Physicochemical and functional properties of Phaseolus coccineus L. protein isolate obtained by isoelectric precipitation method.

Recently, due to ease of access to information consumers are more aware and conscious about their eating habits. Carbohydrates, lipids and, proteins are very important for a balanced diet and provide energy. However, proteins not only provide energy, but also contribute to construction of muscle and enzymes. If there is lack of protein in human diet, there might be several diseases occurs. On the other hand, proteins are like a key due to their functional and physicochemical properties in foods. Proteins interact with solvents, ions, polysaccharides, lipids and other proteins in food matrix and alter the physical structure of foods. Protein solubility, water and oil binding/absorption capacity, viscosity, foaming capacity and foaming stability, emulsification, and gelation are critical functional parameters, which are role on final product quality. The World population is growing dramatically and food security is one of the biggest concerns of agro-food industry and governments. Land plants are included in human diet to give energy and nutrients for sustainable life style for a long time ago. However, the usage of plant proteins less than expected level even if they are fairly cheap and more abundant than animal proteins. Legumes are considerable interest of academia due to sufficient nutritional composition, and alternative to animal originated foods among plant proteins. Despite the thousands of species only soybeans, peas, chickpeas, broad beans, lentil, and cowpeas are comprehensively studied. To date, there was not enough studies in literature found regarding to Phaseolus coccineus L. (Cranberry Bean). On the other hand, altering functional properties of proteins are gaining importance by novel and sustainable methods. Among them, microfluidization that is dynamic high-pressure advanced technique and alters several functional properties of protein isolates reported. It has been reported that microfluidization(HPH) is environmentally friendly way while comparing to conventional techniques. The aim of this study is obtaining protein isolate from Cranberry bean (Phaseolus coccineus L.) by isoelectric precipitation. Then, subject to isolates microfluidization treatment and investigate the effects of microfluidization treatment on several functional and physicochemical properties of protein isolates. Initially, the proximate composition analysis performed for PCLF (Phaseolus coccineus L. flour). Then, the flour prepared for protein extraction. The color values of PCLF (Phaseolus coccineus L. flour) and freeze PCLPI (Phaseolus coccineus L. protein isolate) measured instrumentally. After that, protein content of PCLPI was measured. Oil absorption capacity (OAC), water absorption capacity (WAC), emulsifying and foaming properties were of protein isolates also examined. The analysis of composition showed that Phaseolus coccineus L. that was grown in Çanakkale province, contains 4.8% ash, 2.86% moisture, 27.01% protein and 1.53% lipid and 63.73% carbohydrate content on dry weight. The protein content of Phaseolus coccineus L. protein isolate (PCLPI) were determined 83.53% with 2.37% standard deviation on dry weight. According to color result of color analysis, Phaseolus coccineus L. flour shows L* value 89.763 which is higher than Phaseolus coccineus L. isolate with 81.751. However, the redness value and yellowness values of the isolates higher than the flour a* value of the flour is 0.173 and b* value is 6.907 while isolates a* value is 0.253 and b* value is 10.783. Water absorption capacity (WAC) of freeze dried PCPLI was 2.63 g of water/g of protein on dry weight (dw). In this study oil absorption capacity (OAC) was detected 3.95 g of oil/g of protein isolate on dry weight (dw). Foaming capacity (FC) and foaming stability (FS) of freeze- dried Phaseolus coccineus L. isolate (PCLPI) were 247.400% and 132.000% respectively. The emulsifying activity of freeze-dried Phaseolus coccineus L. isolate were 50.957% and emulsion stability were 100%. High pressure treatment carried out 20 Psi (pounds per square inch) - 4 or 6 Cycle levels and 40 Psi(pounds per square inch )- 4 or 6 cycle selected. Investigating effect of microfluidizitaion or high-pressure homogenization (HPH) on foaming and emulsifying properties, turbidity, particle size, ζ- potential microstructure and secondary structure analysis were conducted. The highest foaming capacity (FC) and foaming stability (FS) observed for 40 Psi- 6 Cycle treatment. The highest foaming capacity and stability were 612.000% and the 182.500% for 40 Pi- 6 Cycle treatment. The lowest foaming capacity (FC) and foaming stability (FS) detected for control sample 235.000% and 88.100% respectively. The emulsifying activities were changing from 55.06% to 52.80%. Emulsifying stability were 100% for all samples, including control. However, High Pressure treatment statistically were not changed EA (emulsifying activiy) or ES (emulsifying stability). Turbidity, zeta (ζ)- potential, particle size, measurements were conducted from pH 2 to pH 10. The lowest turbidity value detected as 0.138 nm au for 40 Psi-6 Cycle at pH 10, while the highest absorbance was between 2.639 and 2.853 nm au at pH 5 and all samples were statistically same. The lowest net charge was observed at pH 4 that was very close to isoelectric point 0.924 mV and belong to 40 Psi – 6 Cycle treatment. The highest zeta (ζ)- potential observed at pH 10 and all the samples were statistically same and the net charge were between -13,22 and -14,25 mV. According results of statistical analysis, after or at neutral pH values microfluidization reduced particle diameter. However, when pH approach to isoelectric point of PCLPI, proteins showed agglomeration potential and particle size were increased. And the highest diameter was observed at pH 4 with 7920.00 nm which belonged 40 Psi- 4 Cycle treatment and, the lowest mean diameter belonged to 40 Psi- 6 Cycle with 61.138 nm at pH 8. According light microscope images, microfluidization treatment broke into fragments and more homogenous particles by reducing big cluster to small clumps. Secondary structures of PCPLIs were imaged by FT-IR spectrum. PCPLI showed absorption band between amide I region at 1635.47 cm-1. The FT-IR images support that PCPLP was in amide I region and consist of β-sheet structure, ~ % 80 peptide bonds exist and C=O exhibited stretch vibrations. As a result, HPH improved foaming, reduced particle diameter and turbidity and increased zeta (ζ)- potential at and after neutral pHs. However, more research proposed to be done by changing pressure and cycle number, to understand effect of microfluidization (HPH) on physicochemical and functional properties of proteins.