B Figure I. Sequential processing steps on TEM images of Mozzarella. (A) Photographic print. (B) Digitized image of photographic negative. (C) Flattened, brightness-enhanced, and contrast-enhanced. (D) Binary image from gray level segmentation. (Reprinted from reference 8 with kind permission from Elsevier Science Ltd. , The Boulevard, Langford Lane, Kidlington OX5 1GB, UK). changes of chloroform to remove lipids, the samples were transferred into ethanol, freeze fractured into liquid nitrogen, thawed into ethanol, and dried at the critical point in carbon dioxide. The dried blocks were mounted on aluminum stubs, coated with a thin layer of gold in a DSM-5 Cold Sputtering Module (Denton Vacuum, Inc., Cherry Hill, NJ), and examined by secondary electron imaging in a JEOL model 840A scanning electron microscope (JEOL USA, Peabody, MA) at an instrumental magnification of 1OOOX. Transmission electron microscopy (TEM) was used to examine the ultrastructure of cheese samples after I d and 6 wk of storage 8·9 . Samples were cut, fixed, washed, and dehydrated as above. They were then transferred to propylene oxide, infiltrated overnight with 50% propylene oxide-50% epoxy resin embedding medium (Electron Microscopy Sciences, Fort Washington, PA), and embedded with 100% epoxy resin. Thin sections measuring ) . Volume ratio, which describes the fraction of the total volume in the particulate phase, is a very important parameter in the ER phenomenon. Generally, the shear stress and apparent viscosity of ER suspensions increase with concentration 10' 14 .1t has been observed that volume fractions are generally in the range 0.1 : -: : 4> : -: : 0.4 2.4' 14'21. Below this range, there is generally no observable viscosity enhancement associated with ER. However, high concentrations of solid matter can cause the loss of fluidity of the materiaL An optimum volume ratio exists where the shear stress can be maximized while still maintaining fluidity when exposed to electric fields 7 • In addition, higher concentrations may lead to contact across the electrode gap, essentially shorting the system, causing loss ofER activity4. C. R. Daubert and J. F. Steffe 22 /./ .5. Dielectric Properties (s). Dielectric properties of a two phase ER system determine the magnitude of the suspension response to an electric field. The continuum, usually an insulating oil, must have a low dielectric constant so it can withstand exposure to large electric fields without suffering from dielectric breakdown 4 •5·w. For water based ER materials, water absorbed in the particles create a large dielectric mismatch between the phases (£c*EP). This is why many researchers have concluded that a certain amount of water is essential for a strong ER response. The permittivity of the solid phase is significantly greater than the insulator permittivity ( Ec ;:[' J _... \ Tr;:['-J'_,. l ~ :;;~,~- ~ _,\TP£ - e ., "l Infection of ho t by bacteriophage ~­ ' _..1\ TP;:[' ...,,~ t :.-r.TI; Lysi ofhost by bacteriophage Figure 3. The principle of the phage-lysis ATP assay. ever, problems were encountered due to non-specific binding of non-Salmonella and the presence of adenylate kinase as a contaminant in the bovine serum albumin used as a blocking agent to try and prevent that problem. The second strategy described by Murphy et al. 20 is probably more promising. This involves the use of host-specific bacteriophage to specifically lyse bacterial cells. An indication of the level of contamination by the target organism can then be obtained by either assaying for ATP directly 23 · 24 or indirectly using the adenylate kinase assa/ 0 (Fig. 3). The sensitivity using the ATP bioluminescence assay is about I 0 5 cells and results can be achieved in about 60 minutes (Fig. 4). This is an extremely promising approach for the rapid and specific detection of foodbome pathogens. 100000 ...-... :::> ...J a: 10000 (l) --- (.) c (l) (.) (/) 1000 (l) c E :::J '• --- --- -· -.. ... 100 ...J 10 0 30 120 90 60 Time (mins) ;e (JQ - ·;;: ~ .. ...l =..= 4 rl:l ~ ! 2 0 0 20 40 60 80 100 Time (sec) Figure 2. Thermal inactivation of microorganisms based on first order rate kinetics. V. K. Juneja and A. J. Miller 134 t Shoulder Tailing t Time Figure 3. Thermal inactivation of microorganisms showing a shoulder, a linear decline and a tailing. when the bacterial populations remain at the inoculation level; b) a tailing, i.e., a subpopulation of more resistant bacteria that decline at a slower rate (Figure 3). 