Reduction of acrylamide formation in potato slices during frying

Reduction of acrylamide formation in potato chips was investigated in relation to frying temperature and three treatments before frying. Potato slices (Tivoli variety, diameter: 37 mm, width: 2.2 mm) were fried at 150°C, 170°C and 190°C until reaching moisture contents of ∼1.7 g water/100 g (total basis). Prior to frying, potato slices were treated in one of the following ways: (i) soaked in distilled water for 0 min (control), 40 min and 90 min; (ii) blanched in hot water at six different time-temperature combinations (50°C for 30 and 70 min; 70°C for 8 and 40 min; 90°C for 2 and 9 min); (iii) immersed in citric acid solutions of different concentrations (10 and 20 g/l) for half an hour. Glucose and asparagine concentration was determined in potato slices before frying, whereas acrylamide content was determined in the resultant fried potato chips. Glucose content decreased in ∼32% in potato slices soaked 90 min in distilled water. Soaked slices showed on average a reduction of acrylamide formation of 27%, 38% and 20% at 150°C, 170°C and 190°C, respectively, when they were compared against the control. Blanching reduced on average 76% and 68% of the glucose and asparagine content compared to the control. Potato slices blanched at 50°C for 70 min surprisingly had a very low acrylamide content (28 μm/kg) even when they were fried at 190°C. Potato immersion in citric acid solutions of 10 and 20 g/l reduced acrylamide formation by almost 70% for slices fried at 150°C. For the three pre-treatments studied, acrylamide formation increased dramatically as the frying temperature increased from 150°C to 190°C.     

The effect of asparaginase on acrylamide formation in French fries

Acrylamide formation in French fries was investigated in relation to blanching and asparaginase soaking treatments before final frying. Par-fried potatoes of Bintje variety were prepared by cutting strips (0.8 × 0.8 × 5 cm) which were blanched at 75 °C for 10 min. Unblanched strips were used as the control. Control or blanched strips were then dried at 85 °C for 10 min and immediately partially fried at 175 °C for 1 min. Finally, frozen par-fried potatoes were fried at 175 °C for 3 min to obtain French fries. Pre-drying of raw or blanched potato strips did not generate acrylamide formation as expected. Partial frying of pre-dried control potato strips generated 370 μg/kg of acrylamide and the final frying determined French fries with 2075 μg/kg of acrylamide. When control potato strips were treated with a 10000 ASNU/l asparaginase solution at 40 °C for 20 min, the acrylamide formation in French fries was reduced by 30%. When blanched potato strips were treated in the same way, the produced French fries have 60% less acrylamide content than blanched strips without the enzyme treatment. Soaking of blanched potato strips (75 °C, 10 min) in an 10000 ASNU/l asparaginase solution at 40 °C for 20 min is an effective way to reduce acrylamide formation after frying by reducing the amount of one of its important precursors such as asparagine.     

Effects of nitric oxide fumigation on phenolic metabolism of postharvest Chinese winter jujube (Zizyphus jujuba Mill. cv. Dongzao) in relation to fruit quality

The effect of nitric oxide fumigation on phenolic metabolism of harvested Chinese winter jujube in relation to the fruit quality was investigated. The fruits were fumigated for 3 h with NO (0, 10, 20 and 30 μl/l) then stored at 22 °C and RH 95%. Changes in color, phenol and anthocyanin levels in pericarp, activities of the related enzymes, and total soluble solids and vitamin C from mesocarp were measured. The results showed that treatment with 20 μl/l NO significantly slowed the increase in red index, inhibited changes of polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) activities, maintained a low total anthocyanin content and a high total phenol content, and delayed the increase of soluble solids and decrease of vitamin C. Treatment with NO solution at less than 1 μmol/l exhibited inhibitory effects on in vitro PPO and PAL activities in a dose-dependent manner.     

