Functional and conformational properties of phaseolin (Phaseolus vulgris L.) and kidney bean protein isolate: a comparative study.
BACKGROUND
Kidney bean (Phaseolus vulgris L.) seed is an underutilised plant protein source with good potential to be applied in the food industry. Phaseolin (also named G1 globulin) represents about 50 g kg(-1) of total storage protein in the seed. The aim of the present study was to characterise physicochemical, functional and conformational properties of phaseolin, and to compare these properties with those of kidney bean protein isolate (KPI).


RESULTS
Compared with kidney bean protein isolate (KPI), the acid-extracted phaseolin-rich protein product (PRP) had much lower protein recovery of 320 g kg(-1) (dry weight basis) but higher phaseolin purity (over 950 g kg(-1)). PRP contained much lower sulfhydryl (SH) and disulfide bond contents than KPI. Differential scanning calorimetry analyses showed that the phaseolin in PRP was less denatured than in KPI. Thermal analyses in the presence or absence of dithiothreitol, in combination with SH and SS content analyses showed the contributions of SS to the thermal stability of KPI. The analyses of near-UV circular dichroism and intrinsic fluorescence spectra indicated more compacted tertiary conformation of the proteins in PRP than in KPI. PRP exhibited much better protein solubility, emulsifying activity index, and gel-forming ability than KPI. The relatively poor functional properties of KPI may be associated with protein denaturation/unfolding, with subsequent protein aggregation.


CONCLUSIONS
The results presented here suggest the potential for acid-extracted PRP to be applied in food formulations, in view of its functional properties.
Yin
Shou-Wei
SW
Department of Food Science and Technology, South China University of Technology, Guangzhou 510640, People's Republic of China.
Tang
Chuan-He
CH
Wen
Qi-Biao
QB
Yang
Xiao-Quan
XQ
D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004220:Disulfides / Q000032:analysis; D004229:Dithiothreitol / Q000494:pharmacology; D004655:Emulsions; D005782:Gels; D027805:Phaseolus / Q000737:chemistry*; D010936:Plant Extracts / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D011489:Protein Denaturation; D017434:Protein Structure, Tertiary; D012639:Seeds / Q000737:chemistry*; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013438:Sulfhydryl Compounds / Q000032:analysis
D004220:Disulfides; D004655:Emulsions; D005782:Gels; D010936:Plant Extracts; D010940:Plant Proteins; D013438:Sulfhydryl Compounds; D004229:Dithiothreitol