Characterisation of malolactic conversion by Oenococcus oeni to reduce the acidity of apple juice

The high concentration of malic acid is responsible for the acidity and sourness in apple juice. Bio‐conversion of malic acid to lactic acid through malolactic conversion (MC) in apple juice using Oenococcus oeni was investigated. When apple juice was inoculated with O. oeni (1 × 10⁶ CFU mL^?1), over 90% of malic acid was converted into lactic acid within 96 h at room temperature. When pH of apple juice was adjusted to 4.1 prior to inoculation, MC was completed within 60 h. MC was enhanced at a higher temperature (30°C) when compared with room temperature. The rate of MC was directly proportional to the number of bacteria added and MC was completed within 24 h at 1 × 10⁹ CFU mL^?1 initial cell density. MC occurred equally under aerobic and anaerobic conditions. The sensory analysis of partial MC‐applied juice when compared against control revealed potential for use of MC for manufacture of low‐acid apple juice.     

Use of ionic chromatography in determining the contamination of apple juice by lactic acid

High-performance anion exchange chromatography (HPAEC) with conductometric detection was used for the determination of the lactic acid content of apple juice subjected to fermentation with the strains of Lactobacillus brevis and Lactobacillus plantarum, obtained from a collection, at 20 and 30°C. At the same time, lactate content was determined by means of enzymatic tests and biosensors. Lactic acid concentrations determined by the chromatographic method are similar to those obtained during analysis by enzymatic tests. However, acid concentrations determined by means of biosensors substantially diverge from these results.     

膜技术在苹果汁加工中的应用

应用平板式超滤技术对苹果浊汁进行了过滤澄清和除菌。研究了巴式杀菌酶解或未酶解的苹果浊汁、未巴式杀菌未酶解的苹果浊汁、温度对膜通量的影响,超滤组件形式、操作参数对3种不同预处理料液的滤液质量的影响及反渗透系统的浓缩效果。结果表明:平板式超滤膜通量能满足工业需求且大于管式超滤膜,操作温度宜为50℃,当加水倍数0.09倍时,可使浓缩倍数达到20倍。苹果汁超滤液的透光率在97%以上、色值在50%以上、浊度指标小于0.3,pH值、总酸、糖度、氨基态氮等却未发生明显的变化。苹果汁超滤液质量指标和耐热细菌检查结果比较表明,平板式超滤可代替对苹果汁巴式杀菌及酶解。反渗透系统对苹果汁超滤液进行浓缩,浓缩倍数为2～2.3倍,糖截留率为100%。     

Modeling and Optimization of Lactic Acid Production using Cashew Apple Juice as Substrate

The production of lactic acid by Lactobacillus casei B-442 was studied and modeled. Sugar feedstock was provided using cashew apple juice, an alternative glucose and fructose feedstock that proved to yield high concentrations of lactic acid. The fermentations were carried out in a 1-L fermenter under constant agitation (150 rpm) and controlled pH (6.5). Lactic acid production was evaluated through a dynamic study, varying the initial concentration of sugar in the range of 20 to 60 g/L. Biomass, reducing sugars, and lactic acid concentration were measured throughout the experiments. The highest production of lactic acid (59.3 g/L) was obtained operating the fermentation with 60 g/L of reducing sugar from the cashew apple juice. A rigorous kinetic model was developed for batch fermentation of cashew apple juice for lactic acid production by L. casei B-442. The growth of biomass and lactic acid production were affected by substrate limitation, substrate inhibition and lactic acid inhibition. The model assumed growth- and non-growth-associated lactic acid production and a term for microorganism death was also included in the model. Parameters of the kinetic model were determined based on experimental data by using the least mean squares method and Levenberg–Marquardt algorithm. The model validation was performed and the model was statistically able to fit the profiles for growth of biomass, sugar consumption and lactic acid production. The optimization of the process, using the model, was carried out and the optimum operating conditions aiming highest productivity, lowest production cost and highest gross profit are presented.     

Changes in Apple Juice Flavor Compounds During Processing

Apple juice flavor fractions were collected at several stages during a commercial process. Replicated experiments were designed to collect samples from untreated pulp, from enzyme treated pulp, after pectinase treatment, after microfiltration (MF), and after pasteurization. Additional juice heating experiments were carried out. Six apple juice flavor compounds were identified based on to retention times and reported studies. The flavor profile changed at the different stages of the production line. Temperatures used (～57.2°C) for enzyme activation and MF tended to increase flavor compounds in apple juice except iso-butyl acetate. The higher temperatures used (～85°C) for pasteurization decreased all flavor compounds except propyl butyrate which increased. Results indicate apple juice may contain heat activated precursors of identified flavor compounds.     

