No abstract

Orange concentrate (OC) 66"Brix, was tested for effect of storage temperature and storage time on product quality. OC was stored at -12.2, -6.6, -1.1, and 4.4'C, and analyzed for "Brix, % acid, ascorbic acid, furfural, serum viscosity, apparent viscosity, browning, Hunter color values, and taste panel scores at monthly intervals for 1 yr. Significant (p > 0.01) decreases were found in ascorbic acid content and Hunter color value (Y) due to storage time, and temperature. Nonenzymatic browning increased and taste panel scores significantly decreased with storage temperature and time. Taste panelists were able to detect significant differences in flavor after 5 and 9 months at 4.4 and -l.l"C, respectively.

Resting cells of Saccharomyces cerevisiae Y2.5 were heated at 56°C for O-5 mm. Viability and thermal injury were evaluated using various media. Delayed plating after storage in water at 22°C resulted in increased counts primarily due to repair of thermal injury. Repair of injured cells was prevented by storage at 4°C or in the presence of 2,4-dinitrophenol, but was not affected by storage in the presence of actinomycin D, chloramphenicol, cycloheximide or hydroxyurea. Recovery of injured cells was inversely related to glucose concentration in autoclaved media. However, counts on a yeast nitrogen base-glucose medium were considerably higher when glucose was filter-sterilized rather than autoclaved.

The aqueous discharge produced by centrifuges in a citrus peel-oil recovery system was chemically and microbially characterized. The discharge contained 3.82 "Brix, 2.60% sugars, 0.28% recoverable oil, and a BOD of 22,600 mg/L. Minerals in ppm included K(604), Na (248), Fe(185), and Ca(105). Citric and malic were the major acids, 0.78 and 0.31 mg/mL, respectively. Concentration ratios of sugars were 3.6:1.7:1 for sucrose:glucose:fructose.Aerobic plate counts were 7.3x 10' colony forming units (cfu) per mL while indogenous yeast and mold counts were 1.8 X lo5 cfu/mL. Four yeasts isolated from the effluent were presumptively identified as members of the genus Saccharomyces.

Commercial orange drink concentrate and two orange juice concentrates were aseptically packed in flexible bags and stored at 4°, 15°, 22°, and 30°C for 6 months. Ascorbic acid, nonenzymatic browning and sensory quality were measured monthly. Sensory characteristics for drink concentrate deteriorated after 3 and 4 months at 30°C and 22°C, respectively. Juice concentrates were unacceptable after 2 and 5 months at 30°C and 22°C, respectively. Drink concentrate ascorbic acid loss was greater than juice concentrates at 4°, 15°, and 22°C. Changes in nonenzymatic browning as measured by Hunter color and by absorbance at 420 nm were similar to changes in other containers. The quality of refrigerated aseptic drink (15°C) and juice (4°C) was similar to frozen concentrates (−18°C).

No abstract

Injury and survival of thermally stressed yeast in orange juice were assessed by plating on plate count agar, acidified potato dextrose agar, and orange serum agar. Thermally stressed yeast were found to have reduced plate counts on both orange serum agar and acidified potato dextrose agar in comparison to plate count agar. Severely injured populations were not able to repair injury in orange juice held at 25°C but survived storage at 25,6, and -18°C.

Resting cells of Saccharomyces cerevisiae Y25 were heated at 560C for 0 to 2 min. Respiratory activity of the cells reflected the severity of the heat stress. The endogenous respiration was approximately 50 IlI of 02/mg per h for cells heated for 2 min at 560C as compared with 2 ,ul of 02/mg per h for nonheated cells. There was a distinct decrease in respiration after 1 to 3 h, and after 20 h the respiration rate of heated cells was less than that of nonheated cells. Along with increased rates of endogenous respiration, respiratory quotients of cells were altered after heat stress. Addition of 2,4-dinitrophenol stimulated 02 uptake in nonheated cells but decreased 02 uptake of heated cells. Due to the high rate of endogenous respiration, addition of glucose resulted in no substantial change in the rate of respiration of heated cells. However, addition of glucose prolonged the presence of the high rates of respiration observed in heated cells. t Michigan State Agricultural Experiment Station journal article no. 8965.