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...