Impact of long-term storage at ambient temperatures on the total quality and stability of high-pressure processed tomato juice

High-pressure processing (HPP) can produce tomato juice of high quality and safety with a short shelf life under refrigeration temperatures. Long-term higher temperature storage studies are rare and temperature tolerant products are challenging to develop. The effect of high-pressure processing (HPP) on the total quality (colour, microbial counts, phytochemical levels, antioxidant and enzymatic activities) and stability (retention over time) of tomato juice during long-term storage was investigated. Thermal processing (TP) was used as a control treatment, and overall, two different ambient conditions (20 °C and 28 °C) were tested. Immediately after processing, HPP products proved superior to TP ones (enhanced redness, total carotenoids and lycopene, stable total phenols and inactivation of pectin methyl esterase). During initial storage (30 d) most quality attributes of HPP juice remained stable. Prolonged storage, however, led to losses of most quality attributes, although HPP (20 °C) showed lower quality degradation rate constants comparison to TP and HPP (28 °C).Industrial RelevanceThere is a demand for ambient stable tomato products, especially in some parts of the world, and current industrial practices (canning, pasteurisation) either compromise in product quality or require refrigeration conditions. High-pressure processing has been investigated as milder technology, with a potential to deliver superior quality. The drawback is that is also requires chill storage. The results of this study show how quality parameters behave in a high-pressured tomato product and pave the way for further development that could optimise this technology. This could be of economic importance for the tomato juice industry to develop new products stable in ambient temperatures and perhaps beneficial for cutting down the refrigeration costs under specific conditions.     

Comparison of thermal,ultraviolet-c,and high pressure treatments on quality parameters of watermelon juice

The effect of thermal, ultraviolet-c, and high pressure treatments on colour, browning degree, dynamic viscosity, and lycopene content of watermelon juice was evaluated based on its pectin methylesterase residual level. Each treatment had a different impact on parameters studied. Ultraviolet-c treatments were rapid and effective to inactivate the pectin methylesterase of the watermelon juice compared to the thermal and high pressure treatments in the same time and temperature. High pressure treatments at 600 MPa kept the colour of the treated watermelon juice close to an untreated one, and that at 600–900 MPa held the browning degree and dynamic viscosity of the treated watermelon juice comparable to an untreated one. Moreover, the high pressure treatment had a slight impact on the all-trans-lycopene, total cis-lycopene, and total lycopene concentration of the watermelon juice compared to the other treatments. In summary, the high pressure treatment showed the lowest changes in colour, dynamic viscosity, browning degree, and lycopene content of the treated watermelon juice amongst the three treatments.     

Effect of combined treatments of high-pressure,citric acid and sodium chloride on quality parameters of tomato puree

Tomato puree was subjected to combined treatments of high hydrostatic pressure and natural additives [citric acid and sodium chloride (NaCl)]. Their effects on the most important quality parameters of tomato puree as colour and viscosity, and biochemical parameters as enzymatic activities (polyphenoloxidase, peroxidase, and pectin methylesterase) and total protein content, and microorganisms (total microbial counts and yeasts and moulds) were studied. Response surface methodology was employed where the experiment was carried out according to a central composite face-centred design. The variables ranges used were: 50–400 MPa (pressure), 0–0.8% w/w (concentration of NaCl) and 0–2% w/w (concentration of citric acid) while temperature and holding time of high pressure treatments were constants at 25 °C and 15 min respectively. The results showed that enzymatic inactivation was significantly improved with these combined treatments at high values of pressure and concentration of additives. A very significant reduction of 4 logarithmic units was observed when pressure was increased to 400 MPa for total microbial counts. Thus, combined "hurdles" may be effective to produce minimally processed tomato products with optimal sensorial and microbiological characteristics.     

