Sucrose, sodium dodecyl sulfate, urea, and 2-mercaptoethanol affect the thermal inactivation of R-phycoerythrin

Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant-Derived, Low-Acid Foods, and Biomaterials

Cycle threshold (Ct) increase, quantifying plant-derived DNA fragmentation, was evaluated for its utility as a time-temperature integrator. This novel approach to monitoring thermal processing of fresh, plant-based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time-temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low-acid product and simple linear regression, Ct value was highly correlated to time-temperature treatment (R(2) = 0.87); the logarithmic reduction (log CFU/mL) of the spore-forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R(2) = 0.87); and cumulative F-value (min) in a canned retort process (R(2) = 0.88), all comparisons conducted at 121 °C. D121 and z-values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D121 and z-values for a 174-bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof-of-concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low-acid plant products.

Effect of heat on phycoerythrin fluorescence: Influence of thermal exposure on the fluorescence emission of R-phycoerythrin

The goal of this work was to measure and model the effect of thermal exposure on the fluorescence emission of R-phycoerythrin (R-PE). The long-term objective of our work is to assess the feasibility of encapsulating R-PE for use as the critical component of a time-temperature integrator (TTI) for ascertaining the degree of inactivation of food pathogens such as Salmonella. In this article we present a study to measure and model the thermally induced fluorescence emission decay of R-PE in several isothermal experiments. We used the isothermal data to determine the kinetic parameters, based on a general n(th) order reaction, and evaluated the utility of the resulting model by using it to predict R-PE fluorescence emission decay for several nonisothermal experiments based on published USDA safe harbor guidelines for cooked beef products. The transient experiments were conducted over the same temperature range used in the isothermal study. Very good agreement was obtained between theory and experiment at temperatures of 62.8 degrees C and above, although the model slightly underpredicted the extent of fluorescence emission decay at 60 degrees C. Our results indicate that R-PE fluorescence emission decay kinetics is well behaved and that the protein is a strong candidate for use as a time-temperature integrator.