No description available.

No description available.

Recent increases in chronic cardiovascular diseases, such as hypertension, have put pressure on the food industry to reduce sodium levels. Dairy products, though full of vital nutrients, are perceived as being high in sodium. However, the reduction of salt in dairy products could potentially alter the microbial stability, as well as cause unfavorable changes in flavor. In order to reduce the sodium level, while maintaining acceptable flavor and microbial stability, salt replacers and alternative antimicrobial agents may need to be introduced into the food matrix. To identify potential antimicrobials for use in reduced sodium dairy products, this study evaluated the efficacy of eight commercially available antimicrobials in TSA, milk agar, and cheese agar. Antimicrobials included MicroGard 100, MicroGard 430, Nisaplin, NovaGard CB1, Protect-M, PuraQ Verdad RV75, SEA-i F75 and VMY1P. Antimicrobials were also tested in combination with six commercial sodium reduction agents (potassium chloride, Puracal PP/USP, Purasal Hi Pure P Plus, PuraQ Verdad NV10, SaltWise 0029 and SaltWise 1029) to if there were any interference with antimicrobial activity. Antimicrobials with and without sodium reduction agents were added to the agar systems, then a five-strain cocktail of Listeria monocytogenes, Salmonella or Escherichia coli O157:H7 was spread plated at three concentrations: 101, 102 and 104 CFU/plate. Samples were then incubated at 35°C and observed for growth after 24 and 48h. SEA-i F75 was the most effective antimicrobial in each of the agars tested. Additionally, no interactions were observed between SEA-i F75 and any of the sodium replacement agents. SEA-i F75 was selected for use in a final challenge study using six formulations of LMPS mozzarella cheese: regular sodium control cheese (1.7% NaCl, no antimicrobial added); low sodium control cheese (0.7% NaCl, no antimicrobial added); low sodium treated cheese (0.7% NaCl, treatment with SEA-i F75); low sodium cheese with KCl as salt replacer (0.7% NaCl, 1.0% KCl, treatment with SEA-i F75); low sodium cheese with Alta 2345 as salt replacer (0.7% NaCl, 0.25% Alta 2345, treatment with SEA-i F75); and low sodium cheese with Salona as salt replacer (0.7% NaCl, 0.95% Salona, treatment with SEA-i F75). Fifteen gram cheese pieces from each formulation were dipped in an antimicrobial solution containing 0.25% SEA-i F75 then inoculated with L. monocytogenes, Salmonella, or E. coli O157:H7 at a target inoculum concentration of 102-103 CFU/g and incubated at either 4° or 12°C. In all trials, over all formulations and temperatures tested, initial decreases in counts, followed by organism recovery were observed. Therefore, SEA-i F75 was not effective at reducing the counts of pathogenic bacteria in LMPS mozzarella cheese. Results from this study highlight the effect of the food matrix, and its components on antimicrobial efficacy. Future research includes examining the effect of one of the other antimicrobials in LMPS mozzarella cheese.

Thesis: M.S., Massachusetts Institute of Technology, Department of Food Technology, 1960 / Includes bibliographical references (leaves 46-51). / by Kyoung Sook Kim. / M.S. / M.S. Massachusetts Institute of Technology, Department of Food Technology

Abstract not available

Effect of water migration on physico-chemical properties of bread during storage was investigated. When breadcrumbs were stored with crust, moisture and aw decreased significantly, whereas for those stored without crust, these properties remained unchanged (no moisture loss from crumb). Addition of glycerol retarded amylopectin recrystallization but increased breadcrumb firmness suggesting that breadcrumb firming in this case was not directly related to amylopectin recrystallization. Biopolymers in bread might be locally dehydrated (osmotic dehydration) in the presence of hygroscopic solutes. Stress-strain curves showed the typical sigmoidal shape described by three-parameter empirical model with C1, C2, and C3 representing scale factor, prominence of the shoulder and densification level, respectively. C1 correlated well (r 2 = 0.96) with firmness, whereas recoverable work decreased over the first 3 days of storage but did not show the effect of glycerol and crumb moisture loss effect. The self-diffusion coefficient (D) of water (by PFG-NMR) in fresh breadcrumbs increased with increasing glycerol content at the same moisture content suggesting an increased water partitioning with glycerol as compared to a starch and gluten matrix and more water was free to diffuse. Although dependent on moisture, the diffusion coefficient did not proportionally change with moisture content during storage suggesting other factors (water-biopolymer interactions, geometry, restricted diffusion in complex domains etc.) might be related. 13C CP/MAS NMR peak intensity indicating relative amount of 13C solids was found to increase with increasing storage time in all cases. A lower 13C CP/MAS NMR peak intensity was observed in breadcrumb stored without crust than that of breadcrumb stored with crust at given glycerol content because less disordered-to-ordered chain rearrangement occurred. This confirmed that an amylopectin ordered structure (observed by DSC) was formed contributing to rigid crystalline solids ( 13C CP/MAS NMR). Data confirmed that the hardening effect of added glycerol during storage was unrelated with the amylopectin recrystallization. Therefore, the hardening of bread during storage in this case was related to other changes such as local dehydration and stiffening of the amorphous domains. Future investigation is warranted on the molecular origins of these changes. This could lead to further development in engineering physical properties of many bakery products.