High pressure versus heat treatments for pasteurisation and sterilisation of model emulsions

Heat treatments can have considerable influence on the droplet size distribution of oil-in-water emulsions. In the present study, high-pressure (HP) pasteurisation and sterilisation were evaluated as alternatives for heat preservation of emulsions. HP conditions used were 600 MPa, 5 min, room temperature and 800 MPa, 5 min, 80 °C initial temperature, 115 °C maximum temperature for HP pasteurisation and HP sterilisation respectively. The effects on droplet size of these conditions were compared to heat treatments for whey protein isolate (WPI) and soy protein isolate (SPI) emulsions at two pH values and two ionic strengths. For WPI, also the effect of protein in the bulk phase was evaluated.Both HP and heat pasteurisation treatments resulted in similar or slightly decreased average droplet sizes compared to the untreated samples. For neutral SPI emulsions, heat sterilisation increased the average droplet size from 1.6 μm to 43.7 μm, while HP sterilisation resulted only in a small increase towards an average droplet size of 2.1 μm. The neutral WPI emulsions, except those with a high ionic strength, gave similar results with respect to the droplet size, showing that for neutral pH WPI or SPI emulsions HP sterilisation is preferable above heat sterilisation. Concerning the low pH WPI emulsions, the droplet sizes were unaffected after both heat and HP sterilisation.Industrial relevanceHeat pasteurisation and sterilisation are effective treatments to preserve food products that are based on emulsions with respect to microbial safety. However, heat treatments can negatively affect emulsion stability. Currently, in addition to high pressure at room temperature, high-pressure treatments at elevated temperature received a great deal of interest to achieve sterilised products. This study evaluated the effects of both heat and high-pressure pasteurisation and sterilisation on droplet size of whey protein isolate and soy protein isolate emulsions. It was shown that for pasteurisation treatments, both heat and high pressure have minor effects on the droplet size of the emulsion. However, for sterilisation purposes high-pressure treatment is preferable for emulsion at neutral pH. High-pressure sterilisation can therefore be interesting alternatives to heat treatments to preserve emulsion stability.     

Evaluation of processing qualities of tomato juice induced by thermal and pressure processing

Effects of processing conditions including hot-break processing (92 °C for 2 min), cold-break processing (60 °C for 2 min) and hydrostatic pressure treatments (100-500 MPa) at different temperatures (4, 25 and 50 °C) for 10 min on quality aspects of tomato juice were investigated. Both hot- and cold-break processing induced significant changes in color, viscosity and radical-scavenging capacity of tomato juice compared with control (fresh tomato juice); moreover, hot-break processing induced a specific range of reduction of pectin methylesterase (PME) and polygalacturonase (PG) activities. Pressure treatments at and below 200 MPa at 4 and 25 °C maintained the color, extractable total carotenoids and lycopene, and radical-scavenging capacity; further, those at 500 MPa at 4 and 25 °C improved all the quality attributes the most except inactivation of PME in this study. The residual activity of PME showed the lowest after treating by 200 MPa at 25 °C; however, the PME activity was enhanced by treatments at 300-500 MPa and various temperatures. The residual activity of PG decreased gradually to 72% with pressure elevated from 100 to 400 MPa at 4 and 25 °C, further, that declined quickly to 10% after 500 MPa treatments. This research clearly shows that it is possible to selectively produce good tomato juice products by high pressure processing at ambient temperature.     

In vitro oral processing of raw tomato: Novel insights into the role of endogenous fruit enzymes

During consumption of fruits, the breakdown of the fruit tissue due to oral processing (chewing, mixing with saliva) may activate or increase the rate of endogenous enzyme activities via the disruption of the cell wall, cellular decompartmentalization, and particle size reduction allowing the enzymes to reach their substrates. The aim of this study was to investigate the activity of one such endogenous fruit enzyme (pectin methylesterase [PME] [E.C. 3.1.1.11]) during in vitro oral processing of raw tomatoes and associated changes in viscosity and microstructure. Oral processing of tomatoes purees was examined in the presence of artificial saliva (AS) at 37°C. in vitro oral processing was followed using immunofluorescence microscopy, apparent viscosity measurements, spectrophotometric, and titrimetric techniques. The results demonstrated that PME had slight but significant activity in the tomato fruit during in vitro oral processing generating methanol as a function of oral processing time, which was further evidenced using immunolabeling techniques to detect methylated pectin epitopes. A significant shear‐thinning behavior of the tomato puree was observed due to dilution and/or endogenous fruit enzyme activity. These results suggest that activity of other fruit enzymes, such as polygalacturonase, which catalyzed the depolymerization of unmethylated pectin chains, might have resulted in a decrease in viscosity, which compensated for the increased potential for gel formation (if any) caused by PME. These interesting insights into the role of endogenous fruit enzymes might pave the way to the understanding of fruit viscosity modification occurring in the mouth and help in rational design of new fruit‐based products.     

