Our laboratory is the only one in the U.S. that is currently conducting advanced high-moisture extrusion research. As a result of this work, I was invited to present AHigh Moisture Extrusion and Protein Texturization@ at USDA-ERRC, Wyndmoor, PA, Mar. 25, 2003. In addition, I was an invited speaker and gave a technical presentation, AThe Science and Technology of Soy-based Meat Analogs,@ at the ARecent Advances in Science and Technology of Soy Foods Symposium@ in the Annual Meeting of the Institute of Food Technologists (IFT) in Chicago on July 15, 2003. A PhD student and an undergraduate student gained useful experience through working on this project. Based on the results obtained from this project, we are developing a new proposal, AStudies on High Moisture Extrusion of Soy Protein: Elucidation of Fiber Formation Mechanism and Animal Feeding for Nutritional Performance,@ in collaboration with Ruth MacDonald, Jay Thelen and Gang Yao. This proposal will be submitted to DuPont in the near future to be considered for funding. A technical paper from this project was published in the Journal of Food Science. The full citation is:

Lin, S., Huff, H. E. and Hsieh, F. 2002. Extruder responses, sensory characteristics, and structural properties of high moisture soy protein meat analog. J. Food Sci., 67(3):1066-1072.

 

Executive Summary:

We have produced a high-quality fibrous meat analog in the laboratory by high-moisture twin-screw extrusion process using soy protein and corn starch as the major ingredients. We have confirmed that the production rate could be doubled from 20-25 to 40-50 kg/h by doubling the width of the cooling die. Tripling the production rate by tripling the die width may be possible if a circulating bath with a higher cooling capacity than the existing one is available. Both cooking temperature and extrusion moisture content were significant for the texture attributes of hardness, gumminess and chewiness. The lower the moisture content, the harder and chewier the product. At the same moisture content, the higher the cooking temperature, the softer and less chewy the product. Products that were high in hardness or chewiness had more protein that was not extractable. Extractable protein decreased as extrusion moisture content decreased, indicating the formation of higher molecular weight polymers or intramolecular bonding as the extrusion became more severe.

 

Project Highlights:

The overall goal of this project was to produce a high-quality and competitive meat analog by high-moisture twin-screw extrusion process using soy protein and corn starch as the major ingredients. Specific objectives were: 1) To investigate critical factors that limit the production rate and commercial scale-up of soy protein-corn starch meat analog and 2) To elucidate the mechanisms of protein texturization during high-moisture twin-screw extrusion of meat analog. These objectives have been completed as follows:

I. Critical Factors that Limit the Production Rate of Meat Analog

Two factors that could limit the production rate of meat analog were examined: cooling die width and cooling die length. The cooling die is used to prevent product expansion at the die exit and is essential in the production of fibrous meat analog using high moisture extrusion. A Julabo circulating bath with PID temperature control (Model FP-50MD) was used to control the cooling water temperature. With cooling die height fixed at 10 mm, the cooling die width was varied from 30 mm to 60 mm in 15 mm increment and the die length was varied from 100 to 300 mm in 100 mm increment. The results show that the meat analog could be produced with a cooling die as wide as 60 mm and as short as 200 mm. The overall heat transfer coefficient of all cooling dies varied from 0.5 to 0.8 kW/m2K. While the minimum die length was limited to at least 200 mm, the potential of increasing the die width beyond 60 mm exists. Increasing the die width to 90 mm would have tripled the meat analog production rate. However, a circulating bath with a higher cooling capacity will be needed since it was found the cooling water could no longer be kept at constant with a shorter and wider cooling die.

II. The Effects of Moisture and Extrusion Process Parameters on the Physicochemical and Texture Properties of Meat Analog

We have found that as the moisture content decreased or the cooking temperature increased during extrusion, the product temperature increased. The increase in product temperature reduced the extrudate=s viscosity, which, in turn, resulted in a lower die pressure and a lower percent torque. Both cooking temperature and extrusion moisture content were significant for the texture attributes of hardness, gumminess and chewiness. The lower the moisture content, the harder and chewier the product. At the same moisture content, the higher the cooking temperature, the softer and less chewy the product. Protein solubility provided the information on the amount of protein that was supported by the combinations of disulfide bonds, hydrogen bonds, and hydrophobic bonds. According to the Texture Profile Analysis (TPA) and protein solubility results, products that were high in hardness or chewiness had more protein that was not extractable. Extractable protein decreased as extrusion moisture content decreased, indicating the formation of higher molecular weight polymers or intramolecular bonding as the extrusion became more severe. The texture differences in products extruded at 65% and 60% moisture contents were probably due to their moisture content. Partial Least Square (PLS) regression showed that, in general, the data from TPA, protein solubility, and extruder responses correlated well and these three data sets could partially represent each other.