FACTORS ASSOCIATED WITH MICROBIAL GROWTH IN GROUND BEEF EXTENDED WITH VARYING LEVELS OF TEXTURED SOY PROTEIN

Abstract

ABSTRACTThree separate batches of ground beef containing 25% fat were extended to 0, 10, 20 and 30% by weight with rehydrated defatted textured soy protein (TSP). Five samples of each soy level were wrapped in a polyethylene oxygen‐permeable film and stored at 5°C for 4 days. Samples were analyzed daily for changes in bacterial numbers (total plate counts and coliforms), pH, titratable acidity, proximate analysis, ninhydrin reactive material, carbohydrate content, and gas liquid chromatographic (GLC) analysis of individual amino acids to assess spoilage in TSP extended ground beef. Total bacterial numbers increased significantly as days of storage progressed and in proportion to added TSP. Coliforms increased during storage, but not proportional to increased levels of soy protein. Spoilage in soy extended samples, as determined by off‐odors and bacterial numbers, was evident by day 4 as total bacterial counts approached 108 bacteria/g. The differences of pH were significant among soy levels, but did not change appreciably during storage. Titratable acidities were not significantly changed with increases in soy protein. As soy level increased, percentages of moisture and ash increased, but percent fat decreased. No differences were noted for percent protein. Total carbohydrate as determined by proximate analysis increased with TSP levels. Concentration values for carbohydrates were proportionately larger with added amounts of TSP, but varied little during 4 days of storage. Ninhydrin reactive material differed significantly among samples, but not proportionate to added TSP, and decreased in the 30% soy level between days 3 and 4. Decreases in individual amino acids could not be shown from the qualitative results obtained by GLC analysis. Further investigation is suggested using more definitive measuring techniques to determine the factor(s) causing accelerated spoilage in soy extended ground beef.