Comparison of high pressure treatment and thermal pasteurization effects on the quality and shelf life of guava puree

The effects of high pressures and thermal pasteurization on the survival of microorganisms, enzyme inactivation and quality changes of guava puree during storage at 4°C were investigated and compared with untreated samples. After treatment at a pressure of 600MPa and 25°C for 15 min, the microorganisms in guava puree were inactivated to less than 10 cfu mL⁻¹ and the product exhibited no change in colour, pectin, cloud and ascorbic acid content as compared with fresh samples. The inactivation of enzymes in guava puree by thermal pasteurization was greater than by high pressures. The microbial count in guava puree reduced to 200 cfu mL⁻¹ and the product showed marked changes in viscosity, turbidity and colour when heated at 88–90°C for 24s. The content of pectin, cloud and ascorbic acid as well as colour in untreated and high pressurized (400MPa) guava puree gradually decreased, whereas these changes were not observed in pasteurized (88–90°C) and high pressurized (6000MPa) puree during storage at 4°C for 60 days. The guava puree treated at 600MPa and 25°C for 15 min retained good quality similar to the freshly extracted puree after storage at 4°C for 40 days.     

Comparative study on color,viscosity and related enzymes of tomato juice treated by high-intensity pulsed electric fields or heat

The effects of high intensity pulsed electric fields (HIPEF) processing (35 kV/cm for 1,500 μs using bipolar 4-μs pulses at 100 Hz) on color parameters and viscosity, as well as peroxidase (POD), pectin methylesterase (PME) and polygalacturonase (PG), were evaluated during 77 days of storage at 4 °C and compared to thermal treatments at 90 °C for 1 min or 30 s for unprocessed tomato juice. HIPEF-treated tomato juice showed higher values of lightness than the thermally processed and the untreated juice throughout storage time (P < 0.05). Viscosity of HIPEF-treated tomato juice was also greater than both thermally treated and untreated for the first 35 days of storage. POD of HIPEF-treated tomato juice was inactivated by 97% whereas in the case of the thermally treated, 90 and 79% inactivation was achieved after 1 min and 30 s, respectively. The highest PME inactivation in tomato juice was obtained by PEF (82%) and heat treatment at 90 °C for 1 min (96%). PG of PEF-treated tomato juice was inactivated by 12% whereas thermal treatments at 90 °C for 1 min or 30 s achieved 44 and 22%, respectively. Despite the low rates of PG inactivation obtained, the pattern followed in the residual activity along the storage time was similar in the tomato juice treated by HIPEF than the thermally processed.     

Flavour characterisation of fresh and processed pennywort (Centella asiatica L.) juices

The flavour characteristics of fresh and processed pennywort juices treated by pasteurisation, sterilisation and high pressure processing (HPP) were investigated by using solid-phase micro-extraction combined with gas chromatography–mass spectrometry. Sesquiterpene hydrocarbons comprise the major class of volatile components present and the juices had a characteristic smell due to the presence of volatile compounds including β-caryophyllene, humulene, E-β-farnesene, α-copaene, alloaromadendrene and β-elemene. All processing operations caused a reduction in the total volatile concentration, but HPP caused more volatile acyclic alcohols, aldehydes and oxygenated monoterpenoids to be retained than pasteurisation and sterilisation. Ketones were not present in fresh pennywort juice, but 2-butanone and 3-nonen-2-one were generated in all processed juices, and 2-nonanone and 2-hexanone were present in pasteurised and sterilised juices. Other chemical changes including isomerisation were also reduced by HPP compared to pasteurisation and sterilisation.     

Impact of Thermal and Pressure-Based Technologies on Carotenoid Retention and Quality Attributes in Tomato Juice

The aim of this study was to investigate the impact of thermal processing (TP) (90 °C, 90 s), high-pressure processing (HPP) (600 MPa, 46 °C, 5 min), and high-pressure homogenization (HPH) (246 MPa, 99 °C, <1 s) on product quality parameters, specifically carotenoid content, and physicochemical attributes of particle size, color, viscosity, total soluble solids, and pH in tomato juice. Unprocessed tomato juice was used as control. The four major species of carotenoids (lycopene, β-carotene, phytoene, and phytofluene) in tomato juice were analyzed by HPLC. The content of total lycopene, all-trans-lycopene, cis-lycopene isomers,  phytoene, and phytofluene, in TP-, HPP-, and HPH-treated tomato juice did not significantly differ from that in unprocessed (control) juice. Significant reduction in β-carotene content was observed after TP treatment but not after HPP and HPH treatments. HPH significantly reduced tomato juice particle volume mean diameter from ～330 μm in control, HPP-, and TP-treated tomato juices to ～17 μm. A concomitant increase in apparent viscosity was observed in HPH-treated juice versus control. HPH-treated juice had increased redness (a*) and yellowness (b*) than that in control and HPP-treated tomato juices. These results indicate that high-pressure-based technologies (HPP and HPH) can preserve carotenoids as well as improve physicochemical properties.     

