Ultrasonic-assisted leaching of glucose and fructose as an alternative mitigation technology of acrylamide and 5- hydroxymethylfurfural in potato chips

The effect of ultrasound (480 W, 40 kHz) on the leaching of reducing sugars during the water soaking of potatoes slices (60, 70 and 80 °C- 1, 8 and 15 min) was investigated to reduce the formation of acrylamide (AA) and 5-hydroxymethylfurfural (5-HMF) in potato chips.Ultrasound (US) influenced abruptly the reducing sugar leaching during the first 15 min, significantly increasing their extraction rate (glucose: 60%, fructose: 30%) at all evaluated temperatures. When potato slices were treated with US, the formation of AA (~95%) and 5-HMF (~96%) were reduced significantly after frying. Although AA content did not correlate with glucose and fructose concentrations, 5-HMF did (r²: 0.80 and 0.83, respectively), probably because reducing sugars are their main precursors. The AA and 5-HMF concentrations of potato chips presented good correlation coefficient (r²:0.76), suggesting the use of 5-hydroxymethylfurfural as an acrylamide indicator for potato chips.     

Apple polyphenoloxidase inactivation during heating in the presence of ascorbic acid and chlorogenic acid

It was recently reported that during osmotic dehydration of ascorbic acid (AA)-treated apple cubes, losses in AA and phenolics could partly arise from enzymatic oxidation, provided polyphenoloxidase (PPO) was still active under the processing conditions. To determine the impact of dehydration temperatures on PPO action, as well as chemical and enzymatic oxidation reactions, apple PPO inactivation alone or with AA (1 mM) and/or chlorogenic acid (CG, 3 mM), as well as AA and CG levels evolution, during heating of the model solutions at 45 and 60 °C were investigated. At pH 3.8, PPO was still functional, keeping 61 and 4% residual activity after 2 h of heating at 45 and 60 °C, respectively. The combined treatment of heating and AA was more effective in reducing PPO activity, while incubation at 60 °C with AA and CG minimised the losses of PPO activity. CG remained stable during heating, even in the presence of AA which, in turn, was more affected by heating. Thus, during heating, provided PPO remained active with enough available O₂ in the model systems, CG oxidation and coupled oxidoreduction with AA could readily develop.     

Inactivation of Salmonella enterica serovar Typhimurium and Escherichia coli O157:H7 in peanut butter cracker sandwiches by radio-frequency heating

A multistate outbreak of Salmonella enterica serovar Typhimurium recently occurred in the USA, which was traced back to various food products made with contaminated peanut butter. This study was conducted to investigate the efficacy of radio-frequency (RF) heating to inactivate S. Typhimurium and Escherichia coli O157:H7 in peanut butter cracker sandwiches using creamy and chunky commercial peanut butter and to determine the effect on quality by measuring color changes and sensory evaluation. Samples were treated for a maximum time of 90 s in a 27.12 MHz RF heating system. Samples were prepared in the form of peanut butter cracker sandwiches and placed in the middle of two parallel-plate electrodes. After 90 s of RF treatment, the log reductions of S. Typhimurium and E. coli O157:H7 were 4.29 and 4.39 log CFU/g, respectively, in creamy peanut butter. RF treatment of chunky peanut butter for 90 s also significantly (P < 0.05) reduced levels of S. Typhimurium and E. coli O157:H7 by 4.55 log CFU/g and 5.32 log CFU/g. Color values and sensory characteristics of the RF treated peanut butter and crackers were not significantly (P > 0.05) different from the control. These results suggest that RF heating can be applied to control pathogens in peanut butter products without affecting quality.     

