Zeaxanthin biofortification of sweet-corn and factors affecting zeaxanthin accumulation and colour change

Zeaxanthin, along with its isomer lutein, are the major carotenoids contributing to the characteristic colour of yellow sweet-corn. From a human health perspective, these two carotenoids are also specifically accumulated in the human macula, and are thought to protect the photoreceptor cells of the eye from blue light oxidative damage and to improve visual acuity. As humans cannot synthesise these compounds, they must be accumulated from dietary components containing zeaxanthin and lutein. In comparison to most dietary sources, yellow sweet-corn (Zea mays var. rugosa) is a particularly good source of zeaxanthin, although the concentration of zeaxanthin is still fairly low in comparison to what is considered a supplementary dose to improve macular pigment concentration (2 mg/person/day). In our present project, we have increased zeaxanthin concentration in sweet-corn kernels from 0.2 to 0.3 mg/100 g FW to greater than 2.0 mg/100 g FW at sweet-corn eating-stage, substantially reducing the amount of corn required to provide the same dosage of zeaxanthin. This was achieved by altering the carotenoid synthesis pathway to more than double total carotenoid synthesis and to redirect carotenoid synthesis towards the beta-arm of the pathway where zeaxanthin is synthesised. This resulted in a proportional increase of zeaxanthin from 22% to 70% of the total carotenoid present. As kernels increase in physiological maturity, carotenoid concentration also significantly increases, mainly due to increased synthesis but also due to a decline in moisture content of the kernels. When fully mature, dried kernels can reach zeaxanthin and carotene concentrations of 8.7 mg/100 g and 2.6 mg/100 g, respectively. Although kernels continue to increase in zeaxanthin when harvested past their normal harvest maturity stage, the texture of these 'over-mature' kernels is tough, making them less appealing for fresh consumption. Increase in zeaxanthin concentration and other orange carotenoids such as p-carotene also results in a decline in kernel hue angle of fresh sweet-corn from approximately 90 (yellow) to as low as 75 (orange-yellow). This enables high-zeaxanthin sweet-corn to be visually-distinguishable from standard yellow sweet-corn, which is predominantly pigmented by lutein

Differences in the anthocyanin profile of different tissues of the strawberry fruit

Strawberries are most commonly red in colour, which is largely due to the anthocyanin, pelargonidin-3-glucoside, a bioactive flavonoid with potential health benefits. Variation in the intensity of red colour across strawberry varieties, from a light pink to a deep cherry colour, is solely associated with a change in concentration of this single anthocyanin, rather than the synthesis of an anthocyanin with a different colour. In this study, the anthocyanin profiles of the two constituent edible tissues of strawberry fruit were determined. The main tissue of the strawberry consists of a swollen fleshy receptacle. The second tissue consists of the achenes, visible on the surface of the strawberry, with each achene consisting of a dry single-seeded fruit formed from a fertilised ovule. The current study showed that the anthocyanin profile of a strawberry achene is totally different from that of the receptacle. While red-coloured pelargonidin-3-glucoside is the main anthocyanin component (about 94%) in the receptacle, purple-coloured cyanidin-3-glucoside accounts for approximately 90% of the anthocyanin content in the achene. This would indicate that flavonoid 3’-hydroxylase (F3’H), the enzyme responsible for shifting anthocyanin biosynthesis towards cyanidin and away from pelargonidin, is functional in strawberry achene tissue, but not in the receptacle tissue. This may indicate that other factors, such as transcription factors, can modulate the anthocyanin profile of different strawberry tissues, rather than strawberries having a non-functional F3’H gene. However, the relevance of these findings for potential strawberry breeding programs and subsequently the nutritional quality of strawberry fruit needs to be investigated further

Zinc biofortification of immature maize and sweetcorn (Zea mays L.) kernels for human health