Total phenolics,antioxidant properties and quality of fresh-cut onions (Allium cepa L.) treated with mild-heat

This study investigated the effect of mild-heat on fresh-cut onion slices by treating in hot water (50, 60, 70 °C) for 1 min. Total phenolics (TP), antioxidant properties, colour, and weight loss of slices were evaluated during 4 °C storage at 7-day intervals (21 days total). The 60 °C heat treatment resulted in a significant increase in TP, from 44.92 to 52.32 mg GAE/100 g. Except for 50 and 70 °C treatments, TP in control and 60 °C treated fresh-cut onions decreased during storage. The antioxidant properties of fresh-cut onions were 1.31, 0.99, and 62.49 μM TE/g using ABTS, DPPH, and ORAC assays, respectively. The mild-heat treatments did not affect ABTS and DPPH antioxidant activities and the colour of fresh-cut onions. The storage time had mixed effect on the antioxidant properties (ABTS decreased; DPPH and ORAC remained fairly stable). The 50 °C samples exhibited the lowest weight loss during 21-day storage.     

Effect of 1-methylcyclopropene on shelf life,visual quality,antioxidant enzymes and health-promoting compounds in broccoli florets

The effect of 1-methylcyclopropene (1-MCP) on quality, antioxidant enzymes and glucosinolate contents in broccoli (Brassica oleracea var. italica) florets was investigated in the present study. Broccoli florets were treated with air (control) and 2.5 μl/l 1-MCP for 6 h at 20 °C, and were then stored at 20 °C for 5 days. 1-MCP treatment markedly extended shelf life, reduced postharvest deterioration, retarded chlorophyll degradation and inhibited the increase of malondialdehyde amount and activities of polyphenol oxidase and lipoxygenase in florets. The activities of superoxide dismutase, peroxidase and catalase in florets treated with 1-MCP were higher than those in control florets. 1-MCP treatment reduced the rate of decrease of total carotenoids, ascorbic acid and glucosinolates in florets when compared to those in the control. These results indicated that 1-MCP treatment could be a good candidate for extending shelf life, maintaining visual quality and reducing loss of health-promoting compounds, particularly glucosinolates in broccoli.     

Biogenic amine changes in barramundi (Lates calcarifer) slices stored at 0 °C and 4 °C

The biogenic amines formation in barramundi (Lates calcarifer) slices kept for 15 days at 0 °C and 4 °C were investigated using nine biogenic amines, total plate counts and biogenic amines formers. Significant differences in biogenic amines concentrations of barramundi slices stored at 4 °C and at 0 °C after 3 days of storage were observed. All amines, except tryptamine, 2-phenylethylamine, tyramine and agmatine in the slices increased with time during storage at both temperatures. At the end of the storage period, histamine concentrations were 82 mg/kg and 275 mg/kg for samples kept at 0 °C and 4 °C, respectively. At day 15, the total plate count was approximately 8.6 log CFU/g for sample kept at 0 °C and 9.7 log CFU/g for samples kept at 4 °C. Histamine-forming bacteria (HFB) in all samples ranged from 5.4 to 6.1 log CFU/g at 0 °C and 4 °C, respectively. The observed shelf-life of barramundi slices were 6–9 days.     

Physiological and quality changes of fresh-cut pineapple treated with antibrowning agents

The physiological responses of pineapple slices to antibrowning agents have been studied. Slices were immersed for 2 min in solutions of isoascorbic acid (IAA) 0.1 mol/l, ascorbic acid (AA) 0.05 mol/l or acetyl cysteine (AC) 0.05 mol/l, packaged in polystyrene trays, prior to storage for up to 14 days at 10°C. The use of these antibrowning agents reduced browning and decay of pineapple slices significantly. These treatments also reduced changes in L^* and b^* values as well as firmness loss. Changes of in-package atmosphere did not adversely affect quality of slices. Slices treated with 0.1 mol/l IAA had the best visual appearance and were more acceptable compared with the control slices. The best results were obtained using IAA, followed by AC and AA. Organoleptic attributes were not affected and no off-flavors were detected in the treated slices. We conclude that pineapple slices can be maintained in good condition for up 14 days at 10°C following treatment with antibrowning agents.     

