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Juices from three strawberry cultivars were stored at 2°C and 25°C for 6 wk and evaluated for the sensory attributes fresh strawberry, strawberry-jam, off-flavor, green, and sweet. Fresh flavor declined while off-flavor increased during storage, with the largest changes occurring at 25°C. Juice color and ascorbic acid also degraded much faster at 25°C. Fifteen volatiles were measured using headspace solid phase microextraction and gas chromatography. 2,5-dimethyl-4-hydroxy-3(2H)-furanone and 2,5-dimethyl-4-methoxy-3(2H)-furanone were positively related to fresh flavor and negatively related to off-flavor, while -terpineol was inversely related to fresh flavor. These volatiles explained almost 90% of the variation for fresh and off-flavor attributes.

The 5-methyltetrahydrofolate (5mTHF) polyglutamates in citrus products were analyzed by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). Folate species were purified from citrus products and concentrated from 2- to 100-fold using combined folate-affinity chromatography and C18 extraction. Seven polyglutamyl 5mTHFs were found in most not-from-concentrate (NFC) orange juices (OJ) in total amounts of approximately 1 nmol/mL, with varying distributions of individual polyglutamates. Folate amounts and distributions were also measured in orange fractions, single-strength OJ from concentrate, NFC grapefruit juice, and citrus peel molasses. Models containing ascorbic acid had folate thermal degradation rates one-seventh that of models without ascorbic acid. Pasteurization studies demonstrated that folate loss was

Commercial cold-pressed citrus oils containing terpene chlorohydrins may have quality and safety implications for end-users of these oils. Concentrations of (1S, 2S, 4R)-2-chloro-8-p-menthen-1-ol (1), (1R, 2R, 4R)-2-chloro-8-p-menthen-1-ol (2), and (1R, 2R, 4R)-2,9-dichloro-8-p-menthen-1-ol (3) in some citrus essential oils ranged from less than 1 ppm to 30 ppm measured by gas chromatography with a halogen detector. Reduction reactions of these compounds were accomplished by continuous mixing (reaction) of the oil with dilute solutions of KOH. Greater than 95% reduction of 1 and 3 were accomplished after reaction for 15 h with 0.5 N KOH or after 24 h with 0.25 N KOH in oils with either 25 or 30 ppm (1). Similar treatment of an oil containing 5 ppm (1) resulted in reduction to below the threshold limit of quantification (0.4 ppm). Sensory analyses of tasting solutions did not detect any flavor difference between untreated or KOH-treated oils.

Screening commercial cold-pressed oils revealed the presence of terpene chlorohydrins, which may have quality and safety implications for end-users. Concentrations of (1R, 2R, 4R)-2-chloro-8-p-menthen-1-ol in some citrus essential oils ranged from less than 1 to 140 ppm. More than half of the oils tested contained less than 2 ppm of (1R, 2R, 4R)-2-chloro-8-p-menthen-1-ol. A pilot plant study used different concentrations of chlorinated water during the oil-recovery process. Cold-pressed oil, produced from a 30-ppm chlorine solution, contained (1R, 2R, 4R)-2-chloro-8-p-menthen-1-ol at detection threshold. The presence of (1R, 2R, 4R)-2-chloro-8-p-menthen-1-ol in citrus essential oils results from processing conditions and can be reduced through the reduction of chlorine levels in treatment water.

Three terpene chlorohydrins found in cold-pressed orange oil were concentrated by silica adsorption chromatography and purified by preparative HPLC. Formation of these chlorohydrins was determined to be the result of a reaction of d-limonene, the major component of cold-pressed oil, with hypochlorous acid, found in chlorinated treatment water used in the oil recovery process. NMR analyses indicated that the major chlorohydrin present was the diequatorially substituted (1R,2R,4R)-2-chloro-8-p-menthen-1-ol (1). The other two compounds were the diaxial trans stereoisomer, (1S,2S,4R)-2-chloro-8-p-menthen-1-ol (2), and the dichlorohydrin, (1R,2R,4R)-2,9-dichloro-8-p-menthen-1-ol (3).

