Non-enzymatic browning of peach juice concentrate during storage

The effect of storage temperature and soluble solids concentration (Brix) on non-enzymatic browning of peach juice concentrate was studied by measuring absorbance at a 420-nm wavelength. The light absorbance of 70°Brix concentrate stored at 3 and 37°C was measured. Comparing the results with literature data for other fruit juices stored at 37°C, it was found that PJC browning rate is noticeably higher. Samples stored at 3, 15 and 30°C in the range of 12°Brix to 89°Brix followed a browning kinetics that can be satisfactorily fitted by means of a parabolic model. The maximum browning rates were found at high solids concentration. Lowering the storage temperature provoked those maximum to shift towards lower concentrations, probably due to the viscosity effect on reacting ions mobility. The browning rate followed an Arrhenius type of dependence upon temperature. It was found that PJC stored at 3°C underwent almost no colour changes, which suggests that it is a good storage option instead of the −20°C adopted by some manufacturers.     

Effect of Storage Temperature on the Stability of Aseptically Packaged Concentrated Orange Juice and Concentrated Orange Drink

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).     

Nonenzymatic Browning in Apple Juice Concentrate during Storage

Rate of browning in Red Delicious and Granny Smith apple juice concentrates during storage was investigated. Color development at 65°, 70° and 75°Brix and storage temperatures of 5°, 20° and 37°C were compared over 120 days. Color deterioration occured at a faster rate in Red Delicious. Reaction at different concentration and storage conditions was exponential, following an Arrhenius-type dependence with temperature. Activation energy for a solids content of 65 - 75°Brix ranged from 16.4 - 19.3 Kcal/mole. Influence of juice variety on activation energy was negligible. Water activity results are in general agreement with those reported by other investigators. A satisfactory correlation to predict commercial concentrate browning has been obtained. All other things being equal, thermal history is a critical factor to obtain a lighter color concentrate.     

Factors Affecting Storage of Orange Concentrate

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 −1.1°C, respectively.     

Comparison of the Stability of Pelargonidin-based Anthocyanins in Strawberry Juice and Concentrate

Strawberries were processed into juice (8° Brix) and concentrate (65° Brix) and different lots were fortified with pelargonidin 3‐glucoside, pelargonidin 3‐sophoroside, and acylated pelargonidin 3‐sophoroside 5‐glucoside. Changes in pigment concentration, color (CIE L*a*b*) and ascorbic acid content were monitored during storage at 25 °C. Anthocyanin and ascorbic acid degradations followed 1^st order reaction kinetics. Fortification increased the half‐life of the pigments from 3.5 to 5 d in concentrate and from 5 to 12 d in juice. The half‐life of ascorbic acid was 2 d in juice samples and ranged from 3 to 10 d in concentrate samples. Both systems showed changes in chroma and hue angle, but maintained L* values.     

Clarified Natural Apple Juice: Production and Storage Stability of Juice and Concentrate

Thermal treatment (90°C, 20 sec) of Red Delicious apple mashes followed by Pectinase (0.02%;v/w), centrifugation, bentoniting and filtration resulted in a clear natural apple juice. Whole apple mash juice was faintly pink due to extracted skin anthocyanins and the 70° Brix concentrate prepared from the juice was ruby red. Pink juice browned extensively over 648 hr storage at 37°C and browning was associated with development of an absorption maximum at 446 nm. The ruby red concentrate stored at 37°C, turned orange (167 hr) darkening to brown (648 hr) and gave visible spectral scan typical of Maillard browning development.     

Preparation and Storage of 72° Brix Orange Juice Concentrate

Each year, thousands of tons of citrus concentrate are stored and transported throughout the world at 62° Brix. Increasing this concentration to 72° Brix can result in substantial savings. Fresh orange juice, treated mechanically or with pectic enzymes to reduce its viscosity, was concentrated to 72° Brix in a commercial processing plant, then samples were stored in barrels in a tank farm at ?7 or at 4°C. At monthly intervals, samples were blended to make 41.8° Brix Frozen Concentrated Orange Juice. The enzyme-treated samples had lower viscosity than those mechanically treated. Vitamin C retention levels were > 94% after 6 months storage at 4°C. Taste evaluations rated the product ‘very good’ and furfural levels were well below that which indicates off flavors. Browning tended to increase with storage time and temperature.     

EFFECT OF SOLUBLE SOLIDS AND TEMPERATURE ON ASCORBIC ACID DEGRADATION IN LEMON JUICE STORED IN GLASS BOTTLES

Lemon juice at concentrations of 9°, 20°, 30°, 40° and 50°Brix was stored at 10°, 20° and 36°C for 16 weeks and sampled regularly for total soluble solids (TSS), pH, titratable acidity and ascorbic acid. No significant differences were found in the first two of these factors as a function of storage time. There was a small but significant decrease in citric acid concentration over 16 weeks. Ascorbic acid loss was greater at higher temperatures; at a constant temperature, the loss was smaller as TSS increased. Ascorbic acid degradation data fitted zero-, first- and second-order models equally well at all five TSS. Rate constants in 9°Brix juice were significantly higher than those for the other four concentrations at all three temperatures. E_a values of 47.8 and 24.1 kJ mol^?1 were calculated for ascorbic acid degradation in 9° and 20°Brix juices. The effect of temperature far outweighed the effect of TSS on ascorbic acid degradation. Over the 16-week storage period, maximum retention of ascorbic acid (95.7%) was obtained in the 50°Brix lemon juice concentrate stored at 10°C.     

