Thesis (M. Sc.(Agric.))(Food Science)--University of Pretoria, 2005. / Includes summary. Includes bibliographical references). Available on the Internet via the World Wide Web.

Fractions from white and tannin sorghums were processed into extrudates, thick porridges, and breads. The effects of sorghum type and fraction on the in vitro starch availability of the products were evaluated, and the estimated glycemic indexes (EGI) of the products were obtained. Sorghum extrudates were significantly more slowly digested than corn meal extrudates for all preparation methods (whole, cracked and decorticated kernels). Furthermore, tannin extrudates were less digestible than white sorghum extrudates. The soft endosperm nature of the tannin sorghum limited friction formation inside the extruder, reducing starch gelatinization. On the other hand, condensed tannins also interfered with the starch availability for digestion. White sorghum was more 'suitable' for extrusion, giving extrudates with higher starch degradation and expansion than the tannin sorghums. However, tannin sorghums also gave acceptable products offering the benefit of lower EGI values. Sorghum porridges were more slowly digested than a corn flour porridge when using whole and decorticated flours. In addition, tannin sorghum porridges had a lower starch digestibility compared to all the samples. Tannin sorghum flours produced soft porridges with enhanced initial starch digestibility. However, condensed tannins seemed to offset the starch digestion by limiting starch availability. All sorghum porridges had significantly lower EGI values than the corn porridge. Extrudates and porridges had reduced starch digestibilities and EGI values when using whole grains compared to using the decorticated fractions. This was observed in both the white and the tannin sorghum. Therefore, whole-grain products from sorghum have health benefits attributed to whole grain foods and slower digesting starches; for instance, prevention and treatment of diseases such as diabetes, insulin resistance, obesity, cardiovascular disease, and some types of cancer. When 12% of tannin bran was added to a wheat bread formulation, a slower rate of starch digestion was observed compared to a wheat bread. The high concentration of non-starch components of the bran (i.e. dietary fiber, condensed tannins) affected starch digestion. The addition of tannin sorghum bran significantly reduced the EGI value of wheat bread, besides being a natural source of brown color, and an excellent source of antioxidants and dietary fiber.

Most of the calories in cereal foods come from starch. Decreasing starch digestibility is fundamental to prevent obesity and diabetes. This study investigated interactions of condensed tannins (proanthocyanidins-PA) and other sorghum phenolic compounds with starch molecules and their effect on in vitro starch digestibility. High tannin (predominant in large molecular weight PA, 80%), black (monomeric polyphenols) and white (low in polyphenols) sorghum phenolic extracts were cooked with starches varying in amylose content. Starch pasting properties, polyphenol profile and in vitro starch digestibility were evaluated. Unlike other treatments, samples with tannin phenolic extracts had significantly (P ≤ 0.05) lower setback in the test using a Rapid Visco Analyser (RVA) compared to control. The same treatments had the least extractable phenol and PA contents after cooking with all starches. These evidences suggest interactions between starch molecules and PA. Furthermore, after mixing tannin phenolic extracts with pure amylose/amylopectin, extractable polymeric PA was in much lower concentration (62% less) in presence of amylose compared to amylopectin. This drop in concentration increased to 85% when purified tannin extract (90% polymeric PA) was used. This indicates a stronger interaction between amylose and large molecular weight PA. When high amylose starch was used in an autoclave cooking/cooling technique, the RS content of control (26.4%) was similar (P > 0.05) to samples with black phenolic extracts (27%); samples with tannin phenolic extracts increased RS to about 40%. The RS increased to 46% when purified tannin extract was used. All these evidences suggest that sorghum condensed tannins, specifically the polymeric PA, directly interacted with amylose, increasing RS content, whereas the monomeric polyphenols did not. This study opens opportunities to use tannin sorghum to develop products for diabetics and weight control, high in dietary fiber and natural dark color. In the other part of this project, polyphenols from black and tannin sorghum bran were extracted using an Accelerated Solvent Extractor (ASE) and eco-friendly solvents such as water, and mixtures ethanol/water. ASE at 120 and 150 degrees C using 50 and 70% ethanol/water was efficient in extracting as much phenols (45 mg GAE/g) and 12% more antioxidants (628 μmol TE/g) from black sorghum compared to conventional methods using aqueous acetone and acidified methanol. Therefore, ASE extracts from black sorghum could be used in beverages and in colorants containing high antioxidant content.

