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THE IMPACT OF ENZYMATIC HYDROLYSIS ON THE NUTRITIONAL AND FUNCTIONAL PROPERITES OF AN AIR-CLASSIFIED PEA PROTEIN-ENRICHED FLOUR

Date

2019-05-09

Journal Title

Journal ISSN

Volume Title

Publisher

ORCID

0000-0002-3676-1368

Type

Thesis

Degree Level

Masters

Abstract

The overall goal of this research was to improve the protein quality and functionality of air-classified protein-enriched flour (pea protein-enriched flour; PPEF) using different enzymes and levels of hydrolysis. Initially, PPEF was hydrolyzed using seven different enzymes, and based on the initial degree of hydrolysis (DH) results, four were chosen for further investigation (Savinase, trypsin, pepsin and papain). The conditions of hydrolysis (time, temperature, pH and enzyme substrate ratio) were altered to modify the protein to have degree of hydrolysis of 2-4% and 10-12%. Each of the chosen enzymes has different substrate specificities and preferred solvent conditions, which were hypothesized to lead to differences in protein unfolding, surface characteristics, functionality, and protein quality. The physicochemical (surface hydrophobicity and charge) and functional properties (solubility, oil and water holding capacity, emulsification and foaming) were initially examined for hydrolyzed PPEF as a function of enzyme type and DH. The surface hydrophobicity was found to increase from 13.3 A.U. (arbitrary units) in the untreated flour to between 22.8 and 48.5 A.U. in the hydrolyzed flours, with the greatest increase occurring with papain hydrolysis. The surface charge of untreated PPEF was found to be -12.6 mV, whereas it became more negative with hydrolysis (ranging between -14.0 to -19.0 mV) with the greatest increase occurring with the pepsin treatment. The emulsion activity and stability index of the untreated flour was higher at all pH values tested compared to the hydrolyzed flours, regardless of the enzyme used. A similar trend occurred for foaming capacity and stability, as well as solubility parameters. In contrast, water (WHC) and oil (OHC) holding capacities were found to both increase with hydrolysis. For instance, WHC increased from 0.6 g/g to 1.4-2.0 g/g following hydrolysis, with the greatest improvement occurring using the papain treatment; whereas, OHC increased from 0.7 g/g to 1.0-1.5 g/g following hydrolysis, with the greatest improvement occurring using papain. Changes to the levels of bioactive compounds (total phenolics, condensed tannins, trypsin and chymotrypsin inhibitors) within the PPEF with hydrolysis was also investigated. The total phenolic contents (gallic acid equivalents; GAE) were found to be reduced from 8.1 to 5.4-7.1 mg GAE/g following with pepsin being most effective hydrolysis treatment. Similarly, condensed tannins were reduced from 0.7 mg catechin equivalents/100g to values that were undetectable by the assay for all enzymes and DH. In addition, both protease inhibitors decreased in concentration (i.e., chymotrypsin inhibitor units (CIU) and trypsin inhibitor units) with hydrolysis. For instance, chymotrypsin inhibitors were reduced from 63.9 to 3.5-7.1 CIU/mg following hydrolysis, with the greatest decrease observed with the papain treatment. Trypsin inhibitors were reduced from 38.4 to 9.9-17.3 TIU/mg, with the greatest decrease observed with Savinase. The protein quality of untreated and hydrolyzed PPEF was also analyzed by determining the amino acid score, in vitro protein digestibility (IVPD) and in vitro protein digestibility corrected amino acid score (IVPDCAAS). Methionine and cysteine remained the limiting amino acids in the PPEF for all hydrolysis treatments. However, the limiting amino acid score was found to improve from 0.70 for the untreated flour to 0.79-0.84 with 2-4% DH, and then decline with higher levels of hydrolysis (DH 10-12%) 0.66-0.72 for trypsin and papain, with pepsin having the greatest improvement to 0.79. The IVPD increased from 83.9% in the untreated flour to 85.5-88.8% following hydrolysis, with the greatest improvement occurring with the papain treatment. IVPDCAAS of the untreated flour was determined to be 66.7%, which then declined with 2-4% DH (59.2 to 64.6) before increasing at higher levels of hydrolysis (DH 10-12%) (68.6 to 72.9), with the greatest increase occurring with pepsin treatment. It was observed that hydrolysis was found to improve the nutritional quality of the PPEF based on the lower amounts of bioactive compounds and higher IVPDCAAS values. Overall, enzymatic hydrolysis improved non-solubility dependent functional properties (WHC and OHC), with 10-12% papain-hydrolyzed samples having the most improvement. Improvements in WHC and OHC could mean the ingredient could be applied into baked goods or used as a meat binder. However, increases in surface hydrophobicity and low zeta potential may have led to decreases in solubility-dependent functional properties (EAI, ESI, FC, FC) as solubility decreased with all hydrolyzed samples. The bioactive compounds decreased with all enzymatic treatments, and the IVPDCAAS was increased with 10-12% DH with the greatest improvement using pepsin treatment. Enzymatic hydrolysis as a means of protein modification could improve the functional and nutritional properties for a value-added PPEF ingredient.

Description

Keywords

Pea protein enriched flour, Savinase, Trypsin, Pepsin, Papain, Enzymatic hydrolysis

Citation

Degree

Master of Science (M.Sc.)

Department

Food and Bioproduct Sciences

Program

Food Science

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DOI

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