Effect of pH on Enzyme Inactivation Kinetics in High-Pressure Processed Pineapple (Ananas comosus L.) Puree Using Response Surface Methodology

Effect of pH and high-pressure process treatments viz. pressure, temperature, and dwell time on inactivation of polyphenoloxidase (PPO), peroxidase (POD), bromelain (BRM), and pectinmethylesterase (PME) in pineapple puree was studied. Experiments were conducted according to rotatable central composite design (RCCD) within the range (?α to?+?α) of 100–600 MPa, 20–70 °C, and 0–30 min at three different pH levels (3.0, 3.5, and 4.0) followed by analysis through response surface methodology (RSM). Enzyme inactivation was significantly (p?k in min^?1) revealed that PPO was the most resistive (k ranged between 0.0020 and 0.0379 min^?1) when compared with other three enzymes within the experimental domain. Increased k at lower pH with constant pressure and temperature depicted that pH had negative effect on the inactivation process. The optimized conditions targeting maximum inactivation of PPO, POD and PME with simultaneous retention of BRM in pineapple puree, were 600 MPa/60 °C/9 min, 600 MPa/60 °C/10 min and 600 MPa/60 °C/10 min for the samples of pH 3.0, 3.5, and 4.0, respectively.     

Changes in Quality Attributes During Storage of High-Pressure and Thermally Processed Pineapple Puree

The primary issue of the pineapple puree processing industry is its limited stability. The study compares the quality changes in high-pressure and thermally processed pineapple puree at different storage conditions and estimates the shelf-life. The untreated (S1) and treated samples (S2, S3, and S4 treated at 600 MPa/50 °C/13 min, 600 MPa/70 °C/20 min, and 0.1 MPa/95 °C/12 min, respectively) packed in ethylene vinyl alcohol (EVOH) and multi-layered (ML) polyethylene terephthalate (PET) pouches were stored up to 125 days at 5, 15, and 25 °C. The total color change (?E*) and browning index during storage increased according to zero-order kinetic model, whereas ascorbic acid (AA), total phenolics, and total antioxidant capacity followed the first-order decay. The overall sensory acceptability (OA) of S2 was higher than both S3 and S4 at 5 °C, and it dropped rapidly at 15 and 25 °C. The activity of polyphenol oxidase and pectin methylesterase in S3 and S4 was less than 10 % up to 120 days at 5 °C. The consistency (κ) and residual enzyme activity in S2 decreased with storage duration and temperatures. For estimating the shelf-life, the change in OA was crucial for S2 and S3, whereas retention of AA served as the critical parameter for S4. The sample S2 packed in ML pouch was found to be the best sample having the shelf-life (microbial count?<?6-Log cfu g^?1, ?E*?<?12, OA?>?5, and AA?>?200 mg kg^?1) of 120, 50, and 25 days at 5, 15, and 25 °C, respectively.     

Selection of Process Conditions for High Pressure Pasteurization of Sea Buckthorn Juice Retaining High Antioxidant Activity

Sea buckthorn berries juice is a nutritious beverage, rich in vitamin C and carotenoids with high antioxidant activity. The main requirements for a freshly squeezed sea buckthorn juice production are the cloud stability and antioxidant activity retention after processing. Appropriate process technologies and conditions have to be applied in order to inactivate pectin methyl esterase (PME), responsible for cloud loss, while maintaining the nutritional characteristics and antioxidant activity of the juice. The objectives of the present work were to study and model the effect of thermal treatment and high pressure (HP) processing on the inactivation kinetics of endogenous PME and on total antioxidant activity alteration. Thermal treatment significantly affected PME inactivation and residual antioxidant activity. Processing even at mild process conditions (60 °C for 1 min) resulted in 2.5-fold antioxidant activity reduction and 50 % PME inactivation compared to untreated sample. Pressure and temperature acted synergistically for PME inactivation that followed first-order kinetics with a residual PME activity at all pressure–temperature combinations used (200–600 MPa and 25–35 °C). The effect of temperature and pressure on the inactivation rate constants was expressed through the activation energy and activation volume, respectively. Values of 163 kJ/mol and ?17 mL/mol at reference pressure of 600 MPa and reference temperature of 35 °C were estimated, respectively. Antioxidant activity of the samples was expressed through the determination of the effective concentration (EC₅₀). A slight increase in sea buckthorn antioxidant activity when applying pressures (200–600 MPa) at ambient temperature (25 °C) was observed compared to the corresponding value of untreated juice. Processing at higher temperatures did not significantly alter the total antioxidant activity of sea buckthorn juice. For sample treated at 600 MPa–35 °C for 5 min, a 5 % reduction of total antioxidant activity was observed. These conditions are proposed as effective process conditions for sea buckthorn juice cold pasteurization, based on the higher antioxidant activity retention and simultaneous PME inactivation.     

