Technical note: Effect of low pH preservation on the colour and consistency of tomato juice

The changes in colour and consistency are reported for tomato juice produced by low pH preservation and stored under ambient conditions. The juice preserved under acid conditions showed higher consistency, probably due to the higher concentration of pectin and the presence of low methoxyl pectin. The furfural and hydroxymethyl-furfural which were detected in the juice indicated that darkening of the juice colour was due to non-enzymic browning involving both ascorbic acid and sugars (hexoses). Although the retention of ascorbic acid was higher under low pH conditions, it led to a significant darkening of the juice colour due to non-enzymic browning involving mainly ascorbic acid.     

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.     

浓缩苹果汁酶促褐变及其控制

酶促褐变是引起苹果浓缩汁色值降低、品质劣变的主要原因之一 ,本文介绍了浓缩苹果汁酶促褐变的三个必要生化条件 :酚类物质、多酚氧化酶 (PPO)和氧气 ,并综述了浓缩苹果汁生产中酶促褐变的控制方法 ,如加热钝化酶、调节pH值、添加酶或底物的抑制剂、使用膜技术、添加漆酶等 ,均能有效控制浓缩苹果汁的酶促褐变 ,提高果汁的品质     

酶促诱发儿茶素对模拟苹果汁非酶褐变特性的影响

以苹果中含量较多的儿茶素为研究对象,以磷酸缓冲液为苹果汁褐变模拟体系,在多酚氧化酶（polyphenol oxidase,PPO）酶促诱发儿茶素后,钝化PPO,通过色差仪连续测定模拟体系亮度（L*）值、红度（a*）值、黄度（b*）值及总色差（ΔE*）值的变化趋势,研究酶促诱发条件对模拟果汁体系非酶褐变特性的影响。结果表明：酶促诱发时间及诱发体系温度对儿茶素参与的非酶褐变无显著性影响（P＞0.05）,而酶促诱发体系pH值以及儿茶素浓度对模拟体系褐变程度影响显著（P＜0.05）,pH 4.0时,模拟果汁体系褐变程度较大,褐变程度随儿茶素浓度的增大而增强;本实验同时发现,PPO诱发儿茶素发生非酶聚合,并与聚合产物相互作用而沉淀,导致果汁产生后浑浊。     

COMPOSITION AND QUALITY OF CLARIFIED CANTAAOUPE JUICE CONCENTRATE

Cantaloupe fruit was processed into clarified juice and juice concentrate. Greater yields were obtained from pressing fruit containing the rind in contrast to pressing cantaloupe flesh with the rind removed. Juice pressed from cantaloupe flesh without rind was particularly difficult to filter, filtration being easier if the flesh had been frozen and thawed. Juice compositional measurements included °Brix, pH, titratable acidity (TA), formol values, ascorbic acid content, total carotenoids, browning indices, sugars, and nonvolatile acids. Ascorbic acid degraded rapidly during processing. Concentrates stored at 25C for 120 days showed extremely high rates of browning. Sensory evaluation demonstrated that rind aroma and flavor were removed during concentration. The high juice yields (ca. 80%), low TA (0.04 g/100 mL as citric acid) and sweet, fruity flavor suggest the potential use of clarified cantaloupe juice concentrate as an alternate sweetener and blended juice base.     

Ascorbic acid,aroma compounds and browning of orange juices related to PET packaging materials and pH

The ascorbic acid content of orange juice made from concentrate was measured after 9 months of storage at 20 °C in glass, standard monolayer polyethylene terephthalate (PET₁), multilayer PET (PET₂) and plasma‐treated PET (PET₃) containers. Glass enabled the best preservation of ascorbic acid and, in plastic packaging materials, ascorbic acid losses were correlated with their oxygen permeability. PET₂ and PET₃, which exhibit oxygen permeability 10 times less than that of PET₁, enabled a gain of 100 mg L^?1 after 9 months of storage. Freshly hand‐squeezed orange juice samples were adjusted to various pH values using sodium hydroxide; a rise in the pH from 3.2 to 4.0 significantly reduced the amounts of off‐flavours (i.e., furfural and α‐terpineol) appearing during storage, by 79% and 65%, respectively. Moreover, an increase in the pH from 3.2 to 4.0 enabled the protection of ascorbic acid levels without detrimentally increasing non‐enzymatic browning. Copyright © 2006 Society of Chemical Industry     

