A series of studies was conducted using SEM in conjunction with chemical analysis, in situ and in vitro digestion techniques, to characterize the anatomical components from barley, corn, sorghum and wheat grains which constitute "fiber" and investigate their susceptibility to rumen microbial digestion. Fractured grains were used to identify anatomical features and cell types prior to and after extraction or digestion. Certain anatomical features, including pericarp tissue, aleurone cells, endosperm cell walls, corneous and floury endosperm tissue and lemma and palea from barley, were easily identifiable in fractured and ground grains, and in neutral detergent extracted or digested residues. In situ and in vitro incubation conditions were varied to assess the effect of concentrate and/or reduction of pH on the disappearance of identifiable grain fractions. In situ incubations were conducted using steers adapted to 0-, 30- and 90% concentrate diets. In vitro inoculum buffered at pH 7 or 6 was provided by a steer fed 0- or 90% concentrate. Tissues resistant to rumen microbial digestion during extended (144-h) in situ incubations and shorter term (12- to 48-h) in vitro incubations were primarily those identified in NDF, and included pericarp, lemma and palea, and small amounts of corneous endosperm. Remaining tissues identified included barley lemma, palea and pericarp; corn pericarp, tip cap and small amounts of corneous endosperm; sorghum pericarp and corneous endosperm with matrix and protein bodies; and wheat pericarp. In vitro disappearance of isolated NDF after 48-h ranged from 43% for barley to 89% for corn. Labile structures included embryonic tissue and portions of endosperm cell walls, protein matrix and residual starch. Resistant tissues included pericarp, aleurone cell walls, tip cap and portions of the corneous endosperm. Relative rankings of NDF digestibility under all conditions studied were similar (corn > sorghum > wheat > barley) whether determined using isolated NDF or calculated from TIVDMD residues. Neither concentrate level fed to the host animal nor pH of the in vitro incubation flask affected rankings among grains, although increasing concentrate level and/or reducing pH appeared to reduce in vitro NDF disappearance. Evaluation of electron micrographs of fractured grains suggested that similar anatomical structures in the various grains differed in their resistance to microbial digestion. For example, pericarp from barley and wheat appeared to be more resistant than that from corn or sorghum. Endosperm of barley was less resistant than that of sorghum.

Exotic germplasm has potential to provide new alleles for disease and insect resistance. US maize (Zea mays L.) currently lacks genetic resistance to Aspergillus flavus, a fungal pathogen that produces aflatoxin in maize kernels. Aflatoxin is one of the main limitations to maize production in hot, dry regions like the Southern US because of the harmful effects on humans and animals and subsequent marketing regulations. Two experiments were conducted to evaluate different exotic maize collections for response to aflatoxin. Exotic adapted maize lines, known as LAMA lines, were found to accumulate less aflatoxin than US hybrids in tests across Southern Texas. Exotic introgression lines developed by The International Center for Maize and Wheat Improvement (CIMMYT) including inbred lines, yellow hybrids, and white hybrids, were more resistant to aflatoxin than US inbred lines and hybrids in field trials in Texas, Georgia, and Mississippi. Another experiment evaluated the grain composition of hybrids with exotic adapted LAMA maize lines and a collection of US hybrids, quality protein maize (QPM) hybrids, and advanced breeding lines using near-infrared spectroscopy. Individual LAMA lines and advanced breeding lines have higher starch content than US hybrid checks. Starch content was the primary grain composition trait of interest as an enhanced-value market has emerged for high starch maize hybrids. Limited germplasm has been analyzed for grain composition because wet chemistry analysis methods required large sample sizes and were time and labor intensive. The near infrared spectroscopy (NIR) method requires a relatively small sample and is a non-destructive analysis method. In this study, NIR was effective at ranking genotypes based on starch, oil, and protein content of the grain.

Exotic germplasm has potential to provide new alleles for disease and insect resistance. US maize (Zea mays L.) currently lacks genetic resistance to Aspergillus flavus, a fungal pathogen that produces aflatoxin in maize kernels. Aflatoxin is one of the main limitations to maize production in hot, dry regions like the Southern US because of the harmful effects on humans and animals and subsequent marketing regulations. Two experiments were conducted to evaluate different exotic maize collections for response to aflatoxin. Exotic adapted maize lines, known as LAMA lines, were found to accumulate less aflatoxin than US hybrids in tests across Southern Texas. Exotic introgression lines developed by The International Center for Maize and Wheat Improvement (CIMMYT) including inbred lines, yellow hybrids, and white hybrids, were more resistant to aflatoxin than US inbred lines and hybrids in field trials in Texas, Georgia, and Mississippi. Another experiment evaluated the grain composition of hybrids with exotic adapted LAMA maize lines and a collection of US hybrids, quality protein maize (QPM) hybrids, and advanced breeding lines using near-infrared spectroscopy. Individual LAMA lines and advanced breeding lines have higher starch content than US hybrid checks. Starch content was the primary grain composition trait of interest as an enhanced-value market has emerged for high starch maize hybrids. Limited germplasm has been analyzed for grain composition because wet chemistry analysis methods required large sample sizes and were time and labor intensive. The near infrared spectroscopy (NIR) method requires a relatively small sample and is a non-destructive analysis method. In this study, NIR was effective at ranking genotypes based on starch, oil, and protein content of the grain.