Inactivation kinetics of polygalacturonase in tomato juice

The inactivation kinetics of polygalacturonase (PG) in tomato juice was studied during thermal and high-pressure/thermal processing. In the temperature range of 55–70 °C the thermal inactivation of polygalacturonase in tomato juice followed a fractional conversion model, with a thermostable fraction of approximately 14%. Under conditions of combined high-pressure/thermal processing, 200–550 MPa/5–50 °C, PG inactivation presented first order kinetics. A mathematical model to describe the inactivation rate constant as a function of pressure and temperature was formulated. Industrial relevance: Polygalacturonase is responsible for the decrease of viscosity in tomato-based products. However, little research on thermal and high pressure/thermal inactivation kinetics of tomato Polygalacturonase has been reported. This research clearly shows that it is possible to selectively inactivate PG by high pressure/thermal processing without applying high temperatures. This leads to tomato-based products with improved functional properties while other quality attributes (color, flavor, nutritional value) are maintained.     

Process stability of Capsicum annuum pectin methylesterase in model systems, pepper puree and intact pepper tissue

Process stability studies towards temperature and/or pressure on pepper pectin methylesterase (PME) were carried out in different systems (purified form, crude extract, pepper pieces and puree) at pH 5.6. Within the temperature range studied (22–80 °C, 5 min), pepper PME in pure form and crude extract was gradually inactivated showing a biphasic inactivation behaviour, indicating the presence of isoenzymes of different thermostability. Pepper samples heated for 15 min showed a maximum of residual PME activity around 55 °C. Isothermal inactivation of pepper PME in purified form and crude extract at pH 5.6 could be described by a biphasic inactivation model for the temperature range studied (62–76 °C). A stable behaviour towards high-pressure/temperature treatments (400–800 MPa/25–60 °C) was observed for crude extract and purified pepper PME. PME in pepper puree samples revealed to be very pressure stable. Mild temperatures combined with pressure treatments seem to increase the extractability from PME in pepper tissue, probably due to the effect on the cell structure.     

Unravelling process-induced pectin changes in the tomato cell wall: An integrated approach

The activity of the pectin-modifying enzymes pectin-methylesterase (PME) and polygalacturonase (PG) in tomato fruit was tailored by processing. Tomatoes were either not pretreated, high-temperature blanched (inactivation of both PME and PG), or high-pressure pretreated (selective inactivation of PG). Subsequently, two types of mechanical disruption, blending or high-pressure homogenisation, were applied to create tomato tissue particle suspensions with varying degrees of tissue disintegration. Process-induced pectin changes and their role in cell-cell adhesion were investigated through in situ pectin visualisation using anti-pectin antibodies. Microscopic results were supported with a (limited) physicochemical analysis of fractionated walls and isolated polymers. It was revealed that in intact tomato fruit pectin de-esterification is endogenously regulated by physical restriction of PME activity in the cell wall matrix. In disintegrated tomato tissue on the other hand, intensive de-esterification of pectin by the activity of PME occurred throughout the entire cell wall. PG was selectively inactivated (i.e. in high-pressure pretreated tomatoes), with de-esterification of pectin by PME, which resulted in a high level of Ca²⁺-cross-linked pectin and a strong intercellular adhesion. In non-pretreated tomato suspensions on the other hand, combined PME and PG activity presumably led to pectin depolymerisation and, hence, reduced intercellular adhesion. However, because of the high amount of Ca²⁺-cross-linked pectin in these samples, cell-cell adhesion was still stronger than in the high-temperature blanched tomatoes, in which the absence of PME activity during suspension preparation implied few Ca²⁺-cross-linked pectic polymers and extensive cell separation upon tissue disruption.     

