Michael F. Kozempel

Inactivation of microorganisms with microwaves at reduced temperatures

We developed a pilot-plant nonthermal flow process using microwave energy to inactivate microorganisms. The process consists of multiple passes through the microwave generator. Each passed material goes to a receiving tank for subsequent passes. The flow rate was 0.96 to 1.26 kg/min and the dwell time per pass was 1.1 to 1.5 min. Five passes were used. The microwave energy is instantaneously and simultaneously applied to the system, and thermal energy is removed by a cooling tube within the process line in the microwave generator. The cooling tube maintains the temperature below 40 degrees C. There was significant reduction in microorganisms in water, 10% glucose solution, and apple juice, and in yeast in beer. There was a slight decrease in microorganisms in tomato juice, pineapple juice, apple cider, and beer; and no effect in skim milk.

Radio frequency energy effects on microorganisms in foods

Abstract Liquids containing microorganisms were exposed to radio frequency (RF) energy to study non-thermal inactivation. RF energy was applied to the liquids while heat was simultaneously removed to control temperature. Turbulent flow was maintained to minimize localized heating. An 18 MHz RF processor applied an approximately 0.5 kV/cm electric field strength to the liquids. It was capable of pasteurizing the liquids provided that cooling was minimized. There were no non-thermal effects of RF energy detected on Escherichia coli K-12, Listeria innocua , or yeast in apple cider, beer, deionized water, liquid whole egg, and tomato juice; nor were there any synergistic effects of RF energy with heat. The low temperature effects of RF energy at 18 MHz and 0.5 kV/cm were due to heat.

A novel technique for the preparation of secondary fatty amides

A low-temperature synthesis of fatty alkanolamides, fatty diamides and fatty aralkylamides directly from triglycerides and primary amines provides essentially quantitative yields of the various products. The reactions run to completion in 3–12 h at temperatures of 50–60°C, approximately 100°C lower than employed in present conventional practice. The amines are used in excess and serve as solvent, reagent and, perhaps, as catalyst. The amides were characterized by melting point and spectroscopic (infrared and nuclear magnetic resonance) methods. If the mixed amides produced from the various natural triglyceride mixtures of fats and oils are acceptable products, this synthetic method provides these products in satisfactory quality while conserving energy and avoiding the intermediate production of free fatty acids or their esters.

Rapid hot dog surface pasteurization using cycles of vacuum and steam to kill Listeria innocua.

The vacuum/steam/vacuum surface pasteurization process was applied to hot dogs inoculated on the surface with non-pathogenic Listeria innocua. Using the optimum conditions previously found for processing chicken carcasses as a starting point, optimum process conditions were determined for a hot dog treatment compatible with current process line speed. Cycling the treatment significantly improved the microbiological kill. At the optimum conditions of steam time of 0.3 s at 138 degrees C (two cycles), a bacteria kill >3 log CFU/ml was attained. Pasteurization, frequently considered to be a kill of >5 log CFU/ml, was reached by increasing the number of cycles to three. The surface pasteurization process should ensure that hot dogs reaching the consumer are free of Listeria.

Influence of growth medium on thermal resistance of Pediococcus sp. NRRL B-2354 (formerly Micrococcus freudenreichii) in liquid foods.

Pediococcus sp. is a nonpathogenic heat-resistant spoilage organism that has been used as a test organism in milk pasteurization studies. These characteristics make this bacterium an attractive test organism to study the mode of bacterial thermal inactivation in a food pilot plant. We report here the effect of growth medium on the thermal D value of this organism in skim milk, whole liquid egg, 10% glucose solution, pineapple juice, apple juice, tomato juice, and water at 60 degrees C. Thermal inactivation was done in a submerged coil; D values were calculated from the linear portion of the survival curves by linear regression analysis. The range of D values of stationary-phase cells grown at 28 degrees C in tryptone glucose yeast extract (TGY) or tryptic soy broth (TSB) was 0.14 to 12.05 min in all heating menstrua tested. The TSB-grown cells exhibited the highest thermal resistance with skim milk and 10% glucose solution as the heating menstrua. Survival curves of the TGY-grown cells indicated the presence of a cell population heterogeneous in thermal resistance. The TSB-grown cells exhibited a cell population uniform in thermal resistance and with a lag time for thermal inactivation. When compared to TGY-grown cells, Pediococcus sp. grown in TSB showed a significant (P < 0.05) increase in D values by up to eightfold in all heating menstrua. Results from this study suggested that thermal inactivation of Pediococcus sp. was dependent on the growth medium and on the heating menstruum with respect to both pH and composition.

