Design and evaluation of a continuous flow microwave pasteurization system for apple cider

The purpose of this project was to design a continuous flow microwave pasteurization system and to evaluate the following process parameters: volume load size (0.5 and 1.38 l), input power (900–2000 W), and inlet temperature (3°C, 21°C, and 40°C). Water and two apple ciders, one from a cold press and the other from a hot press extraction, were the fluids used to study the heating characteristics. Volumetric flow rate and absorbed power were criteria in the evaluation. The microwave pasteurization system consisted of helical coils throughout a large cavity oven, which was shown to produce uniform and reproducible heating throughout the cavity. Fluid viscosity of water and cider was measured at temperatures between 20°C and 70°C to characterize the flow in helical coils based on the Dean number. Process lethality was verified based on inoculation of Escherichia coli 25922 in apple cider, in which the pasteurization process resulted in a 5-log₁₀ reduction.     

Thermal inactivation of Pediococcus sp. in simulated apple cider during high-temperature short-time pasteurization

Prompted by concerns regarding outbreaks of food-borne illness which have occurred due to the consumption of commercial, nonpasteurized fruit juices contaminated with Escherichia coli O157:H7, the US Food and Drug Administration and Canadian Food Inspection Agency are considering several new safety standards to apply to fresh juices, including mandatory pasteurization of all apple cider. In support of these initiatives, a study was conducted to evaluate the pasteurization of simulated cider using a heat-resistant nonpathogenic test bacterium, Pediococcus sp. NRRL B-2354. Thermal inactivation of the Pediococcus sp. was determined using a pilot scale high-temperature short-time (HTST) pasteurizer with a plate heat exchanger. The cumulative lethal effect, or pasteurization effect (PE), was obtained by converting times at different temperatures in the various sections of the pasteurizer to the equivalent time at the reference temperature (72 degrees C). PE was then related by a simple linear function to the log(10) of the percentage of viable counts with a power transformation of the PE values to improve linear fit. r(2) values for the four Pediococcus sp. trials varied from 0.921 to 0.981. Intertrial variation was incorporated into the model using @RISK simulation software. Output from simulations confirmed that treatment at 71 degrees C for 16 s can ensure a 5-log reduction of Pediococcus sp.     

Polyphenol oxidase activity of oregano at different stages

The effects of pH and temperature on polyphenol oxidase (PPO) activity of organs such as root, stem and leaf, of Origanum vulgare ssp. hirtum, collected at different stages (vegetative and generative) and from various localities around Balikesir, Turkey, were investigated using catechol as a substrate. PPO obtained from organs of Origanum was partially purified by (NH₄)₂SO₄ precipitation, followed by dialysis. The PPO activities of organs of Origanum varied among the different localities and between the different stages, and leaf had the highest PPO activity, followed by stem and root, in both stages. Optimum pH of Origanum in the transition from the vegetative stage to the generative stage decreased by 0.4 of a unit, approximately, whereas optimum pHs of Origanum-PPO collected from various localities were closely similar. Optimum temperature decreased very little in the transition from the vegetative stage to the generative stage. Activation energy values were calculated from the Arrhenius equation.     

Polyphenol oxidase activity and browning of three avocado varieties

A comparison between the in vitro total and specific activity of polyphenol oxidase of three avocado varieties, Fuerte, Horeshim and Lerman, showed clear differences that were correlated with the in vivo rate of browning of the corresponding freshly cut mature fruit; Fuerte had the highest values, followed by Horeshim and then Lerman. A good correlation existed between the PPO activity in the crude homogenate of the fresh fruit and the crude enzyme extracted from the acetone powder prepared from each variety. The possibility that the relatively low PPO activity in the crude enzyme of the Lerman avocado was due to the presence of an inhibitor and to factor(s) degrading the enzyme, or that the relatively high activity of the Fuerte enzyme was due to an activator, was tested in various ways and ruled out. It was therefore concluded that the differences in the rate of browning of the three avocado varieties studied were directly related to the PPO activities as expressed in the crude enzyme fraction.     