Changes in selected quality characteristics of minimally processed carambola (Averrhoa carambola L.) when treated with ascorbic acid

‘B 10’ carambola of ripening stage (RS) 3 and 4 were minimally processed (MP) and then dipped in 0, 15 and 30 mg L^?1 ascorbic acid (AA). The 1‐cm‐thick slices were then dried, packed into cling‐wrapped‐foam tray and stored at 7 °C for 0, 3 and 5 days. Skin colour (L*, C* and h°), flesh firmness, soluble solids concentration, vitamin C content, titratable acidity, pH, degree of browning, polyphenoloxidase (PPO) activity and sensory attributes of MP carambola treated with AA were determined. AA treatment had significant effect in decreasing cut surface browning degree but no significant effect on all the selected quality characteristics of the MP carambola. In the sensory evaluation, flesh colour, sweetness, flavour and overall taste were significantly affected by AA treatment especially at 15 mg L^?1. The RS of fruit significantly affected skin colour (C* and h°), pH and sensory attributes of colour and flavour of the MP carambola. As storage day (SD) progressed, skin colour (C* and h°), flesh firmness and vitamin C content, cut surface browning, PPO activity and all the sensory attributes of MP carambola decreased significantly. Flesh firmness of the MP carambola was affected by the interaction between AA × SD. Sensory attributes of MP carambola were affected significantly by AA × RS. All the sensory attributes of MP carambola positively correlated to each other but negatively correlated with browning degree. PPO activity positively correlated with browning degree. Copyright © 2007 Society of Chemical Industry     

Effect of high-pressure processing on flavonoids,hydroxycinnamic acids,dihydrochalcones and antioxidant activity of apple ‘Golden Delicious’ from different geographical origin

The influence of high-pressure processing (HPP) (400, 500 and 600 MPa at 35 °C for 5 min) on different classes of phenolic compounds and antioxidant activity (AA) of ‘Golden Delicious’ apple from two different growing regions, northeastern of Spain (lowland climate) (S-apples) and north of Italy (mid-mountain climate) (I-apples) was investigated. Total hydroxycinnamic acids, total dihydrochalcones and total flavan-3-ols content were higher in S-apple (untreated and HPP-treated) than in I-apples and total flavonols content was higher in I-apples. HPP affected phenolic compounds and AA depending on the apple geographical origin. 400 MPa/35 °C/5 min increased total flavonols (30%) and maintained total phenolic compounds determined by HPLC (TP-HPLC) in S-apples. The higher increase of TP-HPLC (54%) was achieved when I-apple was treated at 600 MPa. Untreated and HPP-treated I-apples displayed higher AA than S-apples. HPP (400 and 600 MPa) increased AA in I-apple. Positive correlations were found between TP-HPLC and AA (TP-FC, DPPH^·, ABTS^·+ and FRAP) in both Italian and Spanish apples.Industrial relevanceThe apples of cultivar ‘Golden Delicious’ are one of the most consumed fruits in the UE. High-pressure processing (HPP) of these fruits acquires great importance to obtain ingredients and apple functional foods highly demanded by consumers. For this, it is necessary to know the process variables and plant material that favor greater extraction of phenolic compounds and antioxidant activity characteristics. This paper provides useful results to help fruit processor to select the appropriate HPP conditions and the geographical origin of ‘Golden Delicious’ apple to obtain apple-based products with high content on different classes of phenolic compounds with beneficial health effects.     