Optimization of analytical procedures for GC–MS determination of phytosterols and phytostanols in enriched milk and yoghurt

The aim of the present study is to contribute to a correct determination of vegetal sterol and stanols found in enriched milks and yogurts, used as functional foods, using GC–MS. The optimization of the method, specially the saponification step, as well as the corresponding analytical validation, is the main goal of this study. Saponification temperatures and times that gave the best results were 80 °C/45 min for milk, and 60 °C/90 min for yoghurt samples. KOH concentration solutions of 2.0 and 2.5 M were selected as the best saponification reagents for milk and yoghurt, respectively. It was also verified that volumes of 1500 μl and 2500 μl KOH were enough to react with 250 μl of milk and 100 μl of yoghurt. Accuracy, repeatability and intermediate precision of the method were calculated at 89.2% and 91.5%, 6.0% and 4.45%, 11.8% and 9.4%, for milk and yoghurt, respectively, while the limit of detection was determinate at 0.1 μg/ml for both matrices.     

Inhibition of browning on the surface of peach slices by short-term exposure to nitric oxide and ascorbic acid

The effect of 0.2% ascorbic acid (AA), 5 μM nitric oxide (NO), and the simultaneous use of 0.2% AA and 5 μM NO solutions on inhibiting surface browning of fresh-cut peach slices stored at 10 °C and RH 95% was investigated. The browning index, relative leakage rate, microstructure, total phenol content, and activity of the phenol metabolism-associated enzymes phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) were evaluated. The results indicate that treatment with 0.2% AA, 5 μM NO and simultaneous use of 0.2% AA and 5 μM NO resulted in higher total phenol content, inhibition of PPO and POD activity, reduced membrane permeability and protection of cell microstructure to maintain compartmentation between enzymes and their substrates. In addition, NO increased PAL activity. The causes of inhibition in the browning of peach slices by NO are discussed.     

Determination of volatile N-nitrosamines in meat products by microwave-assisted extraction coupled with dispersive micro solid-phase extraction and gas chromatography – Chemical ionisation mass spectrometry

A sensitive procedure, microwave-assisted extraction (MAE) coupled dispersive micro solid-phase extraction (D-μ-SPE), was developed to extract N-nitrosodimethylamine (NDMA) and other six volatile N-nitrosamines (NAms) from meat products. Parameters affecting the efficiency of MAE and D-μ-SPE were systematically investigated. For MAE, 5-g of a homogenised meat sample was extracted with 30 mL of a sodium hydroxide (0.025 M) solution at 100 °C for 10 min. The optimum D-μ-SPE conditions were immersing 100 mg of Carboxen™ 1000 adsorbent in the MAE extract. After vigorously shaking for 30 min, the NAms were then desorbed by treatment with 200 μL of dichloromethane. A 10 μL aliquot was determined by gas chromatography with chemical ionisation mass spectrometry (GC–CI-MS) using the selected-ion-storage (SIS) mode. The limits of quantitation (LOQs) were 0.03–0.36 ng/g. Preliminary results revealed that NDMA was present in the highest concentration, ranging from 0.8 to 3.2 ng/g.     

Different postharvest strategies to preserve broccoli quality during storage and shelf life: Controlled atmosphere and 1-MCP

Broccoli (Brassica oleracea var. italica) is a vegetable that requires the application of postharvest techniques to extend its marketability. Controlled atmosphere and 1-MCP treatments are most used to extend the shelf life of broccoli and reduce post-harvest deterioration. The aim of this study was to evaluate the visual, physicochemical and functional changes of broccoli head samples stored at 1–2 °C and 85–90% relative humidity (RH) in air (Control samples), under controlled atmospheres (10% O₂ and 5% CO₂) (CA samples) and treated with 1-MCP (0.6 μL/L). After storage all samples were maintained at 20 °C for 2 and 4 days, in order to assess their shelf life. The most suitable postharvest treatment to extend broccoli quality during storage and shelf life, in terms of maintaining the visual quality and reducing loss of health-promoting compounds, was achieved by storage under controlled atmosphere conditions. The use of 1-MCP reduced the loss of green colour and chlorophyll pigments, but only during cold storage not during shelf life at 20 °C.     