Application of ohmic heating/vacuum impregnation treatments and air drying to develop an apple snack enriched in folic acid

The changes of lifestyle and eating habits of consumers have induced a growth in the demand for functional food. The aim of this work was to study the incorporation of folic acid into apple slices by using ohmic heating (OH) and vacuum impregnation (VI) at 30, 40 and 50 °C and air drying at 50, 60 and 70 °C to obtain an apple snack that is rich in folic acid. The kinetic impregnation of folic acid, texture and color were evaluated. The impregnated samples (VI) at 40 °C and vacuum-impregnated samples with ohmic heating (VI/OH) at 50 °C presented a high content of folic acid, whereas the samples air dried at 60 °C presented an important retention of folic acid. The lowest loss of firmness and color was obtained with the VI/OH treatment at 50 °C with drying at 60 °C. Therefore, the VI/OH treatment at 50 °C followed by drying at 60 °C was determined to be the best process for creating dehydrated apple slices that are rich in folic acid.Industrial relevanceThe aim of this research was to study the incorporation of folic acid into dehydrated sliced apples by using vacuum impregnation/ohmic heating (VI/OH) treatments and air drying technologies and evaluating the mechanical and optical properties of the resulting product. Two technologies, vacuum impregnation (VI) and ohmic heating (OH) were performed at 30, 40 or 50 °C with an electric field intensity of 13 V/cm using conventional heating. The results showed that the samples impregnated of apple slices by VI and VI/OH treatments reached the highest content of folic acid. However, the samples that were dried at 60 °C after impregnation by the VI/OH treatment at 50 °C exhibited an increase in folic acid due to the electropermeabilization effect, which induces retention of folic acid and an increase in the folic acid concentration by decreasing the water content. Under the investigated conditions, the VI/OH treatment at 50 °C followed by air drying at 60 °C may be considered the best processing method to obtain an apple snack that is rich in folic acid.     

Fermentation characteristics,aerobic stability and ruminal degradation of ensiled pea/wheat bi‐crop forages treated with two microbial inoculants,formic acid or quebracho tannins

This study evaluated the effects of two commonly used microbial inoculants (Lactobacillus buchneri (LB) and Lactobacillus plantarum (LP)), formic acid (FA) and quebracho tannins (QT) on the fermentation quality, aerobic stability and in situ rumen degradation of pea/wheat bi‐crop forages. Precision‐chopped spring pea (Pisum sativum, var Magnus) and wheat (Triticum aestivum, var Axona) bi‐crops (3:1 pea/wheat ratio) harvested at a combined dry matter (DM) content of 301 g kg^?1 were used for the study. The bi‐crops were conserved without (Control) or with inoculants based on lactic acid bacteria (LB (10⁵ CFU g^?1 fresh weight (FW)) or LP (10⁶ CFU g^?1 FW)), QT (16 g kg^?1 FW) or FA (2.5 g kg^?1 FW) in laboratory silos of 1.5 kg capacity, with each treatment being replicated six times. The pH, chemical composition, aerobic stability and in situ rumen degradation of DM, nitrogen (N) and neutral detergent fibre (NDF) after 112 days of ensilage were measured. The average pH at silo opening was 4.0, suggesting that the silages were well fermented. There were no significant effects of additive treatment on water‐soluble carbohydrate, total N, soluble N, ammonia N and NDF. Lactic acid and acetic acid were the main fermentation products. High concentrations of acetic acid were found in all the treatments, indicating a heterofermentative pathway. Although FA treatment gave the most aerobically stable silage, the Control and QT‐treated silages did not heat up by more than 1 °C until after 6 days of exposure to air. There were no effects of additives on DM degradation characteristics. However, the inoculants increased the rate of N and NDF degradation in the rumen, and both FA and QT reduced the effective and potential degradation of N. © 2001 Society of Chemical Industry     

Combined pressure–temperature effects on the chemical marker (4-hydroxy-5-methyl- 3(2H)-furanone) formation in whey protein gels