This study explores the potential for genetic biofortification of sweetcorn (Zea mays L.) by quantifying immature kernel zinc (Zn) concentrations across a broad range of Zea mays L. germplasm. Varieties examined included commercial sweetcorn cultivars, high zeaxanthin sweetcorns, purple sweetcorns, blue maize, quality protein maize and popcorns. Though all kernel samples were harvested at a physiologically immature stage typical of sweetcorn harvest and consumption (21 days after pollination, DAP), the varieties accumulated distinctly different kernel dry matter concentrations depending on whether they were classified as sugary or starchy varieties. The difference in dry matter concentration between types confounded comparisons of kernel Zn concentration when assessed on a fresh mass basis, which is typically used to quantify dietary intake. Kernel mass (indicative of kernel size) and the ratio of embryo-to-kernel mass also contributed to variation in kernel Zn concentration. Analysis of a broader range of nutrient concentrations suggested that variation in kernel Zn concentration was more closely associated with variations in S concentration than P concentration in the sugary varieties. This suggested the possibility of biofortifying sweetcorn kernel Zn without necessarily increasing kernel P and associated anti-nutrient compounds like phytate

Sulfur Nutrition Affects Garlic Bulb Yield and Allicin Concentration

Improving bulb yield and allicin content of garlic is important in meeting fresh and pharmaceutical market demands. Garlic plants have a high demand for sulfur (S) since allicin contains S atoms. Two experiments were conducted to identify the effect of S application rate on garlic yield and quality. In a field trial assessing six S application rates (0–150 kg S ha−1), cultivar ‘Glenlarge’ produced the greatest bulb weight (~90 g) and allicin content (521 mg bulb−1) with the application of 75 kg S ha−1. In contrast, cultivar ‘Southern Glen’ showed no response in bulb weight or allicin. This was likely due to high soil background S concentrations masking treatment effects. Subsequently, a solution culture experiment with cv. ‘Glenlarge’ evaluated six S application rates (188 to 1504 mg S plant−1, nominally equivalent to 25–200 kg S ha−1). In solution culture, bulb weight and allicin concentration increased with S rate. Highest bulb weight (~53 g bulb−1) and allicin concentration (~11 mg g−1 DW) were recorded at an S application of 1504 mg S plant−1. This is the first report to conclusively demonstrate the effect of S on yield and allicin in garlic grown in solution culture

Breaking the tight genetic linkage between the a1 and sh2 genes led to the development of anthocyanin-rich purple-pericarp super-sweetcorn

Abstract The existence of purple-pericarp super-sweetcorn based on the supersweet mutation, shrunken2 (sh2), has not been previously reported, due to its extremely tight genetic linkage to a non-functional anthocyanin biosynthesis gene, anthocyaninless1 (a1). Generally, pericarp-pigmented starchy purple corn contains significantly higher anthocyanin. The development of purple-pericarp super-sweetcorn is dependent on breaking the a1–sh2 tight genetic linkage, which occurs at a very low frequency of < 1 in 1000 meiotic crossovers. Here, to develop purple-pericarp super-sweetcorn, an initial cross between a male purple-pericarp maize, ‘Costa Rica’ (A1Sh2.A1Sh2) and a female white shrunken2 super-sweetcorn, ‘Tims-white’ (a1sh2.a1sh2), was conducted. Subsequent self-pollination based on purple-pericarp-shrunken kernels identified a small frequency (0.08%) of initial heterozygous F3 segregants (A1a1.sh2sh2) producing a fully sh2 cob with a purple-pericarp phenotype, enabled by breaking the close genetic linkage between the a1 and sh2 genes. Resulting rounds of self-pollination generated a F6 homozygous purple-pericarp super-sweetcorn (A1A1.sh2sh2) line, ‘Tim1’. Genome sequencing revealed a recombination break between the a1 and yz1 genes of the a1–yz1-x1–sh2  multigenic interval. The novel purple-pericarp super-sweetcorn produced a similar concentration of anthocyanin and sugar as in its purple-pericarp maize and white super-sweetcorn parents, respectively, potentially adding a broader range of health benefits than currently exists with standard yellow/white sweetcorn