High pressure processing of cocoyam,Peruvian carrot and sweet potato: Effect on oxidative enzymes and impact in the tuber color

High pressure processing (HPP) is a non-thermal technology used to activate or inactivate enzymes. This study investigated the effects of HPP (600 MPa for 5 or 30 min at 25 °C) on cocoyam, Peruvian carrot and sweet potato color, and the polyphenoloxidase (PPO) and peroxidase (POD) activities in tuber cubes, puree, and enzyme extract subjected to HPP. The results showed enzyme inactivation by HPP in cocoyam (up to 55% PPO inactivation in puree and 81% POD inactivation in extract) and Peruvian carrot (up to 100% PPO and 57% POD inactivation the extract). In contrast, enzyme activation was observed in sweet potato (up to 368% PPO and 27% POD activation in puree). The color results were compatible to enzyme activity: the color parameters remained unchanged in cocoyam and Peruvian carrot, which showed high PPO and POD inactivation after HPP. Furthermore, the impact of HPP on the enzymes was influenced by the matrix in which HPP was carried out, evidencing that the enzyme structure can be protected in the presence of other food constituents.Industrial relevanceThe enzymes PPO and POD are an important concern for vegetable processing, due its ability to induce browning after vegetables are cut. The HPP at 600 MPa for 5 or 30 min can be used to inactivate these enzymes in cocoyam and Peruvian carrot, guaranteeing the color and freshness of the tubers similar to the fresh cut vegetable.     

Polyphenoloxidase Activity and Color of Blanched and High Hydrostatic Pressure Treated Banana Puree

The effects of blanching and high hydrostatic pressure (HHP) treatments on natural flora evolution, polyphenoloxidase (PPO) activity and color of banana puree adjusted to pH 3.4 and water activity (a_w) of 0.97 were evaluated during 15 days storage at 25°C. Standard plate as well as yeast and mold counts of HHP treated purees were <10 CFU/g throughout storage. Blanching time was found to affect (P<0.05) puree color. HHP treatments retained the initial color of the banana purees. Longer browning induction times and slower browning rates were observed when a longer blanching time was combined with a 689 MPa pressure treatment. A residual PPO activity < 5% was observed in the puree when a 7 min blanch was followed by HHP treatment at 689 MPa for 10 min.     

Effects of High‐Hydrostatic Pressure on Inactivation of Human Norovirus and Physical and Sensory Characteristics of Oysters

The purpose of the study was to determine the effect of high‐hydrostatic pressure (HHP) on inactivation of human norovirus (HuNoV) in oysters and to evaluate organoleptic characteristics of oysters treated at pressure levels required for HuNoV inactivation. Genogroup I.1 (GI.1) or Genogroup II.4 (GII.4) HuNoV was inoculated into oysters and treated at 300 to 600 MPa at 25 and 0 °C for 2 min. After HHP, viral particles were extracted by porcine gastric mucin‐conjugated magnetic beads (PGM‐MBs) and viral RNA was quantified by real‐time RT‐PCR. Lower initial temperature (0 °C) significantly enhanced HHP inactivation of HuNoV compared to ambient temperature (25 °C; P < 0.05). HHP at 350 and 500 MPa at 0 °C could achieve more than 4 log₁₀ reduction of GII.4 and GI.1 HuNoV in oysters, respectively. HHP treatments did not significantly change color or texture of oyster tissue. A 1‐ to 5‐scale hedonic sensory evaluation on appearance, aroma, color, and overall acceptability showed that pressure‐treated oysters received significantly higher quality scores than the untreated control (P < 0.05). Elevated pressure levels at 450 and 500 MPa did not significantly affect scores compared to 300 MPa at 0 °C, indicating increasing pressure level did not affect sensory acceptability of oysters. Oysters treated at 0 °C had slightly lower acceptability than the group treated at room temperature on day 1 (P < 0.05), but after 1 wk storage, no significant difference in sensory attributes and consumer desirability was observed (P > 0.05).     