Chemical markers, such as furanone, are intrinsically formed in foods at elevated process temperatures, and have been successfully used as indirect indicators of heating patterns in advanced thermal proces-ses such as aseptic processing, microwave sterilization and ohmic heating. However, very limited information is available on suitability of these chemical markers during combined pressure–heat treatment. The present study was conducted on the formation and stability of chemical marker M-2 (4-hydroxy-5-methyl-3(2H) furanone, a by-product of Maillard reaction) as a function of pressure, temperature and pH. Whey protein gels (containing 1g ribose/100g gel mix) at pH 6.1 and 8.3 were subjected to pressure assisted thermal processing (PATP; 350 and 700 MPa, 105 °C), high pressure processing (HPP; 350 and 700 MPa, 30 °C) and thermal processing (TP; 0.1 MPa, 105 °C) for different holding times. Unprocessed gel was used as control. The marker yield was quantified using HPLC. The initial concentrations of M-2 in the gels were 9.17 and 6.1 mg/100 g at pH 6.1 and 8.3, respectively. As expected, heat treatment at 105 °C, 0.1 MPa increased M-2 concentration. The marker yield increased with increase in holding time, following a first order kinetics and decreased with increasing pH. Pressure treatments from 350 to 700 MPa at 30 °C reduced the chemical marker formation for both pH values investigated. Marker formation during combined pressure-temperature (105 °C, 350 and 700 MPa) was influenced by both heat (which favored the marker formation) and pressure (which hindered marker formation). The net final concentration of the marker formed during PATP was higher than HPP, but lower than thermal treatments. This study suggests that 4-hydroxy, 5-methyl, 3(2H) furanone may not be a suitable marker for evaluating pressure–heat uniformity during PATP.     

Aseptic processing of apricots in syrup by means of a continuous pilot scale ohmic unit

In the present study the effect of ohmic heating processing on the quality and shelf-life of apricots in syrup was investigated.Each 100 g of product contained 30 g of pre-heated syrup (15°Brix) and 70 g of blanched apricot pieces with a cubic shape (size 1.2 cm). The liquid-solid mixture (pH < 4) was pasteurized at 90 °C for about 113 s in a 30 kW aseptic continuous pilot ohmic system using a 25 kHz alternating electric current. The aseptically packaged samples were stored at 25 °C and periodically examined over one year period. The parameters measured during the preservation period were: pH, °Brix, color, ascorbic acid content, and microbial spoilage.During the shelf-life, no swelling of the packages was detected. Moreover, the product kept its microbiological stability during the whole storage period of 52 weeks. The ascorbic acid content was slightly reduced by the elctrothermal treatment. However, it was well preserved for the entire storage time. Similarly, the quality characteristics of the fresh apricots in syrup were not adversely affected by ohmic processing and a high retention of the quality attributes was observed during the storage time.     

Recovery of phenolic compounds from peach pomace using conventional solvent extraction and different emerging techniques

The study compared high-pressure, microwave, ultrasonic, and traditional extraction techniques. The following extraction conditions were implemented: microwave-assisted extraction (MAE) at 900 W power for durations of 30, 60, and 90 s; ultrasonic-assisted extraction (UAE) at 100% amplitude for periods of 5, 10, and 15 min; and high-pressure processing (HPP) at pressures of 400 and 500 MPa for durations of 1, 5, and 10 min. The highest yield in terms of total phenolic content (PC) was obtained in UAE with a value of 45.13 ± 1.09 mg gallic acid equivalent (GAE)/100 g fresh weight (FW). The highest PC content was determined using HPP-500 MPa for 10 min, resulting in 40 mg GAE/100 g, and MAE for 90 s, yielding 34.40 mg GAE/100 g FW. The highest value of antioxidant activity (AA) was obtained by UAE in 51.9% ± 0.71%. The PCs were identified through the utilization of Fourier transform infrared (FTIR) spectroscopy and high-performance liquid chromatography (HPLC). Utilizing multivariate analysis, the construction of chemometric models were executed to predict AA or total PC of the extracts, leveraging the information from IR spectra. The FTIR spectrum revealed bands associated with apigenin, and the application of HPP resulted in concentrations of 5.41 ± 0.25 mg/100 g FW for apigenin and 1.30 ± 0.15 mg/100 g FW for protocatechuic acid. Furthermore, HPLC analysis detected the presence of protocatechuic acid, caffeic acid, p-coumaric acid, and apigenin in both green extraction methods and the classical method. Apigenin emerged as the predominant phenolic compound in peach extracts. The highest concentrations of apigenin, p-coumaric acid, and protocatechuic acid were observed under HPP treatment, measuring 5.41 ± 0.25, 0.21 ± 0.04, and 1.30 ± 0.15 mg/kg FW, respectively.     

