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Mudau N. Fhatuwani and Makunga P. Nokwanda

Bush tea (Athrixia phylicoides DC.) is a root perennial shrub used as indigenous tea and medicinal tea in South Africa. Thus, concurrent trials were conducted under different growing conditions as follows: in the glasshouse, field planted and wild, naturally grown, to investigate the effects of seasonal harvests and growing environments on carbohydrate reserves and quality parameters of bush tea. Of 50 plants, 25 single plants were allotted to each respective environment in a field and glasshouse conditions—and were arranged in a randomized complete block design. These were then harvested in summer, autumn, winter, and spring, respectively. For the wild bush tea trial, 25 single plants were randomly selected. Selected sugars and starch were quantified together with other quality parameters [total polyphenolic content (TPC), total flavonoid content (TFC), total tannin content (TTC), and total antioxidant activities). The study revealed that the glucose content of bush tea plant organs was significantly higher during winter, followed by autumn, as compared with the other seasons. Similar fructose and sucrose trends were evident. However, the content of amylopectin was also significantly higher during summer, followed by autumn, compared with the other seasons. In winter, plants exhibited higher amylopectin content when compared with other seasons. No significant differences were found in the amylose content. Both wild and cultivated bush tea plants yielded the highest specific sugars in the study. The phytochemicals present in the leaves of field-grown bush tea and wild bush tea during winter were higher than in those grown in summer, autumn, and spring. No significant difference in tannin contents was observed, irrespective of seasons and growing conditions. Regardless of growing conditions, autumn yielded lower total antioxidant activities using both the DPPH and ferric reducing antioxidant power (FRAP) assays when compared with other seasons. To better resolve the metabolomic data, principal component analysis (PCA) was used and the first principal component showed a strong correlation within all parameters recorded over PC2. Future ecophysiological studies are recommended to establish region- and season-specific metabolomic biomarkers with canonical distinction on beverage, pharmacological, and organoleptic attributes of bush teas.

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Ambani R. Mudau, Puffy Soundy and Fhatuwani N. Mudau

Manipulation of microenvironments by means of photoselective nettings is widely used to improve the productivity and quality of high-value vegetables. The aim of this study was to investigate the effect of photoselective nettings on growth, productivity, and postharvest quality attributes of baby spinach. Baby spinach cv. Ohio was grown from seeds, and the trial was repeated. Plants were planted in an open field (control) and under closed nets, viz., black, pearl, yellow, and red nets. At harvest, baby spinach leaves were subjected to 4, 10, and 20 °C storage temperatures for 12 days. Crops grown under black nets and stored at 4 °C retained higher level of antioxidant activity (0.23 g·kg−1), whereas the least level of antioxidant activity was observed in baby spinach grown under red and yellow shade nets (0.01 g·kg−1). Similar trend was evident with flavonoid content where baby spinach leaves grown under black nets maintained high level of flavonoids at 4, 10, and 20 °C during storage period compared with other shade nets and the control. The study control showed a better potential in retaining antioxidant activity over red and yellow shade nets. Results showed that black shade nettings have the potential to reduce water loss, decay incidents, and maintain flavonoid content and antioxidant activity followed by pearl and yellow nets.

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Fhatuwani N. Mudau, Ambani R. Mudau, Mpumelelo Nkomo and Wonder Ngezimana

Reserve carbohydrates are critical for herbage yields, productivity as well as management strategies of bush tea (Athrixia phylicoides DC). This study was conducted to evaluate carbohydrate accumulation in response to pruning seasons (summer, autumn, winter, and spring) involving different organs grown under different conditions and to determine mean dry matter production of bush tea. Three separate parallel trials were conducted under wild, field, and glasshouse conditions. Seasons and different growing sites were considered as treatments. Treatments for all controlled trials (field and glasshouse) consisted of seasonal pruning (winter, spring, summer, and autumn). Trials were arranged using a randomized complete block design with 25 single plants as replicates per treatment. Seasonal responses revealed that winter had the highest starch (145.0 mg·g−1) in the stems and reserve carbohydrates (480.6 mg·g−1) in the roots, whereas in the roots sugar (400.6 mg·g−1) was highest in summer. The highest significant root reserve carbohydrates occurred in winter (594.6 mg·g−1) and the lowest in autumn (fall) (313.3 mg·g−1). Bush tea plants pruned during winter had the highest overall reserve carbohydrates in the stem (598.7 mg·g−1). Under glasshouse conditions, the highest dry matter production was observed in December (midsummer) (170 g per plant); while in field-grown plants in the same month dry matter production was 400 g per plant. Therefore, the best time to maximize production of bush tea is during the spring and summer seasons.