2.1. Traditional Methods Existing methods for thermal inactivation of microorganisms include thermal death time tube, flask, thermoresistometer, and capillary tube methods 4 . These methods suffer from many disadvantages including: l) time consuming operations; 2) appreciable heating and cooling lags; 3) splashing of contents; 4) flocculation; 5) high initial cost; and 6) hazard of contamination during subculturing, etc.4 . Additionally, using traditional methods the published literature on the heat resistance of certain organisms, such as L. monocytogenes is conflicting. While strain diversity, physiological conditions of the microbial cells, and methodology used for the detection of survivors affect the thermal resistance of microorganisms, the disagreement among the results obtained by different researchers, in addition, is attributed to the method used for assessing the heat resistance. Using the holding technique of pasteurization in screw-capped test tubes in a water bath (61.7"C, 35 min), survival occurred when L. monocytogenes population levels exceeded 3 log cfu/ml 5 • In contrast, using sealed borosilicate glass tubes, Bradshaw reported that L. monocy togenes was unable to survive pasteurization6 . Donnelly eta!. (1987) compared heat resistance of L. monocytogenes using the sealed tube and test tube methods and concluded that survival of the organism at pasteurization temperatures depended on the method used to inactivate cells, and is not a biological phenomenon. Using the sealed tube method of inactivation, L. monocytogenes was easily inactivated at pasteurization temperatures. However, when an identical cell population was heated using the test tube inactivation method, extensive tailing of survivor curves was consistently observed, regardless of the heating temperature which was 62, 72, 82 or 92 oc. As an explanation for the tailing observed using the test tube method, the authors stated that the condensate and splashed cells could collect in the cap of the test tube above the level of the water bath, and drip back into the heating menstrua; tubes will have various levels of survivors depending on the amount of condensation in the cap. Also the authors indicated that cells could coat the walls of the test tubes 135 Use of the Submerged-Coil Heating Apparatus above the level of water bath; the only cell population exposed to the inactivation temperatures would be that which is below the level of water in the water bath 7• 2.2. Data Collected Using Submerged-Coil Heating Apparatus A number of researchers have used the submerged coil heating apparatus to assess the heat resistance of various foodborne pathogens. Juneja used the apparatus to determine the influence of pH, acidulant and growth temperature history on the heat resistance of L. monocytogenes strain Scott A. In that study, brain heart infusion broths (BHIB, I00 ml), adjusted with appropriate amounts of one molar stock solution of lactic or acetic acid to pH values 7 or 5.4, were inoculated with 0.1 ml of an I 8 h L. monocytogenes culture, and then incubated at 37", 19 ° or IOoC to late exponential phase (OD600nm = 0.6). Thereafter, the broth suspensions were tested for inactivation kinetics variability at 60oC using the submerged coil heating apparatus. During the heating procedure, samples (0.2 ml) were removed at predetermined time intervals. Where low cell numbers were expected 0.6 ml aliquots were removed. Samples were cooled rapidly in room temperature peptone (0.1% w/v) water. The recovery plating medium used for enumeration of survivors was tryptic soy agar (Difco) supplemented with 0.6% yeast extract and 1% sodium pyruvate. In this study, D-values significantly decreased (p < 0.05) with increased growth temperature, when the pH of the growth medium was 5.4; the values significantly increased (p < 0.05) with increased temperature at pH 7, regardless of acid identity (Table I). As depicted in Table I, low standard deviations (repeatability) permit accurate separation of means of treatments. The shape of the survivor curves