Although citrus processors recover most of the essential oils in the peel, the amount remaining is released as air pollutants and volatile organic compounds (VOCs) during cattle feed manufacturing. Citrus processing plants are required to obtain permits allowing emission of 91 t/year (100 tons/year) of VOCs, an amount exceeded by most processors. The objective of this study was to develop an accurate, on-site method to measure VOC emissions, accomplished by use of adsorbent traps subsequently analyzed by gas chromatography. Over 90 percent of the oil entering the feed mill was accounted for, with d-limonene as the major VOC, including other terpenes, β-pinene and myrcene. Of sampling locations in a typical feed mill, error analysis determined the least precision (16.9%) was associated with determining the input rates of peel to the dryer. The sampling technique developed is a viable method for monitoring VOCs with reproducible results.

SUMMARY –Malonaldehyde has been identified as a component of commercial aqueous orange juice essences and a procedure for its isolation and identification is described. Fluorescence and phosphorescence spectra of the purified pink complex formed from the reaction of thiobarbituric acid with malonaldehyde exhibited several excitation and emission maxima in the region from 200–550 nm and proved to be a sensitive and highly selective method for confirming the presence of malonaldehyde in a sample. The method is applicable to all citrus essences and should be applicable to the evaluation of malonaldehyde from lipid autoxidation in other fruit juice essences.

After induction of alcohol oxidase, active Pichia pastoris cells were grown in model alcohol solutions and orange aroma, a by-product rich in potential alcohol substrates for bio-oxidation to aldehydes. Acetaldehyde production efficiency was 60% at 0.1% ethanol, decreasing with increasing ethanol. Acetaldehyde, propanal, and octanal were generated using the Pichia system with orange aroma as substrate. Acetaldehyde concentration doubled during a 24h reaction time at 30°C. In contrast to use of isolated alcohol oxidase, the whole cell system had the advantage of cofactor regeneration and associated enzyme systems, including formaldehyde dehydrogenase. Sensory differences were found in the full strength biomodified aroma. Presented in a paired comparison aroma test, to a trained panel it rated higher for the attributes orange character, freshness, and fruitiness than the unmodified control.

The enzyme pectinesterase (PE) reduces the quality of citrus juices. Current inactivation of the enzyme is accomplished by heat, resulting in a loss of fresh fruit flavor in the juice. We explored the use of pressurized treatments of orange and grapefruit juices to bypass the use of extreme heat during processing. PE inactivation using isostatic high pressure in the range of 500−900 MPa was accomplished in orange and grapefruit juices. The higher pressures (>600 MPa) caused instantaneous inactivation of the heat labile form of the enzyme but did not inactivate the heat stable form of PE. Treatment times caused significantly different (α = 0.05) total PE activity losses in orange but not in grapefruit juices, and PE inactivation at different pressures was significantly different in both juices. Heat labile grapefruit PE was also more sensitive than orange to pressure. Dp values for orange PE inactivation at 500 and 600 MPa were 83.3 and 2.4 min, respectively; while the zp value between 500 and 600 MPa was ...

Pectinesterase (PE) heat inactivation at various Brix did not obey first order reaction kinetics. Inactivation of PE at 10 - 35° Brix did follow straight line semilogarithm plots of enzyme activity versus time. However, at 40° Brix and above the semi-log graph between PE activity versus time was unclear. At high Brix levels a protective effect seemed to occur because the rate of enzyme inactivation declined. Increasing enzyme concentration in the 40° Brix sample showed that the curve was S-shaped or sigmoidal. Increasing pH from 4 to 7 decreased the “Thermal Death Time” from 18 set to 4 sec.

Losses of volatile compounds in orange juice during ultrafiltration and subsequent evaporation were studied. Alcohols and esters predominated in the permeate, while terpenes (d-limonene and valencene) and nonpolar aldehydes (octanal and decanal) were distributed in the retentate from the ultrafiltration (UF) system. Fractions of some flavor compounds were lost during ultrafiltration process. An aqueous phase essence was recovered from the permeate during evaporative concentration. No oil phase was observed. When whole juice was concentrated, both oil and aqueous phases were recovered. Essence recovery efficiency of individual compounds was 3 to 13% when concentrating permeate and

The kinetics of ascorbic acid loss and nonenzymatic browning in clarified orange juice (serum) were investigated in an anaerobic environment from 70.3 to 97.6°C and from 11.7 to 80.6°Brix. Data were fitted to first-order kinetic models. Rate constants of ascorbic acid degradation in serum were not different from rate constants in whole juice. Activation energies were 30 kcal/mol and largely independent of solids concentration. Rate constants of browning pigment formation were 30-50% greater in serum. Activation energies were 19-25 kcal/mol and increased slightly with solids concentration.

