Effects of pulsed electric fields (PEF) at 35 kV/cm for 59 micros on the quality of orange juice were investigated and compared with those of heat pasteurization at 94.6 degrees C for 30 s. The PEF treatment prevented the growth of microorganisms at 4, 22, and 37 degrees C for 112 days and inactivated 88% of pectin methyl esterase (PME) activity. The PEF-treated orange juice retained greater amounts of vitamin C and the five representative flavor compounds than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0.05). The PEF-treated orange juice had lower browning index, higher whiteness (L), and higher hue angle (theta) values than the heat-pasteurized orange juice during storage at 4 degrees C (p < 0. 05). The PEF-treated orange juice had a smaller particle size than the heat-pasteurized orange juice (p < 0.05). degrees Brix and pH values were not significantly affected by processing methods (p > 0. 05).

Effects of commercial-scale pulsed electric field (PEF) processing on the microbial stability, ascorbic acid, flavor compounds, color, Brix, pH, and sensory properties of orange juice were studied and compared with those of thermal processing. Freshly squeezed orange juice was thermally processed at 90°C for 90 s or processed by PEF at 40 kV/cm for 97 ms. Both thermally processed and PEF-processed juices showed microbial shelf life at 4°C for 196 d. PEF-processed juice retained more ascorbic acid, flavor, and color than thermally processed juice (P < 0.05). Sensory evaluation of texture, flavor, and overall acceptability were ranked highest for control juice, followed by PEF-processed juice and then by thermally processed juice (P < 0.01).

Effects of packaging materials, storage temperature, and time on the stability of pulsed electric field (PEF) processed orange juice were investigated. Single-strength orange juice was treated with PEF at an electric field strength of 35 kV/cm for 59 micros using an integrated pilot plant scale PEF processing and glovebox packaging system. The retention of eight orange juice aroma compounds, color, and vitamin C in glass, polyethylene terephthalate (PET), high-density polyethylene, and low-density polyethylene were evaluated at 4 and 22 degrees C for 112 days. Packaging material had a significant effect (p < or = 0.05) on the retention of orange juice aroma compounds, color, and vitamin C. PEF-treated orange juice had a shelf life of>16 weeks in glass and PET at 4 degrees C.

No abstract

Orange juice was treated with pulsed electric fields (PEF) in a pilot-plant system to optimize PEFprocessing conditions for maximum microbial inactivation and to investigate the effects of PEF on pectin methyl esterase (PME) activity. Electric-field strengths of 20, 25, 30, and 35 kV/cm and total treatment times of 39, 49, and 59 s were used. Higher electric-field strengths and longer total treatment times were more effective to inactivate microorganisms and PME (p Ͻ Ͻ Ͻ Ͻ Ͻ 0.05). PEF treatment of orange juice at 35 kV/cm for 59 s caused 7-log reductions in total aerobic plate count and yeast and mold counts. About 90% of PME activity was inactivated by PEF treatment at 35 kV/cm for 59 s. PEF-treated orange juice at 35 kV/cm for 59 ms did not allow growth of microorganisms and recovery of PME at 4, 22, and 37 Њ Њ Њ Њ ЊC for 112 d.

Pulsed electric fields (PEF) treatments were applied to nonpasteurized orange juice using a bench top PEF system to study effects of PEF on the activity of pectin methyl esterase (PME). Effects of electric strength on PME activity at a constant water bath temperature were studied using electric field strengths up to 35 kV/cm at 30 °C. Increase of electric field strength caused a significant inactivation of PME with increase in orange juice temperature (p < 0.05). A thermal inactivation study showed that heating of orange juice at the same temperature as orange juice during PEF treatment was not effective as PEF treatment in inactivating PME. Effects of electric field strength at different water bath temperatures were studied using electric field strengths up to 25 kV/cm and water bath temperatures of 10 -50 °C. Higher electric field strengths at higher water bath temperature were the more effective to inactivate PME. A combination of PEF treatment at 25 kV/cm and a water bath temperature of 50 °C caused 90% inactivation of PME.

Yogurt‐based products similar to a dairy pudding dessert were formulated and processed by mild heat and pulsed electric fields (PEF) to investigate the effects of combined mild heat and PEF treatment on the microbial stability and quality of high viscosity foods. Commercial plain low fat yogurt was mixed with fruit jelly and corn syrup and processed by mild heat treatment at 60C for 30 s and 30 kV/cm electric field strength for 32 μs total treatment time using OSU‐2C pilot plant scale PEF system. Control and processed products were aseptically packaged and stored at 4 and 22C. Mild heat combined with PEF treatment significantly decreased the total viable aerobic bacteria and total mold and yeast of yogurt‐based products during storage at both 4 and 22C (P ≤ 0.05). Mild heat treatment alone without any PEF treatment did not prevent the growth of microorganisms in yogurt‐based products. Sensory evaluation indicated that there was no significant difference between the control and processed products (P ≤ 0.05). Color, pH and °Brix were not significantly affected by mild heat and PEF processing conditions.

Yogurt‐based drink samples were prepared by mixing plain yogurt, water, sugar, and strawberry flavored fruit syrup. the samples were treated by both the mild heat (60C for 30 s) combined with a pilot plant pulsed electric field (PEF) system and the mild heat only in order to determine changes in the product safety and quality. Changes in the product safety were measured as microbial count, and changes in the product quality as L, a, b, oBrix and pH values. the treated and control samples were stored at 4 and 22C for microbial, physical and sensory evaluations. Since the 60C‐treated samples exploded after 14‐day storage, the safety and quality evaluations for 91 days were performed for the 60C? and control samples, only. Microbial count of the 60C? samples was significantly lower than that of the control samples at the two temperatures for the 91‐day storage (P < 0.05). There was no significant difference in the L, a, b values, oBrix and pH between the control and 60C? samples (P < 0.05). the control and 60C? samples revealed no significant difference in the selected sensory attributes (P < 0.05).