was linear, i.e., log number of survivors declined in a linear manner with time (first order). At pH 5.4 adjusted with lactic acid, Dvalues ranged from 1.30 min for !OoC grown cells to 1.14 min for 37"C grown cells. At pH 5.4 adjusted with acetic acid, L. monocytogenes failed to grow at !O oC; the D-values were 1.32 and 1.22 min when the organism was grown at 19 ° and 37" C, respectively. Dvalues of cells cultured at a particular temperature were significantly lower (p < 0.05) when lactic acid was used to acidify the medium to pH 5.4. At pH 7 adjusted with lactic acid, D-values were 0.95, 1.1 2, and 1.28 min for 10 °, I9 °, and 37"C grown cells, respectively; the values ranged from 0.83 min for Io oc grown cells to I. I I min for cells grown at 37 °C and pH adjusted with acetic acid. Alternatively, if conditions can be found that produce a more susceptible cell, this can be exploited8 • In another study by Juneja9 , the authors used the submerged coil heating apparatus to determine the effect of heat shocking Escherichia coli 0157:H7, inoculated in a model beef gravy (formulation: Protease peptone 1.5%, Beef extract 5.0%, Yeast extract 0.5%, Soluble starch I. 7%) on its thermotolerance and the persistence of the thermotolerance at 4, 15, and Table 1. Influence of pH, acidulant and the growth temperature on the D-values of Listeria monocytogenes at 60°C pH 5.4 Temperature 10 19 37 Lactic 1.30' b ± 0.02 1.22"" ± 0.01 1.14 .:::~ oii Q "'""'c :I r.IJ= ! 7 6 5 4 3 2 0 500 1000 1500 2000 Time (sec) Figure 6. Survivor curves of Escherichia coli 0 157:H7 grown in acidogenic (.A.) and non-acidogenic (e) medium and then heated in UHT non-fat, milk (pH 6.5) at 58 °C. and their time for 5-D values were equivalent. While enhanced heat resistance did not occur with the TSB+G grown cells, their survivor curves (not shown) did continue to deviate from the linear inactivation kinetics associated with the TSB-G grown cells. This study demonstrated that the pH-dependent stationary phase can increase substantially the thermal tolerance of E. coli 0157:H7. If not considered when developing thermal process specifications, this could lead to insufficient heating times. These studies clearly indicate that the submerged coil apparatus can be used to assess the heat resistance of bacteria in a variety of liquid foods. Jorgensen 12 used the submerged coil apparatus, set at 58 °C, to assess the effect of growth temperature and post heat shock incubation temperature on heat shock induced thermotolerance and the persistence of this thermotolerance in L. monocytogenes. The authors reported that the cells, grown at W or 30 °C, showed no differences in thermotolerance but were significantly (p < 0.001) more heat resistant (1.5-fold) than cells grown at 4 oc (Table 5). In this study, exposing cells grown at woe and 30 °C to a heat shock resulted in similar increases in thermotolerance but this increase was significantly (p < 0.001) higher when cells were grown at 4 oc prior to the heat shock. The authors reported that the loss of heat shock induced thermotolerance after a temperature downshift was clearly dependent on the temperature at which the cells were held after the heat shock. Cells held at 4 oc and woe after heat shock maintained heat shock-induced thermotolerance for longer than cells held at 30°C. Even after 48 h, cells grown and held at 4 oc after the heat shock were two-fold more heat resistant than non-heat shocked cells grown at 4 °C. The effect of growth temperature prior to inactivation had negligible effect on the persistence of heat-shock-induced thermotolerance. For example, cells grown at 4, I 0 or 30 oC showed the same decrease when held at 30°C after the heat shock. In another study, Jorgensen 13 used the submerged coil heating apparatus to determine the effect of osmotic up-shock and down-shock, and osmotic adaptation using different levels ofNaCI on the corresponding changes in thermotolerance of L. monocytogenes. In this study, subjecting cells to an osmotic down-shift (1.5 moles/ml to 0.09 moles/ml) caused a rapid loss of thermotolerance rendering cells 10-fold more heat sensitive than cells grown and heated in TPB containing 1.5 moles/ml NaCl (Table 6). Subjecting cells V. K. Juneja and A. J. Miller 140 Table 5. Influence of incubation temperature and time after heat shock on the inactivation of Lis feria mono(:l'fogenes cells grown at 4. I 0, or 30 °C. Temperature of post heat shock incubation (C) Heat-shock (30 min at 46 ' C) Growth temperature of cells (°C) 4 10 30 4 10 30 4 10 4 10 30 No No No Yes Yes Yes Yes Yes Yes Yes Yes Time after heat shock (h) Time to 4 log cfu/ml reductions (min) 0 0 0 48 24 4 4 4 3.4 5.4 5.1 19.8 15.0 14.8 7.1 6.6 7.6 6.5 7.1 4 10 30 30 30 (Adapted from .Jorgensen. ct a\. 