Ethanol, a major component of lemon juice, was analyzed to indicate degree of lemon juice aroma concentration. Aroma solution was concentrated from 12.2 to 23.4% ethanol at 8.3 MPa and 19 o C by reverse osmosis. Ethanol rejected by the membrane decreased from the initial 87.7% to 78% at the final aroma concentration of 23.4% ethanol. Membrane rejection of neral, geranial, and terpinene-4-ol was >96% while rejection of the alcohols, n-propanol, 2-methyl-3-buten-2-ol, and 3-methyl-2-buten-1-ol, ranged from 6.9% to 83.5%. Sensory analysis indicated no difference between initial aroma and aroma concentrated by reverse osmosis. Mass balance determined the true recovery of total volatiles was 79.7%. Loss of volatiles was attributed to adsorption in the polymeric matrix of the membrane and some loss was attributed to cleaning

Chemical stability of a pasteurized, noncarbonated, alcoholic orange juice beverage, (8% ethanol and 30% reconstituted Valencia frozen concentrated orange juice), was investigated. It was hot-filled into clear glass bottles under nitrogen and subjected to 14-wk storage at 4, 25, and 40°C. pH, °Brix, titratable acidity, and % alcohol remained constant throughout storage. Accumulation of furfural and darkening paralleled ascorbic acid degradation. The beverage exhibited 25 times more browning at 40°C and 9 times more at 25°C than at 4°C after 14-wk. d-Limonene decreased at all temperatures. Nitrogen headspace slightly improved stability at 40°C. Time and temperature were most significant in storage and long-tem shelf-life could only be achieved with refrigeration.

High pressure inactivation kinetics (D and z values) of Saccharomyces cerevisiae ascospores were determined in fruit juices and a model juice buffer at pH 3.5 to 5.0. Approximately 0.5 to 1.0 × 10 6 ascospores/mL were pressurized at 300 to 500 MPa in juice or buffer. D-values ranged from 8 sec to 10.8 min at 500 and 300 MPa, respectively. The range for z-values was 115 to 121 MPa. No differences (P≥0.05) in D (at constant pressure) or z-values among buffers or juices at any pH were determined, indicating little influence of pH in this range and absence of protective or detrimental effects of juice constituents.

A GLC method was developed for detection of diacetyl (2,3-butanedione) and acetoin (3-hydroxy-2-butanone) in orange juice. Retention times for diacetyl and acetoin were 2.8 ± 0.03 and 6.8 ± 0.02 min, respectively. Concentration by distillation was essential to detect small quantities by GLC of diacetyl but was ineffective for acetoin. A linear response of diacetyl concentration to peak area was observed between 0.05 and 0.5 ppm. The peak areas at 0.05 and 0.5 ppm diacetyl were 1242 ± 203 and 20142 ± 1120, respectively. Elevating the column temperature and decreasing the carrier gas flow rate, increased the limit of detection for acetoin from ≥ 100 ppm to ≥ 10 ppm, but diminished the resolution of the diacetyl peak from juice volatiles.

Extraction of terpene hydrocarbons was studied using a dynamic flow system. Phase equilibrium data are presented for temperatures from 40 to 70°C and pressures from 8.3 to 12.4 MPa. The data have been correlated with a simple model using vapor fugacity coefficients from the group contribution of state and unsymmetric convention activity coefficients

Limonin glucoside (LG) and phlorin were extracted from citrus fruit tissues and assayed by capillary electrophoresis (CE). LG was determined in dried [1.20 +/- 0.10 mg of dry weight (dw)] and wet peel residues (1.16 +/- 0.04 mg of dw), orange juice finisher pulp (0.58 +/- 0.03 mg of dw), dried grapefruit seeds (2.70 +/- 0.15 mg of dw), and 50 degrees Brix molasses (2225 +/- 68 mg/L). Phlorin was purified from orange peel residue and grapefruit albedo, and concentrations were determined in some citrus products. Phlorin and LG were extracted from residues with water/pectinase or with water solutions of methanol and ethanol. Efficient LG extraction from grapefruit seeds (2.40 +/- 0.15 mg/g) was achieved with 50-65% methanol, solvent polarity P' approximately equal to 7-8. Extracts were purified and concentrated by adsorptive resins and HPLC to obtain 95% pure compounds of LG and phlorin. CE analysis did not require extract purification beyond filtration. LG and phlorin migrated as anions in electropherograms containing peaks representing other citrus flavonoids and limonoid glucosides.

