| As many people are becoming more conscious about their health and theenvironment in which they live, there have been grave concerns about the ever-increasing use of synthetic chemicals in various products for human or animalconsumptions including food. This skepticism has been exacerbated by thecontinuous emergence new health conditions and development of therapeuticallyresistance of the previously curable or alleviable ones, such as cancer, tuberculosis,cardiovascular, and many others, which are critically putting human life at greaterrisk than before. People are now questioning the safety of these synthetic chemicals,especially their unknown effects when they interact with one another in the humanor animal bodies. As such, the number of people opting for consumption of naturalor near-naturally produced products is increasing at an alarming rate, such that ifmanufacturers do not swiftly identify alternative consumer-acceptable productiontechniques, time will come when demand will be too great to manage.Soy protein isolate (SPI) is one of the fundamental ingredients applicable in manymanufactured food systems. However, the conventional technique of producing SPIinvolves use of strong non-food synthetic chemicals (SC), such as n-hexane, sodiumhydroxide (NaOH),95%alcohol and hydrochloric acid (HCl), many of which havewell known hazards if handled without taking precautions, a thing which makesconsumers doubt the safety of the food products in which SPI is used as aningredient and to the ecosystem upon disposal.The aim of this study was to (1) produce a natural soy protein isolate using purelynatural, food-plant-based extraction chemicals from native (full-fat) soy flour,following the usual isoelectric precipitation technique, in an attempt to address theconcerns and fears of the healthy conscious food consumers,(2) compare the qualityand characteristics of these natural-chemicals extracted SPIs to those producedconventionally using the synthetic chemicals. Briefly, an alkaline solution of pH>12.5was prepared by filtering distilled waterthrough amaranth (Amarathus tricolor L.) ash, while the acid of pH <2.5wasextracted from ripe lemon (Citrus limon) fruits, to substituted the conventionallyused synthetic NaOH and HCl, respectively. These natural chemicals (NC) wereused to isolate native protein from the full-fat soybean flour (FF) coded NCFF.Samples for comparison were prepared from either the FF or n-hexane-defattedflours (DF) using either the natural chemicals (amaranth ash and lemon fruitextracts) or the synthetic ones and were coded NCDF, SCFF and SCDF, with thefirst two letters referring to the type of chemical used and the last two, to the type offlour.The first set of comparisons was on yield, composition and protein quality, basingon protein digestibility correlation amino acid score (PDCAAS). On dry basis thepurely-natural SPI (prepared from FF using the natural chemicals) contained aminimum of91.21%crude protein, thereby qualifying to be called a ‘proteinisolate'. It showed a protein yield of43.62%(about7.54%lower than theconventional SPI) and the PDCAAS of0.77, which was about22%higher than thatof the laboratory prepared conventional SPI, but still lower than the maximum of0.99reported by some literature. Methionine and cystein-s were significantly higherin the natural SPI while glutamine and serine were higher in synthetic SPI. The restof amino acids did not differ significantly. Anti-nutritional factors (Trypsininhibitors and phytic acid) were considerably lower in the natural than the syntheticSPIs. Many of the determined minerals were higher in the natural SPI withpotassium being the highest. Sodium was very high in the synthetic SPI.Secondly, functional properties, total polyphenol content, and antioxidant activity ofthe natural and conventional synthetic SPIs were compared. The natural SPI showedsignificant increase in emulsion stability (p <0.05). While higher values withnarrow margins were shown by the synthetic than the natural SPIs in oil absorption(0.66±0.02%,0.50±0.01%, respectively), emulsion capacity (56.53±0.57%, 55.50±0.39%) and foam stability (11.33±0.61%,10.40±0.40%). No significantdifference was observed in water absorption capacity. The DPPH assay showedincreased antioxidant activity in the natural SPI although its total polyphenol contentwas lower. Thus, the natural SPI was superior in some functional propertiescompared to its synthetic counterpart.On sensory evaluation, the SpectrumTMdescriptive analysis revealed somedistinctive characteristics among the natural, conventional and some commercialSPIs. Principal component analysis (PCA) results accounted for90.11%of thesamples variability on a two dimensional component space based on the attributeeigenvector loadings of?0.3, and associated the traditional SPI with opacity, pasta,sweet, sour, and bitter (principal component1,55.14%), but not color, cardboard,cereal, brothy, ashy, astringent, salty, and viscosity, which were also characteristicto the conventional and commercial SPIs (principal component2,36.53%). Thesefindings signified that the traditional SPI had comparatively no unique characteristicthat would affect its application in food systems.Finally, the effects of the natural and synthetic chemicals on oxidation and themolecular structure modification of the resultant protein products as they interactwith the proteins in the DF and FF systems were examined. Determination oflipoxygenase (LOX) activity showed that those prepared from full-fat flour hadsignificantly (p <0.05) higher values (5.28x103±132.45for NCFF and6.57x103±143.28for SCFF) compared to their defatted flour counterparts (1.28x103±10.93for NCFF and1.15x103±18.92for SCDF), with SCFF being the highest.There was no significant difference in samples prepared from defatted flours. Thedegree of oxidation, free and total sufhydryl content, and intrinsic fluorescenceindicated increased structural changes in the FF-based samples as compared to thoseprepared from DF. Circular dichroism spectroscopy showed existence of ?-helicesand ?-sheets protein secondary structures. However, DF samples showed increase inunordered structural conformation changes than the FF sample. Characteristic variability in surface hydrophobicity, size exclusion chromatography and SDS-PAGE results were more related to the extraction chemicals than the type of flourused, with samples prepared with SC showing an increase. These molecularstructure modifications could explain some functional and sensory characteristics incertain specific SPIs.It was therefore generally concluded that a purely natural SPI with preferablenutritional quality, functional properties and sensory characteristics can be producedisoelectrically, solely using amaranth ash and lemon extracts as natural food-plants-based chemicals, to address the ever-increasing health and environmental concernsregarding the use of strong non-food synthetic chemicals. The use of thesechemicals cannot cause serious distinctive changes that would prevent applicabilityof the resultant SPI products into other food systems. |
PDF Full Text Request