Improvement of Thermal and Alternative Processes for Foods

NON-TECHNICAL SUMMARY: There is a need to improve quality and retain nutritional value for processed food products, and to develop novel methods of processing food products. An engineering study of thermal and alternative processes used to manufacture food products will be conducted.
<P>APPROACH: Heat and mass transfer occurring during microwave heating of foods will be studied. The effect of composition on dielectric properties of foods will be investigated. Technologies to implement modified atmosphere and modified humidity packaging for fresh produce will be developed.

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PROGRESS: 2000/10 TO 2005/09<BR>
Microwave based instruments provide on-line measurement of the bulk sample due to the relatively long wavelength. Characterization of Guided Microwave Spectrometry was conducted. Coaxial cables did not have a significant effect on the spectrum and the characteristic dip in the passband region was due to antenna resonance. The antenna affected the number of the resonances present in the spectrum, the frequency location and the amplitude of the resonances. GMS system has both a lower and upper amplitude limit beyond which its resolution decreases significantly. This can be resolved by using a signal attenuator and a smaller sensor body. Dielectric properties of starch slurries (0-20%) with high-methoxy pectin at levels ranging from 0-2%, were measured at diffent temperatures by using a network analyzer and an open-ended coaxial cable in order to study gelatinization. The frequency of measurement of dielectric properties did not have much effect on the dielectric constant, but the loss factor of the starch slurries increased with frequency. Increasing starch concentration led to a significant decrease in the dielectric constant and increase in the loss factor. Addition of pectin led to a significant decrease in the dielectric constant and an increase in the loss factor, when compared to a starch slurry with no added pectin. A new approach for investigating moisture diffusion through heterogeneous food systems was developed. This was used to understand diffusion in chocolate-based coatings, containing fat, sugar, cocoa powder and lecithin. The predicted diffusion coefficient through a coating containing fat and varying amounts of sugar and cocoa powder were determined by incorporating the diffusivity data from the time-lag experiments and the partition coefficient obtained from the moisture sorption isotherms. The effect of sugar, cocoa powder, emulsifier, fat type, and storage environment on the water vapor permeability of a chocolate-based coating was studied. The vane method was used to measure the yield stress of dark chocolate. Dark chocolate did not exhibit a peak startup stress during controlled shear rate (as observed with other food products). The controlled-stress resulted in a gradual change in the curvature for the displacement versus shear stress, and hence an actual point of yield could not be determined. The effect of different ratios of sucrose:corn syrup:moisture on the Tg as measured by differential scanning calorimetry and dynamic mechanical thermal analysis was studied. A direct correlation exists between DSC glass transition temperatures (enthalpy) and DMTA glass transition temperatures (structure). Both DSC and DMTA Tg data were modeled using the Gordon and Taylor equation. The effect of growth temperatures on the inactivation of L. monocytogenes in UHT whole milk by high-pressure processing is being currently investigated. A patent was obtained for the experimental setup that was developed for measuring the oxygen transmission rate of micro-perforated films. Work is being continued to develop a technique to measure the water vapor transmission ratios of micro-perforated films.
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IMPACT: 2000/10 TO 2005/09<BR>
On-line measurement of food composition plays an important role in ensuring good quality control during processing operations. Dielectric-property based sensors offer a non-invasive technique to measure food properties. Moisture diffusion in food materials is of fundamental importance to many food processes and stydying diffusion helps to control food quality. The ingredients and processing conditions have a profound influence on physical characteristics of hard candy and product quality. Hard candy manufacturing is very empirical and no systematic research has been published on the relationship between ingredients and glass transition temperatures. L. monocytogenes is a Gram positive foodborne pathogen which causes the rare, but potentially fatal, disease listeriosis. Listeriosis is commonly associated with consumption of raw milk, soft cheeses, hot dogs and deli meats. Alternative processes such as high-pressure processing can result in safer processes to manufacture fresh cheeses which cannot be thermally processed. There are a variety of factors that affect the sensitivity of microorganisms to high-pressure procerssing, and these need to be better understood in order to develop a safe high-pressure process. In order to develop modified atmosphere and modified humidity packaging technologies to improve the shelf-life of fruits and vegetables, microperforated film technology is being currently used, Film permeabilities to oxygen and water vapor are essential to design appropriate packaging systems.