The kinetics of inactivation of pectin methylesterase and polygalacturonase in tomato juice by thermosonication

The ultrasonic inactivation kinetics of polygalacturonase (PG) and pectin methylesterase (PME) in tomato juice were studied at a frequency of 20 kHz, amplitude of 65 μm and temperatures between 50 and 75 °C. Thermal treatments at the same temperatures were conducted to separate the effects of heat and ultrasound. The thermal inactivation of PG was described by a fractional conversion model with PG 1 remaining stable, whereas the inactivation of PG by combined ultrasonic and heat treatment (thermosonication) was best described by first order biphasic kinetics, with both PG1 and PG2 inactivated at different rates. The thermal and thermosonication inactivation of PME was described well by first order kinetics. The inactivating effect of combined ultrasound and heat was synergistic. Thermosonication enhanced the inactivation rates of both PME and PG. The inactivation rate of PME was increased by 1.5–6 times and the inactivation rate of PG2 by 2.3–4 times in the temperature range 60–75 °C, with the highest increase corresponding to the lowest temperature.     

Effect of pilot-scale aseptic processing on tomato soup quality parameters

Tomatoes are often processed into shelf-stable products. However, the different processing steps might have an impact on the product quality. In this study, a model tomato soup was prepared and the impact of pilot-scale aseptic processing, including heat treatment and high-pressure homogenization, on some selected quality parameters was evaluated. The vitamin C content, the lycopene isomer content, and the lycopene bioaccessibility were considered as health-promoting attributes. As a structural characteristic, the viscosity of the tomato soup was investigated. A tomato soup without oil as well as a tomato soup containing 5% olive oil were evaluated. Thermal processing had a negative effect on the vitamin C content, while lycopene degradation was limited. For both compounds, high-pressure homogenization caused additional losses. High-pressure homogenization also resulted in a higher viscosity that was accompanied by a decrease in lycopene bioaccessibility. The presence of lipids clearly enhanced the lycopene isomerization susceptibility and improved the bioaccessibility. PRACTICAL APPLICATION: The results obtained in this study are of relevance for product formulation and process design of tomato-based food products.     

Effect of high-pressure processing on Listeria spp. and on the textural and microstructural properties of cold smoked salmon

Investigation of the effect of high-pressure processing (HPP) at very short time on the inactivation of Listeria innocua was conducted as well as the effect on texture and microstructure. Lipid oxidation, colour and background bacterial flora were studied as well. HPP at 700-900 MPa for 10 s increased the inactivation of L. innocua in cold smoked salmon from 4500 cfu/g to nondetectable level (<0.3 cfu/g). L. innocua was more sensitive to HPP than the background flora tested. The product presented good microbiological quality and there was no indication of lipid oxidation. The effect of HPP on the redness of the product was not observed, however immediate effect on the lightness was noticed and the salmon becomes lighter in colour as a function of both time and pressure. The effects on the microstructure increased with both time and pressure and were most significant at 900 MPa and 60 s. The effect on microstructure coincides with the reduction of the bacteria. The knowledge from this study provides information for the industry on the development of HPP at 400-900 MPa with short pressure time of less than 60 s.     

Enzyme inactivation of tomato juice by ohmic heating and its effects on physico‐chemical characteristics of concentrated tomato paste

Fresh juice of fully ripe tomato was subjected to ohmic heat (OH) treatment (90°C for 1 min) and the effectiveness of treatment was compared with conventional hot break (CT) treatment (90°C for 5 min). PG (Polygalacturonase) and PME (Pectin methyl esterase) enzyme inactivation achieved by the OH (1 min.) was similar as compared to CT of 5 min. During the kinetic analysis it was observed that the inactivation of PME & PG enzyme and degradation of ascorbic acid followed first order trend in ohmic as well as conventional treatment of tomato juice, however total color change (DE) was found to follow least‐squares non‐linear parameter algorithm behavior. Thermal treatments leads to the increased release of phyto‐chemicals from the matrix which results in a significant (p<0.01) increase in lycopene content during the early phases of the treatments. The Paste (28±0.5 °Brix) obtained after pre‐treatment was analyzed for lycopene, ascorbic acid content and apparent viscosity and color. OH Paste was found more viscous than CT treatment with maximum viscosity of 2.33×103 mPa‐s. The color of OH treated paste was bright red as compared to CT treatment, however the lycopene and ascorbic acid content of paste were found similar in OH and CT. Based on results of present study it is concluded that the ohmic treatment may be applied as an efficient alternative to the conventional method of enzyme inactivation in tomato juice.     

