Effect of Inert Atmosphere on the Postharvest Browning of Manzanilla Olives and Optimization by Response Surface Methodology of the Aqueous Treatments

Abstract: Subjecting bruised olives to a nitrogen atmosphere during the postharvest period prevented the oxidation of phenols and subsequent browning. However, a rapid phenol oxidation and browning occurred when fruits were re‐exposed to air. Based on models deduced from the effects of aqueous antioxidant solutions on changes in different color parameters in the fermented product, the treatments to prevent browning were optimized. The recommended procedure consists of placing the harvested olives in a cold (4 to 8 °C) solution of 3% sodium metabisulfite with the pH adjusted to 3.0 (by adding food grade HCl) and applying the lye treatment before 8 h from picking. The use of these conditions led to mechanically harvested Spanish style olives with hardly any visible browning. Practical Application: The procedure developed may be applicable to prevent browning on the bruised areas of manually or mechanically harvested olives. The system is simple, requires low investment, and may lead, in fermented olives, to undetectable differences between undamaged and bruised areas and better ratings in the visual observation of healthy fruits.     

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.     

热处理对荔枝果汁品质的影响

为探讨热处理对荔枝果汁品质的影响,将荔枝原果汁在60～100℃温度下进行热处理,测定果汁的褐变度、pH 值、固形物含量、化学成分(糖分、抗坏血酸、5- 羟甲基糠醛(5-HMF)、总酚)及挥发性风味成分等指标的变化。结果表明：荔枝果汁在0～60min 内褐变度的变化符合零级反应动力学模型。热处理过程中抗坏血酸和总酚含量下降明显,而糖含量变化不大,因此抗坏血酸降解和多酚聚合可能是影响荔枝果汁褐变的主要因素。热处理后荔枝果汁风味出现明显变化,采用顶空固相微萃取- 气相质谱对加热前后风味成分进行分析,发现低级醇和酯类含量明显下降,同时,产生了含硫化合物和高级醇等新物质。     

INHIBITION OF SURFACE BROWNING, CUT AVOCADO

Browning prevention of avocado halves using polyphenol oxidase (PPO) inhibitors along with sulfites was investigated. Browning inhibitiors were selected on the basis of the inhibition of a crude extract of avocado PPO. The most effective inhibitors were ascorbic acid and sodium sulfite, these compounds plus citric acid were mixed to get an inhibitory solution. In vivo experiments were performed on avocado halves by measuring Hunter color values after 15 days' storage to test the potential of solutions to prevent browning. Results showed that immersion in solutions along with refrigerated storage was needed to get an inhibitory effect. Color preservation was not due to oxygen exclusion nor to low pH and sulfite was unnecessary. The best treatment was the storage of avocado halves in a 1% ascorbic acid/1 % citric acid solution at pH 5 and 7C.     

Effect of sonication on orange juice quality parameters during storage

Freshly squeezed orange juice was sonicated at various amplitude levels (40%, 70%, 100%), treatment times (2, 6 and 10 min) at a constant frequency of 20 kHz. Samples were stored for periods of up to 30 days at 10 °C. The combined effect of amplitude level, treatment time and storage period on pH, ^oBrix, titratable acidity, colour values ( L* , a* , b* ), non-enzymatic browning (NEB), cloud value and ascorbic acid content were investigated. Second order polynomial models were employed to investigate the effect of independent variables. No significant differences ( P <  0.05) in ^oBrix and titratable acidity were observed. Significant changes were observed in juice pH and colour values. During storage NEB increased while both cloud value and ascorbic acid content decreased. Predictive models developed for colour values, cloud value, NEB and ascorbic acid content were highly significant and were closely correlated to experimental data. Degradation mechanisms are proposed for the key quality parameters.     

