Chilling effect on soluble sugars, respiration rate, total phenolics, peroxidase activity and dormancy of onion bulbs

Abstract

Besides onions being one of the most cultivated and consumed vegetables, during storage onion bulbs are still affected by many physiological, biochemical and technological factors which can influence their quality. Respiration rate (RR O2 ), soluble sugars (SS), total phenolics (TP), and peroxidase (POD) activity were measured in inner bud tissues during a dormancy break of onion bulbs treated four weeks at 0ºC and stored in the dark at 20ºC. Control bulbs were stored simultaneously in the same condition. Breakage of dormancy was checked by the appearance of first green internal leaves by cutting longitudinally 30 bulbs. After eight weeks, RR O2 of sprouted onions was 52% higher than that of freshly harvested and dormant bulbs. One week after cooling SS decreased from 15 to 9 mg g -1 fresh weight, and then peaked from 9 to 19 mg g -1 after three weeks. For control bulbs, a similar peak was observed after six weeks. For inner buds of cold-treated onions, a slight increase of TP (from 0.17 to 0.2 mg g -1 ; fresh weight) was observed during the first two weeks of cooling, and then a decrease to 0.11 mg g -1 was observed after eight weeks. For inner buds of control bulbs, TP also increased slightly from 0.17 to 0.2 mg g -1 after five weeks, and decreased to 0.15 mg g -1 after seven weeks when bulbs began to sprout. POD activity showed a similar pattern in relation to TP. For cold-treated bulbs, POD activity increased to 1.7 U g -1 fresh weight after two weeks, and decreased to 1.1 U g -1 during the last four weeks. For control samples, POD activity was stable during 4 weeks and decreased progressively by 29% during the last four weeks. This decrease in POD activity coincided with the decrease in TP, and coincided with onset of sprouting. With cold treatment, first sprouts were observed during the third week, while total sprouting was observed after eight weeks. In comparison, only 20% of the control bulbs sprouted after the period of 8 weeks. Key words: O 2 consumption, saccharides, phenolics, peroxidase, sprouting EFEITO DO RESFRIAMENTO SOBRE AÇÚCARES SOLÚVEIS, TAXA DE RESPIRAÇÃO, FENÓIS TOTAIS, ATIVIDADE DE PEROXIDASE E DORMÊNCIA DE BULBOS DE CEBOLARESUMO: Além de ser uma das hortaliças mais cultivada e consumida, bulbos de cebola são afetados, durante a armazenagem, por fatores fisiológicos, bioquímicos e tecnológicos, que podem afetar seus atributos de qualidade. Taxa de respiração (RR O2 ), açucares solúveis (SS), fenóis totais (TP) e atividade de peroxidase (POD) foram medidos em tecidos internos de brotos, durante uma quebra de dormência de bulbos de cebola, tratados por quatro semanas a 0ºC e armazenados no escuro a 20ºC. Bulbos controle foram armazenados simultaneamente na mesma condição. A quebra da dormência foi verificada através do aparecimento das primeiras folhas internas verdes, cortando 30 bulbos longitudinalmente. Depois de oito semanas a RR O2 de bulbos brotados foi 52% maior em relação a bulbos recentemente colhidos e bulbos dormentes. Os SS diminuíram uma semana após resfriamento, de 1...

Implications of spatial and temporal changes in concentration of pyruvate and glucose in onion (Allium cepa L.) bulbs during controlled atmosphere storage

“…Rouge Amposta (pungent, high dry matter) bulbs stored under ambient conditions peaked at 22 mg g −1 FW between 5 and 7 weeks, which was seen to coincide with the onset of sprouting. 20 In the present study and in agreement with others, 16 glucose concentrations in cv. SS1 declined rapidly before increasing again when the incidence of sprouting (results not shown) increased and may represent the transition from dormancy to the period of sprout suppression and beyond.…”

A comparative study of anaerobic and aerobic decomposition of quercetin glucosides and sugars in onion at an ambient temperature

“…In the case of onion, the antioxidant activity increased continuously during storage (Kevers et al 2007). Benkeblia and Shiomi (2004) reported a slight increase in total phenolics during 5 weeks of storage, and a decrease after 7 weeks with the initiation of internal sprouting. In the present case, total phenolic and antioxidant activity decreased during 1 month of storage, and then a slight increase was observed.…”

“…The individual parameters (phenolics, flavonoids and antioxidant activity) are reported to be increased during the maturation and storage of various fruits and vegetables (Yoo et al 2004;Kevers et al 2007). In the case of onion, total phenol fluctuates with the increase and decrease during 10 weeks of storage under controlled conditions (Benkeblia & Shiomi 2004). To gain further understanding of these parameters, the coefficients of correlation between antioxidant activity, total phenolics and flavonoids were calculated (Table 1).…”

Taste Compounds from Crude Extract of Bekkai lan (Albertisia papuana Becc.)

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