Changes in headspace volatile attributes of apple cider resulting from thermal processing and storage

One attribute that frequently reflects a product's organoleptic impact is its aroma. In research presented here, a Fox-3000 Electronic Nose was used to determine and compare the aromatic profiles of samples of apple cider subjected to various thermal treatments. Initial results have indicated that exposure to temperatures of up to 90 °C for approximately 28 s acts to stabilize the aromatic properties of apple cider over a 7-day period. In contrast, there are significant changes in the aromatic profiles of fresh apple cider having no such thermal treatment over the same time period. A comparison of samples thermally treated at 60, 70, and 80 °C to non-processed cider showed minimal statistical difference on the basis of similarity indices obtained after 24-h of storage of the samples at 4 °C. Treatment at 90 °C showed significant differences from the unprocessed samples in the same test sequence. After storage for 7-days, samples that were thermally treated exhibited minimal differences from each other, however, were quite different from the non-processed sample on the basis of similarity index analysis. GC analysis was done to confirm potential differences between the samples measured using the electronic nose. Sensory testing is required to determine whether these differences affect the overall quality perception by consumers.     

Validation of apple cider pasteurization treatments against Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes.

Time and temperature pasteurization conditions common in the Wisconsin cider industry were validated using a six-strain cocktail of Escherichia coli O157:H7 and acid-adapted E. coli O157:H7 in pH- and degrees Brix-adjusted apple cider. Strains employed were linked to outbreaks (ATCC 43894 and 43895, C7927, and USDA-FSIS-380-94) or strains engineered to contain the gene for green fluorescent protein (pGFP ATCC 43894 and pGFP ATCC 43889) for differential enumeration. Survival of Salmonella spp. (CDC 0778. CDC F2833, and CDC H0662) and Listeria monocytogenes (H0222, F8027, and F8369) was also evaluated. Inoculated cider of pH 3.3 or 4.1 and 11 or 14 degrees Brix was heated under conditions ranging from 60 degrees C for 14 s to 71.1 degrees C for 14 s. A 5-log reduction of nonadapted and acid-adapted E. coli O157:H7 was obtained at 68.1 degrees C for 14 s. Lower temperatures, or less time at 68.1 degrees C, did not ensure a 5-log reduction in E. coli O157:H7. A 5-log reduction was obtained at 65.6 degrees C for 14 s for Salmonella spp. L. monocytogenes survived 68.1 degrees C for 14 s, but survivors died in cider within 24 h at 4 degrees C. Laboratory results were validated with a surrogate E coli using a bench-top plate heat-exchange pasteurizer. Results were further validated using fresh unpasteurized commercial ciders. Consumer acceptance of cider pasteurized at 68.1 degrees C for 14 s (Wisconsin recommendations) and at 71.1 degrees C for 6 s (New York recommendations) was not significantly different. Hence, we conclude that 68.1 degrees C for 14 s is a validated treatment for ensuring adequate destruction of E. coli O157:H7, Salmonella spp., and L. monocytogenes in apple cider.     

Acceptability of a multi-step intervention system to improve apple cider safety

A multi-step intervention system against Escherichia coli O157:H7 in apple cider was studied. The system consisted of adding 0.05% (w/v) each of sodium benzoate and potassium sorbate, holding cider at 35 °C for 6 h, followed by freezing and thawing the cider. This system was tested in triplicate 10 ml volumes of eight lots of cider throughout the 2000 season. For all ciders, E. coli O157:H7 numbers were reduced by ⩾3.0 log units, with ⩾5.0 log unit reductions for 6 of 8 ciders. For blends of early- and late-season (2000) ciders treated and then thawed in 3.5 l volumes (jugs), no survivors were detected (⩾3.3–4.3 log unit reductions). In consumer acceptance panels (one cider tasted per panel) each treated cider received a mean (n of 191–201) score of 5.5–6.1 (5=“like slightly”; 6=“like moderately”). In a direct comparison, the treated cider had a significantly (P<0.05) lower mean score (n=189) of 5.6 compared to heat-pasteurized cider (mean score of 6.1). Although the multi-step intervention system may provide sufficient lethality under certain conditions, its inconsistent lethality and lower consumer acceptability reduce its usefulness as an alternative to high-temperature short-time pasteurization.     