The effect of ascorbic acid on oxidative browning of white wines and model wines

The effects of ascorbic acid addition to white wines and model wines were either anti-oxidative or pro-oxidative, and depended, inter alia , on the duration of storage. Soon after its addition, ascorbic acid decreased the redox potential and brown colour of model wines and white wines. However, with time, these effects were reversed, and redox potential, SO₂ consumption and browning were greater in samples with added ascorbic acid. The point at which the net effect of ascorbic acid addition was to increase browning occurred earlier at higher SO₂ levels. Under a variety of accelerated (45®), or prolonged (ranging from three months to five years) storage conditions, the browning of model wines and white wines was invariably enhanced by ascorbic acid addition, and this enhancement took place whether or not SO₂ was present. The addition of SO₂ alone, rather than ascorbic acid alone or SO₂ plus ascorbic acid, appears to be the most effective and least expensive way of protecting white wine from browning during bottle conservation.     

Polyphenoloxidase Activity, Polyphenols Concentration and Browning Intensity during Soursop (Annona muricata, L.) Maturation

Values for polyphenoloxidase (PPO), total phenols and ascorbic acid, browning intensity and pH in soursops (Annona muricata, L.) decreased during maturation. Optimum pH was 7.5 (fully developed immature, mature unripe and ripe fruits) or 7.0 (fully ripe fruits). High correlation was found between PPO activity and phenolic compounds. The enzymic browning of soursops occurred during maturation. The least browning intensity was in fully ripe fruits.     

果蔬褐变及其影响因素研究进展

果蔬贮藏、加工过程中的褐变包括酶促褐变和非酶褐变(Maillard反应、焦糖化反应、抗坏血酸氧化变色和多酚类氧化缩合)。发生酶促褐变必须具备酚类物质、酚酶和氧3个条件,影响因素有pH、温度和O2等。非酶褐变的影响因素因褐变类型的不同而存在差异。     

Role of anthocyanins,polyphenol oxidase and phenols in lychee pericarp browning

Postharvest browning of lychee fruits is investigated in relation to anthocyanins, polyphenol oxidase (PPO) and phenols, using a purified PPO, anthocyanin extract and phenolic extract. Lychee PPO cannot oxidise the degradation of anthocyanins, but the presence of phenolic extract stimulates pigment degradation by PPO, leading to the development of brown pigments. The absorbance at 410 nm of the reaction solution is correlated well with the peel browning index. Pyrogallol, catechol and 4‐methylcatechol are good stimulators, but no action with chlorogenic acid, p‐cresol, resorcinol or tyrosine is observed. A decrease in the ascorbic acid content of lychee pericarp is associated with an increase in the peel browning index, and the addition of ascorbic acid to the reaction mixture exerts a preventive action on the anthocyanin degradation. Data here suggest that anthocyanins, PPO and phenols contribute to lychee pericarp browning involved in anthocyanin–PPO–phenol reactions. © 2000 Society of Chemical Industry     

Effect of pH on non-enzymatic browning reaction during γ-irradiation processing using sugar and sugar–glycine solutions

Effects of pH on the non-enzymatic browning reaction caused by γ-irradiation processing were investigated. The brown colour development of irradiated sugar–glycine solutions was greater in a buffer system than in deionized distilled water (DDW) with higher pH. Although browning of irradiated sugar solution without glycine was highly increased was in alkaline buffer, no browning was developed in DDW. The maximum browning of the solutions of sugar and sugar–glycine were observed at pH 10 and pH 8, respectively. The browning intensity was in the following order: sucrose ? fructose > glucose. Non-constant pH was observed in DDW (dropped pH between 1.58 and 2.03 units); however, the use of buffers was partially effective in keeping pH constant (pH dropped between 0.03 and 0.56 units). When the irradiated solutions of sugar with and without glycine were analyzed using reverse phase high performance liquid chromatography with diode-array detection (HPLC-DAD), three peaks were separated at 3.37 ± 0.04, 4.60 ± 0.02, and 2.53 ± 0.26 min, and the λ_max values of these peaks were the range 259–288 nm. The sum of the areas of these peaks at 260 nm increased with increasing pH. The results of this study indicated that conditions of the system, such as pH and media, can influence the non-enzymatic browning reaction during γ-irradiation.     

