Date of Graduation

12-2011

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor

Ruben O. Morawicki

Committee Member

Ron Buescher

Second Committee Member

Luke Howard

Third Committee Member

Andy Mauramoustakos

Fourth Committee Member

Casey Owens

Keywords

Health and enviromental sciences, Social sciences, Biological sciences, Additives, Protein hydrolysis, Subcritical water, Superheated water, Water hydrolysis, Whey protein

Abstract

Hydrolyzing food by-products is a unique approach to potentially increase by-product value and reduce waste. An abundant by-product of cheese production, whey, contains all essential amino acids and some distinctive peptides with functional and nutraceutical properties. Typically, proteins from whey are tailored for specific uses by chemical or enzymatic hydrolysis; however, subcritical water hydrolysis is a novel alternative used successfully to hydrolyze various substrates. Nevertheless, minimal research exists on: (1) the hydrolysis of whey protein; (2) the incorporation of additives; (3) the hydrolysis of whole whey; and (4) the production of volatiles when using subcritical water hydrolysis.

Therefore, whey protein isolate and whole whey were hydrolyzed in a 100-mL batch, high-pressure vessel under various treatment conditions. Degree of hydrolysis, peptide molecular weight profiles, amino acid content, and volatiles were monitored and the predicted maximum outcomes determined by statistical analysis. During treatment of whey protein isolate, an interaction of temperature and time significantly affected the degree of hydrolysis with a predicted maximum of 12.3% using 250 °C for 50 min. The total amino acid concentration was 57.4 mg g-1 whey protein isolate with treatment at 300 °C for 40 min. Sodium bicarbonate significantly affected hydrolysis of whey protein isolate, and in its presence, the maximum predicted degree of hydrolysis was 50% (four-fold increase compared to water alone) and concentration of total amino acids was 83.0 mg g-1 protein. The predicted maximum degree of hydrolysis of whole whey was 17.8% at 200 °C and 10 min and the total amino acids concentration was 32 mg g-1 whole whey at 250 °C and 30 min. Approximately 35 and 45 volatiles were produced during hydrolysis of whey protein isolate and whole whey, respectively, and several were considered malodorous, and a few were classified as potentially toxic. Therefore, whey protein isolate and whole whey were successfully hydrolyzed by

subcritical water with reasonable control of the end-products. Furthermore, the use of additives and the elimination of pre-processing steps reduced the temperature and time requirements of subcritical water hydrolysis; however, additional improvement to positively identify, quantify, and alleviate malodorous compounds and potentially toxic compounds should be explored