Modified atmosphere packaging inhibits browning in fennel

The effects of modified atmosphere packaging (MAP) to inhibit browning of the butt end cut zone of fennel bulbs stored during 14 days at 0°C followed by complementary air storage during 3 days at 15°C were studied. Selected bulbs were placed in 35 μm oriented polypropylene bags or in plastic baskets heat-sealed with nonperforated or perforated (control) polypropylene film. Changes in respiratory rate, ethylene emission, colour of both external leaves and butt end cut, as well as chemical and sensory attributes and browning development were monitored. A low to moderate nonclimacteric respiratory behaviour at 0°C with a respiration rate of 8-9 mg CO₂ kg⁻¹ h⁻¹ and an ethylene emission of 0.2-0.5 μl C₂H₄ kg⁻¹ h⁻¹ were found. Development of fungal attacks, chilling injury, decay and browning of external leaves were not detected for any treatment. All the MAP inhibited browning development of the butt end cut when evaluated after cold storage. However only the atmosphere of 6-7 kPa O₂ and 10-12 kPa CO₂ delayed that process at the end of complementary shelf life.     

The effect of calcium dips combined with mild heating of whole kiwifruit for fruit slices quality maintenance

The effect of moderate heat treatment combined with calcium dips on the quality of minimally processed kiwifruit was studied. Whole fruits were treated for 25 min at 45 °C by dipping in deionised water or CaCl₂ solutions (1%, 2% and 3% (w/v)) and cooled to 4 °C. Twenty-four hours later fruits were peeled, sanitized, cut into slices and packed. The firmness of kiwifruit slices’ was subsequently evaluated during 8 days of storage. Calcium content, pectinmethylesterase activity and heat shock proteins accumulation were also investigated. Heat treatment conducted in water induced a firming effect and avoid softening of fruit slices while calcium dips had a marginal effect on this parameter. A calcium loss was observed due to dip treatment, but this effect was minimized when treatment was conducted in 3% CaCl₂ solution. The firming effect provided is due to the activation of pectinmethylesterase and the presence of calcium in treatment solution reduces or inhibits enzyme activation. Under the tested conditions, no heat shock proteins de novo synthesis was detected.     

1-Methylcyclopropene delays arazá ripening and improves postharvest fruit quality

Six different experiments were conducted to give some practical recommendation to apply 1-MCP during the postharvest handling chain of arazá fruit (Eugenia stipitata McVaugh). Fruit were harvested in three stages of maturity (mature-green primarily, turning and mature) and treated for 1 to 12 h with 0 (control in air) or 1 μL L⁻¹ 1-Methylcyclopropene (1-MCP) at 20 °C. The mature-green fruit were subjected to different storage conditions (7, 10, 12, 13, 20 or 27 °C). The treatment of mature-green fruit with 1-MCP for 1 h, and storage at 12 °C for up to 2 weeks prolonged the shelf-life about one week by delaying or reducing the respiration and ethylene production rates, skin colour changes, the loss of organic acids, and softening, with or without a further shelf-life period of 3 days at 20 °C. At 7 °C, 1-MCP also reduced mature-green fruit weight loss and shrivelling. Extending 1-MCP treatment periods at 20 °C to 6 or 12 h caused partial and uneven ripeness. Treating fruit in their post-climacteric stage of maturity had little effect on ripening compared with the mature-green stage. 1-MCP increased the respiration rate and/or the ethylene production in certain combinations of advanced harvest maturities and/or unfavourable storage temperatures. Recommendations for maintaining postharvest quality are harvesting at the mature-green stage, treatment with 1 μL L⁻¹ of 1-MCP for 1 h, and storage at 12 °C for up to 2 weeks.     