Efficacy of sanitation and cleaning methods in a small apple cider mill

The efficacy of cleaning and sanitation in a small apple cider processing plant was evaluated by surface swab methods as well as microbiological examination of incoming raw ingredients and of the final product. Surface swabs revealed that hard-to-clean areas such as apple mills or tubing for pomace and juice transfer may continue to harbor contaminants even after cleaning and sanitation. Use of poor quality ingredients and poor sanitation led to an increase of approximately 2 logs in aerobic plate counts of the final product. Reuse of uncleaned press cloths contributed to increased microbiological counts in the finished juice. Finally, using apples inoculated with Escherichia coli K-12 in the plant resulted in an established population within the plant that was not removed during normal cleaning and sanitation. The data presented in this study suggest that current sanitary practices within a typical small cider facility are insufficient to remove potential pathogens.     

Polyphenol oxidase activity,phenolic acid composition and browning in cashew apple (Anacardium occidentale, L.) after processing

This study describes the extraction and characterisation of cashew apple polyphenol oxidase (PPO) and the effect of wounding on cashew apple phenolic acid composition, PPO activity and fruit browning. Purification factor was 59 at 95% (NH₄)₂SO₄ saturation. For PPO activity, the optimal substrate was catechol and the optimum pH was 6.5. PPO K_m and V_max values were 18.8 mM and 13.6 U min⁻¹ ml⁻¹, respectively. Ascorbic acid, citric acid, sodium sulphite and sodium metabisulphite decreased PPO activity, while sodium chloride increased PPO activity. Wounding at 2 °C and 27 °C for 24 h increased PPO activity but storage at 40 °C reduced PPO activity. Gallic acid, protocatechuic acid and cinnamic acid (free and conjugate) were identified in cashew apple juice. Cutting and subsequent storage at 40 °C hydrolysed cinnamic acid. 5-Hydroxymethylfurfural content in cashew apple juice increased after injury and storage at higher temperatures, indicating non-enzymatic browning.     

Relationship between the enzymatic determination of starch and the starch iodine index in two varieties of cider apple

Monitoring the hydrolysis or disappearance of starch by the starch iodine test is a simple procedure for determining the maturity of cider apples, but it does not indicate the exact amount of starch present. So far, studies of starch in apples have dealt exclusively with dessert apples. In this paper the relationship between the visual starch index, the dark‐coloured surface area and the real starch content was studied in two varieties of cider apple commonly used in Normandy (France). Starch determination in cider apples required adapting the protocol provided by the Boehringer enzymatic kit. The work led to proposing a simplified index with five scales instead of 10. This index gives the correspondences between the new and old scales as well as the probable starch contents for each new scale. © 2002 Society of Chemical Industry     

Polyphenol oxidase inactivation and vitamin C degradation kinetics of Fuji apple quarters by high humidity air impingement blanching

In this study, polyphenol oxidase (PPO) and vitamin C were used as the indicators of enzymes and nutrients to evaluate the apple quality during high humidity air impingement blanching (HHAIB) process. The PPO can be completely inactivated within 7 min at 90–120 °C and can retain relatively more vitamin C in the case of PPO fully inactivation. PPO inactivation followed zero‐order kinetics model at 90 and 100 °C, and followed first‐order fraction model at 110 and 120 °C. Activation energy (E_a) of PPO inactivation was between 11.61 and 13.66 kJ mol^?1 by Arrhenius equation. Vitamin C degradation under all processing temperatures was well described by first‐order model and its E_a value was 26.69 kJ mol^?1. Therefore, the HHAIB process was proved to be an effective pretreatment for Fuji apple quarters to inactivate PPO fast and meanwhile to maintain produce quality.     