Cashew Apple Juice as Substrate for Lactic Acid Production

The aim of the present work was to investigate the use of cashew apple juice as a low cost substrate for Lactobacillus casei B-442 cultivation and lactic acid production. Ammonium sulfate was employed as the only exogenous nitrogen source. The effect of cashew apple juice reducing sugars and ammonium sulfate concentration and the fermentation pH and temperature on biomass formation, lactic acid production, and productivity were evaluated. The highest productivity (2.36 g/L.h) was obtained applying 50 g/L of reducing sugar from the cashew apple juice supplemented with 6 g/L of ammonium sulfate. The process yield was about 95% when fermentation was carried out at 37 °C with pH controlled at pH 6.5 using NaOH (120 g/L).     

复合乳酸菌发酵枸杞汁的工艺优化

以枸杞干果为主要原料,研究了肠膜明串珠菌(Leuconostoc mesenteroides)和植物乳杆菌(Lactobacillus plantarum)作为复合乳酸菌发酵剂对枸杞汁品质的影响,并采用响应面法对枸杞汁的发酵工艺进行优化,旨在开发一种富含功能因子的发酵枸杞汁,以提高枸杞产品的多样性。通过对发酵过程中pH、可溶性固形物、乳酸、蛋白质、总黄酮、总糖与乳酸菌菌落总数含量及感官指标进行测定分析,以乳酸含量和感官评分为评价指标,探讨发酵过程中枸杞汁品质的变化规律。结果表明,复合乳酸菌最佳发酵工艺条件为:肠膜明串珠菌:植物乳杆菌1:1,接种量5%,白砂糖加量5%,发酵时间10 h。其发酵枸杞汁pH4.01、可溶性固形物8%、乳酸342 mg/100 mL、蛋白质20 μg/100 mL、总黄酮410 mg/100 mL、总糖124 mg/100 mL、乳酸菌菌落总数2.1×108 CFU/mL,感官评分92.01分。所得复合乳酸菌枸杞汁发酵饮品组织均匀、口感细腻、酸甜适中、具有枸杞特有的滋味和芳香。     

Inactivation of in Apple Juice by Radio Frequency Electric Fields

ABSTRACT: Heat pasteurization may detrimentally affect the quality of fruit and vegetable juices; hence, nonthermal pasteurization methods are actively being developed. Radio frequency electric fields processing has recently been shown to inactivate yeast in water at near-ambient temperatures. The objective of this study was to extend the radio frequency electric fields (RFEF) technique to inactivate bacteria in apple juice. A converged-field treatment chamber was developed that enabled high-intensity RFEF to be applied to apple juice using a 4-kW power supply. Finite element analyses indicated that uniform fields were generated in the treatment chamber. Escherichia coli K12 in apple juice was exposed for 0.17 ms to electric field strengths of up to 26 kV/cm peak over a frequency range of 15 to 70 kHz. The population of E. coli was reduced by 1.8 log following exposure to an 18 kV/cm field at an outlet temperature of 50 °C. Raising the temperature increased inactivation. Intensifying the electric field up to 16 kV/cm increased inactivation; however, above this intensity, inactivation remained constant. Radio frequencies of 15 and 20 kHz inactivated E. coli better than frequencies of 30 to 70 kHz. Inactivation was independent of the initial microbial concentration between 4.3 and 6.2 log colony-forming units (CFU)/mL. Applying 3 treatment stages at 50 °C increased inactivation to 3 log. The electric energy for the RFEF process was 300 J/mL. The results of the present study provide the 1st evidence that RFEF processing inactivates bacteria in fruit juice at moderately low temperatures.     

