Thermal Processing of Sour Cream using Continuous Flow Microwave Heating - Feasibility Study
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Date
2007-07-26
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Abstract
The purpose of this research was to develop a sour cream that could withstand the effect of UHT continuous microwave processing. The major benefit to the manufacturer of the UHT processing would be extended shelf-life, especially in conjunction with asceptic packaging. This would result in less spoilage, thus increased profits. This becomes increasingly important as sour cream increases in popularity and is sold and marketed at greater distances from the point of processing
One major problem with UHT processing of acidic dairy products is that high temperatures cause milk proteins to aggregate, especially at pH's around the pI (isoelectric point) of casein. Fouling (or burn-on) of the heat-exchanger tube walls is another factor that excludes the use of UHT processing to sterilize sour cream.
The proper formulation of sour cream with the use of stabilizers such as starch and gelatin can also minimize aggregation, reduce syneresis, and increase the viscosity of the final products. The addition of gelatin is often used in sour cream formulations as it increases water binding, whey retention, and adds to mouthfeel, and gives the final product sheen-like appearance.
In order to characterize the performance and functionality of sour cream under continuous flow microwave thermal processing conditions, seven sour cream formulations with different gelatin and starch content were produced and processed. Yield stress and viscosity tests were performed and compared to rheological tests performed on commercial brands to determine if they were within the upper and lower commercially accepted limits. Viscosities were dynamically measured with the Stresstech. Dielectric properties of the sour cream samples were also analyzed. Dielectric measurements were taken at 5#176; C intervals. Microwave processing was performed using a 5 kw microwave system. Processing was performed at an output power of 3 kilowatts at 915 MHz at flow rate of 4 liters per minute to determine dielectric properties and estimate the need for formulation adjustments.
Rheological analysis of the seven NCSU sour cream formulations showed no correlations between stabilizer levels and yield stress or viscosity. Measurement of time and temperature data showed that variations were present and that processing conditions had an influence on the rheological behavior of the sour creams. Because of this, a single formulation could not be determined as optimal. All seven formulations were more viscous than the commercial brands tested but had lower yield stresses. Also, none of the seven formulations had visual casein aggregation. Rheological analysis of the seven formulations indicated that UHT continuous microwave processing was feasible using any of the formulations. This new process will allow sour cream to be ascetically packaged which had never been done. Aseptic packaging would allow manufactures to increase profit margins by reducing spoilage and eliminate refrigeration costs.
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Keywords
asceptic, sour cream, microwave, UHT
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Degree
MS
Discipline
Food Science
