Citrus Tissue Extracts Affect Juice Cloud Stability

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 80ЊC (HDS) were added to pasteurized, reconstituted frozen concentrated orange juice at 5 U ⅐ mL Ϫ1 of pectinmethylesterase. Samples were incubated either at 25ЊC for 14 days or 4ЊC for 28 days and periodically sampled to determine the effects 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 4ЊC.

Inactivation of plant pectin methylesterase by thermal or high intensity pulsed electric field treatments

“…The relative ratio of the thermostable PME to total-PME can vary between 0 and 33% depending on the citrus cultivars. In the case of oranges, the percentage of PME fractions depends on the variety of the oranges (Rombouts et al, 1982;Snir et al, 1996;Van den Broeck et al, 1999), geographic location, growth practice, post-harvest handling, seasonal differences (Snir et al, 1996), fruit tissues (Cameron, Baker, & Grohman, 1997), and experimental changes in protocol (Wicker, 1992). A 5% thermostable PME fraction was observed for Valencia oranges ( Van den Broeck et al, 1999).…”

Quality degradation kinetics of pasteurised and high pressure processed fresh Navel orange juice: Nutritional parameters and shelf life

“…Cloud stabilization of HHP processed orange juice has been reported for values up to 20% of remaining enzymatic activity (Boff, Truong, Min, & Shellhammer, 2003;Goodner et al, 1998;Nienaber & Shellhammer, 2001b) during storage at 4-30 8C for long time periods (4 months). In comparison, such inactivation values for a thermally processed orange juice would lead to cloud loss within 4 weeks (Cameron et al, 1997;Versteeg et al, 1980). Application of more intense HHP conditions (pressure, temperature or time) resulted in faster or further inactivation of PME, affecting however negatively the sensory quality of orange juice.…”

“…About 95% inactivation of initial PME activity of untreated juice was achieved. The remaining 5% of the enzyme activity corresponds to the more heat resistant isoenzyme which can cause cloud loss after long periods of storage (Cameron et al, 1997;Versteeg et al, 1980). More intense thermal treatment in order to inactivate this portion would greatly affect sensory characteristics of orange juice without contributing substantially to further PME inactivation.…”

“…A major problem associated with orange juice quality deterioration during storage is cloud loss accompanied by gelation of juice concentrates. This action has been primarily attributed to the activity of pectin methylesterase (PME) (Cameron, Baker, & Grohmann, 1997;Versteeg, Rombouts, Spaansen, & Pilnik, 1980), the inactivation of which is generally used to determine the intensity of thermal processing during commercial pasteurisation (Snir, Koehler, Sims, & Wicker, 1996;Versteeg et al, 1980). Pasteurisation conditions used to inactivate the most heat resistant PME iso-enzyme (90 8C for 1 min) reduce bfreshnessQ, affecting sensory and nutritional characteristics of orange juice (Manso, Oliveira, Oliveira, & Frias, 2001;Yeom, Streaker, Zhang, & Min, 2000).…”

Inactivation of pectin methylesterase and stabilization of opalescence in orange juice by dynamic high pressure

“…Juice stability was determined by measuring loss of opalescence by the method of Cameron, Baker, and Grohmann (1997) which we modified by eliminating the juice stirring and centrifugation steps. Two milliliters of liquid were removed from the upper portion of the bottle and percent transmission at 660 nm was measured using a UV-visible spectrophotometer (model 8453, Hewlett Packard).…”