Apple juice preservation through microbial adsorption by nano/micro-tubular cellulose

A novel continuous preservation process of apple juice using a nano/micro-porous cellulosic material (or “tubular cellulose”, abrrev. TC), is presented in this study. This investigation aims to the development of a non-thermal system for microbial stabilization, avoiding the degradation of food quality caused by heat. TC was used as filter in a packed-bed type bioreactor supplied with commercial apple juice contaminated with Saccharomyces cerevisiae or Lactobacillus plantarum cells at 4 °C. The effect of the filter size on the microbial load removal and chemical/sensory properties of the juice was evaluated. The system presented good operational stability during 55 and 30 days for the removal of yeast and bacteria, respectively. The increase of filter size improved the microbial removal yield and the system effectiveness. The organoleptic parameter values decreased after ΤC regeneration but then reached almost initial levels. The proposed process is a low-cost and promising alternative to existing thermal pasteurization technologies.Industrial relevanceConventional thermal pasteurization treatments are applied industrially for microbial stabilization of foods but significantly affect the organoleptic characteristics of the products. This study evaluated a novel non-thermal preservation method of contaminated apple juice that meets the consumer's demand for less processed products with high nutritional value. Commercial apple juice was contaminated with S. cerevisiae or L. plantarum cells and then was continuously pumped through tubular cellulose. The increased size of the filter leads to improved microbial removal yields. Despite the decrease of volatile compounds and colour at the start up of the process and after each filter regeneration with hot water, almost initial parameter values were achieved as the process evolved. The proposed technology can be a promising alternative of industrial pasteurization techniques for food applications.     

Inactivation of Escherichia coli by ozone treatment of apple juice at different pH levels

This research investigated the efficacy of gaseous ozone on the inactivation of Escherichia coli ATCC 25922 and NCTC 12900 strains in apple juice of a range of pH levels, using an ozone bubble column. The pH levels investigated were 3.0, 3.5, 4.0, 4.5 and 5.0. Apple juice inoculated with E. coli strains (10⁶ CFU/mL) was treated with ozone gas at a flow rate of 0.12 L/min and ozone concentration of 0.048 mg/min/mL for up to 18 min. Results show that inactivation kinetics of E. coli by ozone were affected by pH of the juice. The ozone treatment duration required for achieving a 5-log reduction was faster (4 min) at the lowest pH than at the highest pH (18 min) studied. The relationship between time required to achieve 5 log reduction (t_5d) and pH for both strains was described mathematically by two exponential equations. Ozone treatment appears to be an effective process for reducing bacteria in apple juice and the required applied treatment for producing a safe apple juice is dependant on its acidity level.     

Evaluation of hybrid pressure-driven and osmotically-driven membrane process for non-thermal production of apple juice concentrate

This study investigates the potential of hybrid membrane processes including microfiltration (MF), ultrafiltration (UF) and forward osmosis (FO) for non-thermal concentration of apple juice. The process performance and characteristics (physicochemical properties, nutritional and aroma components and microbiological quality) of apple juice were studied. The clarity of apple juice was significantly promoted as pore size of membrane reduced. MF and UF can also ensure microbiological safety in pre-treated apple juice. According to its efficiency of filtration as well as performance of simultaneous clarification and cold-sterilization, 0.22 μm MF membrane was identified as the optimal membrane for the pre-treatment. The pre-treated apple juice can be concentrated up to 65°Brix by subsequent single stage FO. FO retained nutritional and volatile compounds of apple juice while significant reductions were found in the juice concentrated by vacuum evaporation. Hybrid MF-FO can be a promising non-thermal technology to produce apple juice concentrate with high quality.     

Bio-silage of mussel work-processing wastes by lactobacilli on semi-solid culture

The aim of this work was to evaluate the fermentability of mussel work-processing wastes by lactic acid bacteria in order to remove and to upgrade a material that generate important focuses of pollution in coastal areas. With this perspective, three lactobacilli (Lactobacillus casei, Lactobacillus plantarum and Lactobacillus buchneri) were employed, and the production of metabolites, as well as the nutrient uptake, was evaluated. The effects of inoculum concentration and previous sterilization process were also studied. The kinetic tests were performed in semi-solid cultures and the results indicated the high feasibility of these materials as substrate for bio-silage production. Cultivations of 24 h led to productions of more than 90 g L⁻¹ of lactic acid and 9 g L⁻¹ of final protein. All the fermentation assays were stable for various days without contaminations by other bacteria.     