EFFECTS OF pH ON QUALITY OF STORED TOMATO JUICE

Tomato juice was prepared by the hot-break method and filled hot into cans containing sufficient concentrated HCl to adjust pH to 4.0, 3.5, 3.0, 2.5 and 2.0. Controls were also prepared with no HCl added. Product was stored at ambient (18–22°C) and 40°C up to 3 months. As pH decreased below 4.0, consistency also showed a significant decline through pH 2.0. At the same time there was no apparent pH effect on serum viscosity. Further studies indicated that this effect was noticeable after 4 hr, at pH 3.0 to 5.0. Addition of as much as 1% NaCl to tomato juice had no effect on consistency of tomato juice. Lightness (Hunter color L ) decreased with pH after 3.5, redness (a_L) decreased after pH 4.0, and yellowness (b_L) decreased after pH 3.0. All storage effects were more profound at the higher temperature. The storage of tomato juices at pH less than 4.0 does not appear to be advantageous to the processor.     

浓缩苹果汁生产中褐变因素及其控制措施的探讨

通过分析浓缩苹果汁的生产工艺,阐明了目前苹果汁生产中防止褐变的基本措施以及引起果汁后期贮藏发生褐变的原因。浓缩苹果汁的生产工艺基本消除了果汁贮藏期的酶促褐变,在贮藏期的褐变限于非酶促褐变,主要是Maillard反应和焦糖化反应。     

Action of A ring-cleaving oxygenase in preventing oxidative darkening of apple juice

Prevention of browning of apple juice by catechol oxidase was brought about through enzymic cleavage of the aromatic ring of juice-darkening constituents. Protocatechuate-3,4-dioxygenase in the presence of ascorbate oxidatively attacked the catechol compounds in juice, nullifying their darkening capacity.     

Treatments to inhibit the browning reactions in model solutions of olive fruit extracts

Crude enzymatic and polyphenol extracts from olives were subjected to reaction at diverse buffered pH values. At pH values similar to those found in olive flesh (pH 5.0), the colour of the solution increased with reaction time and, simultaneously, a consumption of phenols and oxygen in the reaction medium was observed, especially under aerated conditions. In alkaline solutions (pH 12.4), a strong initial solution browning was noticed while the phenols from the extract reacted with the oxygen present in the solution and caused a significant decrease in the total phenols and oxygen concentrations. This darkening was due to the appearance of non-enzymatic browning reactions since, at this pH, the polyphenoloxidase is not active. Under acidic conditions (pH 3.0), and in solutions with ascorbic acid added (100 mM), the consumption of oxygen and total phenols was negligible, under both aerated and non-aerated conditions; as a result, no significant changes in the colour of the solutions were observed. So, low pH or ascorbic acid solutions may be useful to prevent browning in the bruised areas of hand- or mechanically-harvested table olives.     

包装材料对苹果浓缩汁贮藏期非酶褐变的影响

研究了苹果浓缩汁贮藏过程中,3种包装材料对褐变指数(A420)、氨基态氮、还原糖和5-羟甲基糠醛含量的影响。结果表明,3种包装材料对苹果浓缩汁的非酶褐变阻遏作用玻璃瓶最佳;20d内,PE/TIE/PA/TIE/PE5层共挤蒸煮袋>PE(聚乙烯)袋;20d后,PE袋>蒸煮袋。     

Thermal kinetics on antiradical capacity of mulberry fruit extract

The effects of temperature and pH on the kinetics of the antiradical capacity of mulberry fruit extract were investigated. The browning index (A₄₂₀/A₅₁₀) increased as pH increased. The change in browning index at pH 2.0 was less than that at pH 4.0. The antiradical capacity increased as browning index increased. The correlation values (slop) of antiradical capacity and browning index were 135.8 (80 °C), 164.4 (90 °C), and 179.7 (100 °C). The antiradical capacity variation was adequately described by both first order and zero order kinetics; however, a zero order kinetic model was proposed because of a better fit. According to the Arrhenius model, the activation energies for antiradical capacity in the range 80–100 °C for the three different pH values were 82.0 kJ/mol for pH 2.0, 70.8 kJ/mol for pH 3.0, and 41.1 kJ/mol for pH 4.0.     

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.     

