Wilbur Widmer

Pretreatment effects on orange processing waste for making ethanol by simultaneous saccharification and fermentation

Citrus processing waste (CPW) pretreated under different times, pH and temperatures was investigated. Pretreatments at 160 degrees C for longer than 4 min with steam purging were needed to remove limonene, an inhibitor for fermentation, to below 0.1%. While hemicelluloses were solubilized well following all pretreatments at 160 degrees C, just 70% of the pectin was solubilized in natural CPW compared to over 80% after pretreatments using acid modified CPW (pH 2.8). Pretreatments at 160 degrees C on base modified CPW (initial pH 6.8) quickly destroyed pectin, had significantly lower dissolved solids, and were excessively viscous. Total sugars fermentable by Saccharomyces cerevisiae were not changed after pretreatment at 160 degrees C for up to 8 min in CPW between pH 2.2-8.2. Ethanol yields based on sugar content after enzymatic hydrolysis after 48h simultaneous saccharification and fermentation ranged from 76% to 94%. Ethanol yields were slightly lower but not statistically different using base modified pretreatments.

Changes in Volatile and Non-Volatile Flavor Chemicals of “Valencia” Orange Juice over the Harvest Seasons

Florida “Valencia” oranges have a wide harvest window, covering four months after first reaching the commercial maturity. However, the influence of harvest time on juice flavor chemicals is not well documented, with the exception of sugars and acids. Therefore, we investigated the major flavor chemicals, volatile (aroma), non-volatile (taste) and mouth feel attributes, in the two harvest seasons (March to June in 2007 and February to May in 2012). Bitter limonoid compounds, limonin and nomilin, decreased gradually. Out of a total of 94 volatiles, 32 increased, 47 peaked mid to late season, and 15 decreased. Juice insoluble solids and pectin content increased over the season; however, pectin methylesterase activity remained unchanged. Fruit harvested in the earlier months had lower flavor quality. Juice from later harvests had a higher sugar/acid ratio with less bitterness, while, many important aroma compounds occurred at the highest concentrations in the middle to late season, but occurred at lower concentrations at the end of the season. The results provide information to the orange juice processing industry for selection of optimal harvest time and for setting of precise blending strategy.

Effect of copper hydroxide sprays for citrus canker control on wild-type Escherichia coli.

Aims:  To show that application of copper hydroxide citrus sprays mixed with field source water (possibly contaminated) will not support Escherichia coli on plant surfaces. Environmental stresses of transient phyllosphere bacteria and presence of copper will eradicate these bacteria before harvest.