Improvements in viability recovery at low water activities of imbibed willow seeds subjected to vacuum drying and freeze-drying

SANTAGAPITA, PATRICIO R.; OTT, HELENA; BUERA, M. PILAR

Córdoba

Congreso; IV Congreso Internacional de Ciencia y Tecnología de los Alimentos; 2012

UNC/MinCytCBA

The so-called orthodox seeds tolerate dehydration up to low water contents (wc), and can remain viable for several years. Although willow seeds are orthodox, they exhibit some recalcitrant characteristics: they lose viability in a few weeks at 20°C. Collected seeds are usually first dehydrated at 20°C for 3h from wc 41% to 9-11% (wet basis), leaving the seeds with water activities (aw) values between 0.8 and 0.7. Then, seeds are kept at -70/-80°C in order to avoid viability loses, but this increases storage time-dependant costs. The aim of this work was to improve the conservation of willow seeds (Salix nigra L.), as a model of sensitive materials to dehydration, through imbibition in solutions and later vacuum (VD) or freeze-drying (FD). Imbibition was conducted with 45%w/v trehalose or polyethylene glycol 400 –PEG– or water for 16h at 4°C prior to dehydration treatments. The germination capacity and wc, aw, thermal transitions (by differential scanning calorimetry –DSC-), low-field nuclear magnetic resonance transversal relaxation times and water diffusion coefficients were determined. A germination capability increment was observed during seed imbibition with water and trehalose. This effect is related to the priming effect. However, only 70% of the imbibed seeds with PEG germinated after imbibition. Water and especially trehalose imbibed seeds subjected to VD showed better germination capability with respect to the freeze-dried ones. Water crystallization was mainly responsible for the great germination capability loss observed in water or trehalose imbibed seeds subjected to FD. PEG behaviour was better when seeds were FD instead of VD. Trehalose imbibed seeds maintained a very high level of germination capacity (> 75%) among all the dehydration range (from imbibed -45% of wc- to very dried -5% wc-). Water imbibed seeds showed a great loss in germination capacity by dehydration below 13% wc. Seeds DSC thermograms showed a broad lipid melting (between -40 and 10°C) and protein denaturation (between 55 and 110°C). This last transition seems to be a good indicator for germination capacity among the VD seeds. In the case of the FD ones, the damage produced by water crystallization was not reflected in major changes on protein denaturation. Changes in water self-diffusion coefficient and in relaxation times allowed to follow the dehydration process in a non-destructive way. Present work reveals that the presence of adequate protective agents as well the dehydration method were the main critical factors involved in willow seed conservation. Protein denaturation as determined by DSC seems to be a promising indicator for germination capacity. Acknowledgments: CONICET (PIP 100846), ANPYCT (PICT 0928) and UBA (2002100100397).