Usually, for Moraceae pollen grains as for Cupressaeceae pollens, the defatting step using acetone is not necessary. This might cause the degradation and/or solubilization of certain proteins located within the pollen wall. I suggest you to perform your extraction overnight at 4 °C and to analyse your extract within 48 hours after extraction. Otherwise, it is preferable to store it at - 20 °C until use. To avoid refreezing, you can aliquot your samples in small volumes before freezing.
Grind the samples in phosphate buffer saline in cold state gently. then dialyse it with membrane dialysis at 4 degree Celsius. You can us PMSF to save protein from degradtion.