The formol value of fruit juices is an approximate measure of the concentration of free amino acids in the juice. Sugar addition to juices will result in declines in the formol value. Figure 11 shows the distribution of formol values in a set of pure Florida orange juices. The arrows indicate how a 20% substitution of sugar would affect the average sample in the distribution. A 20% substitution pulls the average sample completely outside of the normal range. Relative concentrations of proline and other individual amino acids can also provide diagnostic information about the purity of a juice.
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