Environmental and political concerns centered on energy use from gasoline have led to a great deal of research on ethanol production. The goal of this thesis is to determine if it is profitable to produce ethanol in Texas using sweet sorghum juice. Four different areas, Moore, Hill, Willacy, and Wharton Counties, using two feedstock alternatives, sweet sorghum only and sweet sorghum and corn, will be analyzed using Monte Carlo simulation to determine the probability of economic success. Economic returns to the farmers in the form of a contract price for the average sweet sorghum yield per acre in each study area and to the ethanol plant buying sweet sorghum at the contract price will be simulated and ranked. The calculated sweet sorghum contract prices offered to farmers are $9.94, $11.44, $29.98, and $36.21 per ton in Wharton, Willacy, Moore, and Hill Counties, respectively. The contract prices are equal to the next most profitable crop returns or ten percent more than the total cost to produce sweet sorghum in the study area. The wide variation in the price is due to competing crop returns and the sweet sorghum growing season. Ethanol production using sweet sorghum and corn is the most profitable alternative analyzed for an ethanol plant. A Moore County ethanol plant has the highest average net present value of $492.39 million and is most preferred overall when using sweet sorghum and corn to produce ethanol. Sweet sorghum ethanol production is most profitable in Willacy County but is not economically successful with an average net present value of $-11.06 million. Ethanol production in Hill County is least preferred with an average net present value of $-712.00 and $48.40 million when using sweet sorghum only and sweet sorghum and corn, respectively. Producing unsubsidized ethanol from sweet sorghum juice alone is not profitable in Texas. Sweet sorghum ethanol supplemented by grain is more economical but would not be as profitable as producing ethanol from only grain in the Texas Panhandle. Farmers profit on average from contract prices for sweet sorghum when prices cover total production costs for the crop.

In order to test the dietary effects of bioactive compounds present in whole grains, we decided to observe the effect of varying types of sorghum bran on colon cancer promotion. We used 40 rats consuming diets containing 6% fiber from either cellulose or bran from white (contains phenolic acids), brown (contains tannins), or black (contains anthocyanins) sorghum (n=10). Diets were fed for 10 wk, during which two azoxymethane (AOM) injections (15 mg/kg BW) were administered in wk 3 and 4. We observed that the total number of aberrant crypts (AC) and high multiplicity aberrant crypt foci (HMACF) were lower in rats consuming black (p < 0.04) and brown (p < 0.006) sorghum diets when compared to the cellulose diet, and that these decreases were an inverse function of diet antioxidant activity (ABTS). These observations led us to evaluate the effect of these diets on endogenous enzymatic activities (superoxide dismutase, SOD; catalase, CAT; and glutathione peroxidase, GPx), redox status as measured by reduced and oxidized glutathione, and cell cycle processes, proliferation and apoptosis, in the rat colon. Total SOD activity was higher (p < 0.04) in rats consuming black sorghum when compared to all other diets. A similar, but not significant, trend occurred in mitochondrial SOD. The white sorghum diet had enhanced (p < 0.02) CAT activity compared to the cellulose diet, but the black and brown sorghum diets were intermediate. Finally, all sorghum diets suppressed GPx activity relative to cellulose (p < 0.04). However, no changes were seen in levels of reduced and oxidized glutathione or the ratio of the two. The black sorghum fed rats had a lower proliferative index (p < 0.01) and zone (p < 0.04) compared to cellulose; brown and white sorghum rats were intermediate. Apoptotic index was highest in brown sorghum rats compared to cellulose (p < 0.03), while other sorghum diets were intermediate. These data suggest that the suppression of AC and HMACF formation in rats consuming sorghum bran may have resulted through the differential actions of the sorghum brans on endogenous antioxidant enzymes, which may affect colonocyte proliferation and apoptosis.

