Functionality And Nutritional Properties Of Foxtall Millet Protein And Its Hydrolysates Mohamed Tabita Kamara

Millet is highly nutritious, non-glutinous; like buckwheat and quinoa, is not an acid forming food so is soothing and easy to digest. In fact, it is considered to be one of the least allergenic and most digestible grains available and it is a warming grain so will help to heat the body in cold or rainy seasons and climates. Millet is tasty, with a mildly sweet, nut-like flavor and contains a myriad of beneficial nutrients. It is nearly 15% protein and B-complex vitamins including niacin, thiamin, and riboflavin, the essential amino acid, lecithin, and some vitamin E. It is particularly high in the minerals iron, magnesium and potassium. The seeds are also rich in photochemicals, including phytic acid, which is believed to lower cholesterol, and phytate, which is associated with reduced cancer risk.Proteins are important constituents of human diet, as they are a source of essential amino acids and nitrogen. For application of proteins in several food products and in the pharmaceutical industry, it is necessary to hydrolyse proteins. Protein hydrolysis can be performed with a range of different proteolytic enzymes under various process conditions, to determine the final peptide composition. The peptides resulting from protein hydrolysis differ from the parental material in various molecular properties like molecular weight and charge. These altered molecular properties causes changes in techno-functional properties of hydrolysates like solubility, bitterness, emulsifying and foaming properties. Moreover, apart from the nutritional change (e.g. improved digestibility); hydrolysis may result in liberation of bioactive peptides. The aim of this research was to study the functional and nutritional properties of foxtail millet protein isolate and its hydrolysates prepared with different commercially available proteases.In order to elucidate the correlations between functional and nutritional properties, hydrolysates were characterised in a standardized manner and the data were analyzed using multivariate data analysis. In this study, a thorough literature review was done; followed by an assessment and comparison of the biochemical properties of cream and yellowish foxtail millet flour (CFMF and YFMF). The seeds were purchased in Wuxi and defatted using hexane. From the results, the defatted yellowish foxtail millet flour (DYFMF) has a relatively higher protein, fat and moisture contents than defatted Cream foxtail millet flour (DCFMF). But the carbohydrate and ash contents were higher in (DCFMF) compared to (DYFMF). There was a significant improvement on the protein content after defatting. However, both samples are good sources of minerals, sugars and vitamins. Furthermore, both varieties are rich in oleic and linoleic acids as the major unsaturated fatty acids, and also palmitic and stearic acids as the major saturated fatty acids were in moderate amount. The essential amino acids were above the amounts recommended by the Food and Agricultural organization/World Health Organization (FAO/WHO/UNU) for humans. The Infrared (IR) spectra of both samples show variant peak structures and they possess different functional groups at different regions of their spectra. From the foregoing, it is obvious that, the two varieties have some common characteristics; they however, have marked differences in their biochemical compositions.Four protein fractions (albumin, globulin, glutelin and prolamin and protein isolate) from DCFMF and DYFMF were fractionated and then characterized by amino acid analysis, SDS-PAGE, and differential scanning calorimetry (DSC). Prolamin was the major fraction (43.5,44.4%) extracted, followed by glutelin (39.2,39.8%), albumin (8.5, 8.6%), and globulin (7.4,6.3%). Protein isolate was mainly composed of prolamin and glutelin. There was a significant difference (P<0.05) between the various protein fractions. These protein fractions and protein isolate showed an excellent balance of all essential amino acids, with a relatively high level of glutamic acid, arginine and leucine, whereas cystine was lacking and lysine which is the first limiting amino acids in most cereals is found to be in a moderate amount in both samples. All the estimated nutritional parameters based on amino acids composition showed that defatted foxtail millet proteins exhibited an appreciable level of good nutritional quality. The fractions and isolates have molecular sizes between 14.0 kDa and 97.0 kDa. The globulin fractions possessed