PROCESSING AND QUALITY EVALUATION OF SOURSOP (ANNONA MURICATA L) NECTAR

Soursop (Annona muricata L) nectar was processed from pasteurized unstored or pasteurized frozen pulp. Nectars of pH 3.6–3.7 with 0.1% xanthan gum were produced from either 6° or 8° Brix pulp and increased to 13° or 15° Brix by addition of sucrose. The effect of storage (4C or 30C for 12 weeks) was investigated on nectar pH, titratable acidity (TA), browning, consistency, microbes and sensory attribute. At 8 weeks of storage, consistency was similar in all nectars, except for thinning of nectar from pasteurized, unstored pulp (8°–15° Brix) stored at 4C for 12 weeks. Nectars produced from frozen pulp had significantly (p < 0.01) lower pH and higher TA than nectars from unstored pulp. Browning increased in all products except nectar produced from unstored 8° Brix pulp adjusted to 15° Brix and then stored at 4C. This nectar was most highly ranked and had an overall rating of being liked moderately to liked very much after 12 weeks of storage. Microbial growth occurred in all nectars between 8–12 weeks of storage.     

Nonenzymatic Browning in Pear Juice Concentrate at Elevated Temperatures

The effect of temperature and soluble solids (°Brix) on nonenzymatic browning in pear juice concentrate was determined by following absorbance at 420 nm (A₄₂₀) over the temperature range of 50–80°C. Browning could be modeled as a zero order rate process with rates of 22.2 × 10⁻⁴ (45.2 °Brix), 36.9 × 10⁻⁴ (55.4 °Brix), 53.5 × 10⁻⁴ (65.1 °Brix) and 107 × 10⁻⁴ (72.5 °Brix) A₄₂₀· min⁻¹ at 80°C. Temperature dependence was described by the Arrhenius relationship with an average activation energy of 21.9 kcal · mole⁻¹. Formol titration indicated a 20% loss of amino acids during heating 4.4 hr at 80°C and no loss of carbohydrates was observed after any heating period.     

Viscosity Reduction by Homogenization of Orange Juice Concentrate in a Pilot Plant Taste Evaporator

Controlling viscosity is critical to efficient evaporation and pumping of citrus concentrates. Viscosity was reduced by a commercial homogenizer installed between the third and fourth stage of a pilot plant TASTE evaporator. Juice was concentrated to 65°Brix with and without homogenization. The results showed a 13% decrease in viscosity due to homogenization. Mean non-homogenized values were 279 mPa.s (s.d. = 7.5) on the 65°Brix control and 242 mPa.s (s.d. = 10) on the homogenized concentrate, both measured at 3.50 set¹, which was calculated to be the shear rate for these samples within the third stage of this evaporator. This decrease in viscosity also reduced the energy consumption about 3 to 4% or produced a higher (2 to 3) °Brix concentrate. Homogenization did not significantly affect the juice color, acid, pulp or vitamin C.     

Heat Resistance of Eurotium herbariorum, a Xerophilic Mold

Eurotium haerbariorum, isolated from a spoilage outbreak involving grape preserves, was a true osmophile in that optimal growth was obtained in media containing 40-60% sucrose. Survival curves showed logarithmic death of heated spores followed by a tailing. In 5° Brix grape juice D-values at 70°C and z-values were 2.5 min and 9.1°C compared to 5.2 min and 7.1°C in 65°C Brix juice. Low concentrations of sorbic acid and fumaric acid in the heating menstruum had little effect on heat resistance.     

Physical-Chemical Characteristics of Partially Clarified Guava Juice and Concentrate

Partially clarified guava juice concentrate was prepared from single strength guava puree (5.5°Brix) by treatment with pectinase (2 hr at 50°C), extraction of juice with a rack-and-cloth press, and vacuum concentration to 23°Brix. The concentrate had the following characteristics: density, 1.10; pH, 3.16; total acids, 4.67%; ash, 1.51%; moisture, 72.4%; ascorbic acid, 867 mg%; viscosity, 4.4 cp; and CIE L* 39.2, CIE a* 10.33, CIE b* 27.11.     

