Silicon, in hydroponics, in postharvest American 'Lucy Brown' lettuce minimally processed/Aplicacao de silicio, em hidroponia, na conservacao pos-colheita de alface americana 'Lucy Brown' minimamente processada

This study aimed to verify the effect of silicon in hydroponics in postharvest of american 'Lucy Brown' lettuce minimally processed. Lettuces were grown hydroponically and silicon source used was potassium silicate at concentrations of 0, 28, 56 and 84mg [L.sup.-1]. After harvesting, the selected leaves were washed in tap water, and semiprocessed by cutting leaves 20mm wide, immersed in solutions Sumaveg®. These leaves were centrifuged manually and packed in polypropylene bags, after, were sealed and stored at 3°C and 85 ± 3% of relative humidity (RH). During 16 days of storage, leaves were evaluated every four days and in triplicate, gas composition, firmness, chlorophyll content and titratable acidity, activities polyphenol oxidase activities and peroxidase enzymes and microbiological analyzes. By the 4th day storage it was observed reductions in [O.sub.2] levels for all treatments. However, for levels of C[O.sub.2], it was observed an increased percentage of 5% in the treatment with 28mg [L.sup.-1] of silicon. The highest concentrations of silicon in the leaves mantained higher firmness. Total chlorophyll remained stable during the storage period. Enzyme polyphenoloxidase activity reduced until the 8th day. Peroxidase activity showed an increase during the study period at a concentration of 84mg [L.sup.-1] silicon. Microbial counts of thermotolerant coliforms remained low during storage. A concentration of 84mg [L.sup.-1] silicon provided greater firmness of minimally processed leaves of lettuce making them more turgid and preserving its useful life for 16 days. Key words: Lactuca sativa, silicon fertilization, post-harvest conservation. Este trabalho teve por objetivo verificar o efeito da aplicacao de silicio em hidroponia na conservacao pos-colheita de alface americana 'Lucy Brown' minimamente processada. As alfaces foram cultivadas hidroponicamente e a fonte de silicio utilizada foi o silicato de potassio nas concentracoes de 0; 28; 56; e 84mg [L.sup.-1]. Apos a colheita, as folhas selecionadas foram lavadas em agua corrente, semiprocessadas mediante o corte de 20mm de largura e sanitizadas por imersao em Sumaveg®. Estas foram centrifugadas manualmente e acondicionadas em sacos de polipropileno, que, posteriormente, foram selados e armazenados a 3°C e 85 ± 3% de umidade relativa (UR). Durante 16 dias de armazenamento, foram avaliadas a cada quatro dias e em triplicata, a composicao gasosa, a firmeza, o teor de clorofila e de acidez titulavel, as ati