Pectinesterase (PE) was extracted from orange juice and pulp with 1 M NaCl, desalted, and separated using capillary electrophoresis (CE) gel procedures (CE-SDS-CGE) and isoelectric focusing (CE-IEF). PE resolved as a single peak using noncoated fused silica columns with CE-SDS-CGE. CE-IEF separation of PE required acryloylaminoethoxyethanol-coated columns, which had limited stability. Thermal stability of PE extracts before and after heating at 75 degrees C for 30 min and at 95 degrees C for 5 min established heat labile and heat stabile fractions with identical PE migration times by CE-SDS-CGE or CE-IEF. Peak magnitude decreased to a constant value as heating time increased at 75 degrees C. Regression analysis of CE-SDS-CGE peak migration times of molecular weight (MW) standards estimated both heat labile and heat stable PE at MW approximately 36 900. Traditional SDS-PAGE gel separation of MW standards and active PE isolated by IEF allowed estimation of MW approximately 36 000. CE-SDS-CGE allowed presumptive, but not quantitative, detection of active PE in fresh juice.

Dilute aqueous essences of 2 to 20% ethanol obtained from commercial orange juice evaporators when concentrated to 31% ethanol by reverse osmosis resulted in increased concentration of the small aroma molecules and acetaldehyde. Rejection of ethanol varied from 90% at 2% ethanol to 40% at the highest concentration achieved (31%). Acetaldehyde rejection varied from about 65% at 2% ethanol, to an extrapolated low value of 25% at 31% ethanol. Rejection was generally greater than 85% for larger aroma molecules, e.g., ethyl butyrate, hexanal and terpenes. Permeate flux rates followed a first order decay with increasing ethanol concentration, from greater than 300 at 0.01% ethanol to 26 L/H/module at 31% ethanol, 8.3 MPa, 30°C.

The ability of low density polyethylene (LDPE) to absorb citrus flavor compounds was examined. The LDPE sample was mounted on an oxygen electrode. As volatiles were absorbed, oxygen permeation through the polymer increased. Limonene, ethyl butyrate, myrcene, and α-pinene were readily absorbed by LDPE. Octanal, citral, linalool, and α-terpineol were absorbed at much lower levels. Time-course changes in readings were used to calculate diffusion coefficients of volatiles in the polymer. Diffusion coefficients were proportional to the volatile's solubility in the polymer.

High hydrostatic pressures affect chemical reactions and phase changes of matter, denaturing proteins, solidifying lipids and disrupting biological membranes. The consequences of this in food systems has importance in killing spoilage microbes without the need for heat. Some applications of high pressure treatment to the processing of citrus juices are included herein. Effective pressures for pasteurization of yeasts and yeast ascospores in citrus juice fall in the range of 43,000–72,000 psi. The corresponding Dp (time for 1 log cycle reduction) values for inactivation of ascospores were 10 min at 43,000 psi or 8 sec at 72,000 psi. Pressure treatments of orange and grapefruit juices to by-pass thermal processing for pectinesterase (PE) inactivation were in the range of 72,000–130,000 psi. Dp values for orange PE inactivation at 72,000 and 87,000 psi were 83.3 minutes and 2.4 minutes, respectively. Pressures ≥87,000 psi caused instantaneous inactivation of the heat labile form, but did not inactivate the heat stable form of PE. Heat labile grapefruit PE was also more sensitive than orange to pressure. Orange juice pressurized at 100,000 psi for 1 minute had no cloud loss for >50 days. Paper published with permission.

