AN ABSTRACT OF THESIS OF YIH HERHON CHANG for the degree of MASTER OF SCIENCE Food Science in and Technology presented on January 11,1979 Title: CHEMICAL ANALYSIS OF ACID PRECIPITATED COLLOID OF RIPE BARTLETT PEAR JUICE

approved: D.V. Beavers Nu. -J*" ' ^' With acidification, the clarification-filtration difficulties of the 1975 ripe Bartlett pear juice were generally overcome. Chemical analyses were conducted to determine the composition of the acid precipitated colloid in an attempt to determine the reason that the 1975 juice was so difficult to clarify and filter. Samples of the acid precipitated colloid were obtained from the clarification process of the 1975, 1976 and 1977 juices. The process includes acidification with citric acid and depectinization with pectinase enzyme. After conducting the tests with different washing media, the precipitate was washed with the selected medium (citrate buffer), air dried, powdered, freeze dried and stored in a desiccator. A wide variation of copper, iron, magnesium, calcium, sodium and potassium was detected in all the precipitate samples. High calcium content was noted in all samples. This might be part of the reason for the clarification-filtration difficulties of pear juice. No pectin or starch was detected in any of the precipitate samples. Fructose, galactose and glucose were found in the precipitates. Lipids were found in the precipitates, linoleic, palmitic and oleic acids were the major fatty acids. Amino acid analyses and the determination of total phenolics and crude protein were also conducted. The percent compositions of the precipitates are summarized below: 1975 1976 1977 precipitate precipitate precipitate Protein 30.8 i 0.5 36.6 + 0.7 35.6 + 0.7 Mineral 1.6 ' 1.4 1.8 Phenolics 38.1 ± 0.5 33.9 * 0.4 29.1 ± 0.4 Sugars 7.8 8.9 7.4 Lipid 26.5 ± 0.4 21.3 i 0.5 20.4 + 0.4