Effects of high-pressure processing on color and microbial quality of raw ground pork and pork livers

April Johnson Author

03/29/2021 Added

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The effects of different pressures and initial product temperatures on color, pH, and microbial quality are investigated.

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[00:00:01.940]Hello, my name is April Johnson.
[00:00:03.900]I'm a senior food science and technology student.
[00:00:06.670]And today I'll be presenting my research project
[00:00:10.320]on Effects of High-pressure Processing on Color
[00:00:12.910]and Microbial Quality of Raw Ground Pork and Pork Liver.
[00:00:19.010]High-pressure processing
[00:00:20.270]is a non-thermal cold pasteurization process
[00:00:23.560]used to reduce the number of active microbes in the product.
[00:00:27.560]It's beneficial,
[00:00:28.393]because it has minimal impact
[00:00:29.750]on nutritional quality.
[00:00:31.260]However, qualities such as color
[00:00:32.960]and pH may change after processing.
[00:00:36.090]High-pressure processing causes denaturation of proteins,
[00:00:39.630]so this gives raw meats the appearance of being cooked.
[00:00:44.520]Most studies so far have focused on raw meats
[00:00:47.390]processed at refrigerated and room temperature,
[00:00:50.350]so four degrees Celsius and 20 degrees Celsius.
[00:00:53.610]In this study, the effects of different pressures
[00:00:56.630]and initial product temperatures on raw meat color, pH,
[00:01:00.690]and microbial quality are investigated.
[00:01:05.760]In this experiment, raw ground pork
[00:01:08.170]and pureed pork liver were looked at.
[00:01:11.560]They were processed at pressures atmospheric, 100,
[00:01:16.754]200, 300, 400, 500, and 600 megapascal.
[00:01:20.410]The samples that were inoculated with E.coli 0157:H7
[00:01:25.500]were held at pressures atmospheric, 200, 400,
[00:01:31.937]and 600 megapascal.
[00:01:34.060]The product temperatures we were looking at
[00:01:36.640]were frozen versus thawed/refrigerated temperatures.
[00:01:41.960]So negative 10 degrees Celsius
[00:01:43.770]versus four degrees Celsius initial temperature.
[00:01:47.260]And the pressures were held for three minutes
[00:01:51.060]with three replications
[00:01:52.480]that had two sub-samples per replication.
[00:01:56.420]The materials used to help measure quality measures
[00:02:00.520]were Milwaukee pH meter,
[00:02:03.470]LinkSquare visible and infrared handheld spectrometer,
[00:02:08.090]and a portable colorimeter,
[00:02:09.790]and an infrared thermometer.
[00:02:14.820]To do this experiment, ground pork and pureed pork liver
[00:02:18.950]were molded in mini muffin pans,
[00:02:21.280]and then frozen prior to high pressure processing.
[00:02:24.790]Some of these samples were inoculated
[00:02:27.320]with E.coli 0157:H7 cell suspension
[00:02:31.090]before following the same procedure.
[00:02:34.800]24 hours prior to high pressure processing,
[00:02:38.190]the thawed samples were moved to refrigeration to bring them up to temp.
[00:02:44.748]while the frozen samples stayed constant
[00:02:47.450]at their negative 10 degrees Celsius.
[00:02:50.260]And then the samples were processed
[00:02:52.440]in the Stansted fluid power processing machine
[00:02:57.670]for three minutes at four degrees Celsius.
[00:03:05.971]After high pressure processing,
[00:03:08.090]the non inoculated samples had surface temperature taken,
[00:03:12.884]and then the packages were opened 20 minutes
[00:03:16.273]before taking any color samples or pictures.
[00:03:20.371]And then the color of samples, visible spectrum,
[00:03:24.870]and pH were measured.
[00:03:27.496]And then the inoculated samples were refrigerated 24 hours
[00:03:32.150]before enumerating using aerobic plate counts.
[00:03:38.181]Looked at in this presentation
[00:03:40.296]is color, pH, and microbial steps.