六种梨浓缩汁贮藏期间色泽稳定性相关指标研究

通过测定六种梨浓缩汁色泽稳定性相关指标的变化趋势,对六种梨浓缩汁4℃贮藏过程中的色泽稳定性进行了研究。结果表明：褐变度和总色差值逐渐升高,还原糖含量变化不明显,氨基态氮呈下降趋势,可溶性酚和可溶性蛋白含量逐渐减少,pH 值变化不明显。六种梨浓缩汁之间色泽及相关指标差异明显,砀山酥梨、库尔勒香梨、莱阳茌梨浓缩汁褐变较重,中香梨、黄金梨、秋梨浓缩汁褐变较轻。库尔勒香梨浓缩汁可溶性酚类含量较高;中香梨浓缩汁可溶性蛋白含量较高;砀山酥梨浓缩汁pH 值最高(在4.9 以上),莱阳茌梨浓缩汁pH 值最低(在4.4～4.5 之间);六种浓缩汁5- 羟甲基糠醛(5-HMF)的含量变化为：砀山酥梨、莱阳茌梨在第四个月出现峰值,其余品种在第三个月出现峰值。     

甘蔗压榨提汁过程褐变抑制研究？

制糖脱色成本占糖浆精制成本的1/3,而酶促褐变是蔗汁颜色加深的一个主要原因。本文探讨了制糖压榨过程中褐变对蔗汁颜色变化的影响,进一步研究了亚硫酸盐对蔗汁酶促褐变的抑制。结果表明：褐变对蔗汁色值贡献率大于50%,前10 min褐变速度最快;蔗梢蔗汁相对于成熟蔗茎蔗汁酶促褐变程度高;压榨后立即预灰能减少酶促褐变色素生成;多酚氧化酶活性在蔗汁预灰pH大于9.5时为0,在pH6.0~6.5最高;3 mmol/L NaHSO3的添加量能完全抑制蔗汁酶促反应发生。研究可为甘蔗制糖工艺的改进提供依据。     

EFFECT OF pH AND SOLUBLE SOLIDS ON THE SERUM VISCOSITY AND SERUM COLOR OF TOMATO JUICE AT ELEVATED TEMPERATURES1

Effects of heating time and temperature, pH, and soluble solid levels on serum viscosity and serum color of tomato juice were studied. The samples were canned in 18 mL TDT cans and exposed to processing temperatures of 88C, 102C, and 112C for 30, 60, and 120 min. Depending upon the time and temperature of heating, and initial viscosity of the serum, the losses in viscosity ranged from 3.0–55.6% being higher in serum with higher initial viscosity. Percent losses in serum viscosity during heating of juice increased (6–60%) with increase in pH (3.8–4.9) and soluble solids (6°–24°) in the juice. An increase in pH and soluble solids also enhanced heat induced browning in the serum with values varying from 0.1–2.69.     

Storage Stability of Orange Juice Concentrate Packaged Aseptically

Orange juice concentrates were packaged aseptically by a “Dole” aseptic canning machine using 6 oz metal cans. The final juice products (11°, 34°, 44°, 58° Brix) were stored between ?18° and 36°C and tested periodically for nonenzymatic browning, ascorbic acid destruction, furfural and sensory changes. Nonenzymatic browning, the main deterioration phenomena in these products, was satisfactorily retarded at 12°C or lower. Ascorbic acid destruction rate constant was dependent on temperatures between 5 and 25°C, and was affected by degree of juice concentration. Furfural accumulation in juice was higher than that in 58° Brix concentrate. Orange juice concentrate of 58° Brix did not show flavor changes after storage at 5°C or 12°C for 17 or 10 months, respectively, when evaluated after reconstitution to 11° Brix.     

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).     

菠萝浓缩汁在储藏过程中美拉德褐变及其反应动力学研究

研究了两种不同加工工艺生产的菠萝浓缩汁(菠萝果肉浓缩汁和菠萝全果浓缩汁)在储藏过程中的美拉德褐变及其反应动力学,并进一步探讨了美拉德反应对菠萝浓缩汁非酶褐变的影响。结果表明,菠萝浓缩汁在储藏期间,美拉德褐变遵循一级反应动力学;菠萝果肉浓缩汁和菠萝全果浓缩汁在储藏期间美拉德褐变的活化能分别为36.19kJ/mol和29.54kJ/mol。HMF积累对果汁非酶褐变的影响主要作用在储藏后期。     

Nonenzymic Browning in Kiwifruit Juice Concentrate Systems during Storage

The contributions of different nonenzymic browning reactions to color changes in stored kiwifruit juice concentrate were investigated using five synthetic model concentrates. The model systems were stored at 20^oC for 10 weeks and analyzed for browning, haze, ascorbic and dehydroascorbic acids, titratable acidity, formol value. In addition the profiles of sugars, nonvolatile acids, and amino acids were determined. Two different classes of nonenzymic browning mechanisms were found to be of significance: the Maillard browning reactions and ascorbic acid browning reactions. Reactions involving ascorbic acid were found to contribute more to overall browning than Maillard browning.