Vitamin losses: Retention during heat treatment and continual changes expressed by mathematical models

Degradation of vitamin C in citrus juice concentrates during storage

Ultraviolet (UV) with a wavelength of 254 nm tends to inactivate most types of microorganisms. Most juices are opaque to UV due to the high-suspended solids in them and hence the conventional UV treatment, usually used for water treatment, cannot be used for treating juices. In order to make the process efficient, a thin film reactor was designed and constructed from glass with the juice flowing along the inner surface of a vertical glass tube as a thin film. The decimal reduction doses required for the reconstitute orange juices (OJ; 10.5° Brix) were 87±7 and 119±17 mJ/cm2 for the standard aerobic plate count (APC) and yeast and moulds, respectively. The shelf life of fresh squeezed orange juice was extended to 5 days with a limited exposure of UV (73.8 mJ/cm2). The effect of UV on the concentration of Vitamin C was investigated using both HPLC and titration methods of measurements. The degradation of Vitamin C was 17% under high UV exposure of 100 mJ/cm2, which was similar to that usually found in thermal sterilization. Enzyme pectin methylesterase (PME) activity, which is the major cause of cloud loss of juices, was also measured. In contrast to the heat treatment, UV processing does not inactivate enzyme pectin methylesterase. The energy required for UV treatment of orange juice (2.0 kW h/m3) was much smaller than that required in thermal treatment (82 kW h/m3). The color and pH of the juice were not significantly influenced by the treatment. Industrial relevance This paper is of interest since it suggest—despite the low UV transmittance in orange juices—the use of a thin film UV reactor. The data suggest that shelf life extension from 2 to more than 5 days could be achieved with less energy requirements than for thermal processing. However, it seems unlikely that such thin film reactors could provide a real alternative to current conventional or new (e.g. high pressure pulsed electric field) processing.

Ultraviolet treatment of orange juice

Optimization of oven toasting for improving crispness and other quality attributes of ready to eat potato-soy snack using response surface methodology

Effect of freezing rate on quality parameters of freeze dried soursop fruit pulp

The kinetics of ascorbic acid degradation were studied in an intermediate moisture model food system as a function of water activity (0.69-0.90) and temperature (61-105°C). The disappearance of ascorbic acid in each case followed a zero order kinetic model. Rates of ascorbic acid degradation ranged from 1.5-10.5 mg/100g solids/min, while the activation energy was in the range of 14—17 Kcal/mole. It is suggested that dissolved oxygen concentration was limiting above 92°C, resulting in a rate decrease between 92 and 105°C. Rates of ascorbic acid degradation were found to increase with increasing aw, except at 105°C, where the opposite was observed. An equation derived from the integrated zero order rate law was used to predict ascorbic acid losses during an unsteady state heating process approximating a linear temperature rise, with good results. The same equation was much less accurate (predictions were 2-4 times larger), when used to predict ascorbic acid losses during extrusion processing, most likely due to the difficulty in obtaining an accurate temperature history of the extruded product.

B. M. Laing

Papers

Degradation kinetics of ascorbic acid at high temperature and water activity