Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Keith R. Cadwallader

Abstract

Crawfish processing by-products (CPBs) were hydrolyzed using protease to evaluate the potential for bioflavor production. Ten commercial proteases (neutral and alkaline) were tested at both 37$\sp\circ$C and their optimum temperatures using CPBs as substrate. Of these, APL-440 was selected for enzymatic hydrolysis of CPBs on the basis of activity per cost. Response surface methodology (RSM) was used to optimize the hydrolysis of CPBs using APL-440. Optimum hydrolysis conditions for enzymatic hydrolysis of CPBs with APL-440 were determined to be pH 8-9, 65$\sp\circ$C, 2.5 hr reaction time, 75% substrate concentration, and 0.3% APL-440. Two types of CPBs (composite and claw) were hydrolyzed under optimum hydrolysis conditions, Flavor concentrates were prepared using atmospheric evaporation (100$\sp\circ$C) and vacuum evaporation (60$\sp\circ$C). A higher volume of flavor concentrate was obtained by enzymatic hydrolysis. Volatile flavor components of flavor concentrates were analyzed and compared. Concentrations of 12 pyrazines detected in flavor concentrates increased significantly (p $<$ 0.05) after enzymatic hydrolysis. 2,5-Dimethylpyrazine was the most abundant among the pyrazines detected. Concentrations of dimethyl disulfide, dimethyl trisulfide, and benzaldehyde also increased after enzymatic hydrolysis, whereas lipid decomposition products decreased significantly. These results suggested that increased precursors (amino acids and peptides) by enzymatic hydrolysis or increased ammonia by deamidation of glutamine and asparagine led to an increase in thermally generated aromas. Although a number of volatile compounds disappeared after evaporation, the major volatile compounds were pyrazines, which concentrations increased markedly after atmospheric evaporation of CPBs hydrolysate. It is thought that 2-ethyl-3,6 (and 5)-dimethylpyrazines play an important role in flavor concentrate because of their low threshold values. Enzymatic hydrolysis of CPBs was further evaluated on a pilot scale basis. Optimum hydrolysis conditions obtained from laboratory scale could be applied directly to pilot scale hydrolysis of CPBs. It was demonstrated that composite CPBs or claw CPBs could be converted to value-added flavor concentrates by enzymatic hydrolysis, making it possible to utilize such crawfish processing by-products to their full potential and reduce the discharged waste volume.

Pages

213

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