Enhanced destruction of spoilage microorganisms in apple juice during continuous flow microwave heating

Destruction kinetics of two selected spoilage microorganisms, Saccharomyces cerevisiae and Lactobacillus plantarum in apple juice were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a water bath. Inoculated apple juice was heated in a microwave oven (700 W, 2450 MHz) under continuous-flow conditions to selected exit temperatures (52.5–65°C). Aliquots of inoculated juice were also subjected to batch thermal treatments (50–80°C) in a well-stirred water bath. Time-temperature profiles obtained both during heating and cooling of test samples were used to correct both come-up and come-down times. The time-corrected D-values under microwave heating were 4.8, 2.1 and 1.1 s at 52.5, 55 and 57.5°C, respectively, for S. cerevisiae and 14, 3.8 and 0.79 s at 57.5, 60 and 62.5°C, respectively, for L. plantarum with corresponding z-values of 7 and 4.5°C. D-values under batch thermal heating were 58, 25, 10 and 1.9 s at 50, 55, 60 and 70°C, respectively, for S. cerevisiae and 52, 22, 8.4 and 1.2 s at 55, 60, 70 and 80°C, respectively, for L. plantarum with corresponding z-values of 13.4 and 15.9°C. Microbial destruction thus occurred much faster under microwave heating than under thermal heating suggesting some contributory enhanced effects to be associated with microwave heating.     

Degradation of carotenoids in orange juice during microwave heating

Degradation of carotenoids in orange juice was monitored during microwave (MW) heating at different time/temperature conditions. Various carotenoids were identified and quantified by HPLC. Degradation rate of carotenoids was influenced by MW heating temperatures: at 60 °C and 70 °C for 10 min violaxanthin and antheraxanthin were the compounds most unstable, while lutein and provitamin A carotenoids were more stable. At 85 °C a decrease of about 50% was observed for almost all carotenoids after 1 min of MW heating. Temperature sensitivity (z value) for total carotenoids was 14.2 °C, for single compounds z values ranged between 10.9 °C for β-carotene and 16.7 °C for antheraxanthin. These results can indicate an adequate choice temperature conditions for the quality control of carotenoids and the related nutritional values during MW treatment of orange juices.     

The effects of concentration on electrical conductivity of orange juice concentrates during ohmic heating

Ohmic heating is an alternative heating technique, using an electrical current passing through the food product. It can be specially used in pumpable food lines as an alternative heating unit. In this study, orange juice concentrates having 0.20–0.60 mass fraction soluble solids were ohmically heated by using five different voltage gradients (20–60 V/cm). The dependence of electrical conductivity on temperature, voltage gradient and concentration were measured. The ohmic heating system performance coefficients were calculated by using the energies given to the system and taken by the orange juice samples. The mathematical model results, taking system performance coefficients into account, were compared with experimental ones. The predictions of the mathematical model were found to be very accurate.     

常规加热和微波加热对两种植物油维生素E含量的影响

目的 研究常规加热和微波加热两种加热方式对植物油中维生素E的8种异构体的影响。方法 大豆油、棕榈油进行常规加热和微波加热后, 用异辛烷进行超声提取, 最后用正相高压液相色谱法测定。结果 两种加热方式都会使植物油中维生素E的含量降低, 其中微波加热对维生素E的影响更大。结论 加热时间过长会影响植物油的品质, 同时也能通过对植物油中维生素E的检测推论该植物油是否经过加热处理。     

热处理与微波处理对蓝莓汁品质的影响

采用一级反应动力学模型和Arrhenius经验方程,通过对蓝莓汁分别进行热处理和微波处理,研究了两种处理过程中蓝莓汁中花青素含量、色泽(色度)及抗氧化能力(清除DPPH自由基能力)的变化规律,并建立了相关动力学模型。实验结果表明:热处理和微波处理过程中蓝莓汁中花青素含量、色泽及抗氧化能力的变化均符合一级反应动力学模型(R2>0.9),并可用Arrhenius方程拟合(R2>0.99);热处理温度升高或微波处理功率增大,花青素和色泽的变化速率随之增大,而抗氧化能力随之减小;各模型预测值与实验值之间相对误差均不超过1%,所有模型的预测准确性均较高。     

Influence of ultra-high pressure homogenisation on physicochemical and sensorial properties of orange juice in comparison with conventional thermal processing

The effect of different ultra-high pressure homogenisation (UHPH) treatments on physicochemical and sensorial properties of orange juice was studied in comparison with thermal pasteurisation (90 °C, 1 min). UHPH treatments consisted on combinations of two inlet temperatures (10 or 20 °C) and three pressures (100, 200 and 300 MPa). Effect of treatments was assessed on general quality parameters (colour, pH, °Brix, titratable acidity, reducing sugars and non-enzymatic browning index), particle size distribution and cloud stability. None of the UHPH treatments caused significant differences in the °Brix, reducing sugars, pH and non-enzymatic browning index with respect of fresh or pasteurised juice. Only titratable acidity was significantly lower when inlet temperature of UHPH treatments was 20 °C. UHPH treatments significantly reduced the particle size and in consequence the cloudiness and the total colour value (∆E*) increased. The overall consumer acceptability of UHPH and pasteurised juices was similar.     

