Janet Taylor

Kafirin microparticle encapsulation of catechin and sorghum condensed tannins.

To exploit the porous nature of previously developed kafirin microparticles, encapsulation of the bioactive polyphenols, catechin and sorghum condensed tannins, was investigated. The antioxidant release profiles of the encapsulated substances were studied under simulated gastric conditions. Kafirin microparticles encapsulating catechin or sorghum condensed tannins were similar in size to control kafirin microparticles (5-6 mum). TEM showed that kafirin microparticles encapsulating catechin had a rough porous surface. Microparticles encapsulating sorghum condensed tannins were irregular in shape, some apparently joined together, with a mixture of rough and smooth surfaces. Over a period of 4 h, catechin and sorghum condensed tannin encapsulated kafirin microparticles showed virtually no protein digestion but released approximately 70 and 50%, respectively, of total antioxidant activity. Thus, the use of kafirin microparticles to encapsulate catechin and sorghum condensed tannins has potential as an effective method of controlled release of dietary antioxidants.

Factors Affecting the Porridge-Making Quality of South African Sorghums

Research was undertaken to facilitate the breeding and selection of sorghums with both good milling and good porridge-making characteristics. Twenty seven cultivars were grown in the same locality under rainfed and supplementary irrigation conditions. The two measures of milling quality, abrasive hardness index and Brabender hardness (BH) were significantly correlated (P⩽0·001) in all sample sets; ie all data, rainfed samples and supplementary irrigation samples. The genetic basis of kernel hardness was confirmed as the hardest and softest cultivars were the same under both cultivation conditions. For all three sample sets there was a significant negative correlation (P⩽0·05) between kernel hardness according to BH and pasting peak viscosity (PPV). PPV is of importance as consumers prefer stiff porridges. The negative correlation between BH and PPV indicates that to select sorghum cultivars with good milling and good porridge-making quality, both kernel hardness and PPV need to be assessed. The sorghums produced under supplementary irrigation were softer according to BH, had higher PPV and set-back viscosity, and the starch contained a higher proportion of amylose than those produced under rainfed conditions. Thus, cultivation environment as well as genetics has a major effect on sorghum milling and porridge-making quality.

Transgenic sorghum with altered kafirin synthesis: kafirin solubility, polymerization, and protein digestion.

Transgenic sorghum (TG) lines with altered kafirin synthesis, particularly suppression of γ-kafirin synthesis, and improved protein quality have been developed. The proportion of kafirin extracted with 60% tert-butyl alcohol alone was greatly increased in the TG lines. However, the total amount of kafirin remained unchanged. Further, in the TG lines, the kafirin was much less polymerized by disulfide bonding. There was also evidence of compensatory synthesis of other kafirin proteins. Cooked protein digestibility was increased in the TG form, even after removal of interfering starch. The TG protein bodies were intermediate in appearance between the normal type and the invaginated high digestibility mutants. Hence, the increased protein digestibility of these TG lines is probably related to their lower levels of disulfide-bonded kafirin polymerization, allowing better access of proteases. This work appears to confirm that disulfide bond formation in kafirin is responsible for the reduced protein digestibility of cooked sorghum.

Developments in the science of zein, kafirin, and gluten protein bioplastic materials

ABSTRACT Despite much research, there are very few commercial prolamin bioplastics. The major reason, apart from their high cost, is that they have inferior functional properties compared with synthetic polymer plastics. The inferior functional properties are because the prolamins are complex, each consisting of several classes and subclasses, and the functional properties of their bioplastics are greatly affected by water. Prolamin bioplastics are produced by controlled protein aggregation from a solvent or by thermoplastic processing. Recent research indicates that aggregation occurs by polypeptide self-assembly into nanostructures. Protein secondary structure in terms of α-helical and β-sheet structure seems to play a key but incompletely understood role in assembly. Also, there is inadequate knowledge as to how these nanostructures further assemble and organize into the various forms of prolamin bioplastics such as films, fibers, microparticles, and scaffolds. Many methods have been investigated to im...

Protein Biofortified Sorghum: Effect of Processing into Traditional African Foods on Their Protein Quality

Protein biofortification into crops is a means to combat childhood protein-energy malnutrition (PEM) in developing countries, by increasing the bioavailability of protein in staple plant foods and ensuring sustainability of the crop. Protein biofortification of sorghum has been achieved by both chemically induced mutation and genetic engineering. For this biofortification to be effective, the improved protein quality in the grain must be retained when it is processed into staple African foods. Suppression of kafirin synthesis by genetic engineering appeared to be superior to improved protein digestibility by chemical mutagenesis, because both the lysine content and protein digestibility were substantially improved and maintained in a range of African foods. For the genetically engineered sorghums, the protein digestibility corrected amino acid score was almost twice that of their null controls and considerably higher than the high protein digestibility sorghum type. Such protein biofortified sorghum has considerable potential to alleviate PEM.