Determination of Oxygen Solubility in Liquid Foods Using a Dissolved Oxygen Electrode

A rapid method for determining oxygen solubility in foods was introduced. Fructose, glucose, sucrose, orange juice, apple juice, grape juice, grapefruit juice, lemonade, and tomato juice had similar oxygen solubilities at comparable °Brix readings. The equation: In [ppm O₂] = 2.63 ? 0.0179 (°Brix) ? 0.0190 (°C) estimated to within 5% the oxygen solubility of sugar solutions and fruit juices at temperatures between 4°C and 40°C. At likely food concentrations, citric acid, ascorbic acid, and NaCl reduced oxygen solubility by less than 10%. Tests for component interactions were also conducted. There was no measurable synergism or antagonism between fructose, glucose, and sucrose with or without organic acids.     

Quality of Enzymatically Treated 72° Brix Orange Juice Stored at Refrigerated Temperatures

Fresh Valencia orange juice was treated with 0, 70, and 350 ppm of commercial pectic enzymes, concentrated to 72° Brix and stored at –7°, –1°, 7°, and 13°C for up to 6 months. The 70 ppm enzyme treatment successfully reduced initial apparent viscosity by about 25%. For the 70 ppm enzyme treated samples after 6 months storage at all four temperatures, juice cloud remained acceptable, furfural remained below the significant level, and at ?1°C, vitamin C levels were above 32 mg/100 mL. There was no significant difference in taste after 6 months storage at ?7°C between control and 70 ppm enzyme treated samples. Product quality of enzymatically treated orange concentrate stored at refrigerated temperatures was of sufficient quality to realize potential savings of 17% in storage and 30% in refrigeration.     

Heat Induced Browning of Clarified Apple Juice at High Temperatures

A procedure to determine deterioration reaction kinetics of fluid foods at elevated temperatures is described. With this method the nonenzymatic browning (NEB) measured as O.D. at 420 nm of Red Delicious (RD) and Granny Smith (GS) apple juices was examined. Color development at 15°, 30°, 50°, and 70° Brix and temperatures ranging from 90–108°C were compared over 60 min. Results indicated an apparent first order reaction rate depending on temperature, apple juice composition and soluble solids. Browning occurred at a more rapid rate in GS juice. NEB reaction rate was shown to depend critically on the total amino acid content. Temperature dependence followed the Arrenhius equation and the activation energy (E_a) ranged from 22.0–24.8 Kcal/mole.     

Orange Juices and Concentrates Stabilization by a Proteic Inhibitor of Pectin Methylesterase

A proteic inhibitor of pectin methylesterase (PME), recently discovered in kiwi, was used to stabilize cloud of orange juice concentrate with “Cut-back,” 42° Brix. To concentrated and pasteurized orange juice were added increasing amounts of fresh juice (12° Brix) with PME 0.8 U/mL at the fresh to pasteurized ratios 6.6 to 38%. The PME inhibitor (65% pure), from kiwi, was added at 50 mg/L. After 8 mo at 5°C samples were compared with controls containing the same amount of fresh juice with PME inhibited by pasteurization. Pasteurized samples were not different from those treated with PME inhibitor. Conversely, where PME was not inhibited, cloud stability decreased with increasing amounts of fresh juice. Use of kiwi PME inhibitor in fruit juice production has potential advantages.     

QUALITY CHANGES DURING STORAGE IN KOREAN CLEAR PEAR JUICES CONCENTRATED BY THREE METHODS

Pears of Shingo variety were coarsely ground, and subjected to heat treatment by HTST (high temperature short time) and pectinase treatment to produce a cloudy pear juice. The pear juice was then treated with Viscozyme, gelatin and bentonite, and filtered through an ultrafiltration membrane to produce a clear pear juice. The clear pear juice was concentrated to 3 to 5 fold by vacuum evaporation, freeze concentration, and reverse osmosis methods. The concentrates were diluted to 10° Brix and stored at 4C for 15 days. The single strength juice was evaluated for color, turbidity, heat stability, and sensory preference at 5 day intervals during storage. The pear juice concentrated by the three methods showed only small differences in quality. While the clear pear juice with added ascorbic acid had no quality changes at 4C after 15 days' storage, that without the addition of ascorbic acid resulted in some deterioration in browning, turbidity and heat stability after 10 days' storage. There were small, but significant flavor differences among clear pear juices concentrated by evaporation, freeze concentration and reverse osmosis.     

On the Interpretation of °Brix Value for the Juice of Acid Citrus

°Brix, which has been commonly used for expressing the juice quality of the so-called table citrus, has been frequently used also for expressing the juice quality of acid citrus despite no definitive information being available on how good °Brix is for this purpose. Therefore a study to elucidate correlations between °Brix with acid and sugar contents in the juice of acid citrus was carried out. The results showed no correlation at all between °Brix and acid content or sugar-to-acid ratios and low, though significant, correlations between °Brix and sugar contents. °Brix or total soluble solid content seemed to be less informative for expressing the juice quality of acid citrus fruits than for measuring acid and sugar contents individually.     

Chemical Changes during Storage of an Alcoholic Orange Juice Beverage

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.