Kinetics of oil uptake during frying of potato slices:: Effect of pre-treatments

Oil uptake in fresh, blanched and, blanched and dried potato slices was studied during frying. Potato slices blanched in hot water (85 °C, 3.5 min) and potato slices blanched (85 °C, 3.5 min) and then dried until to a moisture content of ∼60 g/100 g (wet basis) were deep fried in sunflower oil at 120, 150 and 180 °C. A control treatment consisted of unblanched potato slices without the pre-drying treatment (fresh samples). It was studied applying two empirical kinetic models in order to fit the oil uptake during frying: (i) a first order model; (ii) a proposed model, with a linear time behavior for short times, while time independent for long times. Oil uptake was high even for short frying times at the different temperatures tested suggesting that oil wetting is an important mechanism of oil uptake during frying. For control slices, oil uptake increased approximately by 32% as the frying temperature decreased from 180 to 120 °C at moisture contents ?1 g water/g dry solid. No apparent effect of frying temperature in oil uptake was observed at moisture contents ?0.5 g water/g dry solid in fried slices previously blanched and dried. The two kinetic models studied fitted properly the values of oil uptake during frying, with similar correlation coefficient r².     

Application of exogenous ethylene on postharvest ripening of refrigerated ‘Ataulfo’ mangoes

Commercial handling of ‘Ataulfo’ mangoes is burdened by lack of uniformity in ripening of the fruit. A viable approach to overcome this problem could be by application of exogenous ethylene. In this work, we evaluated the application to exogenous ethylene on ‘Ataulfo’ mangoes with hot-water treatment after having been stored for 4 days at 13±1 °C, and then transferred to 25±2 °C for ripening. Fruit were exposed to 100, 500 or 1000 μl l⁻¹ ethylene for 6 or 12 h at 25±2 °C. Control fruit were held at 25±2 °C with no previous refrigeration or ethylene exposure; another batch was kept refrigerated for 4 days at 13±1 °C, not treated with ethylene and ripened 25±2 °C. Application of 1000 μl l⁻¹ of ethylene for 12 h caused improper ripening. Best results were observed by application of 100 μl l⁻¹ of ethylene for 12 h, which stimulated the synthesis of 1-amino cyclopropane-1-carboxylic acid (ACC) and increased ACC oxidase activity; these conditions led to a concomitant production of ethylene and the subsequent acceleration of ripening with a net gain of 4 days in the ripening time. External color development of the ethylene-treated fruit was judged as more homogeneous.     

Enzyme inactivation kinetics and colour changes in Garlic (Allium sativum L.) blanched under different conditions

The inactivation kinetics of the enzymes peroxidase, polyphenoloxidase and inulinase and changes in the color parameters L^∗, a^∗ and b^∗ of garlic cloves cut in slices, were studied during steam blanching at 100 °C and water at 80 and 90 °C. The garlic cloves were peeled, cut into slices and distributed uniformly in metal baskets and one batch placed in an autoclave generating steam at a temperature of 100 °C; and the others in water baths at 80 and 90 °C. The best blanching conditions were in steam for 4 min, where no changes in texture were observed, and the enzymatic activities were reduced by 93.53%, 92.15% and 81.96% for peroxidase, polyphenoloxidase and inulinase, respectively. Under these conditions the inulin concentration reduced by 3.72%. The color parameter L^∗ increased with increase in blanching time, the samples becoming lighter in color, and the parameters a^∗ and b^∗ decreased, obtaining slices that were greener and bluer.     

Mild heat and calcium treatment effects on fresh-cut cantaloupe melon during storage

The effect of mild heat fruit pre-treatment on some properties of fresh-cut cantaloupe melon during storage was determined. Whole fruit, previously held at 4 °C, was immersed in heated water (60 °C) with and without dissolved calcium lactate (1%). Fresh-cut processing was done immediately, either after treatment or after storage at 4 °C for 24 h. Headspace gas accumulation during storage indicated reduced respiration in heat-treated fruit. Reduced lipase activity occurred in heat treated fruit during storage at 10 °C, while the fruit that was cut 24 h after treatment had a reduced peroxidase activity, unlike fruit that was processed immediately after heating. Isoelectric focussing indicated production of heat shock proteins (PI = 5.1 and 6.5) as a result of heat-treatment. Textural measurements showed increased hardness, chewiness and cohesiveness, but springiness decreased in heat-treated fruit. Presence of calcium in the treatment solution did not affect respiration and textural changes caused by heat treatment. Lipase activity was, however, higher in fruit heated in calcium solutions. Results indicated the potential improvement of shelf life of cut cantaloupe melon by mild heat pre-treatment of the fruit, and that the addition of calcium to the treatment water did not further improve product quality.     