Antioxidant properties of sorghum are related to sorghum type and method of processing into foods. Tannin and non-tannin sorghums and their products were evaluated for total phenols, tannins and antioxidant activity. Total phenols were determined using the Folin Ciocalteu method, and tannins were determined by the vanillin-HCl method. Antioxidant activity was evaluated using the ABTS (2,2¢- azinobis(3-ethyl-benzothiazoline-6-sulphonic acid) and DPPH (2,2¢-diphenyl-Ipicrylhydrazyl) assays. Tannin sorghums and their products had higher total phenols, tannins and antioxidant activity than non-tannin sorghum grain and products. Fermentation, extrusion cooking and porridge making reduced measurable phenols, tannins and in vitro antioxidant activity. Reduction was probably due to phenols binding to the food components, thus reducing their solubility in the extracting solvents; 1% HCl in methanol and 70% aqueous acetone. The procyanidin profile obtained using normal phase HPLC and fluorescent detection showed that extrusion cooking and porridge making lowered extractability of polymers (DP>8), while that of oligomers (DP 2-8) and monomers in porridges was not significantly changed. This indicated increased interactions of procyanidin polymers with the food matrix, especially with protein. Pepsin treatment of sorghum extrudates and porridges significantly improved the antioxidant activity and recovery. The highest antioxidant activity was in the supernatants of pepsin hydrolysates. Amylase treatment alone did not significantly affect phenol content and antioxidants, except in bread containing non-tannin white sorghum bran, where there was a slight increase in phenols. The combination of pepsin followed by amylase treatment of porridges and extrudates had effects similar to those of pepsin alone. Improved extractability of antioxidants on pepsin treatment was due to either the release of phenolic antioxidants or protein hydrolysates high in aromatic amino acid residues such as tyrosine, also known for their antioxidant activity. In either situation the improved antioxidant activity could mean that once food is digested it can potentially protect the gastrointestinal tract against oxidative stress generated from the diet and that produced by food interactions during digestion. There is scope to explore other biological methods like use of other proteases to improve antioxidant recovery. Further work would thus determine contribution of phenolic compounds to improved antioxidant activity, and also identify the phenolics.

Bottom rounds were shipped to the Rosenthal Meat Science and Technology Center, ground and enhanced with one of the following predetermined treatments: control; 0.4% sodium phosphates and 0.3% salt; 0.25% sorghum bran; 2.0% sorghum bran; 0.25% sorghum bran, 0.4% sodium phosphates and 0.3% salt; and 2.0% sorghum bran, 0.4% sodium phosphates, and 0.3% salt. The ground beef was formed into 226 g ground beef patties, packaged in an 80% O2 and 20% CO2 gaseous environment, and stored under retail display at 4 degrees for 0, 3, 6, or 9d. Measurements to determine rate and extent of oxidation, rate of discoloration, and sensory characteristics were taken to evaluate the effectiveness of sorghum bran. Patties containing the highest amount of sorghum bran had the lowest TBARS values over 9 days of storage, lower a* values, greater amounts of discoloration, darker lean color, and less cook loss (P<0.05) than control patties. Patties enhanced with the highest level of sorghum bran had lower beefy/brothy and bloody flavor aromatics, higher sorghum flavor, more bitter and burnt aftertaste, and more sandy/gritty textures (P<0.05) when compared to control patties. Patties containing the low amount of sorghum had lower TBARS values (P<0.05), but similar amounts of cook loss as the control patties. Patties containing a low sorghum level, 0.4% sodium phosphates (SP) and 0.3% salt (S) had lower (P<0.05) amounts of cook loss when compared to control patties. Patties containing low amounts of sorghum were similar to control patties in terms of redness while the addition of low sorghum, SP, and S decreased (P<0.05) the degree of redness. Patties containing low amounts of sorghum bran had similar amounts of discoloration compared to control (CONT) patties. Also, these had less bloody flavor aromatics (P<0.05), but were similar in sorghum flavor aromatics and bitter taste when compared to control patties. The addition of sorghum bran at low levels can retard oxidative rancidity in ground beef patties without causing detrimental color changes and negatively affecting sensory attributes, while patties enhanced with 2% sorghum bran have extensive discoloration and undesirable sensory attributes.

Global gene expression in Sorghum bicolor, an important crop showing drought tolerance in arid and semi-arid cultivated areas, was monitored to exposure of 8-days seedlings to water deficit (20% polyethylene glycol) or cold stress (4 ºC). A sorghum cDNA microarray, including ~13,000 (milestone version 1) or ~28,000 (milestone version 2) unigenes, was used to examine gene expression in shoots and roots at 3 and 27hours after stress treatment. ~1,300 and ~2,300 genes were modulated by water deficit and cold stress, respectively. Up-regulated genes included previously identified stressinduced genes such as early drought-induced gene, dehydrin, late embryogenesis abundant gene, glycin and proline-rich gene, and water stress-inducible genes as well as unknown genes. Genes involved in signal transduction, lipid metabolism, transporter, and carbohydrate metabolism are induced. Quantitative real-time PCR was used to quantify changes in relative mRNA abundance for 333 and 108 genes in response to water deficit and cold stress, respectively. Stress-induced genes were classified by kinetics. Eighteen of 108 cold-induced genes were modulated by cold but not by ABA and PEG treatment. This research provides the starting point for detailed analysis and comparison of water deficit and cold modulated gene networks in sorghum.

