Thesis (M.Sc.) - Cairo University - Faculty of Agriculture - Department of Food Science and Technology

Endogenous pectin methylesterase (PME) is the enzyme responsible for phase separation and cloud loss in orange juice (OJ) manufacturing.The effect of kiwi{u2019}s PME inhibitor (PMEI), nanomilling and pasteurization on OJ quality was evaluated. The microbial quality, PME activity, OJ separation, pH, ascorbic acid content and the sensory characteristics of the juice were followed during 5 weeks storage (4{u00B0}C). PMEI as freeze-dried kiwi powder (0.3%, w/w) succeeded in inhibiting 89.3% of the OJ PME without affecting the microbial and the sensory quality. Nanomilling of OJ pulp, to prepare nano-particles OJ (NPOJ), reduced the initial microbial load by 1.65 and 1.83 log for psychrotrophs and yeasts and molds, respectively; significantly (P<0.05) inactivated 40.9% of the residual PME activity and the juice separation was significantly reduced by 48.3% (after 14 days of storage).Nanomilling exhibited no effect on OJ pH but slight (P<0.05) decrease in ascorbic acid content was noted. The combination of PMEI with NPOJ resulted in improved OJ stability with reduced separation to 36.4% of that of control. Such combination also allowed to use a lower pasteurization temperature at lower exposure time (60{u00B0}C/5min.) needed to obtain new NPOJ with comparable high quality as fresh OJ and which has a shelf life of 3 weeks (4{u00B0}C)

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