A new method for determining thermal treatment of particulate foods for aseptic processing
Abstract
Safety of the aseptic thermal process for particulates is a major concern; there is a need to develop techniques to indicate if adequate heat processing was achieved. Methylmethionine sulfonium (MMS), found widely in vegetables and fruits, was used as an example of an indicator for thermal process quality. Upon processing, it decomposes to homoserine and dimethyl sulfide (DMS). MMS has principally been measured qualitatively by paper and thin layer chromatography or quantitatively using gas chromatography for its decomposition product DMS. The method of amino acid derivatization and analysis by gas chromatography was adapted for measuring MMS because of its similarity in structure to amino acids. Mass spectrometry confirmed elution patterns and breakdown products, including the intermediary homoserine lactone and 2 new compounds (acetoxyhomoserine and chlorohomoserine) which may be a result of the derivatization. MMS and methionine (MET) elute at the same point; MMS is thermally unstable, whereas MET is stable. Chemical kinetics of MMS in model solution systems of sodium citrate buffers spanning the high/low acid food pH range (pH 4 to 6) were studied at UHT processing conditions of 121.1$\sp\circ$C to 132.2$\sp\circ$C utilizing a TDT system and were first order. Reaction rate kinetics were base driven. This data was compared to that obtained from the study of MMS destruction in chemically set 1.27 and 2.54 cm side sodium alginate food cubes in a pH 5 sodium succinate buffer at 126.7$\sp\circ$C in both a typical canning thermal process and a simulated very rapid heating process. Thermal diffusivity was determined for the cubes. Correlation of the chemical kinetics to decimal reduction of Bacillus stearothermophilus was done through use of equations and by actual thermal process in the model food cubes and showed MMS destruction to overestimate the decimal reduction of the microorganism, providing a margin of safety for the thermal process.
Degree
Ph.D.
Advisors
Nelson, Purdue University.
Subject Area
Food science
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