EFFECT OF pH AND ASCORBIC ACID ON HIGH HYDROSTATIC PRESSURE-PROCESSED MANGO PUREE

Mango puree containing ascorbic acid (AA) (500 ppm) standardized at low pH (3.5) with phosphoric acid and inoculated or noninoculated with Saccharomyces cerevisiae was treated at high pressure (207, 345, 483 and 552 MPa) for selected times. High hydrostatic pressure (HHP)‐processed (552 MPa/5 min) standardized mango puree (SMP) was stored at 3C for 1 month and periodically analyzed for color, residual polyphenoloxidase (PPO) activity and microbial load. The remaining PPO activity average in SMP, after HHP processing at 207, 345, 483 and 552 MPa, at all times, was 35.8 ± 6, 21.5 ± 13.2, 46.8 ± 53.2 and 61.8 ± 5.8% PPO activity units, respectively. The D₂₀₇ values of 8.5 and 7.2 min for total count and yeasts were observed, respectively, after 207 MPa of pressure. A log reduction of 1.62 and 1.35 was observed after applying 345 MPa of pressure (2 s) for total count and yeasts, respectively. However, no microbial growth (<10 cfu/g) was observed after applying 483 or 552 MPa at any time. The addition of AA and the standardization at pH 3.5 reduced the rate of browning during storage.     

超高静压对非浓缩还原杨梅果汁中氧化酶的钝化作用

该研究以非浓缩还原（not from concentrate,NFC）杨梅果汁为研究对象,研究不同超高静压（high hydrostatic pressure,HHP）处理（300~600 MPa/0~30 min）对NFC杨梅汁中多酚氧化酶（polyphenol oxidase,PPO）和过氧化物酶（peroxidase,POD）的影响。对比传统高温灭酶,拟合建立HHP压力与酶活性的一级动力学回归方程,分析得到相关参数（压力脉冲效应PE、压力脉冲数值ND、等效破坏值Dp及酶的失活速率K）。结果表明,较高压力（400~600 MPa）对PPO与POD均起到钝化效果,其中600 MPa/10 min能钝化90%的PPO活性,600 MPa/20 min钝化80%的POD活性。600 MPa/30 min条件下,重复加压不能明显加强钝化效果。将PPO和PPO活性与压力进行一级动力学拟合,得到相应线性回归方程（R2>0.8）。随着压力从300 MPa升高到600 MPa,PPO的K值从3.03×10-2升高到12.12×10-2,POD的K值从1.23×10-3上升到7.67×10-3。600 MPa条件下,PPO和POD的ND分别为1.04和1.59,Dp值都为19。同时,压力和保压时间及其相互作用对PPO和POD活性的影响均有极高的显著性（p<0.001）。因此,HHP对杨梅果汁中关键的氧化酶能起到较好的钝化作用,能够为NFC杨梅汁加工技术的应用提供科学依据。     

Erratum

Abstract

The effects of high hydrostatic pressure treatment (100 to 600 MPa) coupled with heat treatment (0 to 60 °C) on the inactivation of peroxidase (POD) and polyphenoloxidase (PPO) in red grapes (Vitus viniferd) have been studied. The examination of the complex interactions between pressure and temperature has been carried out using a central composite rotatable design (CCRD). The response surfaces show that the lowest activity of POD (55.75%) and PPO (41.86%) was found to be at 60 °C at 600 MPa and 100 MPa, respectively.     

Inactivation of polyphenol oxidase from frozen red raspberry (Rubus idaeus L.) by high pressure carbon dioxide treatment

The effect of high pressure carbon dioxide (HPCD) treatment on polyphenol oxidase (PPO) from frozen red raspberry (Rubus idaeus L.) was evaluated. Moreover, the inactivation kinetics of its PPO was simulated by first‐order reaction theory. The minimum of PPO residual rate was 36.6% under 30 MPa and 55 °C for 60 min by HPCD treatment, while that was 66.8% at 55 °C for 60 min by thermal treatment. Moreover, the decimal reduction time of PPO decreased rapidly after HPCD treatment, compared to that of the thermal treatment. The thermal treatment at 55 °C takes a similar time to reach 10% PPO residual rate with HPCD treatment under 30 MPa at 35 °C. One reason for the results was that activation energy of PPO reduced from 98.9 to 14.6 kJ mol^?1 after HPCD treatment. Therefore, HPCD treatment showed stronger capacity to inactivate PPO from frozen red raspberry than the thermal treatment at same temperature.     

