The effects of plant color, pericarp thickness, pigmented testa, and spreader genes on phenols and antioxidant activity levels of 13 sorghum genotypes were evaluated. Total phenols, condensed tannins, flavan-4-ols, and anthocyanins were measured. Antioxidant activity levels using the 2,2'-azinobis(3-ethyl-benzothiazoline-6-sulfonic acid) and 2,2-diphenyl-1-picrylhydrazyl assays were evaluated. Sorghums with a pigmented testa and spreader genes (B(1)()B(2)()S) had the highest levels of phenols and antioxidant activity. In addition, sorghums with purple/red plants (PQ) and thick pericarp (z) genes had increased levels of phenols and antioxidant activity. Sorghums with a black pericarp had higher levels of flavan-4-ols and anthocyanins than the other varieties. This suggests that genes for plant color, pericarp thickness, presence of a pigmented testa, and spreader genes increase phenols and antioxidant activity levels. This information can be useful in the production of sorghums with increased phenols and antioxidant activity levels.

There is increasing interest in natural food colorants with functional properties. Anthocyanins from black, brown (containing tannins), and red sorghums were characterized by spectrophotometric and HPLC techniques. The antioxidant activity and pH stability of the anthocyanins were also determined. Sorghum brans had 3-4 times higher anthocyanin contents than the whole grains. Black sorghum had the highest anthocyanin content (average = 10.1 mg/g in bran). The brown and red sorghum brans had anthocyanin contents of 2.8-4.3 mg/g. Only 3-deoxyanthocyanidins were detected in sorghum. These compounds are more stable to pH-induced color change than the common anthocyanidins and their glycosides. Additionally, crude sorghum anthocyanin extracts were more stable than the pure 3-deoxyanthocyanidins. The antioxidant properties of the 3-deoxyanthocyanidins were similar to those of the anthocyanins. Pigmented sorghum bran has high levels of unique 3-deoxyanthocyanidins, which are stable to change in pH and have a good potential as natural food pigments.

No abstract

The effects of grain type and processing on ruminal starch digestion are well documented but poorly understood at the biochemical and molecular levels. Waxy grains have starches high in amylopectin and are more readily digested than nonwaxy grains. However, the composition of the endosperm cell matrix and the extent to which the starch granules are embedded within it also affect starch digestion rates. Continued work is needed to determine the influence of specific cell matrix proteins, protein-starch interactions and cell wall carbohydrates on starch availability. The microbial populations that metabolize starch are diverse, differing in their capacities to hydrolyze starch granules and soluble forms of starch. Surveys show that the amylases are under regulatory control in most of these organisms, but few studies have addressed the types of amylolytic enzymes produced, their regulation and the impact of other plant polymers on their synthesis. Research in these areas, coupled with the development and use of isogeneic or near-isogeneic grain cultivars with biochemically defined endosperm characteristics, will enhance our ability to identify mechanisms to manipulate ruminal starch digestion.

The effects of a hydrothermal treatment consisting of tempering (to 41% moisture) and heating to 153 • C (micronisation) on the structural and physicochemical characteristics of two cowpea varieties were studied. The untreated varieties had similar cooking times, although cooked Bechuana white cowpeas were significantly (P ≤ 0.05) softer and had a higher incidence of splitting than Var. 462 cowpeas. This may be due in part to differences in cotyledon structure affecting water uptake during cooking. The hydrothermal treatment changed the physical structure and chemical properties of the cowpea seeds. This led to significant (P ≤ 0.05) reductions in the cooking time of micronised Bechuana white and Var. 462 cowpeas, by 47 and 36% respectively, as compared with control samples. Micronisation caused physical fissuring of the seed coat and cotyledon and significantly (P ≤ 0.05) reduced the bulk density of treated seeds. These changes in the physical structure significantly (P ≤ 0.05) improved the initial water uptake during soaking and cooking, increased the enzyme-susceptible starch and reduced the protein solubility and hydration capacity of the cowpea seeds. Cooked (60 min) micronised cowpeas also had significantly (P ≤ 0.05) more splits and a significantly (P ≤ 0.05) softer texture than control samples.

Structural changes occurred in corn and sorghum during the alkalinecooking process as it progressed from the raw kernel to the tortilla. The alkali weakened the cell walls, facilitating the removal of the pericarp, solubilized cell walls in the peripheral endosperm, caused swelling and partial destruction of starch granules, and modified the physical appearance of the protein bodies. Masa (ground nlxtamal) consisted of small pieces of germ, pericarp, aleurone and endosperrn, and free starch granules, cell fragments, and dissolved or dispersed solids and lipids in water. During tortilla baking, an additional degradation of cell walls, further loss of starch crystallinity, and partial destruction of protein bodies occurred.

A specially designed small-scale foaming apparatus was used to determine dynamic and static foaming properties of proteins. Foam was produced by sparging nitrogen at a known rate through a dilute protein solution. The temperature of the protein solution and protein foam was maintained by a water-jacketed column. Ovalbumin was used as the reference protein. Foaming properties (foaming capacity, foam strength, and stability) were improved when the protein concentration was increased (O.Ol-0.1%); when sodium chloride was added to the protein solution and when the temperature was decreased from 40 to 2°C. Foaming properties were optimum at pH 3.8-4.0, slightly below the isolelectric point of ovalbumin, and at a gas flow of 20 mi/min. The apparatus permits many of the variables affecting foaming properties of proteins, i.e. pH, temperature, ions, carbohydrates and surfactants to be controlled while quantitatively determining foaming properties of small quantities of protein.

A series of laboratory blenders and homogenizers were compared for their capacity to make proteinstabilized emulsions. A Janke-Kunkel blender consistently gave the best emulsions. By use of optimum protein concentrations (0.5%) and temperature (15 °C), the effects of modification on the emulsifying activity (EA) of bovine serum albumin (BSA) over the pH range 2-10 were studied. Reduction of the disulfide bonds reduced the EA, urea (8 M)-eliminated EA, while succinylation significantly enhanced the EA of BSA in the pH range 4-7. These studies indicated the importance of protein structure and charge on emulsifying properties. BSA had superior EA to soy proteins, arachin, /3-casein, ovalbumin, and /3-lactoglobulin.