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. 2012;13(2):1561-1581.
doi: 10.3390/ijms13021561. Epub 2012 Feb 2.

Composition, structure and functional properties of protein concentrates and isolates produced from walnut (Juglans regia L.)

Xiaoying Mao  1   2 , Yufei Hua  1
Affiliations

Composition, structure and functional properties of protein concentrates and isolates produced from walnut (Juglans regia L.)

Xiaoying Mao et al. Int J Mol Sci. 2012.

Abstract

In this study, composition, structure and the functional properties of protein concentrate (WPC) and protein isolate (WPI) produced from defatted walnut flour (DFWF) were investigated. The results showed that the composition and structure of walnut protein concentrate (WPC) and walnut protein isolate (WPI) were significantly different. The molecular weight distribution of WPI was uniform and the protein composition of DFWF and WPC was complex with the protein aggregation. H(0) of WPC was significantly higher (p < 0.05) than those of DFWF and WPI, whilst WPI had a higher H(0) compared to DFWF. The secondary structure of WPI was similar to WPC. WPI showed big flaky plate like structures; whereas WPC appeared as a small flaky and more compact structure. The most functional properties of WPI were better than WPC. In comparing most functional properties of WPI and WPC with soybean protein concentrate and isolate, WPI and WPC showed higher fat absorption capacity (FAC). Emulsifying properties and foam properties of WPC and WPI in alkaline pH were comparable with that of soybean protein concentrate and isolate. Walnut protein concentrates and isolates can be considered as potential functional food ingredients.

Keywords: composition; functional properties; structure; walnut protein concentrate; walnut protein isolate.

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Figures

Figure 1
Figure 1
SDS-PAGE of DFWF, WPI and WPC: (A) Reduced (with β-mercaptoethanol); (B) Nonreduced (without β-mercaptoethanol); Marker (M), WPI (1), WPC (2), DFWF (3).
Figure 2
Figure 2
High performance size exclusion chromatography (SEC-HPLC) profiles of DFWF, WPC and WPI: (A) The calibration curve of standard proteins; (B) DFWF; (C) WPI; (D) WPC; A calibration curve of 10 standard proteins was used for interpreting the results. Ten standard proteins were thyroglobulin (MW: 669,000), aldolase (MW: 158,000), BSA (MW: 67,000), ovalbumin (MW: 43,000), peroxidase (MW: 40,200), adenylate kinase (MW: 32, 000), myoglobin (MW: 17,000), ribonuclease A (MW: 13,700), aprotinin (MW: 6500), and vitamin B12 (MW: 1350), respectively.
Figure 2
Figure 2
High performance size exclusion chromatography (SEC-HPLC) profiles of DFWF, WPC and WPI: (A) The calibration curve of standard proteins; (B) DFWF; (C) WPI; (D) WPC; A calibration curve of 10 standard proteins was used for interpreting the results. Ten standard proteins were thyroglobulin (MW: 669,000), aldolase (MW: 158,000), BSA (MW: 67,000), ovalbumin (MW: 43,000), peroxidase (MW: 40,200), adenylate kinase (MW: 32, 000), myoglobin (MW: 17,000), ribonuclease A (MW: 13,700), aprotinin (MW: 6500), and vitamin B12 (MW: 1350), respectively.
Figure 3
Figure 3
(A) Far-UV circular dichroism spectra of DFWF; (B) Far-UV circular dichroism spectra of WPI; (C) Far-UV circular dichroism spectra of WPC.
Figure 3
Figure 3
(A) Far-UV circular dichroism spectra of DFWF; (B) Far-UV circular dichroism spectra of WPI; (C) Far-UV circular dichroism spectra of WPC.
Figure 4
Figure 4
Scanning electron microscope pictures (1200× magnifications, bar 50 μm) of DFWF (A) WPC (B), WPI (C).
Figure 5
Figure 5
Effects of pH on solubility of DFWF, WPC, and WPI.
Figure 6
Figure 6
Effects of pH on emulsifying activity and emulsion stability of DFWF, WPC, and WPI: (A) emulsifying activity; (B) emulsion stability.
Figure 7
Figure 7
Effects of pH on foam capacity and foam stability of DFWF, WPC, and WPI: (A) foam capacity; (B) foam stability.
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