Effect of high-pressure processing on reduction of Listeria monocytogenes in packaged Queso Fresco

The effect of high-hydrostatic-pressure processing (HPP) on the survival of a 5-strain rifampicin-resistant cocktail of Listeria monocytogenes in Queso Fresco (QF) was evaluated as a postpackaging intervention. Queso Fresco was made using pasteurized, homogenized milk, and was starter-free and not pressed. In phase 1, QF slices (12.7 × 7.6 × 1 cm), weighing from 52 to 66 g, were surface inoculated with L. monocytogenes (ca. 5.0 log₁₀ cfu/g) and individually double vacuum packaged. The slices were then warmed to either 20 or 40°C and HPP treated at 200, 400, and 600 MPa for hold times of 5, 10, 15, or 20 min. Treatment at 600 MPa was most effective in reducing L. monocytogenes to below the detection level of 0.91 log₁₀ cfu/g at all hold times and temperatures. High-hydrostatic-pressure processing at 40°C, 400 MPa, and hold time ≥15 min was effective but resulted in wheying-off and textural changes. In phase 2, L. monocytogenes was inoculated either on the slices (ca. 5.0 log₁₀ cfu/g; ON) or in the curds (ca. 7.0 log₁₀ cfu/g; IN) before the cheese block was formed and sliced. The slices were treated at 20°C and 600 MPa at hold times of 3, 10, and 20 min, and then stored at 4 and 10°C for 60 d. For both treatments, L. monocytogenes became less resistant to pressure as hold time increased, with greater percentages of injured cells at 3 and 10 min than at 20 min, at which the lethality of the process increased. For the IN treatment, with hold times of 3 and 10 min, growth of L. monocytogenes increased the first week of storage, but was delayed for 1 wk, with a hold time of 20 min. Longer lag times in growth of L. monocytogenes during storage at 4°C were observed for the ON treatment at hold times of 10 and 20 min, indicating that the IN treatment may have provided a more protective environment with less injury to the cells than the ON treatment. Similarly, HPP treatment for 10 min followed by storage at 4°C was the best method for suppressing the growth of the endogenous microflora with bacterial counts remaining below the level of detection for 2 out of the 3 QF samples for up to 84 d. Lag times in growth were not observed during storage of QF at 10°C. Although HPP reduced L. monocytogenes immediately after processing, a second preservation technique is necessary to control growth of L. monocytogenes during cold storage. However, the results also showed that HPP would be effective for slowing the growth of microorganisms that can shorten the shelf life of QF.     

Development of a solid phase microextraction protocol for the GC–MS determination of volatile off-flavour compounds from citral degradation in oil-in-water emulsions

The conditions for headspace solid phase microextraction (HS-SPME) analysis of volatile off-flavour compounds in citral emulsion were determined. Type of SPME phase (65 μm PDMS/DVB, 100 μm PDMS and 75 μm CAR/PDMS), adsorption temperature and salt concentration were significant factors affecting total peak area in the gas chromatogram and optimised in one factor experiments. Then, adsorption temperature (30–50 °C), adsorption time (20–40 min), and salt concentration (0–6 M) were studied to develop HS-SPME condition for obtaining the highest extraction efficiency. PDMS/DVB in 65 μm was the optimum fiber because of high adsorption efficiency and good reproducibility. The optimal condition was adsorption at 50 °C for 40 min and 6 M salt added to sample. Good Linearity, high recovery, good reproducibility and low limit of detection (LOD) for all off-odour compounds according to the optimised SPME conditions indicated that the SPME procedure was applicable for the analysis of the degraded citral products in headspace volatile of emulsion.