Calcium content
Influence of citric acid – Ca lactate combination
Since pH has a profound effect on anthocyanin stability and color expression and Ca plays a major role in maintaining the texture of strawberries. For achieving high quality frozen strawberries, a combination of 0.4% citric acid with different levels of Ca lactate dips was used for prefreezing treatments. The experimental results are presented in Table 3. Generally, slight differences are observed between citric acid – Ca lactate combination treatments frozen directly and after cooling for overnight. Adhering 0.4% citric acid in Ca lactate dips prefreezing treatments lead to relative improvement in quality indices, where drip loss reduced by 61–132% relative to untreated and by around 12–19% compared to Ca lactate treatments and by around 44–105% for 0.4% citric acid treatment while firmness raised by around 34–69%, 14–18% and 39–64% for untreated, Ca lactate and 0.4% citric acid treatments, respectively. A considerable reduction in browning index was also observed. The retention of both ascorbic acid and anthocyanin content The obtained results show that the untreated fruits exhibited lighter color, more yellower (highest L* and b* values) and lower in redness (a* value) than the pretreated frozen berries. These findings can be attributed to occurring color bleaching after storage as mentioned by Espin et al. (2000). As expected, the pretreatment with Ca lactate dip had a slight enhancer affect in the color indices of thawed berries. Otherwise, the incorporation of citric acid in Ca lactate dip promoted the color improvement. The pretreatment with either citric acid or citric acid – Ca lactate combination was more effective for maintaining the color of frozen berries. Accordingly, the redness (a* value) increased by only around 4% by Ca lactate dip compared to around 24% by citric acid dip and 31% by citric acid – Ca lactate combination dip relative to untreated berries.
Generally, chroma values exhibited the same trends (Fig. 4). Since chroma reflects color brilliance or purity and is correlated with the content of anthocyanin, it will increase with pigment concentration. The pretreated frozen berries with either citric acid or citric acid – Ca lactate combination dip had higher chroma values than untreated or treated by Ca lactate alone by about 14–28%. Hue° (Fig. 4) of the untreated frozen berries was significantly increased compared to other treatments which, in relation with a comparatively low chroma value, describe the pale- reddish color. However, these results in general accordance