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Fhatuwani N. Mudau, Puffy Soundy and Elsa S. du Toit

Bush tea (Athrixia phylicoides L.) contains high concentrations of polyphenols that are the primary indicator of antioxidant potential in herbal teas. The objective of this study was to determine the seasonal effect of nitrogen (N), phosphorus (P), and potassium (K) nutrition on total polyphenol content in bush tea leaves. Treatments consisted of 0, 100, 200, 300, 400 or 500 kg·ha−1 of N, P, or K in a randomized complete block design under 50% shade nets. Three (N, P, and K) parallel trials were conducted per season (autumn, winter, spring, and summer). Total polyphenols were determined using Folin-Ciocalteau reagents and analyzed in a spectrophotometer. The results of this study demonstrated that, regardless of season, application of nitrogenous, phosphorus, and potassium fertilizers increased quadratically the total polyphenols in bush tea, with most of the increase occurring between 0 and 300 kg·ha−1 N, 300 kg·ha−1 P, and 200 kg·ha−1 K. Linear relationships between percentage leaf tissue N, P, and K with total polyphenols in bush tea were also observed. Therefore, for improved total polyphenol content in bush tea leaves, 300 kg·ha−1 N, 300 kg·ha−1 P, and 200 K kg·ha−1 N is recommended.

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Fhatuwani N. Mudau, Puffy Soundy and Elsa S. du Toit

The objective of this investigation was to determine the effects of simultaneous applications of nitrogen (N), phosphorus (P), and potassium (K) nutrition on growth and chemical analysis of bush tea (Athrixia phylicoides). Four consecutive trials were conducted at Morgenzon (Louis Trichardt, Limpopo Province, South Africa), a commercial nursery, one at each season (autumn, winter, spring, and summer) under 50% shade. Treatments comprised three levels of N (300, 350, 400 kg·ha−1), three levels of P (250, 300, 350 kg·ha−1), and three levels K (150, 200, 250 kg·ha−1). The experimental design was a 3 × 3 × 3 factorial experiment arranged in a randomized complete-block design with four replications. Parameters recorded were plant height, number of branches and leaves, fresh and dry stem weight, fresh and dry root weight, stem girth, fresh and dry shoot weight, leaf area, and percent concentration of leaf and root tissue N, P, K, and total polyphenol concentrations as influenced by season in a shaded nursery environment. Treatment combinations of N and P at rates of 300 kg·ha−1 and K at 200 kg·ha−1 increased fresh and dry shoot weight, number of leaves, leaf area, and concentration of total polyphenols. Other treatments did not consistently affect concentrations of leaf N, P, or K during the study period, although the treatment that received combinations of N and P at rates of 300 kg·ha−1 and K at 200 kg·ha−1 always had the highest concentrations of leaf N, P, and K and lowest root N, P, and K concentrations. No differences in plant height, number of branches, number of flower buds (autumn and winter), stem girth, fresh and dry root weight, and fresh and dry stem weight due to treatment combinations were observed.

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Maedza V. Khathutshelo, Nkomo Mpumelelo, Ngezimana Wonder and Mudau N. Fhatuwani

Bush tea (Athrixia phylicoides DC.) is a herbal beverage and medicinal plant indigenous to South Africa. The aim of the study was to provide the baseline for foliar spray application of micronutrients to enhance the quality of bush tea. A trial was conducted to determine the effect of micronutrients on the quality of bush tea. Four separate trials for boron (B), iron (Fe), zinc (Zn), and copper (Cu) were laid out in a completely randomized block design. Treatments consisted of an unsprayed control and single foliar sprays of B, Fe, Zn, and Cu, with 10 replicates. The levels of each element were unsprayed control, 50 mL·L−1, 100 mL·L−1, and 150 mL·L−1. Parameters recorded were leaf tissue B, Fe, Zn, and Cu, and total polyphenol, total antioxidant, total flavonoids, and total tannin contents. Results from this study demonstrated that foliar application of B did not induce significant response in terms of total polyphenol content after B application. There was a quadratic response for total flavonoids (167 mg·g−1), with most of the total flavonoids reaching maximum at 100 mL·L−1. Foliar application of Fe exhibited a quadratic response, with most of the total polyphenols (45.1 mg·g−1) reaching maximum at 100 mL·L−1. All treatments showed a linear response for total antioxidant, total flavonoids, and total tannin contents. Treatments elicited a quadratic response for total polyphenols (70.6 mg·g−1), total antioxidants (78.3 mg·g−1), total flavonoids (148.9 mg·g−1), and total tannin contents (78.3 mg·g−1) after foliar Zn application, reaching maximum at 100 mL·L−1. Foliar application of essential elements in bush tea led to a significant increase in the Zn, Fe, Cu, and B content; application at 100 mL·L−1 is recommended for improved chemical composition of bush tea. A further trial with treatment combinations is required to determine chemical responses of bush tea.