SUMMARY The enzyme-catalyzed hydration of the citrus by-product, limonene, to the important flavor and aroma chemical, α-terpineol, was investigated. Particulate-associated α-terpineol dehydratase was recovered from Pseudomonas gladioli , solubilized, and partially purified using detergent extraction and gel filtration. Activity of α-terpineol dehydratase was low in non-aqueous solvents. α-Terpineol dehydratase was characterized in buffers containing 0.1% (w/v) Triton X-100. In 10 mM MES, 10 mM BIS-TRIS PROPANE buffer, the pH optimum was 5.5 and the stability optimum was pH 8.0. The temperature optimum at pH 7.0 was 25° in 10 mM HEPES buffer. Using temperature-activity data for 10-25°, E a and Q 10 of α-terpineol dehydratase were determined to be 21.6 ± 2.9 kJ. mol -1 and 1.37 ± 0.07, respectively. Activity was inhibited by Triton X-100. The effects were an increase in apparent K m and decrease in apparent V max . Average apparent K m of α-terpineol dehydratase was 2.18 ± 0.19 mM in 10 mM HEPES buffer, pH 7.0 containing 0.1% (w/v) Triton X-100. α-Terpineol dehydratase stereospecifically catalyzed the hydration of (4R)-(+)-limonene to (4R)-(+)-α-terpineol or (4S)-(-)-limonene to (4S)-(-)-α-terpineol. The enzyme was also stereoselective, since the rate of hydration of (4R)-(+)-limonene was approximately ten times faster than the rate of hydration of (4S)-(-)-limonene.

High pressure processing (HPP) was investigated as a means to preserve cloud in freshly squeezed orange juice. Cloud loss is a major quality defect in orange juice, and methods of preserving cloud without the extreme temperatures used in commercial pasteurization are desirable. Pressures from 500 to 900 MPa were investigated at dwell times of 1 sec, 1 min and 10 min. Higher pressures and longer processing times were more effective at preserving cloud, while all treatments yielded a microbially stable product. A 90-day shelf life under refrigeration conditions could be achieved using pressures of 700 MPa and higher combined with treatment times of 1 min.

Freezing points of orange juices and model sugar-acid-water systems at various solute concentrations were investigated using models of solution theory. The observed freezing point depression values of citrus juice were less than those of the model system of comparable average molecular weight. The differences were characterized by a parameter which accounted for the solute-solvent interactions. Models with generalized values were presented which allowed the prediction of equilibrium freezing curves of fruit juices based on proximate sugar-acid composition.

A procedure was developed to measure adsorption (scalping) of limonene by low density polyethylene. The polymer was mounted on an oxygen electrode. Limonene absorption produced an increase in oxygen permeability which appeared proportional to limonene concentration. Diffusion coefficients calculated from permeation curves were similar to diffusion coefficients calculated on a weight change basis.

Pasteurized Valencia and Temple orange juices concentrated to 45°Brix by freeze concentration retained their fresh juice flavor. Direct steam infusion heating to inactivate enzymes allowed more rapid heating than indirect heating and successfully lowered juice peel oil during vacuum cooling. Except for considerable pulp reduction of feedstream juices, there were few differences from normal citrus juice recovery procedures for freeze concentration. Since the product retained most of the aroma constituents of fresh juice, careful handling and high quality feed juice prior to freeze concentration was much more important than for evaporation. Fresh juice freeze concentrated to 45°B, then pasteurized at temperatures of 80°, 97° and 111°C had reduced sucrose (up to 25%) as the temperature increased to 111°C.

Actual amounts of octanal, decanal, dodecanal, tetradecanal, geranial and neral in various coldpressed citrus oils were determined by quantitatively preparing and analyzing the 2,4-dinitrophenylhydrazone derivatives. These major and other minor carbonyl components in citrus oils were separated and isolated using a combination of column and thin-layer chromatography of the derivatives. Differences in aldehyde composition include nearly equal amounts of octanal and decanal in Valencia orange oil and significantly less decanal than octanal in Pineapple, Hamlin and Temple orange oil. Tangerine oil has nearly equal amounts of octanal and decanal, but lesser quantities than the orange oils. Valencia essence oil, manufactured commercially by decantation from the aqueous essence phase recovered during juice evaporation, contained almost twice as much decanal as octanal. Coldpressed oils generally showed higher aldehyde/ester ratios than essence oils. The higher ester contents of the essence oils accounted for a more juice-like aroma of the latter. Quantitative chemical analyses of total aldehydes, esters, alcohols and acids of eight types of citrus oils were performed. These analyses illustrated basic compositional differences in the oxygenated components of orange, mandarin, grapefruit and essence oils.

The heat of combustion of dried citrus pulp has been found to be 4150 ± 118 cal/g or 7470 ± 212 Btu/lb. Dried citrus pulp has been compared with Bunker “c” fuel as a source of energy and found to be more valuable as a livestock feed.