Pasteurization of carrot juice by combining UV-C and mild heat: Impact on shelf-life and quality compared to conventional thermal treatment

The combination of UV-C radiation and mild heat (UV-H) treatment is a promising strategy for synergistically increasing microbial inactivation in low UV-transmitting juices. In this research, we explored the suitability of UV-H treatment in carrot juice pasteurization and its impact on juice quality during shelf-life compared to that of thermal pasteurization. UV-H treatment at 60 °C (3.92 J/mL, 3.6 min) enabled reductions of over 5 log₁₀ cycles in the reference pathogens and a significant reduction in spoilage yeasts, bacteria, and bacterial spores. The activity of pectin methylesterase and polyphenol oxidase was reduced by UV-H treatment to levels close to those of low-temperature pasteurization (60 °C/18.1 min). The native population of total aerobic bacteria, lactic acid bacteria, and yeasts and molds of UV-H-treated juice remained undetectable during 29 days of cold storage. Furthermore, viscosity, cloud stability, and the color of fresh juice were better preserved by UV-H treatment than by thermal pasteurization throughout storage.Industrial relevanceThis study demonstrates that UV-H treatment is a beneficial alternative to conventional thermal processing in carrot juice pasteurization, since appropriate inactivation levels of pathogenic and spoilage microorganisms can be reached while better preserving the quality attributes of fresh juice throughout its shelf-life.     

Effect of different fermentation parameters on l-lactic acid production from liquid distillery stillage

Expansion of lactic acid applications, predominantly for the preparation of biodegradable polymers increased the research interest for new, economically favourable production processes. Liquid stillage from bioethanol production can be an inexpensive, valuable source of nutrients for growth of lactic acid bacteria. Utilisation of residual biomass with spent fermentation media as a functional animal feed can greatly influence the process value and its ecological aspect. In this paper, the kinetics of lactic acid and biomass production on liquid stillage by Lactobacillus rhamnosus ATCC 7469 was studied. In addition, the impact of temperature, inoculum concentration, shaking and pH control by addition of CaCO₃ was evaluated. Maximal lactic acid yield of 73.4%, as well as high biomass production (3 × 10⁸ CFU ml⁻¹) were achieved under selected conditions (41 °C, 5% (v/v) of inoculum, 1% (w/v) of CaCO₃, initial pH of 6.5 and shaking rate of 90 rpm). These results were achieved without supplementation of the stillage with nitrogen or mineral sources.     

Storage Stability and Acceptance of Probiotic Beverage from Cashew Apple Juice

The stability of nonfermented cashew apple juice (control) and the fermented juice with Lactobacillus casei NRRL B-442 (sweetened and nonsweetened samples) was investigated along the storage at 4 °C for 42 days. The viability of the probiotic bacteria, sugars, lactic acid, and vitamin C content besides color, antioxidant activity, enzyme activity, and sensory characteristics of probiotic cashew apple juice was evaluated. It was observed that viable cell counts increased in the probiotic cashew apple containing sucrose (8 % w/v) along the storage period. Viable cell counts were always higher than 8.00 Log CFU/ml throughout the storage period. Ascorbic acid loss was higher in the nonfermented juice (40 %) compared to the fermented juice (23 %). The same behavior was observed for antioxidant activity and total polyphenolic compounds content, conferring nutritional benefits to this functional food. Browning reactions and nutritional breakdown caused by enzymes were minimized in the fermented samples during storage. In the fermented sample, higher reduction (>70 %) in the polyphenol oxidase enzyme activity was observed. During storage, the increase in the chroma values from 3.2 to 5.0 indicated that the yellow color became more vivid. Sensory analysis of the fermented cashew apple juice revealed that the product was well-accepted, with acceptance percentages above 80 % for the sweetened juice at the end of the storage period.     

Effect of previous enzymatic recirculation treatment through a tubular ceramic membrane on ultrafiltration of model solution and apple juice

The process of ultrafiltration of a model solution and 12% soluble solids apple juice containing pectins through tubular membranes of 100 and 300 kDa (1 and 3 channels) was studied. Furthermore, in order to obtain a higher permeate flow, the fluids were previously treated with pectinolytic enzymes recirculating through a tubular membrane at different concentrations and treatment times. The permeate flow was analyzed with respect to time and the influence of enzymatic treatment on different parameters: viscosity, density, absorbance at 420 nm, reducing sugars, °Brix, color and pH. Depectinization increased the permeate flow for the model solution and apple juice with 67.52% and 53.11% when the pectinolytic enzyme preparation re-circulated across the tubular membrane. Using the lowest concentration of enzyme treatment and the longest recirculation treatment, an increase in permeate flow was obtained leading to a more favourable clarification process and economic benefits.     