Analytical instruments based on ultrasonic spectroscopy have been recently developed to measure the size distribution and droplet concentration of emulsions. Nevertheless, there are a number of problems that currently limit the practical application of these instruments to food emulsions: (i) ultrasonic measurements often have to be made at different temperatures; (ii) many food emulsions are concentrated; and (iii) many food emulsions are flocculated. The objective of this study was therefore to investigate the influence of temperature, droplet concentration and droplet flocculation on the ultrasonic properties of emulsions, hence developing ultrasonic techniques that could be applied to food emulsions. In addition, this study also aimed at testing the efficiency of the newly developed ultrasonic scattering theories (UST) for describing ultrasonic properties of flocculated and concentrated emulsions. The influence of temperature was investigated by measuring ultrasonic velocity and attenuation coefficient of emulsions of different compositions and droplet sizes at 5 to 50°C. The ultrasonic properties of emulsions were sensitive to temperature as well as to composition and droplet size, and could be described by UST. The effect of droplet concentration (0–50 wt%) and diameter (0.2–0.58 μm) on ultrasonic properties was determined in non-flocculated oil-in-water emulsions. The traditional UST gave poor predictions of ultrasonic properties of emulsions at high droplet concentration, small droplet size and low ultrasonic frequency, while an extended UST, which incorporated the thermal overlap effects, gave much better predictions under the same conditions. The effect of flocculation on ultrasonic properties of emulsions was studied over a range of frequency (1–120 MHz) using 5% oil-in-water emulsions, flocculated by either depletion or an electrostatic mechanism. A new theory that took into account the thermal overlap effects could well explain the ultrasonic properties of flocculated emulsions. As flocculation increased, the attenuation coefficient decreased at low frequency due to the thermal overlap effect, while at high frequency the attenuation coefficient increased due to the scattering effect. The usefulness of ultrasonic techniques in characterizing actual foods was tested using salad dressing and chicken. The ultrasonic techniques could provide valuable and accurate information about the composition of these foods.

Encapsulation of lipids and other oxidizable compounds provides a means of protecting these compounds against their environment, including such factors as oxygen and humidity. The physical properties of wall matrices have a major influence on the oxidative stability of encapsulated lipids. This study investigated the effects of composition and processing conditions on physical and chemical stability of encapsulated milk fat powder (dairy creamer). Achieving a stable liquid emulsion is a necessary first step. Emulsifier type and concentration as well as processing conditions affected oil droplet size distribution. Larger oil droplet size led to an unstable emulsion and a consequential increase in surface fat of spray dried powder. At best, about 98% of the milk fat was encapsulated (average oil droplet size ∼0.5 μm, 2.0% lecithin, 36 DE corn syrup solids). The physical properties of spray dried powders that were studied include internal and external morphology, water sorption isotherm, surface fat, true density, and melting and crystallization. Upon storage, physical changes led to a complex change in surface fat with storage humidity, crystallization of carbohydrates (at higher %RH), and caking. These were dependent on maltodextrin dextrose equivalent (DE) and storage humidity. Oxidative stability of milk fat encapsulated in powder with DE-36 corn syrup solids was studied at 14–52%RH and 25°C (Collaborative work with two other investigators; Dr. Nitin Hardas and John L. Foley). Oxidation was negligible for powders stored in the dark at all relative humidities. Under UV light, the encapsulated fat significantly increased in peroxide value (PV) and decreased in 18:2 and 18:3 fatty acids over time. The highest rate of oxidation was found at 52% RH, indicating increased diffusivity of oxygen and other components under this condition. In contrast, surface fat oxidative rate was slower at 52% than at 14% and 44% RH. Overall oxidative stability was dominated by the encapsulated fraction although in general the surface fat fraction was oxidized more rapidly.

Abstract not available

Appearance plays an important role in determining the quality of food products, but little work has been done on the factors that influence the appearance of food emulsions. Appearance depends on the scattering and absorption efficiency of the emulsions. The scattering efficiency is determined mainly by droplet characteristics (size, concentration, aggregation and relative refractive index), while the absorption efficiency is determined by dye characteristics (absorption spectra and concentration). The objective of this study is to investigate the influence of droplet, TiO2 and dye characteristics on the optical properties of oil-in-water emulsions, and apply the knowledge gained from model systems to understand the factors determining the optical properties of a real food system, milk. Droplet and dye characteristics had a pronounced influence on emulsion appearance. The lightness of an emulsion was correlated to the scattering efficiency of the droplets. The color of emulsions (a- and b-values) was mainly determined by the type (red, green, blue) and concentration (0–0.1 wt%) of chromophores present. The lightness of emulsions increased steeply between 0 and 5 wt% oil, and increased slightly at higher concentrations (5–20 wt%). It also increased with decreasing droplet diameter (30–0.2 μm) and increasing refractive index difference between the two phases. The influence of droplet characteristics on the lightness and color of emulsions containing different types of dye was fairly similar. Droplet flocculation did have an impact on emulsion appearance, but the effect was relatively small compared to the effect of droplet size. Small amounts of TiO2 could be used to obtain the same emulsion appearance at lower oil contents. The optical properties of dairy emulsions showed the same trends as those of model ones. The effect was most pronounced below 5% milk fat. There was good correlation between sensory analysis and instrument measurement of emulsion color. Food emulsion appearance therefore can be optimized by carefully controlling droplet and dye characteristics. TiO2 has good potential to improve the appearance of low-fat foods. A mathematical model based on light scattering theory was shown to have good potential for predicting the influence of composition and microstructure on the optical properties of emulsions.