the highest thermal stability (Tp=81.10℃,81.82 andΔH=5.21,5.11 J/g), followed by the protein isolates (Tp=79.87,80.05℃andΔH=0.91,0.76 J/g), while the albumin fractions were the lowest (Tp=66.23,66.42℃andΔH=0.44,0.49 J/g).Furthermore, an investigation was carried out on the functionality and physicochemical properties of the protein isolates compared to soy protein isolate. Foxtail millet protein isolate was easily digested by trypsin in vitro. They have U-shape solubility curves. Water-binding capacity was 6.0 and 7.0 g/g while oil absorption capacity was 5.0 and 6.0 g/g for DCFMPI and DYFMPI. DYFMPI had the highest bulk density (0.22 g/mL) and emulsifying capacity than DCFMPI and soy protein isolates (SPI). Foam capacity and foam stability ranged from 137 to 73 mL for DYFMPI, from 124 to 61 mL SPC and from 124 to 46 mL for DCFMPI.However, we also examined the effect of enzymatic hydrolysis on the functional properties of defatted foxtail millet proteins. Defatted foxtail millet protein isolate (DFMPI) was enzymatically hydrolyzed by several commercially available proteases (Protamex, Papain, Alcalase 2.4L, Flavourzyme and Neutrase), under a defined set of reaction conditions to produce foxtail millet protein hydrolysate, with protein contents of 84.74%,85.88%,91.84%,88.92%, and 83.52% respectively. Hydrolysis with proteases at percentage 1%(enzyme to substrate ratio) developed rapidly in early reaction stage, as shown in by the rise in DH, and then decreased in the rise. Essential amino acids were above the recommended amount by Food and Agricultural organization/World Health Organization (FAO/WHO/UNU) for humans with a significant difference (P<0.05). The molecular Weight ranged below 200 Da and 5000 Da above, surface hydrophobicities of 122.75 and 166.05; At pH 7.0 above, all proteins dissolved between (70% and 91%), with defatted foxtail millet protein hydrolysate (DFMPH) having slight higher solubility (91%) than DFMPI (83%). Emulsifying capacity was 82.33% and 72.32%; foam capacity and foam stability ranged from 185.33 to 137.80 mL and from 185.33 to 111.1 mL for both defatted foxtail millet protein hydrolysates (DFMPH) and defatted foxtail millet protein isolate (DFMPI) respectively. Enzymatic modification was responsible for changes in the protein functionality of DFMPH. Moreover, when the protein hydrolysates were compared with the protein isolate using a scanning electron microscopy (SEM), the hydrolysate had finer particles and evenly distributed than protein isolate which was clustered. The hydrolysates produced could be suitable as protein supplements due to their smaller molecular mass distribution.However, in spite of the nutritive and functional qualities of the hydrolysates obtained using Alacalse 2.4L, they had some bitter and salty tastes which was viewed as a major disadvantage. A less expensive method to debitter and desalt the hydrolysates was employed using a styrene-based macroporous adsorption resin (MAR) and different levels of alcohol concentrations (AC,30%,55% and 70%).30% extracted hydrolysates from defatted foxtail millet flour were tasteless while 55% AC showed mild bitterness. After that process some functional properties, molecular weight distribution, their amino acid content and the sensory attributes of the hydrolysates were significantly enhanced based on the findings.Finally, antioxidant and free radical-scavenging activities of protein hydrolysates was studied. DFMPH was fractionated by gel filtration on Sephadex G-25, by hydrolysis using Alcalase 2.4L with a degree of hydrolysis of 45.15%. The amino acid composition, ABTS, DPPH, inhibition of linoleic acid autoxidation, Metal-chelating free radical scavenging ability, and reducing power were tested to determine their antioxidant efficacy. The antioxidant activity of FIV (85.71%) was closer to that of a-tocopherol (86.27%) but lower than that of BHT (92.44) in the linoleic acid oxidation system. Furthermore, FIV exhibited higher ABTS, DPPH and Metal-chelating activity than FI, FⅡand FⅢwith a significant difference (P<0.05). Amino acid analyses showed that F IV with the strongest antioxidant activity also had the highest hydrophobic amino acids content (51.94%) and hydrophobicity (8.62 kJ/mol Amino Acid Residue). Molecular weight of the fractions varied from 77-1042 Da. DFMPH fractions may have the potential to promote healthy human digestion. The fractions also exhibited notable reducing power and chelating effect on Fe2+ and the data obtained by the in vitro systems obviously established the antioxidant potency of DFMPH fractions.