多菌种共固定化发酵制备枸杞红枣乳酸饮料

该研究以枸杞汁和红枣汁为主要原料,采用海藻酸钠包埋乳酸菌的发酵方式,采用多菌种共固定化发酵制备枸杞红枣乳酸饮料。结果表明,最佳条件为枸杞汁、红枣汁体积比1∶2,氯化钙物质的量浓度0.05 mol/L,海藻酸钠质量分数7%,接种量10%,发酵时间35 h,蔗糖添加量9%,添加甜味剂、乳酸钙等辅料,可调配成酸甜可口、营养丰富的枸杞红枣乳酸饮料;该研究为工业化生产品质优良的乳酸饮料提供理论依据,并且对提高水果产业的附加值具有十分重要的现实意义。     

果粮混酿苹果醋最佳工艺的研究

以苹果汁与大米糖化液为原辅料,酵母菌和醋酸茼作为发酵菌种。深入探讨了酒精发酵与醋酸发酵的工艺条件。结果表明：最佳条件为苹果汁与大米糖化液比例1∶1,调整糖浓度12%、酒精发酵7d、醋酸发酵6d、酒度7°,接种量10%、培养温度30℃及后熟1周。     

气相色谱-质谱法分析乳酸菌发酵苹果汁香气成分

以乳酸菌单一菌种和多菌组合分别发酵苹果汁,采用紫外-可见分光光度计测定发酵过程中苹果汁光密度(optical density,OD)的变化,采用顶空固相微萃取和气相色谱-质谱联用技术检测9组发酵苹果汁的香气成分,结合不同香气物质的阈值与香气值分析特征香气成分,并对各组苹果汁进行感官评价。结果表明:在发酵过程中苹果汁的OD值呈对数上升趋势。各组苹果汁中共鉴定出48种香气成分,主要包含醇类、酯类、醛类、酮类和酚类,其中酯类是各发酵组中种类最多且含量最大的香气类别,其次是醇类。9组苹果汁的主要香气成分和香气值较大并有突出贡献的特征香气成分均为丁酸乙酯、2-甲基丁酸乙酯、2-甲基丁基乙酸酯和乙酸己酯等。多菌发酵和单菌发酵苹果汁的香气成分含量及香气值差异显著(P0.05),说明多菌发酵中醇类、酯类和其他类香气物质的总含量明显高于单菌发酵,且赋予苹果汁更强烈的果香、青香和花香。多菌发酵组的总体感官评分高于单菌发酵组,当副干酪乳杆菌20241、动物双歧杆菌6165、嗜热链球菌6063、嗜酸乳杆菌6005活菌数比为1∶1∶1∶1时,感官评分最优。研究结果为今后乳酸菌在发酵果蔬汁方面的研究和应用提供理论依据。     

Electrophoretic and immunochemical determination of bioindustrial enzymes in apple juice

The present study was undertaken to develop a specific and sensitive method which allows the detection of trace amounts of the potentially allergenic bioindustrial enzymes Pectinex Ultra-SPL (pectinase) and Gamylo 200L (amylase) in apple juice. This was achieved by an immunoblotting procedure based on sodium dodecyl sulfate (SDS) electrophoretic separation, followed by an immunochemical detection step using polyclonal rabbit antisera directed against these enzymes and, secondly, alkaline phosphatase labelled antibodies in combination with a highly sensitive enhanced chemiluminescent (ECL) detection method. In a juice spiked with enzyme at various concentrations between 10,000 and 1 ppm (1.0-0.0001%), the detection limit was 10 ppm (=0.001%) for Pectinex Ultra-SPL and 1 ppm (=0.0001%) for Gamylo 200L, respectively. Since the enzyme preparations contain less than 5% of enzymes, the detection limit for the pure enzymes is markedly lower, at least below 1 ppm. Whereas in the samples withdrawn during the initial stages of the industrial production process of apple juice, Pectinex Ultra-SPL and Gamylo 200L components were detectable in concentrations between 50 and 100 ppm, after clearing, ultrafiltration and pasteurization, neither pectinase nor amylase was detectable in the final consumer's product. Under the conditions employed, the bioindustrial enzymes Pectinex Ultra-SPL and Gamylo 200L were virtually removed during the course of production. The risk of sensitizing consumers by intake of apple juice seems to be marginal. This view is supported by the results of an animal model (anaphylaxis test), in which neither gastro-enteral reactions in guinea pigs and mice, nor IgE or IgG production by orally feeding these animals with apple juice concentrate, could be induced.