An open expiration date (eg use by XXXX) may be a useful means to ensure that a refrigerated food... more An open expiration date (eg use by XXXX) may be a useful means to ensure that a refrigerated food will not be consumed past a date at which it will become unsafe while in distribution in the cold chain. This assumes that the date is the management tool and can be calculated using various pathogen growth kinetics programs based on log normal or logistic functions using data for growth at constant temperature. This assumption is wrought with three problems that could result in an adulterated and unsafe food being consumed before the food reaches the expiration date: (1) it assumes microbial growth models based on measurable lag and log phase kinetics, but we also need to know the initial level of the pathogen and knowledge of the growth rate at below detection levels, i.e. time to detect; (2) It assumes that distribution is at constant temperature while in the real world it will vary; (3) It assumes that if temperature changes, growth kinetics will immediately follow the predicted rate at the new temperature (no history effect). This paper will review the principles of growth kinetics using examples for Listeria, as well as other organisms. The use of both chemical and RFID (radio frequency identity) time temperature integrator tags (TTI) placed on food packages to essentially integrate the time-temperature history and indicate actual shelf life left will be evaluated with respect to cold chain management. Such a tag would be used to make a conservative estimate of time to detect for cold chain management. Thus the time to end of shelf life based on safety criteria would be solved by labeling with the expiration date along with a statement such as "use by the date indicated unless the tag turns red". Shipping based on least shelf life left will reduce loss and potential injury due to pathogens. Expiration dating and food safety Ted Labuza UNIV MINNESOTA
Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly a... more Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly and simply detect ricin and other bioterrisiom agents in complex food matrices such as milk. In this study, we demonstrated a rapid method that combined immunomagnetic separation (IMS) and surface-enhanced Raman spectroscopy (SERS) to detect ricin in whole milk. IMS was used to specifically capture the ricin out of the milk. Then, SERS was applied to analyze the IMS eluate mixed with silver dendrite nanosubstrates. This approach facilitated detection and quantification down to 4 μg/mL ricin in milk within 20 min, based on the results of principal component analysis and partial least squares analysis. The feasibility of using a portable Raman instrument shows great promise for on-site detection in a processing facility.
Moisture-induced protein aggregation through intermolecular interactions such as disulfide bondin... more Moisture-induced protein aggregation through intermolecular interactions such as disulfide bonding can occur in a high-protein-containing food matrix during nonthermal processing and storage. The present study investigated the effect of moisture-induced whey protein aggregation on the structure and texture of such high-protein-containing matrices using a protein/buffer model system. Whey proteins in the protein/buffer model systems formed insoluble aggregates during 3 months' storage at temperatures varying from 4 to 45 degrees C, resulting in changes in microstructure and texture. The level of aggregation that began to cause significant texture change was an inverse function of storage temperature. The protein conformation and the state of water molecules in the model system also changed during storage, as measured by differential scanning calorimetry and Fourier transform infrared spectroscopy. During storage, the model system that had an initially smooth structure formed aggregated particles (100-200 nm) as measured by scanning electron microscopy, which lead to an aggregation network in the high-protein-containing matrix and caused a harder texture.
Moisture-induced protein aggregation in a dry or intermediate-moisture food matrix can contribute... more Moisture-induced protein aggregation in a dry or intermediate-moisture food matrix can contribute to the loss of product acceptability. The present study evaluated the molecular mechanisms and controlling factors for moisture-induced whey protein aggregation in a premixed protein/buffer model system. Insoluble aggregates rapidly formed during the first 3 days of storage at 35°C with a slower rate afterward. Evaluation of the insoluble aggregates by solubility tests in solutions containing SDS/ urea/guanidine HCl/dithiothreitol and gel electrophoresis showed that the formation of intermolecular disulfide bonds was the main mechanism for protein aggregation, and all major whey proteins were involved in the formation of insoluble aggregates. Effects of various factors on aggregation were also investigated, including moisture content, medium pH, and the addition of NaCl. The dependence of aggregation on moisture content was bell-shaped, and the maximal extent of aggregation was achieved at a moisture content of around 70-80% on a dry weight basis.