Master of Science / Department of Agronomy / S.V. Krishna Jagadish / Low temperature is one of the most limiting stresses to crops that are adapted to tropical and subtropical regions, such as maize (Zea mays L.) and sorghum [Sorghum bicolor (L.) Moench], when introduced into temperate regions. However, no studies have compared the chilling tolerance of maize and sorghum grown together. Therefore, the objective of this research was to screen maize hybrids and sorghum genotypes for chilling tolerance at the germination and seedling stages. With the hypothesis that grain composition of maize and sorghum could lead to varying chilling tolerance, the seeds were analyzed for concentrations of protein, starch, and amylose. Five commercial hybrids of maize and 18 genotypes of sorghum were maintained in growth chambers for 31 days at two temperatures: a control temperature (25/20 °C, day/night) and at chilling temperatures (11/8 °C for 14 days; 12.5/9.5 °C for 14 days, and 14/11 °C for 3 days). Emergence and seedling height were measured during the experiment. At the end of the experiment, shoot dry weight, root dry weight, and leaf area were determined. Emergence of sorghum under the chilling temperature regime was low (18%). Average height of the emerged sorghum seedlings in the cold temperatures at the end of the experiment was 1.4 cm compared to 55.5 cm in the control treatment. All maize hybrids emerged, but emergence and growth were slowed by the cold temperatures, and average height at the end of the experiment was 4.6 cm compared to 96.1 cm in the control treatment. Shoot dry weight, root dry weight, and leaf area of the sorghum under the chilling temperatures were too small to measure, and, for maize, they were greatly reduced. The results showed that, for sorghum, temperatures should be above 14 °C for emergence, while maize could emerge at lower temperatures. The analyses of the sorghum seeds showed that Redbine 60 and RTx430 had the highest protein concentrations (15.71% and 15.35%, respectively), and Segaolane had the lowest protein concentration (9.83%). Segaolane had the highest starch concentration (72.71%), and RTx430 had the lowest starch concentration (65.31%). There was an inverse relationship between protein and starch concentrations in the sorghum seeds (R2 = 0.69). Amylose concentrations did not vary significantly among the sorghum seeds. The analyses of the maize seeds showed that Dekalb 51-20 and Pioneer 1151 had the highest protein concentrations (10.98% and 10.95%, respectively), and Pioneer 1105 had the lowest protein concentration (9.26%). Starch and amylose concentrations did not vary significantly among the maize seeds.

Vitamin A deficiency (VAD) is a major public health problem in developing countries, including South Africa. The potential of provitamin A-biofortified maize for use as a complementary strategy to alleviate vitamin A deficiency in developing countries, where maize is the dominant staple food, is currently a subject of research. Although the nutritional composition of white maize is thought to be similar to that of biofortified maize, apart from the differences in provitamin A carotenoid content, the comparative nutritional composition of the two maize types seems not to have been subjected to a comprehensive scientific study. When setting the target level of provitamin A in the provitamin A-biofortified maize, it is important to consider the potential effect of processing on the final provitamin A carotenoid content of the biofortified food products, as the provitamin A carotenoids levels may decrease on processing. Furthermore, the yellow/orange provitamin A-biofortified maize may not be widely accepted by African consumers who are vulnerable to VAD, and are traditional consumers of white maize. This study firstly aimed to evaluate the nutritional composition, including provitamin A composition, and grain quality of provitamin A-biofortified maize varieties, compared to white maize. The second aim was to assess the effect of processing (milling and cooking) on the retention of provitamin A carotenoids and other nutrients in popular South African maize food products prepared with provitamin A-biofortified maize. Thirdly, the study aimed to assess the acceptability of maize food products prepared with provitamin A-biofortified maize by consumers of different age and gender in rural KwaZulu-Natal, South Africa. The grains of the provitamin A-biofortified maize varieties and grain of a white maize variety (control) were analysed for their nutritional composition using standard or referenced methods. The carotenoid content of the grains was analysed by High-Performance Liquid Chromatography (HPLC) and mass spectroscopy. The provitamin A carotenoids β-cryptoxanthin, and trans and cis isomers of β-carotene, and other unidentified cis isomers of β-carotene were detected in varying levels in the provitamin A-biofortified maize varieties. The total provitamin A content in the biofortified maize varieties ranged from 7.3-8.3 μg/g dry weight (DW), with total β-carotene ranging from 3.5-3.6 μg/g DW, and β-cryptoxanthin from 3.7-4.8 μg/g DW, whilst no carotenoids were detected in the white maize variety. Results of the evaluation of the content of other nutrients showed that, when compared with the white maize variety, the provitamin A-biofortified maize varieties had higher levels of starch, fat and protein but were lower in iron. The zinc and phosphorus levels in the white maize and the biofortified maize were comparable. The biofortified maize varieties were better sources of most of the