Chemical changes in powdered infant formulas during storage

Hydroxymethylfurfural (HMF), furosine (FUR), lactulose (LU), lysine loss, ascorbic acid and colour (ΔE) were determined in powdered infant formulas stored under nitrogen and oxygen conditions at 20°C and 55°CC during 15, 30 and 90 days. The indicators of the assay at 20°C showed similar behaviour in nitrogen or oxygen atmospheres. Changes in furosine and lysine loss after 90 days occurred under oxygen. Storage at 55°C produced considerable browning. Browning was always greater in nitrogen than in oxygen. Most of the studied parameters increased with the storage time and are useful in controlling the extent of browning in powdered infant formulas under adverse storage conditions.     

Effects of temperature,pH, organic acids,and sulfites on tagatose browning in solutions during processing and storage

Tagatose browning in solutions might be unacceptable to certain products containing tagatose during processing and storage. The objective of this study was to evaluate the effects of temperature, pH, organic acids, and sulfites on tagatose browning in solutions. Tagatose showed the fastest browning reaction, followed by fructose, xylose, glucose, and sucrose. Tagatose browning was temperature and pH dependent. As temperature and pH increased, tagatose browning was increased. Tagatose browning was slow at temperatures lower than 80°C and pH of 5. Organic acids, such as ascorbic acid, citric acid, and lactic acid, activated tagatose browning. Sodium bisulfite and potassium metabisulfite inhibited tagatose browning, whereas sodium sulfite had no effect on the inhibition of tagatose browning. During storage at 25°C, tagatose browning did not occur regardless of the pH, tagatose concentration, and storage time. It was suggested that tagatose browning in solutions might be prevented by controlling the temperature and pH.     

Spanish‐style green table olive shelf‐life

Changes in the physicochemical and sensory characteristics of commercial whole, pitted and stuffed with pepper, garlic or anchovy paste Spanish‐style green table olives of the Gordal, Manzanilla and Hojiblanca cultivars were studied during a three‐year period. No olives developed any spoilage during this period, and at the end of it, all presentations were classified as ‘extra’ according to the sensory evaluation methodology issued by the International Olive Council. Throughout the shelf‐life, surface colour index and firmness of the olives degraded in accordance with a first‐order kinetics, while a gradual browning of the cover brines was observed; however, products added with ascorbic acid maintained a stable colour, while those with calcium content showed reduced firmness degradation. No significant changes in most of the sensory characteristics were observed by the panel test during shelf‐life and only slight changes in firmness, and surface colour were noticed in samples with significant differences in these attributes when measured instrumentally.     

Colour changes of a preparation from red cabbage during storage in a model system

The objective of our research was to determine, using model studies, changes in anthocyanin concentrations in solutions of red cabbage preparation during storage, in relation to pH, time and temperature of storage, oxygen availability, and ascorbic acid concentration. Pigment degradation increased with increasing pH, storage time and temperature. The addition of ascorbic acid and oxygen availability also contributed to the decomposition of anthocyanins. Pigment concentration was affected most by storage time and temperature. However, colour parameters were affected most by pH and the concentration of ascorbic acid.     

A study on the mechanism of browning in mei liqueur using model solutions

Browning mechanisms of mei liqueur were studied using model solutions containing 28% ethanol in 0.1 M citrate solution (pH 3.0). Catechin alone was stable in the model solution but degraded rapidly to form hydroxymethyl furfural (HMF) in incubation with fructose at 70 °C. The rate of increase in the absorbance at 420 nm also suggested that fructose was more potent than glucose in enhancing browning in acidic ethanolic environment. We propose that the major browning mechanisms in mei liqueur are the oxidation and condensation of tannins and the interactions between tannins and HMF derived from fructose, rather than Maillard reaction, ascorbic acid degradation, or caramelization.     

Effect of Amadori rearrangement products on the non-enzymic browning in model systems

The Amadori product was prepared from D-glucose and L-alanine after Hashiba. The browning process was investigated by determining the absorbance at 520 nm, in aqueous solutions at 110 °C for 5–8 h. Because of the limited access of oxygen and its low solubility in the reaction medium, the browning proceeded after zeroth order kinetics with the maximum browning rate at pH = 8–9. The browning rate remained unaffected by additions of sodium sulphite, rutin. propyl gallate (except when present at high levels), iron(III)chloride or copper(II)chloride but decreased in presence of L-cysteine or iron(II)chloride. Hydrogen peroxide bleached the pigment but did not inhibit the subsequent browning of reaction products. Under experimental conditions the solution of Amadori product did not darken with substantially greater rate than the solution of D-glucose and L-alanine. Lower additions of D-glucose to the solution of Amadori product moderately increased the reaction rate while additions of L-alanine or L-hydroxyproline moderately decreased the browning rate.     