水蜜桃汁热处理过程中的非酶褐变

对水蜜桃汁热处理过程中褐变度(A420)以及还原糖、总酚、Vc、5-羟甲基糠醛(5-HMF)含量的变化进行研究,以确定水蜜桃热加工过程中的主要非酶褐变反应类型。研究表明,果汁的褐变度和5-HMF的生成量均随着加热时间的延长而增大,且温度越高,其变化速率越快。而桃汁加热过程中5-HMF的生成主要与Vc的降解有关。另外,果汁中糖的降解反应也对褐变起着重要的作用。     

An improved sample preparation method for quantification of ascorbic acid and dehydroascorbic acid by HPLC

Ascorbic acid (AA) and dehydroascorbic acid (DHA) are reduced and oxidized forms of vitamin C, which are ubiquitously found in various fruits and vegetables. The present study has evaluated and optimized various factors responsible for AA and DHA stability in grapefruit samples. Furthermore, the optimized method was used to quantify these compounds in different fruits and vegetables. The AA stability in the samples was evaluated by extracting grapefruit juice using 1, 3 and 5 g/100 mL metaphosphoric acid (MPA) and trichloro acetic acid (TCA). The AA levels were stable in grapefruit samples extracted with 1, 3 and 5 g/100 mL MPA, whereas TCA extracts showed degradation in 48 h. Among the three reducing agents studied, tris(2-carboxy ethyl) phosphine hydrochloride (TCEP) has efficiently converted DHA at all concentrations and the samples were stable for 48 h at 2.5 mmol/L TCEP. Lower pH favored complete conversion of DHA by TCEP than dithiothreitol. Among various fruits and vegetables analyzed, the highest levels of AA (260.1 mg/100 g) were observed in guava and DHA (58.6 mg/100 g) in parsley samples. The current optimized method prevents the degradation of AA and DHA from fruit and vegetable samples stored at room temperature for two days.     

Quality of shelf-stable low-acid vegetables processed using pressure–ohmic–thermal sterilization

Pressure ohmic thermal sterilization (POTS) involves ohmic heating of foods by applying an electric field under elevated pressure. Experiments were conducted using a custom made POTS apparatus using carrot as the model food. The samples were processed at a target temperature of 105 °C at 600 MPa and treated for 0, 1, 3, and 5 min by regulating the electric field (30 V/cm). POTS treated carrot sample quality attributes were compared against those processed using ohmic heating (0.12 MPa, 30 V/cm, 105 °C) and pressure-assisted thermal processing (PATP; 600 MPa, 0 V/cm, 105 °C). Within the experimental conditions of the study, the thermal come-up time of the POTS, Ohmic and PATP were 1.45 min, 3.58 min and 6.84 min respectively. PATP come-up time also included the pre-heating time (≈6 min). Results indicate the POTS samples had the least textural damage due to minimal thermal exposure. POTS samples had higher crunchiness index (CI) of 0.76 compared to PATP (CI = 0.57) and ohmic heated (CI = 0.62) carrots. All the technologies investigated had minimal impact on product color. This study demonstrates the potential to produce high quality shelf stable low-acid vegetable products using POTS.     