Juice, extracted from fresh Costa Rican pineapples using a commercial extractor, was adjusted by finishing and centrifugation to two pulp levels, 12% and 2% by volume. Physical, chemical and sensory differences were measured in heat stabilized single strength juices, evaporator concentrated, and freeze-concentrated juices. Results indicated no significant differences between samples for Brix, % acid, total hexose, vitamin C, browning index, color, viscosity. Pulp content was lower in both freeze- and evaporator-concentrated samples. Significant (P < 0.01) flavor differences were detected between freeze-and evaporator-concentrated juices. Juices were ranked according to highest degree of fresh fruit taste as follows: (1) high pulp single strength, (2) freeze concentrate high pulp, and (3) evaporator concentrate high pulp. Flavor of reconstituted freeze-concentrated juice was comparable to single strength juice and preferable to evaporator concentrate.

Soluble solids (SS) recovered by countercurrent washing of citrus juice pulp are concentrated by evaporation and sold primarily for use in beverage bases and other food uses. On a pilot plant scale, treatment of the finisher pulp with pectolytic enzymes resulted in increasing the yield of recoverable SS from 65–80 kg SS/ton pulp (oranges) and from 45–50 kg SS/ton (grapefruit). High viscosity of pulp-wash liquids and other citrus processing liquids was found to be a deterrent during concentration by evaporation. Enzyme-treated liquids were concentrated in a medium-temperature evaporator to over 70° Brix and relative viscosities in the range of 1700–2200 centipoises; however, due to gel formation, nontreated liquids had to be pumped out of the evaporator at 25–35° Brix with a relative viscosity of over 20,000 centipoises. Careful use of enzyine to increase SS yields or lower viscosity during pulpwashing did not adversely affect the °Brix, acid, pH or clouding ability of the concentrated pulp-wash.

Commercial ultrafiltration (UF) and reverse osmosis (RO) membranes were used to concentrate the terpene, limonene, present in cold pressed oil centrifuge effluent and molasses evaporator condensate. UF membrane rejections were 78–97% for mixtures with initial limonene concentrations from 0.04–0.6%v/v. RO membrane rejection of limonene ranged from 87–99% for feed streams containing 0.06–0.23% limonene. Initial membrane flux rates for centrifuge effluents were in the range 10–100 kg/m2/hr. Evaporator condensate fluxes were higher, 25–400, while pure water rates ranged from 25 (RO) to 1000 kg/m2/hr (UF). Contact with limonene adversely affected membrane flux rates in decreasing order of severity: polysulfone > cellulose acetate > teflon-type.

Products were manufactured from cull oranges rejected from processing plant grading lines. Cull fruit juice yields were 20% less than from sound fruit. Frozen concentrate had a detectable stale fruit off-flavor. Total reducing sugars were 10% higher and vitamin C was 8% lower in the juice from the cull fruit, while color, cloud and viscosity were about the same as in juice from sound fruit. The aldehyde content of cold pressed oil from cull oranges was too low to meet U.S.P. specifications. Dried pulp cattle feed and molasses yields from culls were greater than from sound fruit. Crude protein content of the cull dried pulp was 6.6% and total sugars (reducing and sucrose) of cull fruit molasses was 58%; while the cull orange molasses had a viscosity of over 20,000 c.p.

Samples of approximately 350 kg of commercially leached lime and lemon peel were dried in a pilot plant direct fired rotary dryer with inlet air temperatures of 370, 425 and 535°C, yielding dried pectin pomace with a final moisture content of 15–20, 8–12 and 3–7%, respectively. Pectin was extracted from laboratory leached, undried peel, each of the above dried samples, and commercially leached and dried samples. From fresh peel leached in the laboratory, we found a 65.6 and 55.9% yield of 150 grade pectin on a dry weight basis for lime and lemon, respectively. Drying lemon peel to final moistures of 15–20, 8–12 and 3–7% resulted in yields of 41.1, 41.1 and 25%, respectively. Dehydration of lime peel to 3–7% moisture decreased the yield to 37%. Similar losses were found in commercially dried pectin pomace. A separate experiment was conducted to evaluate the effect of drying on pectin yield from fresh, unleached lemon peel. Unleached peel was successfully dried by mixing 1 part unleached peel with 2.5 parts of dry leached peel. There was a slight loss in the percentage yield of pectin 23.3 and 21.8, but not much change in the jelly grade 230 and 232 between the dry leached and dry unleached peel, respectively.

