BACKGROUND

Onion is undoubtedly one of the major sources of flavonoids. However, there exists a varietal difference in composition, concentration and beneficial activities of onion, on the basis of cultivars, day length sensitivity/ripening and types. To characterise such differences, 18 onion cultivars from Korean were evaluated for their total phenolics, flavonoids and antioxidant activity. Simultaneous quantification of quercetin, quercetin-3,4′-O-diglucoside, quercetin-4′-O-monoglucoside and isorhamnetin-3-glucoside was made in methanol and 75% ethanol.



RESULTS

Total phenolic content was examined spectrophotometrically with the Folin–Ciocalteu phenol reagent and total antioxidant activity were studied by the ferric reducing antioxidant power (FRAP) and diphenyl picryl hydrazyl (DPPH) methods. The cultivar ‘Sunpower’ showed the highest level of total phenolics [5016 ± 30.0 µg gallic acid equivalents g−1 dry weight (DW)] and flavonoids (2873.95 ± 60.01 µg Q g−1 DW) among the 18 cultivars in methanol. However, there were fewer total phenolics and flavonoids in ethanol extracts. The antioxidant activity for cultivar Sunpower was highest in ethanol extracts 24.12 ± 1.00 and 16.13 ± 0.35 µmol L−1 Trolox equivalents g−1 DW with FRAP and DPPH, respectively.



CONCLUSION

Among the 18 cultivars, Sunpower is the most promising in terms of total phenolics, total flavonoids and antioxidant activity. Our results suggest that day length sensitivity/ripening among the cultivars do not play any significant role for high values of total phenolics, flavonoids and antioxidant activity. © 2013 Society of Chemical Industry

Evaluation of total phenolics, flavonoids and antioxidant activity of 18 Korean onion cultivars: a comparative study

The response of onion cv Jaquar (Allium cepa L) to sowing date and plant population was investigated in Bloemfontein (Free State Province, South Africa) during the year 2010  Jaquar seeds were sown on 11 and 25 May; and 8 June at five different populations (95, 83, 74, 67 and 61 plants m-2) in a randomized complete block design with each treatment combination replicated three times  Plant height and leaf number were measured 18 weeks after emergence  Bulb yield and quality (bulb mass, diameter, firmness and neck diameter) were recorded at harvesting  Significantly taller plants were obtained with the early sowing date (11 May) and a population between 61 and 74 plants m-2  Leaf production was not significantly influenced by any treatment  Bulb mass, yield and firmness were significantly higher with early sowing dates (11 or 25 May)   Plant population significantly influenced bulb mass, but not yield  Bulb diameter increased as population decreased, irrespective of planting date  The three lowest populations (74, 67 and 61 plants m-2) yielded significantly harder bulbs than denser plants (83 and 95 plants m-2)  The best sowing date for Jaquar in Bloemfontein was from 11 to 25 May at a population of between 61 and 74 plants m-2

	 

	Key words: Bulb diameter, bulb firmness, bulb fresh mass, bulb shape, leaf number, plant height, yield

/pdf/response-of-onion-allium-cepa-l-to-sowing-date-and-plant-2ncu5s2qul.pdf

Response of onion (Allium cepa L.) to sowing date and plant population in the Central Free State, South Africa

Onion cultivar “Sunpower” has growing popularity in Korea due to high storability. The present study considers changes in flavonols, sugars, and two amino acids in onion bulbs during a long-term storage in the ambient dark storage room and in glasshouse equipped with a climate control system. Flavonol and sugar contents were found to fluctuate noticeably during the storage period. Amino acid content remained relatively unchanged till the onset of inner sprouting, increasing afterward. Visible sprouts appeared at week 22 in the dark storage room and for four weeks later in the glasshouse. The bulbs lost 20–30% of their weight depending on storage conditions at the end of the storage trials. At the same time, the content of nutraceutics in study expressed on the dry weight basis remained of the same order of magnitude. The nature of observed variations in chemical composition of onions as well as relation of this phenomenon to physiological development of stored onion bulbs is discussed. A conclusion is mad...