Effect of Storage on the Nutritional Quality of Queen Garnet Plum

Due to high perishability, plums are harvested at an early stage of maturity to extend postharvest storage life. Storage time and temperature can significantly affect the phytochemical and sugar composition of plums, altering their palatability and nutritional quality. In this study, variations in physiochemical properties (total soluble solids (TSS), titratable acidity (TA), color (chroma and hue angle)), phytochemical composition (total phenolic content (TPC), total anthocyanin content (TAC), and carotenoids), and sugars in three different tissues of the Queen Garnet plum (QGP) during storage at two common domestic storage temperatures (4 and 23 °C) were evaluated. There was an increase (p &gt; 0.05) in TSS and a reduction (p &lt; 0.05) in TA of the outer flesh at 23 °C. Chroma values of all the tissues reduced (p &lt; 0.05) at 23 °C. At 4 °C, chroma values fluctuated between storage days. The TAC of the peel was the highest (p &lt; 0.05) among the different tissues and continued to increase up to 10 days of storage at 23 °C (3-fold increase). At 4 °C, the highest (p &lt; 0.05) TAC (peel) was observed after 14 days of storage (1.2-fold increase). TPC showed similar results. The highest (p &lt; 0.05) TPC was recorded in the peel after 10 days of storage at 23 °C (2.3-fold increase) and after 14 days of storage at 4 °C (1.3-fold increase), respectively. Total carotenoids in the flesh samples at both storage temperatures were reduced (p &lt; 0.05) after 14 days. Total sugars also decreased during storage. The results of the present study clearly showed that common domestic storage conditions can improve the nutritional quality of plums by increasing the content of bioactive anthocyanins and other phenolic compounds. However, the increase in phytochemicals needs to be counterbalanced with the decrease in total sugars and TA potentially affecting the sensory attributes of the plums

Assessing fatty acid profiles of macadamia nuts

The kernel of the macadamia nut (Macadamia integrifolia and M. tetraphylla) is very high in oil, accounting for about three -quarters of their mass. In the current investigation, oil extracts from 20 breeding accessions and 14 cultivars had a range of 12.3% to 17.0% saturated fat, averaging 14.2%. Although all samples were found to be very high in "healthy" monounsaturated fats, the level of saturated fat slightly exceeds that of many other nuts that are able to make qualified health claims. The lowest saturated fat content (12.3%) corresponded to 4.6 g saturated fat/50 g kernels, which was slightly greater than the 4.0 g maximum. Despite this, potential exists to develop a reduced-saturated fat macadamia by combining characteristics found in different lines. The current trial indicates that lower total saturated fat was associated with a stronger ability to partition C16 and C18 fats to their monounsaturated fatty acids, or to elongate C16:0 to C18:0 and subsequently desaturate C18:0 to C18:1. It was also observed that the pollinizer parent is likely to have an influence on saturated fat content, although this would need to be confirmed in controlled pollination trials. Macadamia varieties generally outcross, and because the edible kernel (embryo) is formed from a pollinated ovule, it is likely any future reduced-saturated fat line would also require a reduced-saturated fat pollinizer parent

The effects of pollen source on the fatty acid profile of Macadamia kernels

Macadamia nuts are an abundant source of the monounsaturated fats (59 %), oleic (50 %−65 %) and palmitoleic acid (12 %−30 %). As macadamia is generally an outcrossing species, this study focuses on the effect of both the maternal (seed parent) and paternal (pollen parent) genotype on the accumulation of the principal fatty acids in macadamia using a controlled 3 × 3 pollination trial. Both the seed parent and pollen parent were observed to significantly impact the fatty acid profile of macadamia nut kernels. In addition, the general combining abilities (GCA) of the parental cultivars and specific combining abilities (SCA) of parental crosses were determined, as well as identifying maternal/paternal combinations that could significantly increase palmitoleic acid and oleic acid, or decrease saturated fat concentration. These results provide evidence for the first time that pollen source has a significant impact on the fatty acid profile of macadamia kernels, and that previous reporting of the fatty acid profiles of macadamia cultivars is likely to be variable, due to the unknown genotype of pollen sources