Low temperature (-10°F) was considerably more effective than addition of antioxidants for preservation of the carotenoid pigments in stored, dehydrated citrus flavedo. Flavedo dehydrated under conditions similar to commercial practices for dried citrus pulp resulted in losses during drying of from 30–90% of the pigments present in the fresh flavedo. Pigment losses increased with increasing drying temperatures (210°F. 225°F, 290°F). Addition of an antioxidant to the flavedo prior to dehydration aided in retention of pigments during processing. However, none of the common antioxidants effectively prevented pigment destruction during storage of dehydrated flavedo. Much more flavedo color and pigment retention was achieved by carefully controlling dehydration parameters than by adjusting storage variables.

The effect of temperature on pectinesterase activity in crude enzyme extract from Valencia pulp was determined. The effect is best described by the regression equation: LN PEU = 14.3446 −3415 (1/T) with a correlation coefficient of 0.991. The activation energy was determined to be 28,392 joules/mol. This regression equation was used to predict the enzyme activities of different juice samples and verified by assay of Valencia juice at various temperatures. Duncan analysis indicated no significant differences in the predicted pectinesterase activities of the concentration-corrected crude extract and collective means of the Valencia juices at the respective temperature.

Electrical energy consumption and oil recovery were measured during operation of a commercial citrus peel oil centrifugation process. Two parts of a centrifuge's electrical consumption were identified: regular operation and the discharge cycle. During discharge cycles, the electrical energy ranged from 125–189% of the steady-state values. Energy costs were computed for the desludger and polisher centrifuges. Direct electrical costs for the oil mill totaled 0.67/kg oil recovered. Electrical costs calculated for finishing and dewaxing totaled 0.5/kg oil. Actual oil yield (1.1 kg/t) was only 20% of the total in the fruit. A major source of oil loss occurred during extraction from the fruit, where less than 50% of the oil was actually extracted into the dilute emulsion. Inefficient operation of the centrifuges accounted for most of the remaining losses.

The Florida Citrus Industry has come to realize that by-products and specialty products are important ingredients in the overall economic returns from citrus processing. The purpose of this paper is to show the potential recoveries of various commodities that can be produced from Valencia oranges, Marsh and Duncan grapefruit. It is hoped that these data will generate interest in improving present processes to obtain greater recoveries, and at the same time create a desire on the part of citrus processors to produce more sophisticated specialty products of greater economic value. Many different trade-offs and options are available in any given by-product operation, and it must be realized that not all of the products discussed can be produced simultaneously. Certainly future profits to a great extent, will be dependent on an adequate understanding of a more sophisticated by-product and specialty product technology. Paper published with permission.

A complete flow diagram and material balance of a typical citrus pectin pomace manufacturing process is presented. Leach liquids, produced from lemon and lime peel during the process had the following waste treatment properties: COD, 10,000–12,000 ppm: BOD. 6,000–9,000 ppm, settleable matter, 50–250 ppm; turbidity, 215–1200 N.T.U. The presence of water-soluble pectin (40–100 mg/100g) in the dilute leach liquids contributed to high viscosities and made concentration by evaporation difficult. Commercial leaching processes removed approximately 20% of the total solids in the peel, while a more efficient laboratory leaching was able to recover over 30% of the solids.

Digestion of citrus wastes by pectolytic and cellulolytic enzymes was compared to the currently employed lime method of solubilizing solids from citrus peel. Maximal soluble solids removed from the pressed peel occurred after 6 hr incubation at 45°C with a pectinase concentration of 1.0 PGu/g peel mixture. Decreasing the particle size of the peel caused a 4 - 10% increase in solids removal after enzyme treatment. Addition of cellulase enzyme (20 CEu/g peel mixture) to pectinase enzyme (1.0 PGu/g peel mixture) removed an additional 15% soluble solids from peel. Glucose, fructose, arabinose, and xylose were the major sugars extracted from enzymetreated peel, while sucrose was the major sugar in lime-treated peel samples. Organic acids (citric, malic, and quinic) were present at higher concentrations in lime-treated peel extracts than in enzymetreated peel extracts.