Preparation of Free-Standing Films from Kafirin Protein Microparticles: Mechanism of Formation and Functional Properties

A method of preparing free-standing films using kafirin microparticles made by phase separation from acetic acid is described. Film preparation involved the suspension of the microparticles in acetic acid solution containing plasticizer. On evaporation of the acetic acid, a complete, smooth, flexible, transparent film was formed. A minimum concentration of acid was required to form a cohesive film relative to the concentration of kafirin. This was approximately 10.8:1, percent acetic acid to percent kafirin. Film formation appears to be by controlled aggregation of kafirin microparticles, followed by dissolution of the microparticles in acetic acid and drying into a cohesive film. The functional properties of microparticle films were generally superior to films cast directly from a solution of kafirin, at the same protein content. Kafirin microparticle films were very thin (<15 microm), relatively strong but not very extensible, with better water barrier properties and lower protein digestibility than conventionally cast kafirin films.

Physicochemical Modification of Kafirin Microparticles and Their Ability To Bind Bone Morphogenetic Protein-2 (BMP-2), for Application as a Biomaterial

Vacuolated spherical kafirin microparticles with a mean diameter of 5 μm can be formed from an acidic solution with water addition. Three-dimensional scaffolds for hard tissue repair require large structures with a high degree of interconnected porosity. Cross-linking the formed kafirin microparticles using wet heat or glutaraldehyde treatment resulted in larger structures (approximately 20 μm), which, while similar in size and external morphology, were apparently formed by further assisted assembly by two significantly different mechanisms. Heat treatment, which increased the vacuole size, involved kafirin polymerization by disulfide bonding with the microparticles being formed from round, coalesced nanostructures, as shown by atomic force microscopy (AFM). Kafirin polymerization of glutaraldehyde-treated microparticles was not by disulfide bonding, and the nanostructures, as revealed by AFM, were spindle shaped. Both treatments enhanced BMP-2 binding to the microparticles, probably due to their increased size. Thus, these modified kafirin microparticles have potential as natural, nonanimal protein bioactive scaffolds.

Use of falling number and rapid visco analyser instruments to estimate sorghum malt diastatic power

Abstract Diastatic power (DP), a measure of joint alpha - and beta -amylase activities, is the most important quality criterion of sorghum malt. There is a need for a rapid method to estimate sorghum malt DP. Such methods have been developed using both the Falling Number (FN) and Rapid Visco Analyser (RVA) instruments, which measure alpha -amylase activity. Maize starch is used as substrate at a ratio of malt to maize starch of 1:29. Good estimates of DP can be obtained with malts prepared from grain of a single cultivar (FN, r = −0·872; RVA, r = −0·993). The estimate is less good with malts prepared from different cultivars (FN, r = −0·759; RVA, r = −0·759), probably a result of the different cultivars having varying proportions of alpha -amylase relative to DP. The methods are well suited, therefore, to quality control in maltings and breweries, but less suitable for evaluating the malting quality of different cultivars.

Improvement in water stability and other related functional properties of thin cast kafirin protein films

Improvement in the water stability and other related functional properties of thin (<50 μm) kafirin protein films was investigated. Thin conventional kafirin films and kafirin microparticle films were prepared by casting in acetic acid solution. Thin kafirin films cast from microparticles were more stable in water than conventional cast kafirin films. Treatment of kafirin microparticles with heat and transglutaminase resulted in slightly thicker films with reduced tensile strength. In contrast, glutaraldehyde treatment resulted in up to a 43% increase in film tensile strength. The films prepared from microparticles treated with glutaraldehyde were quite stable in ambient temperature water, despite the loss of plasticizer. This was probably due to the formation of covalent cross-linking between free amino groups of the kafirin polypeptides and carbonyl groups of the aldehyde. Thus, such thin glutaraldehyde-treated kafirin microparticle films appear to have good potential for use as biomaterials in aqueous applications.

Biocompatibility and biodegradation of protein microparticle and film scaffolds made from kafirin (sorghum prolamin protein) subcutaneously implanted in rodent models

Kafirin, the sorghum prolamin protein, like its maize homologue zein, can be made into microparticles and films and potentially used as a biomaterial. Zein has good bio- and cyto-compatibility. Kafirin could be advantageous as it is more hydrophobic, more crosslinked, more slowly digested by mammalian proteases than zein and is non-allergenic. The safety and biocompatibility of kafirin implants in two forms was determined in rodent models. One week post subcutaneous injection of kafirin microparticles (size 5-µm diameter) in mice, chronic inflammation, abnormal red blood cells, and gross fibrin formation were observed. This chronic inflammatory response was possibly caused by the release of hydrolysis products such as glutamate during the degradation of the kafirin microparticles. In contrast, films made from kafirin microparticles (50-µm thick, folded into 1 cm(3) ) implanted in rats showed no abnormal inflammatory reactions and were only partially degraded by day 28. The slower degradation of the kafirin films was probably due to their far smaller surface area when compared to kafirin microparticles. Thus, kafirin films appear to have potential as a biomaterial. This study also raises awareness that the form of prolamin based biomaterials, (kafirin and zein) should be considered when assessing the safety of such materials.