[00:03:45.610]So in the figure you can see
[00:03:47.250]the Delta E color change for ground pork
[00:03:49.963]and pureed pork liver.
[00:03:51.128]Ground pork is represented by circular markers,
[00:03:54.472]whilst pork liver is represented by square markers,
[00:03:58.460]and then the thawed samples
[00:04:00.169]are represented by the dashed lines.
[00:04:05.844]Overall, the thawed samples had a higher color change.
[00:04:12.408]All of the samples had a noticeable change,
[00:04:15.705]whereas the thawed ones had a very noticeable change.
[00:04:19.686]A Delta E change of greater than two
[00:04:22.844]means that you will have a noticeable change
[00:04:26.384]to an unexperienced observer.
[00:04:31.032]And as you can see in these pictures,
[00:04:34.069]you can see this slight variation in color
[00:04:37.107]for the frozen samples as you reached the higher pressures,
[00:04:40.998]whereas in the thawed sample of ground pork
[00:04:45.006]you saw this large change around 400 to 500,
[00:04:49.196]400 mega pascals.
[00:04:55.072]Similar to the ground pork,
[00:04:56.960]in the frozen pureed pork liver
[00:04:58.669]you can see the subtle variation in color
[00:05:01.441]as you reach the higher pressures,
[00:05:04.204]whereas in the thawed pork liver
[00:05:06.537]you see this large change in color around 400 megapascal.
[00:05:13.474]On the table on the left,
[00:05:15.473]you can see the pH's of the ground pork and pork liver.
[00:05:22.271]The ground pork has a higher pH
[00:05:24.372]and the pork liver has a lower pH,
[00:05:26.523]because the pork liver is a more acidic environment.
[00:05:30.983]Overall, in the figure on the right,
[00:05:33.913]you can see that there are small changes in pH
[00:05:37.120]not very significant changes overall.
[00:05:42.208]Then for microbial results,
[00:05:45.752]you can see this drop in the
[00:05:48.743]colony formula units per gram of E.coli
[00:05:52.645]in all of the meat samples.
[00:05:55.211]In the table on the right,
[00:05:56.773]you can see the log reduction of these samples.
[00:05:59.927]And a two log reduction means a 99% reduction is achieved,
[00:06:06.098]and this is used to extend the shelf life of a food product.
[00:06:09.823]Whereas a five log reduction equals 99.999% reduction,
[00:06:15.507]and this is required for pasteurization of foods for humans and pets.
[00:06:24.683]In conclusion, there were minimal color changes
[00:06:27.393]for high pressure processing at 100 to 300 megapascal
[00:06:31.420]for all the samples.
[00:06:33.122]Color changes for frozen meats
[00:06:35.195]were lower than those for thawed meats overall,
[00:06:38.385]and there were small pH changes observed.
[00:06:42.553]High pressure processing
[00:06:44.240]at 400 to 600 megapascals for three minutes
[00:06:47.130]was enough to reduce the E.coli counts by 99%,
[00:06:50.781]which extends the shelf life
[00:06:52.637]of the ground pork and pureed pork liver,
[00:06:56.357]and this was observed in all of the samples.
[00:07:01.253]So I'd like to thank the ARD Undergraduate Research Program
[00:07:05.093]for funding my project,
[00:07:06.943]as well as my advisor, Dr. Mary-Grace Danao
[00:07:10.523]in the Department of Food Science and Technology,
[00:07:13.173]and Dr. Gary Sullivan, in the Department of Animal Science.
[00:07:16.583]I'd also like to thank my lab mates, Dr. Isaac Rukundo,
[00:07:20.443]and Mr. Franklin Sumargo, for their technical assistance.
[00:07:25.390]And I'd also like to thank the audience
[00:07:27.620]for viewing my presentation.
[00:07:29.256]If you have any questions,
[00:07:31.130]feel free to contact me at ajohnson18@huskers.unl.edu,
[00:07:37.002]or my advisor at mdanao2@unl.edu.
[00:07:41.364]Thank you.

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Effects of high-pressure processing on color and microbial quality of raw ground pork and pork livers

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