Sorghum (Sorghum bicolor [L] Moench) was first introduced to the United States in the 1800s. These introductions consisted of tropical varieties with a short day photoperiod response that limited their use in temperate hybrid breeding programs. Commercial exploitation of F1 hybrids in grain sorghum started by the mid 1950s with the use of cytoplasmic male sterility system CMS (A1). Even though other CMS are available, most sorghum hybrid seed production still relies on the A1 system. Genetic gain in most agronomic crop species is limited by several factors. In the specific case of sorghum, the uniform use of the CMS (A1) system and the recent introduction of sorghum to the United States have resulted in a reduction of its genetic base. In order to create enough genetic variability, plant breeders might utilize exotic non adapted material, exotic adapted material or existing elite material as a source of new alleles that will protect and improve genetic gain through selection. This study provides an estimate of the genetic diversity existing in a set of sorghum conversion lines. The objectives of this study were: (1) to estimate the genetic diversity present among a set of 16 sorghum conversion lines; (2) to classify this set of lines based on genetic similarities estimated using AFLP markers and (3) to estimate heterosis, general and specific combining ability for grain yield among the set of conversion lines. Genetic diversity was present in the set of conversion lines evaluated. For the lines included only in this study, Caudatum was the most homogenous race (average GS = 0.69), and this race was closely related to the Durra race (Average GS = 0.66). Two other homogenous races were Bicolor and Kafir with average GS of 0.67. Highest GCA effects were obtained from the Kafir and Caudatum races. Good heterotic responses were obtained from DurraKafir races and CaudatumKafir races. Estimation of SCA, MPH and BPH identified specific crosses that were numerically superior than those of the checks. The use of AFLP markers allowed the identification of five strong clusters through estimates of genetic similarities. This classification did not group the lines by either their genetic background or their fertility reaction. This study provides information to identify specific combinations that would help to understand heterotic relationships in sorghum, and support the suggestions made by Menz and Gabriel that races in sorghum are not well defined.

Fractions from white and tannin sorghums were processed into extrudates, thick porridges, and breads. The effects of sorghum type and fraction on the in vitro starch availability of the products were evaluated, and the estimated glycemic indexes (EGI) of the products were obtained. Sorghum extrudates were significantly more slowly digested than corn meal extrudates for all preparation methods (whole, cracked and decorticated kernels). Furthermore, tannin extrudates were less digestible than white sorghum extrudates. The soft endosperm nature of the tannin sorghum limited friction formation inside the extruder, reducing starch gelatinization. On the other hand, condensed tannins also interfered with the starch availability for digestion. White sorghum was more 'suitable' for extrusion, giving extrudates with higher starch degradation and expansion than the tannin sorghums. However, tannin sorghums also gave acceptable products offering the benefit of lower EGI values. Sorghum porridges were more slowly digested than a corn flour porridge when using whole and decorticated flours. In addition, tannin sorghum porridges had a lower starch digestibility compared to all the samples. Tannin sorghum flours produced soft porridges with enhanced initial starch digestibility. However, condensed tannins seemed to offset the starch digestion by limiting starch availability. All sorghum porridges had significantly lower EGI values than the corn porridge. Extrudates and porridges had reduced starch digestibilities and EGI values when using whole grains compared to using the decorticated fractions. This was observed in both the white and the tannin sorghum. Therefore, whole-grain products from sorghum have health benefits attributed to whole grain foods and slower digesting starches; for instance, prevention and treatment of diseases such as diabetes, insulin resistance, obesity, cardiovascular disease, and some types of cancer. When 12% of tannin bran was added to a wheat bread formulation, a slower rate of starch digestion was observed compared to a wheat bread. The high concentration of non-starch components of the bran (i.e. dietary fiber, condensed tannins) affected starch digestion. The addition of tannin sorghum bran significantly reduced the EGI value of wheat bread, besides being a natural source of brown color, and an excellent source of antioxidants and dietary fiber.