essential amino acids relative to the white maize, but, similar to the white maize, they were deficient in histidine and lysine, indicating that further improvement is required. Selected quality attributes (grain density, susceptibility of kernels to cracking, milling quality and resistance of the kernels to fungal infection) of grains of 32 provitamin A-biofortified maize varieties and a white variety (control) were assessed. Overall, the quality of the grains of the provitamin A-biofortified maize varieties were found to be superior to that of the white maize grain, although the biofortified maize grains showed less resistance to fungi, including mycotoxin-producing types. This indicates that the trait of grain resistance to infection by fungi should also be incorporated in the provitamin A-biofortified maize varieties during breeding. To assess the retention of provitamin A carotenoids and other nutrients in maize food products, three selected provitamin A-biofortified maize varieties and the control (white maize variety) were milled into mealie meal and samp. The milled products were cooked into three products: phutu and thin porridge (from the mealie meal) and cooked samp. Nutrient retention during processing was determined. Milling resulted in either an increase or slight decrease in the provitamin A carotenoid levels, but there was no major decrease in the total provitamin A level. Most of the other nutrients were well retained during milling, but there were substantial losses of fibre, fat and minerals. Provitamin A carotenoid levels decreased on cooking. In phutu 96.6 ± 20.3% β-cryptoxanthin and 95.5 ± 13.6% of the β-carotene was retained after cooking. In thin porridge 65.8 ± 4.6% β-cryptoxanthin and 74.7 ± 3.0% β-carotene; and in samp 91.9 ± 12.0% β-cryptoxanthin and 100.1 ± 8.8% of the β-carotene was retained after cooking, respectively. Provitamin A retention seemed to be influenced by both maize variety and food form, indicating that suitable varieties and food forms should be found. There was generally a high retention of the other nutrients in all the three cooked products, except for the substantial losses of fat in thin porridge and iron and phosphorus in cooked samp. These findings indicate that an optimal delivery of provitamin A to the consumer can be achieved by processing provitamin A-biofortified maize into foods that have a good retention of provitamin A carotenoids, such as phutu and samp. These food products would be recommended in areas where VAD is prevalent. In order to assess consumer acceptability of provitamin A-biofortified maize, a total of 212 subjects aged 3-55 years from Mkhambathini Municipality, in KwaZulu-Natal province, South Africa, participated in the sensory evaluation of phutu, thin porridge and cooked samp prepared with provitamin A-biofortified maize varieties and a white variety (control). Preference for yellow maize food products was negatively associated with an increase in the age of the subjects. Overall, preschool children preferred yellow maize to white maize food products: phutu (81% vs. 19%), thin porridge (75% vs. 25%) and samp (73% vs. 27%). In contrast, primary school children preferred white maize to yellow maize food products: phutu (55% vs. 45%), thin porridge (63% vs. 38%) and samp (52% vs. 48%). Similarly, secondary school children and adults also displayed a similar preference for white maize food products. There was no association between gender and preference for maize variety. Focus group discussions revealed that participants had a negative attitude towards biofortified maize due to its colour, taste, smell and texture. However, the participants expressed a willingness to consume biofortified maize if it was cheaper than white maize and was readily available in local grocery stores. These findings indicate that there is a potential to promote the consumption of provitamin A-biofortified maize and its food products in this part of South Africa, thereby contributing to a reduction in the incidence of VAD. This study has shown that provitamin A-biofortified maize has a good potential to be used as an additional strategy to alleviate VAD in poor communities of South Africa, including similar environments in sub-Saharan Africa. However, the study has revealed that there are still challenges to be overcome in order to achieve the target provitamin A content of 15 μg/g in provitamin A-biofortified maize, set by HarvestPlus, an international challenge program. This may also explain why provitamin A-biofortified maize varieties with this level of provitamin A have been scarcely reported in the literature. Thus, more research is required to achieve the target provitamin A level in maize by conventional breeding. The results of this study indicate that besides provitamin A, the biofortified maize is also a good source of other nutrients including starch, fat, protein and zinc. However, improving the consumer acceptability of the provitamin A-biofortified maize remains a challenge, due to the negative attitudes towards the yellow/orange maize by African consumers. On the other hand, the results of this study indicate that there is an opportunity to promote the consumption of provitamin A-biofortified maize food products by preschool children, a finding which has not been previously reported in the literature. Nutrition education on the benefits of provitamin A-biofortified maize, as well as improved marketing are recommended, in this part of South Africa and also in similar environments in other sub-Saharan countries. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.