Determination of total anthocyanins content: The total anthocyanins were determined as reported by Mondello et al. (2000). Ten gm of sample was filtered through glass wool, and the pulp washed with 90 ml of a Ethanol: HCl mixture previously prepared mixing 79.7 ml of anhydrous ethyl alcohol with 20.3 ml of HCl (37%). The absorbance has been measured at 535 nm, by spectrophotometer (Jenway 6405 UV/visible, Taiwan), using 1 cm cells. The calibration was done with respect to standard curve of pelargonidin 3-glucose (Pg 3-G). The results were expressed as Pg 3-G equivalent (mg per 100 ml of sample).
(e)
Drip loss: Frozen samples were put over a weighted absorbent paper and let to thaw at 5 °C ( Agnelli and Mascheroni, 2002). Drip loss (DL) was then evaluated by periodically weighting the absorbent paper until a constant value was reached: DL (%) = (Wt − W0)/Ws × 100. Where W0 is the weight of the dry absorbent paper (g), Wt the weight of the wet absorbent paper at time t (g) and WS the weight of the frozen sample (g).
(f)
Determination of calcium content: This analysis was performed on frozen strawberries according to Fraeye et al. (2009). Homogenized strawberry samples were dried overnight at 105 °C. One gram of the dry sample was calcinated in a muffle furnace at 550 °C during 4 h. The residue was transferred to a 1 N HNO3 solution and incubated at 70 °C for 1 h. The volume was adjusted to 100 mL. The Ca2+ concentration was measured using atomic absorption spectrophotometer (SPY9).