Yield and quality effects of electroplasmolysis and microwave applications on carrot juice production and storage

Electroplasmolysis as a pretreatment and microwave heating as an alternative to traditional heating were used in carrot juice production and the effects of these electrical methods on juice quality were investigated. Electroplasmolysis and microwave applications were optimized by response surface methodology. Optimum conditions were these: voltage gradient of 22.2 V/cm and treatment time of 60 s for electroplasmolysis, and flow rate of 90 mL/min with power of 900 W for microwave heating. Production of carrot juice was carried out by using these optimum conditions. After production, carrot juice samples were stored for 4 mo at +4 °C and analyses were performed at monthly intervals. As a result of electroplasmolysis, a 9.7% increase in juice yield was obtained. In addition, 100% pectin methylesterase inactivation was found with the microwave heating application. The results showed that the highest values for quality characteristics, such as antioxidant capacity and total pectin, total phenolic, and total carotenoid contents, were obtained with the combined applications of the electrical methods. In addition, these quality characteristics were protected better in the group of combined applications of the electrical methods (electroplasmolysis + microwave) during storage.     

Comparison of microwave irradiation and conventional thermal heating on volatile profiles and degree of oxidation in corn oil

Volatile profiles and degree of oxidation in corn oils after microwave treatment for 50 min were compared to oils with conventional heating at 180°C for 4 h. Oil microwaved for 10 and 50 min showed a similar degree of oxidation compared to the oil heated at 180°C for 1 and 3 h, respectively, based on the primary and secondary oxidation products. However, the total volatile contents of 50 min-microwaved oil were significantly lower than that of corn oil heated for 1 h at 180°C (P < 0.05). Microwave treatment accelerated the rates of lipid oxidation by 4.6 times compared to 180°C thermal oxidation. Relatively short treatment with microwave irradiation may not provide sufficient time to generate volatiles from oil. Microwaved corn oil for 50 min had higher contents of hexanal and t-2-heptenal and lower contents of 2,4-decadienal and nonanal than the oils heated at 180°C for 3 h. Reactive oxygen species may be involved in volatile formation in microwave-irradiated oils.     

Effect of thermal pasteurization and concentration on carotenoid composition of Brazilian Valencia orange juice

Changes in carotenoid pigment content of Brazilian Valencia orange juices due to thermal pasteurization and concentration were studied. Total carotenoid pigment content loss was not significant after thermal pasteurization and concentration. However, thermal effects on carotenoid pigment contents, especially violaxanthin and lutein, were clearly observed and significant (P < 0.05). Pasteurization reduced the content of violaxanthin by 38% and lutein by 20%. The concentration process resulted in loss of lutein (17%). With the loss of lutein, β-cryptoxanthin became the major carotenoid in the pasteurized and concentrated juices. The provitamin A content of the juice (β-carotene, -carotene and β-cryptoxanthin) and the amount of zeaxanthin, which are considered to be active against age-related macular degeneration and cataracts, did not significantly decrease after pasteurization and concentration.     

不同气体成分对橙汁胞贮藏品质的影响

为掌握不同气体成分对橙汁胞贮藏期间品质的影响,本实验以72-1锦橙汁胞为原料,采用充气（100%N₂、100%CO₂、50%N₂+50% CO₂）贮藏橙汁胞6个月,以-18℃冷冻贮藏橙汁胞作为对照,对品质相关指标的变化进行监测。结果表明:充气贮藏期间,橙汁胞V_C含量均在保质期含量范围内;p H和可溶性固形物含量变化均不显著;还原糖含量均先上升后下降;橙汁胞菌落总数符合果汁饮料的卫生标准。充气与冷冻贮藏期间,橙汁胞总黄酮含量的变化较小。充气贮藏前期（0²月）,橙汁胞色泽变化不显著。3种充气贮藏方式中,充CO₂贮藏抑菌效果较好;充N₂贮藏更有利于橙汁胞V_C和总黄酮含量的维持,且对橙汁胞的褐变和色差变化抑制效果也较好;充50%N₂+50%CO₂贮藏的橙汁胞还原糖含量变化最小。      

橙汁储藏期非酶褐变控制与感官评定

橙汁作为世界上销量最大的果汁类饮品,其储藏过程中的褐变一直是研究领域的一大难题.综述了目前抑制橙汁褐变的一些方法,并介绍了橙汁储藏过程中的感官评定方法,为橙汁褐变的研究提供一定的理论基础.     