Profiles of carotenoids during post-climacteric ripening of some important cultivars of banana and development of a dry product from a high carotenoid yielding variety

Since vitamin A deficiency is prevalent in many developing countries, we sought to focus research on local, affordable and well-accepted sources of provitamin A carotenoids. As dessert bananas are consumed fresh round the year and processed as products, this study investigated whether post-climacteric biochemical changes are linked to carotenoid degradation in four Indian varieties, one commercial (Cavendish, AAA), one Red banana (genome AAA) and two locally-important ones (genome AAB). Despite large differences in their ripening characteristics, textural loss was lesser in AABs than AAAs. High levels of carotenoids (21.0 μg/g FW), β-carotene (9.14 μg/g FW) and α-carotene (9.32 μg/g FW) were found in Red banana accounting for retinol activity equivalent of 114 μg/100 g FW. The carotenoid levels were lower in two local varieties and lowest in Cavendish, with no post-climacteric loss. Dry grits, prepared using Red banana pulp, milk powder and sugar, retained about 70% carotenoids and appeared useful in confectionaries.     

Pasteurization of fermented red pepper paste by ohmic heating

Ohmic heating was applied to a Korean traditional fermented food containing red pepper paste, called Gochujang with low thermal conductivity (0.458 W/m ∙ K), by varying frequencies (40–20,000 Hz) and applied voltages (20–60 V). Contrary to conduction heating, the entire sample was heated uniformly, and the specific heating rate was found to be highly dependent on the frequency, peaking at 5 kHz and 60 V. The results showed that complex differential equation and the Runge–Kutta fourth-order method are suitable for simulating the temperature profile during ohmic heating. The deactivation of vegetable cells of Bacillus strains on fermented red pepper paste by ohmic heating was indicated by a 99.7% reduction, compared with conduction heating for 8 min at 100 °C producing a 81.9% reduction. The organoleptic and physicochemical qualities of the samples pasteurized by ohmic heating were nearly the same as those of raw samples, and higher than those of conventionally heated samples.Industrial relevanceThe present study designed and implemented a novel sterilization process based on a static ohmic heating system with low-frequency AC at the laboratory scale for fermented red pepper paste with a low thermal conductivity (0.458 W/m ∙ K).The developed system was used to investigate the mechanisms and characteristics underlying the induction of ohmic heating and then, tested the pasteurization effect against microorganisms in fermented red pepper paste.Comparing with conventional heating processes, ohmic heating could provide rapid and uniform heating, thereby is more suitable for pasteurization and sterilization of viscous foods as fermented red pepper paste on industrial thermal processing.     

Pasteurization of citrus juices with ohmic heating to preserve the carotenoid profile

This study was carried out to assess, for the first time, the effect of ohmic heating on the carotenoid profile of two citrus fruit juices: grapefruit and blood orange. Two heat treatments were designed to obtain pasteurization values of 50 and 150 min (Tref = 70 °C and z-value = 10 °C) with ohmic heating as compared to conventional heating. The results showed that xanthophyll losses could reach 70% for epoxyxanthophylls (cis-violaxanthin and cis-antheraxanthin) and 40% for hydroxyxanthophylls (β-cryptoxanthin, lutein, and zeaxanthin) with conventional heating, but losses were under 30% and 20%, respectively, with ohmic heating. Carotene species (lycopene and β-carotene) were stable regardless of the treatment. No negative non-thermal effects of ohmic heating were shown on carotenoids. Loss simulations of the studied carotenoids showed that the high temperatures reached with ohmic heating during pasteurization could substantially increase the organoleptic and nutritional quality of acid carotenoid-rich juices.Industrial relevanceCitrus are the top fruit crops in terms of world trade. This craze for them -particularly orange and grapefruit- is notably due to their high content in organoleptic and nutritional compounds of interest and among them carotenoids. About 50% of the Citrus production is processed in juice. From the growing variety of products, minimal processed juices now have a significant market share. This work assessed for the first time the effect of ohmic heating, a thermal method for stabilizing juices while minimizing the impact on the juice quality, on the carotenoid profiles of blood orange and grapefruit juice. Pasteurization with ohmic heating was proven to be a very good alternative for protecting carotenoids and especially xanthophylls compared to conventional heating. These results will help in designing ohmic heating process parameters for optimizing the overall quality of carotenoid-rich fruit juices.     