Effect of High Hydrostatic Pressure and Temperature on Enzymatic Activity and Quality Attributes in Mango Puree Varieties (cv. Tommy Atkins and Manila)

Pectinmethylesterase (PME), peroxidase (POD), and polyphenoloxidase (PPO) residual activities (RAs) and physicochemical parameters (pH, total soluble solids (TSS), water activity (a_w), viscosity and color) of Tommy Atkins and Manila mango purees (MPs) were evaluated after high hydrostatic pressure (HHP) treatments at 400–550 MPa/0–16 min/34 and 59 °C. HHP treatment applied at 59 °C induced higher enzyme inactivation levels than the treatment applied at 34 °C in both MPs. The lowest RA of PME (26.9–38.6%) and POD (44.7–53%) was achieved in Manila MP treated at 450 MPa/8–16 min/59 °C and 550 MPa/4–16 min/59 °C, respectively. Otherwise, Tommy Atkins puree pressurized at 550 MPa/8–16 min/59 °C had the lowest PPO RA (28.4–34%). A slight decrease in pH and TSS values of both HHP-processed MPs at 34 and 59 °C was observed, whereas the a_w remained constant after processing. The viscosity of MPs tended to augment up to 2.1 times due to the application of HHP. No significant changes were observed in color parameters of Tommy Atkins MP, except at 550 MPa and 59 °C where higher yellow index (YI) (122.4?±?3.3) and lower L* (37.3?±?5.3) were obtained compared to the untreated MP. HHP caused an increase in L* values in Manila MP, whereas no clear trend was observed in YI. HHP processing at 550 MPa combined with mild temperature (59 °C) during 8 min could be a feasible treatment to reduce enzymatic activity and preserve fresh-like quality attributes in MP.     

High-Pressure Processing of Manuka Honey: Improvement of Antioxidant Activity,Preservation of Colour and Flow Behaviour

Manuka honey in New Zealand is known for its superior antimicrobial and antioxidant properties. However, these valuable properties are known to be compromised when raw honey goes through conventional thermal processing, thus reducing its final quality. As such, this present work is undertaken to assess the effect of high-pressure processing on quality of honey, namely, the antioxidant activity, colour and viscosity. The honey was subjected to different pressures (200–600 MPa) at ambient temperatures (25 to 33 °C) and combined with moderate temperatures (53 to 74 °C) for holding times (10 to 30 min). Thermal processing (49 to 70 °C) was also carried out for comparison purpose. In the absence of heat, the antioxidant activity of high-pressure processing (HPP)-treated samples (600 MPa, 10 min) was found to increase by about 30 % with no colour changes detected. The shear-thinning behaviour of the honey was also retained after HPP at ambient temperature, whereas for combined HPP–thermal treatment, no added benefit in antioxidant activity was observed particularly at higher temperature. Colour was significantly degraded when processed for ≥15 min at 70 °C and the flow behaviour was brought about from shear thinning to Newtonian. Thus, it can be concluded that the quality of honey can be enhanced by using high-pressure processing at ambient temperature.     