An open expiration date (eg use by XXXX) may be a useful means to ensure that a refrigerated food... more An open expiration date (eg use by XXXX) may be a useful means to ensure that a refrigerated food will not be consumed past a date at which it will become unsafe while in distribution in the cold chain. This assumes that the date is the management tool and can be calculated using various pathogen growth kinetics programs based on log normal or logistic functions using data for growth at constant temperature. This assumption is wrought with three problems that could result in an adulterated and unsafe food being consumed before the food reaches the expiration date: (1) it assumes microbial growth models based on measurable lag and log phase kinetics, but we also need to know the initial level of the pathogen and knowledge of the growth rate at below detection levels, i.e. time to detect; (2) It assumes that distribution is at constant temperature while in the real world it will vary; (3) It assumes that if temperature changes, growth kinetics will immediately follow the predicted rate at the new temperature (no history effect). This paper will review the principles of growth kinetics using examples for Listeria, as well as other organisms. The use of both chemical and RFID (radio frequency identity) time temperature integrator tags (TTI) placed on food packages to essentially integrate the time-temperature history and indicate actual shelf life left will be evaluated with respect to cold chain management. Such a tag would be used to make a conservative estimate of time to detect for cold chain management. Thus the time to end of shelf life based on safety criteria would be solved by labeling with the expiration date along with a statement such as "use by the date indicated unless the tag turns red". Shipping based on least shelf life left will reduce loss and potential injury due to pathogens. Expiration dating and food safety Ted Labuza UNIV MINNESOTA
Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly a... more Ricin is a potential bioterrisiom agent. There is a critical need for a method that can rapidly and simply detect ricin and other bioterrisiom agents in complex food matrices such as milk. In this study, we demonstrated a rapid method that combined immunomagnetic separation (IMS) and surface-enhanced Raman spectroscopy (SERS) to detect ricin in whole milk. IMS was used to specifically capture the ricin out of the milk. Then, SERS was applied to analyze the IMS eluate mixed with silver dendrite nanosubstrates. This approach facilitated detection and quantification down to 4 μg/mL ricin in milk within 20 min, based on the results of principal component analysis and partial least squares analysis. The feasibility of using a portable Raman instrument shows great promise for on-site detection in a processing facility.
Moisture-induced protein aggregation through intermolecular interactions such as disulfide bondin... more Moisture-induced protein aggregation through intermolecular interactions such as disulfide bonding can occur in a high-protein-containing food matrix during nonthermal processing and storage. The present study investigated the effect of moisture-induced whey protein aggregation on the structure and texture of such high-protein-containing matrices using a protein/buffer model system. Whey proteins in the protein/buffer model systems formed insoluble aggregates during 3 months' storage at temperatures varying from 4 to 45 degrees C, resulting in changes in microstructure and texture. The level of aggregation that began to cause significant texture change was an inverse function of storage temperature. The protein conformation and the state of water molecules in the model system also changed during storage, as measured by differential scanning calorimetry and Fourier transform infrared spectroscopy. During storage, the model system that had an initially smooth structure formed aggregated particles (100-200 nm) as measured by scanning electron microscopy, which lead to an aggregation network in the high-protein-containing matrix and caused a harder texture.
Moisture-induced protein aggregation in a dry or intermediate-moisture food matrix can contribute... more Moisture-induced protein aggregation in a dry or intermediate-moisture food matrix can contribute to the loss of product acceptability. The present study evaluated the molecular mechanisms and controlling factors for moisture-induced whey protein aggregation in a premixed protein/buffer model system. Insoluble aggregates rapidly formed during the first 3 days of storage at 35°C with a slower rate afterward. Evaluation of the insoluble aggregates by solubility tests in solutions containing SDS/ urea/guanidine HCl/dithiothreitol and gel electrophoresis showed that the formation of intermolecular disulfide bonds was the main mechanism for protein aggregation, and all major whey proteins were involved in the formation of insoluble aggregates. Effects of various factors on aggregation were also investigated, including moisture content, medium pH, and the addition of NaCl. The dependence of aggregation on moisture content was bell-shaped, and the maximal extent of aggregation was achieved at a moisture content of around 70-80% on a dry weight basis.
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