Ohmic heating assisted vacuum evaporation of pomegranate juice: Electrical conductivity changes

A novel electrical heating method, named as ohmic heating, was successfully integrated to vacuum evaporation system, and pomegranate juice was concentrated until its total soluble dry matter content reached to 40% by applying three different voltage gradients (7.5, 10, and 12.5 V/cm) at 180 mm Hg absolute pressure in this system. Total evaporation times were determined as 152, 78, and 53 min at the voltage gradients of 7.5, 10, and 12.5 V/cm, respectively. The concentration time of pomegranate juice was shortened about 56% by ohmic heating relative to conventional evaporation. The electrical conductivity values were increased up to reach 25% TSDM for 7.5 V/cm and at 35% TSDM for 10 V/cm, then showed a decreasing pattern. However, it was constant (0.55 ± 0.01 S/m) during evaporation process at 12.5 V/cm. It is recommended that the ohmic heating method could be successfully integrated to vacuum evaporation process to shorten the processing time significantly.Industrial relevanceOhmic heating has been utilized as alternative method for the purpose of heating, pasteurization, cooking etc., and relatively better products can be obtained by ohmic heating. Nowadays, energy efficient systems are needed in concentrated juice production. The integration of ohmic heating to the conventional vacuum systems could serve the production high quality juice concentrates with efficient use of energy. In present study, ohmic heating assisted vacuum evaporation of pomegranate juice was conducted, successfully. This method decreased the total process time for juice concentration, which is critically important for industrial scale productions. This novel method can be implemented to the fruit juice production lines by taking into account of design characteristics of ohmic systems such as electrical conductivity changes depending on both temperature and total soluble solids concentration. The effects of main process parameter, named as voltage gradient, on electrical conductivity changes during electrical heating assisted evaporation process has been also reported in the present study.     

Apple pomace in gluten‐free formulations: effect on rheology and product quality

The objective of the present work was to formulate a gluten‐free (GF) baked product based on a cassava starch, rice flour and egg white mixture and enriched with apple pomace with minimum processing as source of fibre. Effects of apple pomace and water amount on batters and product quality were analysed by response surface methodology (RSM). Dynamic moduli of batters, specific volume and crumb texture were highly dependent on both apple pomace and water. Higher levels of fibre rendered less cohesive and less resilient crumbs and diminished specific volumes. A suitable balance between amounts of apple pomace and water led to products with enough specific volume and sponginess. Up to 12.5 g apple pomace and water ranging from 115 to 150 g (each 100 g mixture), specific volumes were maintained higher than 2 cm³ g^?1; if apple pomace was increased up to 20 g, water amounts higher than 140 g were necessary to obtain similar results.     

High amylose starch thermally processed by ohmic heating: Electrical,thermal, and microstructural characterization

High amylose starch (HAS) exhibits restricted granular swelling, limiting its use in many food applications. In this work, we investigated for the first time the potential of ohmic heating (OH) to enhance the swelling of HAS granules in a very efficient manner in terms of processing times. Specifically, the impact of OH at two voltages (130 and 150 V), two moisture conditions (1:3 and 1:5 w/v), and two final temperatures (160 and 180 °C) on the structural, thermal, pasting, and digestion of HAS (70% amylose, AM) was investigated. The electrical conductivity of native HAS showed a transition at 168 ± 1 °C consistent with the thermal transition at 139–192 °C (DSC) with an enthalpy of 11.39 J/g. Furthermore, OH caused a reduction of resistant starch (RS) from 52.0 to 34.5%, and a significant increase in granular swelling (as represented by the increased initial, maximum, and final viscosities). The above was further corroborated by SEM micrographs, which showed the disruption of the granular structure that aligned with a decrease in the relative crystallinity and shift to a B-type polymorphism. Results showed that the high temperatures reached during ohmic heating result in partial HAS gelatinization and enhanced granular swelling.     