Ultrasound-assisted extraction and antioxidant activity of phenolic and flavonoid compounds and ascorbic acid from rugosa rose (<Emphasis Type="Italic">Rosa rugosa</Emphasis> Thunb.) fruit

The present study aimed to extract total phenolic compounds (TPC), total flavonoid compounds (TFC), and ascorbic acid (AA) from the fruit of rugosa rose (Rosa rugosa Thunb.) by ultrasound-assisted extraction (UAE), and to evaluate their antioxidant activities. UAE significantly increased the extract yield compared with that obtained using the conventional method. TPC, TFC, and AA were extracted, depending on the extraction conditions (temperature, time, and ethanol concentration), in the range of 50.73–96.69, 15.93–31.88, and 3.06–6.08 mg/g, respectively. TPC and TFC were effectively extracted at a relatively high temperature (50 °C) than AA was (30 °C). The solvent condition used to extract TPC, TFC, and AA was 50% ethanol. The UAE condition for the highest antioxidant activity was obtained 30 °C, 30 min, and 50% ethanol, which were the same condition for the highest AA extraction. Among the extracts, AA showed a strong correlation with antioxidant activity at p-value of 0.001.     

High hydrostatic pressure treatment and storage of carrot and tomato juices: Antioxidant activity and microbial safety

The application of high hydrostatic pressure (HHP) (250 MPa, 35 °C for 15 min) and thermal treatment (80 °C for 1 min) reduced the microbial load of carrot and tomato juices to undetectable levels. Different combinations of HHP did not cause a significant change in the ascorbic acid content of either juice (P > 0.05). Both heat treatments (60 °C for 5–15 min and 80 °C for 1 min) resulted in a significant loss (P < 0.05) in the free‐radical scavenging activity as compared to untreated samples. HHP‐treated juices showed a small loss of antioxidants (below 10%) during storage. The ascorbic acid content of pressurized tomato and carrot juices remained over 70 and 45% after 30 days of storage, respectively. However, heat treatment caused a rapid decrease to 16–20%. Colour changes were minor (ΔE = 10) for pressurised juices but for heat‐pasteurised samples it was more intense and higher as a result of insufficient antioxidant activity. HHP treatment (250 MPa, 35 °C for 15 min) led to a better product with regard to anti‐radical scavenging capacity, ascorbic acid content and sensory properties (colour, pH) of the tomato and carrot juices compared to conventional pasteurisation. Therefore, HHP can be recommended not only for industrial production but also for safe storage of fresh juices, such as tomato and carrot, even at elevated storage temperatures (25 °C). Copyright © 2007 Society of Chemical Industry     

Effects of processing and storage conditions on the stability of sweet potato (Ipomoea batatas L.) leaf flavonoids

The effect of heat, high hydrostatic pressure (HHP) treatment, pH, light, temperature and simulated digestion on sweet potato leaf flavonoids (SPLF) stability was studied. Results showed heat treatment at 75 °C for 90 min or HHP treatment at 600 MPa for 30 min did not cause significant effect on SPLF. Heat treatment at 100 °C for 60 min and 90 min led to decrease in antioxidant activity by 20% and 25%, respectively, while pH 7.0 and 8.0 significantly decreased amount of SPLF by approximately 75%, decreased antioxidant activity by about 30% and 47% separately. Light treated samples recorded a decrease in SPLF by 52% and antioxidant activity by 24%. No significant effect on SPLF was observed for samples stored at −18 °C, 4 °C or room temperature. The retention of flavonoids and antioxidant activity was 45.9 ± 3.6% and 56.2 ± 2.6%, individually in SPLF after simulated digestion.     

Effect of high hydrostatic pressure and thermal processing on the nutritional quality and enzyme activity of fruit smoothies

Fruit smoothie samples were thermally (P₇₀ > 10 min) or high hydrostatic pressure (HHP) processed (450 MPa/20 °C/5 min or 600 MPa/20 °C/10 min) and the total antioxidant capacity (TAC), levels of antioxidant groups [total phenols (TP), anthocyanins and ascorbic acid], instrumental colour, polyphenol oxidase (PPO) enzyme activity and dissolved oxygen were examined over a storage period of 10 h at 4 °C. Thermal processing of smoothies reduced (p < 0.001) TAC and TP values, ascorbic acid and L and a colour attributes (lightness and redness respectively) compared to fresh and HHP-450 processed samples. Conversely, it did result in complete inactivation of PPO enzyme, with no activity detected. Of the HHP treatments, HHP-450 samples had higher (p < 0.001) levels of total antioxidant, phenols and anthocyanin content than HHP-600 samples. However, the latter was more effective in reducing (p < 0.001) the endogenous enzyme activity of the smoothies. .Ascorbic acid content degraded over the storage for all smoothies. HHP-600 samples had high initial values, which declined slowly over storage, while thermal samples had the lowest initial value (0.5 h) that fell below detectable limits by 10 h. Despite these data, less pronounced effects were observed for storage. No significant effects were observed for total anthocyanin and phenolic contents as well as L and colour change (ΔE) variables. Overall, HHP processing of smoothies at moderate temperatures may be a suitable alternative to traditional thermal processing.     