Effects of pre‐freezing,puree content and pasteurisation regime on colour stability of strawberry nectar made from puree

BACKGROUND: Heat treatment during processing of strawberry products has been proposed to negatively affect colour stability. Moreover, the role of enzymes with respect to colour stability is ambiguous when consulting the existing literature. The aim of the present study was to investigate the impact of various processing parameters (pre‐freezing, puree content, pasteurisation temperature and heating time) on the colour stability and anthocyanin monomer and L ‐ascorbic acid contents of strawberry nectars made from puree. In addition, the effect of different enzyme activities on colour stability during storage of strawberry nectars was investigated. RESULTS: Pre‐freezing of strawberries before processing had a significant positive effect on the colour stability of nectars made from puree. No significant effect on colour stability was found for higher puree contents. Increasing both the pasteurisation temperature and the heating time had a significant positive effect on colour stability. Results showed that colour degradation during storage was mainly due to residual enzyme activities. The shelf‐life of strawberry nectar could be extended about fivefold by adding an enzyme inhibitor. CONCLUSION: The colour stability of strawberry nectar made from fresh puree may be improved to some extent by an appropriate pasteurisation regime. Enzymes play an important role in colour degradation during storage of the nectar. Inactivation of these enzyme activities, however, could not be achieved even after a heat treatment at 90 °C for 60 min. Copyright © 2008 Society of Chemical Industry     

Effect of combined treatments of high-pressure and natural additives on carotenoid extractability and antioxidant activity of tomato puree (<Emphasis Type="Italic">Lycopersicum esculentum</Emphasis> Mill.)

High-pressure is a new food processing technology aimed at achieving consumer demands for fresher products with reduced microbiological levels. The objective of this work was to evaluate the effect of combined treatments of high-pressure and natural additives (citric acid and sodium chloride) on lutein, lycopene, lycopene epoxide, - and -carotene content, and vitamin A value, and on the in vitro antioxidant activity of tomato puree. The methods used to evaluate the antioxidant activity were the measurement of the DPPH· radical scavenging and the inhibition of lipid oxidation (linoleic acid/CuSO₄ system). The experimental design comprised a response surface methodology according to a central composite face-centred design. The variable ranges were 50–400 MPa, sodium chloride 0–0.8%, and citric acid 0–2%. Total carotenoid content showed the best extraction when pressure was increased up to 400 MPa without sodium chloride and citric acid. The effect of the moderately high-pressure treatment (under 200 MPa) on the structure of the cellular tomato matrix may lead to the different release of various carotenes on the basis of their chemical features and chromoplast location. Radical scavenging activity was higher in the aqueous extract than the organic extract of tomato puree. Significant correlation (P<0.05) was found between the total carotenoid content and the radical scavenging activity and inhibition of lipid oxidation by the organic extract of tomato puree. In conclusion, applying the highest range of pressures (without additives) increased the carotenoid extractability. Further human studies are needed to clarify the effect of high-pressure treatment on the bioavailability of tomato puree constituents.     

Impact of exogenous salicylic acid treatment on the cell wall metabolism and ripening process in postharvest tomato fruit stored at ambient temperature

Tomato is a climacteric fruit susceptible to rapid softening and ripening after harvest. In this study, the changes of physicochemical characters, cell wall-degrading enzymes, cell wall compositions and ethylene production of ‘Hisar Arun’ and ‘BSS-488’ tomato fruits were investigated under the influence of salicylic acid treatment. Salicylic acid treatment effectively delayed firmness decline and increase in PLW, TSS and lycopene content. The treated fruits maintained the integrity of cell wall composition by delay in increase in activities of cell wall-degrading enzymes (pectin methylesterase, polygalacturonase and cellulose) and cell wall components (cellulose, hemicellulose, lignin and pectin) decline. Moreover, salicylic acid treatments significantly suppress expression level of ethylene-producing genes (ACO1 and ACS2) and inhibited ethylene production during storage. Overall, the salicylic acid-induced delay in the ripening process occurs via the strong inhibition of ethylene biosynthesis, lowered cell wall-degrading enzyme activities and slowed cell wall degradation.