Phytochemical composition of onion during long-term storage

The response of onion cv. Jaquar (Allium cepa L.) to sowing date and plant population was investigated in Bloemfontein (Free State Province, South Africa) during the year 2010.  Jaquar seeds were sown on 11 and 25 May; and 8 June at five different populations (95, 83, 74, 67 and 61 plants m-2) in a randomized complete block design with each treatment combination replicated three times.  Plant height and leaf number were measured 18 weeks after emergence.  Bulb yield and quality (bulb mass, diameter, firmness and neck diameter) were recorded at harvesting.  Significantly taller plants were obtained with the early sowing date (11 May) and a population between 61 and 74 plants m-2.  Leaf production was not significantly influenced by any treatment.  Bulb mass, yield and firmness were significantly higher with early sowing dates (11 or 25 May).   Plant population significantly influenced bulb mass, but not yield.  Bulb diameter increased as population decreased, irrespective of planting date.  The three lowest populations (74, 67 and 61 plants m-2) yielded significantly harder bulbs than denser plants (83 and 95 plants m-2).  The best sowing date for Jaquar in Bloemfontein was from 11 to 25 May at a population of between 61 and 74 plants m-2. 
 
   
 
 Key words: Bulb diameter, bulb firmness, bulb fresh mass, bulb shape, leaf number, plant height, yield.

Response of onion (Allium cepa L.) to sowing date and plant population

Onion stored at 4, 10, and 25 °C for 9 months were analyzed for changes in quercetin and its glucosidase content, enzymes, pyruvic acid, and sugar content. During storage, concentration of quercetin and its glucosidase showed an irregular variation at all studied temperature but at 4 °C the rate was high as compared to 10 and 25 °C. The enzymatic activity of Q4’G glucosidase and Q4’glucosyltransferase increased progressively until six months at 4, 10 and 25 °C, but later it started to decrease. At 4 and 10 °C, peroxidase activity increased during the first five weeks then decreased, while at 25 °C peroxidase activity decreased progressively after two months storage. Fructose, glucose and sucrose showed a different although more regular pattern by decreasing progressively at 4, 10 °C. At 4 °C fructose and glucose accumulated in the initial 3 to 4 months of storage while sucrose was unchanged. However, at 10 and 25 °C, fructose and glucose concentration continuously decreased, while sucrose increased consistently. Onion pyruvic acid increased at 4 and 10 °C during the first six months, while at 25 °C the fluctuation was observed during the whole storage period. Overall, we conclude that storage at 4 °C maintained the quality of onions best, as evidenced by the positive changes.

/pdf/erratum-to-effect-of-different-storage-temperature-on-2r7e9yzcny.pdf

Erratum to: Effect of different storage temperature on chemical composition of onion (Allium cepa L.) and its enzymes.

The bulb storability of eight red and ten yellow onion (Allium cepa L.) cultivars grown primarily in Korea was evaluated. During storage, sprouting occurred earlier in red cultivars than in yellow cultivars. In addition, the ratio of sprouted to unsprouted bulbs increased more rapidly in red cultivars than in yellow cultivars. However, not all yellow cultivars had strong storabilities. Bulb storability of three yellow cultivars was as poor as that of red cultivars, suggesting only a slight possibility of a pleiotropic effect of color and bulb storability. Meanwhile, F3 lines of a red cultivar selected based on stronger storabilities showed intermediate storabilities between those of the red and yellow cultivars, implying that strong storability could be obtained by successive selection. In contrast, F1 hybrids from crosses between yellow and red breeding lines showed poor storability compared with the yellow cultivars, indicating that poor storability may be dominant over strong storability. The relationships between color and other traits that potentially affect storability, such as fresh and dry weight, water content, and firmness of bulbs, were evaluated. No significant differences in these traits were observed between the two colors, although the water content of yellow cultivars and the dry weight of red cultivars were slightly higher than their counterparts. Correlation analyses between bulb storability and other traits, including weight, water content, and firmness, also showed no significant correlations. In this study, no correlations were identified between bulb color, storability, and other traits. However, based on these results, red cultivars with stronger storabilities could be developed through successive selection of bulbs with stronger storabilities.

Bulb storability of red and yellow onion (Allium cepa L.) cultivars grown in Korea.

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Bulb storability of red and yellow onion (Allium cepa L.) cultivars grown in Korea.