Azorean macroalgae (Petalonia binghamiae,Halopteris scoparia and Osmundea pinnatifida) bioprospection: a study of fatty acid profiles and bioactivity

The Azorean macroalgae Petalonia binghamiae, Halopteris scoparia and Osmundea pinnatifida are undervalued and require further study regarding their potential use as food. These three seaweed species had low fat contents, and their fatty acid (FA) profiles were characterised by a high proportion of saturated FA (SFA) in the case of O. pinnatifida and similar weights of SFA and polyunsaturated FA (PUFA) in the other two species. Within the PUFAs, the ω3 PUFAs were the most prominent in O. pinnatifida and P. binghamiae, yielding ω3/ω6 ratios that were higher than one. Eicosapentaenoic acid (EPA, 20:5 ω3) was the most important ω3 PUFA (10–14%). Regarding the other bioactive compounds, the polyphenols were found to reach non-negligible levels (140–220 mg/100 g dw). Significant antioxidant activity was detected. Ethanolic extracts of H. scoparia and aqueous extracts of P. binghamiae showed cyclooxygenase-2 (COX-2) inhibitory capacities between 40% and 79%, indicating anti-inflammatory activity.     

Antioxidative and anti‐inflammatory potential of phenolics from purple basil (Ocimum basilicum L.) leaves induced by jasmonic,arachidonic and β‐aminobutyric acid elicitation

The study presents changes in the phenolic levels, antioxidant and anti‐inflammatory potential of purple basil leaves caused by different chemical elicitors: arachidonic acid (AA), jasmonic acid (JA) and β‐aminobutyric acid (BABA). The application of the all tested elicitors increased the concentration of phenolic compounds, including flavonoids and phenolic acids; especially, in comparison with control (457.62 μg g^?1 FW), the rosmarinic acid level significantly increased after AA and JA treatment ‐ 705.0 and 596.5 μg g^?1 FW, respectively. Phenolics from AA‐elicited plants showed the highest anti‐inflammatory activities designated as lipoxygenase (EC₅₀ = 1.67 mg FW mL^?1) and cyclooxygenase inhibition (EC₅₀ = 0.31 mg FW mL^?1). Elicitors' treatments (especially AA and JA) may be a very useful biochemical tool for improving the production of phenolic compounds in purple basil leaves.     

苹果汁中维生素C热降解动力学研究

为了探索温度对苹果汁中维生素C降解的影响以及维生素C的降解动力学规律,采用可逆的一级反应模型,对加热温度30、40、50、60、70℃条件下苹果汁中还原型维生素C(AA)和氧化型维生素C(DHA)含量的变化及降解动力学进行了研究,结果表明:60℃的AA反应速率最大,DHA反应速率基本随着温度升高而增大;温度升高,可逆反应速率常数增大,其它降解途径速率常数变化不明显;AA无氧氧化速率与温度有一定关系,50℃的AA无氧氧化速率最大,70℃的AA无氧氧化速率最小;AA和DHA热降解反应活化能均低于一般化学反应活化能,说明苹果汁中维生素C热稳定性较差。维生素C的降解主要是有氧氧化反应,苹果汁中维生素C无氧降解速率比有氧降解速率慢;温度升高,苹果汁中维生素C有氧降解速度加快,无氧降解速度变化不明显。在苹果汁加工工艺中应尽量隔绝氧气,采用高温(70℃)短时热处理。对成品苹果汁应采用低温贮藏。