Application of the vacuum/steam/vacuum surface intervention process to reduce bacteria on the surface of fruits and vegetables ☆

Abstract A vacuum/steam/vacuum (VSV) surface intervention process has previously been developed for poultry and hot dogs. The process uses a brief exposure to vacuum to remove surface air and water to expose bacteria. After a short treatment with saturated steam (0.1 s), a second vacuum treatment evaporatively cools the surface, resulting in the destruction of bacteria with little or no thermal damage. The VSV surface intervention process has also been applied to fruits and vegetables. Optimization methods were used with cantaloupes, grapefruits, and beets to determine process conditions for steam temperature, steam time, vacuum time, and number of cycles to destroy bacteria with the constraint of little or no thermal damage. Inoculated Listeria innocua was used for the cantaloupe and grapefruit studies and total aerobic plate count (APC) was used for the beet study. Bacteria destruction ranged from 2.5 log cfu/ml APC for beets to almost 4 log L. innocua for grapefruits. The process was successfully applied to other fruits and vegetables such as papayas, mangoes, avocados, kiwis, carrots, cucumbers, and peaches, using the nominal process conditions found with cantaloupes, grapefruits, and beets. Applying the process to bananas, cauliflower, broccoli, and peppers resulted in thermal or mechanical damage. The total process time was 0.5–1.2 s, depending on the number of cycles and the process time per cycle. Assuming that these results with APC and L. innocua are indicative of the treatment of naturally present pathogens, this surface intervention process should ensure that fruits and vegetables suitable for this process will reach the consumer having greatly reduced levels of bacterial contamination.

Use of Vacuum-Steam-Vacuum and Ionizing Radiation To Eliminate Listeria innocua from Ham

Listeria spp. are a frequent postprocess contaminant of ready-to-eat (RTE) meat products, including ham. Vacuum-steam-vacuum (VSV) technology has been used successfully to eliminate Listeria innocua from hot dogs. Ionizing radiation can eliminate Listeria spp. from RTE meats. However, the excessive application of either technology can cause changes in product quality, including structural changes, changes in cure color (redness), and lipid oxidation. In this study, two cycles of VSV were combined with 2.0 kGy of ionizing radiation to obtain 4.40- and 4.85-log10 reductions of L. innocua on ham meat and skin, respectively. The use of both treatments resulted in an additive, as opposed to synergistic, reduction of L. innocua on ham. The combination treatment did not cause statistically significant changes in product structure, color (redness), or lipid oxidation.

Effect of Vacuum-Steam-Vacuum Treatment on Microbial Quality of Whole and Fresh-Cut Cantaloupe†

Minimally processed fruits and vegetables have a limited shelf life because of deterioration caused by spoilage microflora and physiological processes. Cutting may increase microbial spoilage of fruits through transfer of microflora on the outer surfaces to the interior tissue. The objectives of this study were to use the vacuum-steam-vacuum (VSV) process to reduce indigenous spoilage microflora on the surface of cantaloupes and to investigate the effects of such treatments on transfer of spoilage microflora from the cantaloupe surface to the fresh-cut melon during rind removal and cutting. Whole cantaloupes were treated in the VSV processor, and fresh-cut pieces prepared from treated and control samples were stored at 5 and 10 degrees C for up to 9 days. Presence and growth of mesophilic bacteria, yeasts and molds, and Pseudomonas spp. were determined in fresh-cut samples during storage. Texture and color (CIE L*, a*, and b*) also were measured during storage. VSV treatment resulted in a 1.0-log reduction of aerobic mesophilic bacteria, a 2.0-log reduction of yeasts and molds, and a 1.5-log reduction of Pseudomonas spp. on cantaloupe surfaces. VSV treatment significantly reduced transfer of yeasts and molds and Pseudomonas spp. from whole cantaloupe surface to fresh-cut pieces during preparation (P < 0.05). Texture and color of the fresh-cut pieces prepared from the VSV-treated whole melons were similar to those of the controls. The results of this study indicate that the use of the VSV process to reduce the surface populations of yeasts and molds and Pseudomonas spp. on whole cantaloupes will reduce subsequent transfer of these microbes to fresh-cut pieces and enhance the microbial quality of the fresh-cut product.

The development of the ERRC food process simulator

Abstract A simulator was developed for food processing. The simulator links mathematical models for the variouis unit operations encountered in a food process. The models are based on theoretical considerations or in many cases are semi-empirical and developed using laboratory and pilot plant data. The program was written in Fortran using potato processing as a prototype. Models for such critical unit operations as hot water blanching, water cooling, steam cooking, drum drying, and deep fat frying were developed. The models were also adapted for use in real-time computer programs to control processed potato color and degree of cook of potatoes. This paper documents the integration and validation of the models developed.

ASCORBIC ACID DETERMINATION IN PROCESSED POTATOES

A method to determine ascorbic acid at any stage of potato processing was developed. Potato samples are frozen in dry ice, lyophilized and analyzed using a modified spectrophotometric method. This method is simple, accurate, inexpensive and has a detection limit of 1.2 mg ascorbic acid/100 g dry weight potatoes.CompendioSe desarrolló un método para determinar el ácido ascórbico en cualquiera de las etapas del procesamiento de papa. Muestras de papa son congeladas en hielo seco, liofilizadas y analizadas utilizando un método modificado de espetrofotometría. Este método es sencillo, preciso, y de bajo costo y tiene un limite de detección de 1,2 mg de ácido ascórbico/100 g de peso seco de papas.