Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 1996
Publication Date: N/A
Interpretive Summary: Fruit tissue extracts were prepared from peel, rag and juice of Valencia oranges. Each tissue extract was sub-divided into a dialysis supernatant and dialysis precipitate, giving a total of six extracts, two from each tissue. The six different extracts contained differing amounts of total- and thermally tolerant-pectinmethylesterase (PME and TT-PME). The enzyme PME initiates a sequence of events which leads to destabilization of the juice cloud in citrus juices, gelation in frozen concentrated citrus juices and floculation in beverages and drinks that contain citrus juice. A measured amount of total-PME or TT-PME from each of the six different extracts was added to pasteurized, reconstituted frozen concentrated orange juice and the juice was incubated at room temperature and 4 degree C. At periodic time intervals the juice was measured for juice cloud destabilization. Results indicate: (1) tissue specific differences for juice cloud destabilization, (2) the effect on cloud stability at 4 degree C may not be solely dependent on the amount of TT-PME present in the extract and (3) that shelf life of lightly or non-pasteurized orange juice may be extended if fruit is lightly squeezed since peel extracts destabilized the juice cloud most rapidly.
Technical Abstract: Salt extractable proteins were isolated from hand expressed juice, rag and peel of Valencia oranges. Each tissue extract was divided into dialysis supernatant (DS) and precipitate (DP) (forms during dialysis). DP, DS and DS heated for 2 min at 80 degree C (HDS) were added to pasteurized, reconstituted FCOJ at 5 U/mL of pectinmethylesterase. Samples were incubated both at 25 degree C for 14 days and 4 degree C for 28 days and periodically sampled to determine the effect of tissue extracts on juice cloud stability. Tissue specific differences were observed for the rate of juice cloud precipitation and among the HDS, DS, and DP fractions of a given tissue. HDS fractions destabilized juice cloud more rapidly than DS or DP at both 25 and 4 degree C.