The inner quality of orange juice and apple juice : assessment by the use of microbiological methods

A modified Salmonella mutagenicity assay and a cytotoxicity test were developed to. determine the concentration of sensorially inactive Maillard Intermediate Products (MIP) in fruit juices. The formation of MIP is initiated by heat treatments necessary for pasteurization and thermal concentration. In industrial and laboratory prepared orange juices their concentration was seen to be related to the intensity of the heat treatment and to allow a shelf-life prediction in relation to non-enzymatic browning (inner quality). The microbial MIP assay(s) are therefore useful for orange juice manufactures to select concentrated juices for reconstitution and packing and to test equipment and processes. The modification of the tests involve preincubation with the tester bacteria for 4 hr at pH 7.4 and 37°C. Under natural acidic condition orange juice is not mutagenic.

It was further seen that the heat treatments did not hydrolyze orange glycosides to mutagenic aglycones which could have influenced the assay. MIP were characterized to be polar, non volatile compounds which carry no charge and have a molecular weight from 200 to 700 daltons. Automation of the mutagenicity assay by a turbidometric assay system was seen to be only possible for gel filtration and HPLC fractions of juice; in whole orange juice endogenous growth factors and cytotoxicity disturbed the assay. on the other hand measurement of cytotoxicity of whole juice could be carried out conveniently by a kinetic conductance method. Heat treated laboratory prepared apple juice also contained mutagenic fractions but the whole juice had a positive antimutagenic balance. There was a heat load and dose related reduction of the mutagenicity of MNNG (N-methyl-N'-nitro-N-nitrosoguanidine) and 4-NQO (4-nitroquinoline-N-oxide) in the presence of apple juice. These findings give new aspects to apple juice as a healtly food.