Semester

Spring

Date of Graduation

2013

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Human Nutrition and Foods

Committee Chair

Kristen E. Matak

Committee Co-Chair

Jacek Jaczynski

Committee Member

Litha Sivanandan

Abstract

An effective method to recover protein, called ISP processing, uses extreme pH shifts to solubilize protein and then recover it by precipitation and centrifugation. The objective of this study was to determine the proximate composition of the recovered materials from ISP after processing with different acid concentrations and the bactericidal effectiveness of these acids in comparison with hydrochloric acid (HCl) and acetic acid against Staphylococcus aureus during isoelectric solubilization and precipitation (ISP) processing. Headed and gutted silver carp were homogenized and brought to the protein solubilization pH (2.5, 3.0, 11.5, or 12.5) using the acids (glacial L-lactic acid and formic acid (F&L) in sterile distilled water at a 1:1 ratio, glacial acetic acid or concentrated hydrochloric acid) or sodium hydroxide. Concentrations of F&L tested were 30%, 45%, 60%, 75%, 90% and 100% (v/v). Mixture was centrifuged to separate and remove lipid and insoluble fractions. The solubilized protein was brought to the isoelectric point (pH 5.5) with the addition of NaOH or acids and recovered by centrifugation. There were no differences in proximate composition (moisture, total fat, crude protein, ash) of the recovered protein fractions (P > 0.05), regardless of acid concentration, with the average protein concentration at 90.6%. Bactericidal effectiveness was tested on S. aureus at processing pH 11.5 and 12.5 using 30% formic and lactic combination and at processing pH 2.5, 3.0, 11.5 and 12.5 using HCl or acetic acid. Microbial analysis was performed on all fractions (lipid, protein, insoluble and water) and survivors were enumerated on Baird Parker and TSA media. Significant differences were observed between the selective and growth media (P < 0.05) at processing pH 11.5, while using F&L, indicating cell injury. However, no significant differences were observed between the selective and growth media (P > 0.05) while using HCl or acetic acid except for in the insoluble fractions. The greatest microbial reductions occurred at pH 12.5 using F&L and acetic acid with a mean log reduction of 2.6l and 2.49 CFU/g respectively in the protein fraction and a total log reduction of 2.47and 2.45 CFU/g respectively. The results showed that a net-pasteurization effect did not occur (a 6-log reduction in microbial population) at any of the pH conditions and while ISP will significantly reduce S. aureus, further processing is required to achieve a net pasteurization effect.

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