19'16 ) grown in media containing 0.9 moles/ml NaCI to a short osmotic up-shock in media containing 0.5, 1.0 or 1.5 mol/ml NaCI resulted in 1.3, 2.5 and 8-fold increase in thermotolerancc, respectively. When cells were allowed to adapt to high salinities, an additional twoto threefold increase in thermotolerance occurred compared to cells subjected to an osmotic up-shock at the equivalent level of NaCI. Colet 4 determined the inactivation of L monocvtogenes in a submerged coil heating apparatus at 45 combinations of temperature (56, 60, and 62 °C), hydrogen ion concentration (0.1 to 57.5 uM; pH 7.0 to 4.24). and added sodium chloride (0, 3, or 9%). The survivor data did not fit the traditional log-linear relationship. A logistic function of log number of survivors versus log time described the results. N, = a 1 + [(a 2 - a 1)/(I + exp((4k(t- t)/a 2 - a,)))] where N, was the log number of survivors. a 1 was the upper asymptote ( = N0 ), a 2 was the lower asymptote, t was the time of the maximum slope, k was the maximum slope, and t was the log"' time. For these 45 combinations, the values of a 1 , a2 and k were not signi fi- Table 6. EtTect ofNaCI treatment during growth and heating on the heat resistance of Lisreria monocyrogenes at 60 °C NaCI content (moles/ ml) Treatment to NaCI Control Up-shock Adaptation Growth medium Heating menstruum 0.09 0.09 0.09 0.09 0.50 1.00 1.00 1.50 1.50 0.09 0.50 1.00 1.50 0.50 1.00 1.00 1.50 0.09 (Adapted from .Jorgensen ct a\.. I 996) Time to 4-D inactivation (min) 1.6 2.0 4.6 13.2 2.5 7.4 7.4 38.1 3.8 Use of the Submerged-Coil Heating Apparatus 141 cantly different. In this study, a polynomial regression equation for -r was determined with terms for temperature, salt, and hydrogen ion concentration. 3. CONCLUSIONS The submerged coil heating apparatus is easy to operate and its usefulness for determining the thermal tolerance of bacterial pathogens has been demonstrated. Experimental errors due to variability attributed to different technicians are minimal. Since the equilibrium or come-up time of the samples is negligible, no bacterial inactivation occurs during this period. Sampling intervals and the number of samples to be dispensed are electronically controlled. The heat resistance of microorganisms in a variety of liquid foods can be quantified accurately since the reproducibility of the thermal inactivation determinations is excellent. The only disadvantage is that the apparatus cannot be used for assessing the heat resistance of microorganisms in solid foods. REFERENCES I. M.B. Cole and M. V. Jones. 1990. A submerged-coil heating apparatus for investigating thermal inactivation of micro-organisms, Leus. App/. Microbial. II :233-235. 2. R.L. Tomlin and Z.J. Ordal. 1976. Thermal injury and inactivation in vegetative bacteria. Soc. Appl. Bacterial. Symp. Ser. 5:153-190. 3. V.K. Juneja, O.P. Snyder, Jr, and B.S. Marmer. 1997a. Thermal destruction of Escherichia coli 0 157:H7 in beef and chicken: Determination of D- and z-values. In t. J. Food Microbial. 35:23 1- 237. 4. C. R. Stumbo. 1973. 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(Accepted). I 0. A.J. Miller and B.S. Eblen. 1997. Enhanced thermal sensitivity of Listeria mono0.05). For sensory and microbial analyses, replication was not a significant source of variation (P>0.05); however, treatment, time, and treatment by time were significant (P[...]