Influence of canning process on colour,weight and grade of mushrooms

According to Spanish legislation, some of the quality parameters of canned mushroom (colour, weight and grade) have been studied. Different times of blanching treatment and two brines, with and without ascorbic acid, were used. Blanching had an important effect on the final state of mushrooms, decreasing the losses of weight and grade and improving the colour, which was clear and pleasant. A positive effect of ascorbic acid was observed. The presence of this acid in the brine improves colour stability and acceptance. It inhibited the browning process. The pH of brine plus mushroom is independent of brine composition (with or without ascorbic acid). Longer times of blanching had no significant effects on mushroom quality parameters.     

Examination of the sulfur dioxide–ascorbic acid anti‐oxidant system in a model white wine matrix

The effectiveness of sulfur dioxide in inhibiting the ascorbic acid induced oxidation of (+)‐catechin in a matrix simulating white wine was investigated. At a sulfur dioxide:ascorbic acid mole ratio of 0.8:1.0, sulfur dioxide extended the delay prior to the onset of (+)‐catechin browning as measured by the increase in absorbance at 440 nm from 2 to 4 days post reaction initiation. The lengthening of the pre‐browning period was correlated with an increase in the time required to oxidise ascorbic acid completely, the sequence of events being loss of sulfur dioxide (day 3), loss of ascorbic acid (day 4) and on‐set of (+)‐catechin browning (day 4). Increasing the sulfur dioxide to ascorbic acid mole ratio to 3.0:1.0 inhibited the onset of (+)‐catechin browning over the 14‐day reaction period. This inhibition was achieved at considerable cost to the sulfur dioxide concentration, with the ratio of sulfur dioxide consumed to ascorbic acid oxidised being 1.7 compared with the expected fraction of 1.0. Reasons for the enhanced consumption of sulfur dioxide and the implications of this study for maintenance of quality in white wine production are discussed. Copyright © 2004 Society of Chemical Industry     

Effect of pH on the colour formed by Fe-phenolic complexes in ripe olives

The effects of the pH in the flesh of ripe olives processed for table olive production, the type of acid used to correct it, the heating process used and the iron content of the flesh on the colour of the final product were studied. The best colour was obtained by bottling the fruits at pH 7. Additions of acids, especially citric acid, always caused discoloration when olives were bottled at a pH of around 7. On the other hand, when the fruits were packed at a pH higher than 7 the addition of certain amounts of acids produced darker olives. Darker colours are related to higher iron contents in the flesh, but treatment of olives with ferrous gluconate before neutralising the pH of the flesh yielded better colours than those treated after neutralising for the same iron concentration in the olives. Results obtained after adding iron to the oxidation solutions did not show the same pattern as those obtained using fruits. These results suggest that the fixation of the colour formed is not only due to the phenol-iron complexes.     

Color Degradation in an Ascorbic Acid-Anthocyanin-Flavanol Model System

Interactions between ascorbic acid, pelargonidin-3-glucoside, and catechin were studied in pH 3.4 citrate-phosphate buffer at 20°C under anaerobic and oxygenated conditions. Changes in anthocyanin pigment, ascorbic acid, dehydroascorbic acid, and catechin were quantitatively measured during 130 days storage along with Hunter color parameters, browning, and polymeric color. Ascorbic acid had a statistically significant effect on all parameters, including anthocyanin loss under both oxygen and nitrogen environments, catechin loss, increase in browning and polymeric color, decrease in Hunter “a” value and increase in Hunter L value. Ascorbic acid bleached anthocyanin pigment and also induced browning. There is evidence that anthocyanin pigment and ascorbic acid degrade through a direct condensation mechanism.