Low Temperature Conditioning Effect on Secondary Metabolism and Antioxidant Capacity of Garlic during Development

Garlic (Allium sativum L.) is the second most important species of the genus Allium and has gained consumer interest in recent years for both culinary and medicinal purposes. The proper sequence of photoperiod and thermoperiod during the growing season are key factors affecting the formation and differentiation of the bulbs. The storage of ‘seed’ cloves at 5°C for 5 weeks before planting accelerates initiation and development of bulbs compared to cloves stored at room temperature (20ºC). Previous experiments in our laboratory have shown that the conditioning at 5 ºC of ‘seed’ cloves from ‘Coreano’ variety ahead the harvest time up to two months and reduced the incidence of defects in the bulbs. Furthermore it has also been observed that this storage causes changes in the phenolic metabolism. The objective of this work was to evaluate the effect of low temperature conditioning of bulbils prior planting on the vegetative growth, activity of phenylalanine ammonia-lyase (PAL), total phenolics and antioxidant capacity during development of garlic. In plants originated from "seeds" stored at room temperature, leaf number, height and total weight of the plants were significantly higher, showing a favored vegetative growth. Significant differences were observed in enzymatic activity of PAL (µmol/ml) at the end of development (5th month), levels were 60 and 20 % higher in the cataphylls and leafs of garlic from storage at 5 ºC respectively. Total phenolics (mg gallic acid/gfw) and antioxidant capacity (DPPH, radical inhibition %) were also increased in garlic plants due to the conditioning treatment of the “seed” cloves at 5 ºC. The highest phenolic content was found in cataphylls from cold conditioning reaching 73.8 ±2.5 (mg gallic acid/ gfw), and the lowest was observed in aerial leafs (32.6 ± 2.1). Antioxidant capacity levels were increased more than 3 times in cataphylls and ≈ 2 % in aerial leafs of plants originated from conditioned seeds at 5 ºC. The low temperature conditioning of “seeds” prior planting induced changes in the secondary metabolism and reduced vegetative growth of garlic plants while favored differentiation of bulbs.