Effect of microwave heating on optical and thermal properties of rice starch

This study used the oil bath to imitate the high heating rate of the microwave heating (MV) and evaluated the effects of conventional and MV on optical and thermal properties of rice starch at the same heating rate. The results indicated that the time–temperature profiles for microwave and rapid conventional heating fitted well, with a correlation coefficient of 0.9989. During both conventional and MV starch granule did not swell until 60°C, and granule swelling and loss of granule birefringence occurred simultaneously. DSC revealed a 50% decrease in enthalpy when temperature rose from 60 to 65°C, and a further decrease in enthalpy until 70°C. Therefore, microwave irradiation had no effect on the optical and thermal properties of starch during gelatinization.     

橙汁品质评价国内外研究现状

橙汁是世界上最受欢迎的果汁饮料.就国内外橙汁的研究现状进行了综述,介绍了主要的国际标准及国内标准,重点阐明了橙汁品质评价及鉴伪分析的研究进展,分析了当今研究中存在的问题,提出感官评价与其特征成分进行相关性分析,实现定性和定量综合描述,是未来研究工作以及产品标准制定的发展趋势.     

Effect of sonication on orange juice quality parameters during storage

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

高压脉冲电场杀菌技术在橙汁中的应用

食品冷杀菌技术是一类不用热能杀死微生物,不影响食品营养、质构、色泽和风味的新兴杀菌技术。主要阐述了高压脉冲电场杀菌（PEF）的基本原理和优点,讨论了其在橙汁中的应用,并对比了PEF处理和热处理（90℃,15s）对橙汁微生物的杀灭效果及橙汁理化指标的变化。     

Temperature–time relationships for thermal inactivation of pectinesterases in orange juice

The first‐order kinetic model of a two‐component system was applied to calculate the necessary parameters using the commercial Mathcad program package during the experimental thermal pasteurisation of Valencia orange juice. Thermostable and thermolabile pectinesterases, accounting for 6.6 and 93.4% of the total enzyme population in the juice respectively, showed a 5.63 °C Z_s value and a 9.54 °C Z_l value respectively from the thermal destruction curves at temperatures ranging from 75 to 90 °C. The calculated Z_s values were consistent with the literature values for Valencia orange juice. The calculated and experimental non‐linear thermal pasteurisation curves for orange juice were also in good agreement at temperatures between 75 and 90 °C. © 2003 Society of Chemical Industry     

果胶酶对玫瑰香橙汁澄清效果的影响

以果胶酶为澄清剂,研究果胶酶用量、pH、温度和时间对玫瑰香橙汁澄清度的影响。通过单因素试验,并利用Box-Benhnken中心组合设计,进行澄清条件优化。结果表明,果汁透光率测定最佳波长为685 nm,澄清最佳工艺参数为果胶酶用量0.09 g/L,酶解温度31 ℃,果汁pH值为3.9,酶解时间120 min。在此最佳条件下,玫瑰香橙汁的透光率为98.00%。     

Combined effect of microwave and ultrasonication treatments on the quality and stability of sugarcane juice during cold storage

The main objective of this study was to investigate the combined effect of microwave (MW) treatment (2450 MHz for 120 s), ultrasonication (US) (24 KHz, 20 °C for 20 min) and combined treatment (MW-US) on the quality and stability of sugarcane juice (SCJ) during 21 days of storage at 4 °C. The effect of the treatments and storage time on physicochemical, bioactive compounds (total phenolic, flavonoids and ascorbic acid content) and microbial analysis of SCJ. No significant (P < 0.05) changes were observed in °Brix, while there was an increase in pH and a decrease in titratable acidity in all treatments. Compared to US and MW, MW-US treatments was more effective in preserving colour attributes, total phenolic and flavonoids contents, ascorbic acid and antioxidant capacities of the SCJ during storage. The results regarding the microbial count indicate that more microbial safety and longer shelf life was achieved by MW-US. MW-US treatment is an effective technology for improving the safety and shelf life of SCJ by minimising quality changes, retaining bioactive compounds and reducing microbial growth during storage.     

面制品微波加热的研究现状

面制品微波加热的发展状况和微波加热特性。讨论了微波加热对面制品品质造成的影响。综合分析了从提高面制品保水性和加热后风味两方面入手,通过改善面制品配方、优化微波工艺、控制反应条件等方法,从而提高面制品微波加热的品质。