Role of citric acid
Citric acid is the most abundant organic acid in strawberry, followed by malic acid (Holcroft and Kader, 1999). Citric acids
is added as an acidifier in industry to most fruit and berry products and widely used in the food industries for controlling the browning. Citric acid is an anti-browning agent, which pre- vents polyphenoloxidase (PPO) by suppressing the food pH and binding the Cu2+ in an active site of PPO to form an inac- tive complex (Martinez and Whitaker, 1995). Since pH has a profound effect on anthocyanin stability and color expression. The control of the pH in the washing treatments has been con- sidered an important factor (Sistrunk and Moore, 1979). Results of Table 1 showed some physico-chemical properties of frozen strawberries immersed in various aqueous citric acid solutions either alone or combined with cooling for overnight before freezing. The results declared that both citric acid treat- ments had a varying effect on drip loss, firmness and TSS of thawed strawberries on the other hand a slight increment in total acidity related with lowering in pH values and browning index as increasing the level of citric acid in dip solutions. The retention of both ascorbic acid and total anthocyanins was obviously increased as increased citric acid concentration while browning index was reduced due to inhibition of polypheno- loxidase as reported by Altunkaya and Gokmen (2009).