... is over 70% starch which may have minimized the intra-molecular interaction between the protein molecules by physically interrupting the tendency of gluten to clump resulting in a dispersed network of gluten upon denaturation (heating) The dough is worked significantly resulting in an increased chance of protein-protein interaction resulting in aggregation and clumping of Figure 6 Confocal microscopic... with each other but instead in discrete moieties dispersed throughout Gluten appears to form an internal continuous network or web within the cell wall, while starch remains, in the most part, discontinuous, phase separated and covering part of the gluten on the cell wall surfaces To better characterize the origin of the bread microstructure, changes due to hydration and baking were examined Figures... differentiate between the state of the different components (crystalline or amorphous), however a combination of techniques would be necessary to obtain a more complete "picture" of the changes that occurred in the bread Additionally, the light microscope in its various forms has a limited resolution and the information obtained from the observed images reflects this shortcoming Changes occurring in the bread... microscopy In order to maintain the bread structure during sectioning, crumb samples (1-2 em) were dehydrated with 100% ethanol in small vials and kept at -4 oc until sectioning The ethanol was then removed from the samples and replaced with the embedding medium, L R White™ (London Resin Comp Ltd., Hampshire, U.K.) The medium was allowed to penetrate the sample (constant rotation for 24 hours) then poured into... with gluten The starch was stained using the periodic acid-Schiff's reaction which relies on the detection of aldehydes being formed by the reaction of periodic acid and the starch (l 0) The following method was used for staining bread and dough samples: I Oxidize starch for 5 min in periodic acid (0.5% H5106 aq ) 2 Wash in several (5 or more) changes of deionized water 3 Stain 10 min in Schiff's Reagent... in Schiff's Reagent 4 Wash I, 2, 2 min in 0.5% K2Sp5 5 Wash in water 6 Stain with Cy3 dye for 3 min 7 Wash off the excess stain The CH gluten and CH flour were stained with the FluoroLinkT\1Cy3™ only After staining the cover slip was floated on a slide with a preformed wax well containing distilled water (Figure 2) Scanning Laser Confocal Microscopy was performed using a BioRad MRC600 Confocal microscope... rates, the Mn will be less than unity; therefore, the polar forces dominate At large Mn, the viscous forces completely dominate the response and the fluid behaves like it would in the absence of an electric field; the relative viscosity is independent of the electric field According to Klingenberg et al., 33 when Mn >> l, the electric field has no effect on the system viscosity As Mn approaches unity, the. .. force dominance of the ER microstructures At high Pe and low A, a sliding string phase occurred, where the particles were oriented along lines of constant velocity within the shear field; the phase was destroyed by increasing A Few publications dedicated to studying the effects of Peon the ER response were identified 1.3 Objective For the food industry, ER technology may offer new potential in process... placed into the MV cup to start each test The cup was placed in the measurement position and the water jacket temperature was set to the test temperature allowing the chocolate to melt After the molten chocolate attained a uniform temperature, the cup was removed from the viscometer and temporarily set aside Immediately, the ER bob was attached to the viscometer and the sample cup, holding the molten... meaning the polar forces are dominating the response over the thermal forces 13 • ER structures are likely to occur if the electrical forces can overcome the thermal effects For large A, the particles are expected to form highly elongated structures 34 Generally, in all but the very weakest ER fluids, A will be much greater than unity, and polar forces dominate thermal forces when establishing the ... during refrigerated storage 8•9 • Rearrangement of casein submicelles was observed, and a technique for examining their spacing and distribution was developed The rearNew Techniques in the Analysis. .. routinely applied in research and the design of engineering systems They are discussed in great detail in the vast literature on the analysis of time series, chaos and fractals The following will only.. .New Techniques in the Analysis of Foods New Techniques in the Analysis of Foods Edited by Michael H Tunick Samuel A Palumbo Pina M Fratamico and USDA-Agricultural