High Hydrostatic Pressure and Temperature Applied to Preserve the Antioxidant Compounds of Mango Pulp (<Emphasis Type="Italic">Mangifera indica</Emphasis> L.)

High hydrostatic pressure (HHP) processes combined with moderate heating can be used to preserve foods while maintaining general quality. The effect of these conditions on the total phenolic (TP), vitamin C (L-ascorbic acid (AA)), carotenoids, and antioxidant activity (AOA) of mango purees was evaluated. Purees were processed at 400–550 MPa/34 and 59 °C at different holding times. Unprocessed puree had TP of 26.6 mg gallic acid/100 g, 21.1 mg L-ascorbic acid/100 g, AOA of 885 μmol trolox equivalents/100 g, and total carotenoids of 6.0 mg β-carotene/100 g. HHP treatments increased the phenolic concentrations up to 34% (550 MPa/59 °C/2 and 4 min) compared with the initial content, probably due to improvement of their extraction. AA content was reduced significantly (10–45%) after all HHP processes performed at 59 °C, while at 34 °C, they were diminished only after 8 and 16 min of treatment (13–26%). At 34 °C and lower times, AA concentration increased in average 18%. Total carotenoid retention in HHP-treated samples varies from 77 to 98%, being the higher the temperature the lower the retention observed. The concentration of most individual carotenoids remains unchanged, but violaxanthin content was reduced (21–26%) and 9-cis-violaxanthin was increased by about 10%. The AOA was also increased (up to 39%) at some processing conditions. A linear correlation between the TP and AOA was obtained. HHP at 550 MPa combined with moderate temperature (34 °C) at processing times up to 8 min is recommended for the maximum retention of the antioxidant compounds of mango puree.     

High pressure thermal processing of pears: Effect on endogenous enzyme activity and related quality attributes

The effect of high pressure-thermal (HPT) processing (600 MPa, 20–100 °C) on the activity of pear enzymes and related quality attributes was investigated. HPT processing at 20 °C for 5 min resulted in 32%, 74% and 51% residual activities of polyphenol oxidase (PPO), peroxidase (POD) and pectin methylesterase (PME), respectively. Increasing processing temperature to 40 and 60 °C reduced the level of PPO and POD inactivation, with the maximum residual activities of 64% and 123%, respectively observed after 3-min treatments at 40 and 60 °C. Overall, HPT at 20 to 60 °C had minimal effect on quality, although enzymatic browning was observed upon air exposure. HPT at 80 to 100 °C caused almost complete inactivation of PPO and POD with 90% and 92% inactivation respectively after 3-min processing at 100 °C, which reduced browning upon air exposure. Nevertheless, the lowest texture retention of 22% was observed under this condition.Industrial relevanceThe study examined the effects of combined high pressure thermal processing on quality related pear enzymes and related instrumental quality attributes such as colour and texture. The study enabled identification of processing regimes for enzyme inactivation and quality retention. The excellent quality retention following HPP at 20 to 40 °C makes this condition suitable for ‘fresh-like’ small portion products for immediate consumption after unpacking that do not require complete PPO and POD inactivation. On the other hand, the almost complete inactivation of oxidative enzymes PPO and POD at 100 °C makes this condition more appropriate for the production of bulk products for food service applications or pureed ingredients for baby food, or pear pieces for yoghurt, that require PPO inhibition but not necessarily high firmness retention.