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Ambani R. Mudau, Mpumelelo M. Nkomo, Puffy Soundy, Hintsa T. Araya, Wonder Ngezimana and Fhatuwani N. Mudau

Spinach (Spinacia oleracea) is a member of the Amaranthaceae family. Baby spinach leaves have a very high respiration rate, thus postharvest quality is affected mostly by tissue decay and the development of off-odors. Thus, this study was conducted to investigate the influence of storage temperature and time on the postharvest quality of baby spinach. Baby spinach leaves were harvested 36 days after planting and subsequently stored at 4 and 22 °C for 0, 2, 4, 6, 8, 10, or 12 days. Thereafter, the leaves were incubated for 72 hours at 40 °C to dry. Minerals, trace elements, total phenols, total carotenoids, flavonoids, and antioxidant activities were measured. Concentration of magnesium (Mg), zinc (Zn), and iron (Fe) were declined after 8 days of storage at 4 °C, while at 22 °C they declined after 2 days of storage. Mg, Zn, and Fe revealed a similar trend with significantly higher carotenoids found up to 6 days in storage at 4 °C, while at 22 °C the carotenoid levels declined after only 2 days. Total phenolic compounds gradually decreased in samples stored at 4 °C. However, samples stored at 22 °C showed a rapid decrease after 4 days. Both total antioxidant activities and vitamin C content showed a similar trend, with the content remaining constant at 4 °C and decreasing after 6 days, whereas the total antioxidant activities and vitamin C for leaves stored at 22 °C decreased immediately after 2 days. Results demonstrated that quality of baby spinach deteriorates as storage time and temperature increase.

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Ambani R. Mudau, Puffy Soundy, Hintsa T. Araya and Fhatuwani N. Mudau

The aim of the current study was to determine the influence of modified atmospheric pressure on the quality of baby spinach during storage. Treatments consisted of control [(normal air) (78% N2; 21% O2)], modified atmosphere (MA) (5% O2; 15% CO2; balance N2), storage temperature (4, 10, and 20 °C), and number of days after storage (0, 3, 6, 9, and 12). Parameters recorded are gas composition, weight loss, sensory quality, minerals and trace elements (Mg, Fe, and Zn), flavonoids, and antioxidant activity. The results of this study demonstrated that in the headspace gas there was overall reduction in O2 and increase in CO2 levels over the storage period. After 6 days of storage, all samples in normal air irrespective of the storage temperature were found to fall short of acceptable marketability with regard to visual appearance. The total antioxidant activity and flavonoids were well maintained under controlled atmosphere (CA) at 4 °C when stored for 9 days.

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Ambani R. Mudau, Puffy Soundy, Hintsa T. Araya and Fhatuwani N. Mudau

Spinach is an annual, cool-season, green leafy vegetable that in temperate areas can be grown year-round. However, different seasons can influence the quality and shelf life of the produce. The objective of this study was to investigate the influence of different seasons on the quality of baby spinach leaves during growing and postharvest storage. The study was initiated in early Nov. 2013 and culminated toward the end of Oct. 2014, then was repeated from Nov. 2014 until Oct. 2015. A 4 × 5 × 3 factorial experiment was laid out in a randomized complete block design with four replicates per treatment. The treatments were arranged as follows. In autumn, winter, spring, and summer, leaves were kept up to 12 d at three different temperatures: 4, 10, and 20 °C. Parameters recorded are weight loss, leaf length, total flavonoids, and antioxidant activity. Results of the study demonstrate that the level of antioxidants in winter remained stable during storage, specifically at 4 °C, followed by autumn and spring. In contrast, the summer season reflected the worse potential of retaining a level of antioxidants compared with the other seasons. On day 12, at a storage temperature of 4 °C, winter maintained 0.55 mg·g–1 dry weight (DW), whereas autumn, spring, and summer had 0.41, 0.40, and 0.11 mg·g–1 DW, respectively. In conclusion, it is recommended that baby spinach growers consider winter, autumn, and spring for growing baby spinach to manage the quality favorably during the postharvest storage period in South Africa.

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Maedza K. Vuwani, Mpumelelo Nkomo, Wonder Ngezimana, Nokwanda P. Makunga and Fhatuwani N. Mudau

Bush tea (Athrixia phylicoides DC.) is an herbal beverage and medicinal plant indigenous to South Africa. This study evaluated the effects of micronutrients on bush tea quality. Treatments consisted of single applications of zinc (Zn), copper (Cu), boron (Bo), iron (Fe), and magnesium (Mg) at three levels (50, 100, and 150 mL/L) and a combination of all micronutrients. A control treatment with no spray was also included. Tea samples were analyzed using head space solid phase microextraction gas chromatography linked to mass spectrometry (HS-SPME-GC-MS). A significant change in the metabolite profile of bush tea was noted. Five major compounds were identified (>80% identification probability) namely alpha-pinene, beta-pinene, myrcene, beta-caryophyllene, and caryophyllene oxide. A linear relationship between percentage leaf tissues and treatment levels of micronutrients in bush tea was also observed. The liquid chromatography linked to mass spectrometry (LC–MS) showed no significant qualitative difference between the control and the micronutrient treatments. There were significant quantitative differences between the control and treatments applied at 50 and 100 mL/L and the combination (B + Zn + Fe + Cu + Mg) applied at 10 and 20 mL/L. The application of micronutrients did have an influence on the metabolite quantities as has been reported with most secondary metabolite fluctuations caused by plant–environment interactions. Altering the micronutrient application may be a possible solution in achieving commercial agricultural production of this medicinal beverage.