Extraction And Physicochemical Properties Of Kidney Bean Proteins

Kidney beans constitute an important source of export commodities in China, which is next only to soy bean in pulses. Kidney beans are cultivated widely in 11 provinces in China, such as Heilongjiang, Jilin, Shaanxi,Yunnan. Kidney beans are rich in nutrition, which provide energy, dietary fibre, protein, minerals and vitamins required for human health. Recent research studies suggest that consumption of kidney beans may have potential health benefits including reduced risk of cardiovascular disease, cancer, diabetes,and reduction of LDL cholesterol.Pretreatment such as dehulling and defatting is significant in seed properties, especially in starch and protein. Influence of different treatments on nutritional ingredients and protein extraction rate of kidney beans were studied. Dehulling(DH), defatting(DF) and 2 steps above(B) on 8 kinds of kidney beans(YD04-01 ~ 08)were used, full flour(F) as control. It may lay the theoretical foundation in industrial application. And there are little study on properties of different kinds of kidney bean proteins. Our research is focused on the influence of pretreatment on protein extraction and physiochemical properties of kidney bean proteins. The main conclusions are as follows:1. We measured the contents of water, ash, fat, crude protein, and carbohydrate, along with protein extraction rate by alkali ways. It demonstrated that in contrast to nutritional ingredients of F, the content of water decreased, contents of carbohydrate and crude protein increased significantly by DH and DF. Through the procedure of B, content of water decreased, whereas contents of crude protein, ash and carbohydrate increased significantly. Nutritional ingredients of different kinds of kidney bean were different. The content of water was lowest in YD04-04, whereas ash and carbohydrate got the highest value; content of crude fat was highest in YD04-07, YD04-08 achieved the highest content of crude protein. Comparing to DH and DF, B made the protein extraction rate improved obviously, by 29.00%; at the same time, DH occupied a more important role than DF. In contrast to other treatments, DH increased the content of crude protein and improved protein extraction rate more obviously, which implied that DH was the best way to extract protein.2. Physicochemical and functional properties of different kinds of kidney bean proteins(KBP) were studied. Purity of protein was different in different kinds of kidney beans, for 72.53%~78.18%, YD04-07 black kidney bean got the best value. The ratio of essential amino acids to total amino acids of KBP was 57% to 62%, which was higher than soybean protein(47%). Comparing to other varieties of KBI and soybean protein(1.35% ~ 1.89%),black KBP achieved maximum values of the sulfur-containing amino acids(2.59%). SDS-PAGE pattern of KBP suggested 2 or 3 major polypeticides around molecular weights of 45 ku, which is totally different comparing to soy bean protein.3. There are certain differences in KBP functional properties. The solubility of KBP is highest at low acidic and high alkaline pH values. Solubility markedly decreases near the isoelectric point, generally between pH 4.0~4.4 for KBP and pH 4.2 for soy bean protein. Under conditions of alkaline or acid, YD04-01 red KBP has a better performances than other kinds of KBP. On the contrary, YD04-04 yellow KBP and YD04-07 black KBP got a lower value.KBP got a better foaming and foaming stability than soy bean protein. In different cultivars of KBP, YD04-04 and YD04-07 had a worse performance than others. For emulsion and emulsion stability, KBP performed as well as soy bean proteins, except yellow and black KBP. Foam expansion(FE) of KBP were 266%~308%, respectively, when prepared using alkaline extraction. These values were higher than those for soy bean proteins.Protein isolate from kidney bean, however, had significantly lower water absorption capacity(WAC) than those obtained from soy beans. Furthermore, protein isolates from different cultivars reportedly had different WAC which indicated the YD04-01 red KBP perform better than other cultivars, especially yellow and black KBP. And for oil absorption capacity, KBP had a value of 1.69~5.25g/g, which is better than soy bean protein(2.68g/g), and YD04-01 got the best value.In conclusion, DH improved extraction rate of KBP, which imply that DH may be a better way in industry application. KBP had a good scale on amino acids comparing to soy bean protein. In contrast to soybean protein, KBP has perfect properties on oil binding capacity, solubility, least gelation concentration, emulsion and emulsion stability, foam and foaming stability, which imply that KBI maybe a good material on food industry.