Polyphenol oxidase activity of two olive (Olea europaea L.) cultivars as an early criterion of Mn toxicity

BACKGROUND: The time course of polyphenol oxidase (PPO) activity in the leaves of two olive cultivars (Picual and FS‐17) irrigated with nutrient solutions differing in Mn concentration (0, 2 and 1280 µmol L^?1) was studied under hydroponic conditions to determine whether PPO activity could be used as an early criterion of Mn status of olive plants, and to elucidate whether genotypic differences exist between the two olive cultivars studied, concerning the effect of Mn concentration on PPO activity. RESULTS: In all the Mn treatments, PPO activity was greater in Picual than in FS‐17. Under excess Mn (1280 µmol L^?1), PPO activity gradually increased with time, starting from day 30 of the experiment in both cultivars, and this increase preceded the appearance of Mn toxicity symptoms. In contrast, in the other two Mn treatments (0 and 2 µmol L^?1) PPO activity increased and afterwards decreased during the experiment, but the trend was not clear. In the 1280 µmol L^?1 treatment, PPO activity linearly increased (R = 0.8836 for Picual and 0.943 for FS‐17) with the increase of Mn concentration in the leaves of both cultivars. In the 1280 µmol L^?1 Mn treatment, PPO activity was negatively related with Fe and Zn concentrations in the leaves, and positively in the 0 and 2 µmol L^?1 Mn treatments with the Ca, Mg and K concentrations. CONCLUSION: From the differential time course of PPO activity in the three Mn treatments (0, 2 and 1280 µmol L^?1), it is concluded that periodic measurements of PPO activity in the leaves of the olive cultivars Picual and FS‐17 can be used for the early detection of Mn toxicity (before the appearance of symptoms). Copyright © 2010 Society of Chemical Industry     

Polyphenol oxidase activity and implications on the quality of intermediate moisture and dried apples

This study aimed at investigating the water activity threshold for the polyphenol oxidase activity in Golden Delicious apple. Freeze-dried powders obtained from blanched and unblanched apples were equilibrated and stored at four water activity levels, ranging from 0.11 to 0.56, at 20 and 40 °C, to differentiate between nonenzymatic and enzymatic browning. The contents of hydroxycinnamic acids, phloridzin, catechin, epicatechin, polymeric flavan 3-ols, and 5-hydroxymethylfurfural, the antioxidant activity values, and the Hunter colorimetric parameters of apple products were analyzed. Results showed that no polyphenol oxidase activity occurred in unblanched dehydrated apples stored at water activity levels between 0.11 and 0.32. In this water activity range, blanching pre-treatment accelerated the Maillard reaction in the products stored at 40 °C, as observed from both higher 5-hydroxymethylfurfural formation and more intense red color development in blanched apples with respect to the unblanched ones. At the water activity level of 0.56, both increased redness and higher antioxidant degradation were observed in the unblanched apples with respect to the blanched apples, indicating that the threshold water activity for polyphenol oxidase was in the range 0.32–0.56. Among apple antioxidants, epicatechin was mostly affected by polyphenol oxidase activity, either by direct oxidation or by a coupled oxidation mechanism. Therefore, “mild” pre-heating treatments or no pre-treatments could be proposed when the apple is to be stored and used at water activity ≤0.32, whereas blanching should be applied for intermediate moisture apples or in food applications where moisture transfer from other ingredients could bring apples above this critical water activity level.     

Inactivation of spoilage microorganisms in apple cider using a continuous flow pulsed electric field system

The effect of pulsed electric field (PEF) in inactivating naturally occurring microorganisms (yeast and molds) in freshly squeezed apple cider was investigated in a continuous flow system. The microbial count decreased with an increase of applied pulses (17.6-58.7 total) and treatment temperature (45-50 °C), and a decrease of flow rate (3-10 l/h). At field strength of 27-33 kV/cm (3 mm electrode gap in a concentric chamber), 200 pulses/s, 3 l/h flow rate, and 50 °C process temperature, there was a 3.10 log reduction in microbial counts. By PEF treatment in the presence of a mixture of nisin and lysozyme (27.5 U/ml for nisin and 690 U/ml for lysozyme), there was an increase in the microbial count from 1.12 to 1.78 log reductions for 10 l/h flow. When cider samples were treated in the presence of clove oil (3 or 5 ml/100 ml), an additive reduction of 1.99 log cycles in microbial counts was observed.     

Validation of a time-temperature-integrator for thermal processing of foods under pasteurization conditions

In this work, a general theory for the development of a Time Temperature Integrator, TTI-system, is outlined. A z-value (or activation energy) of the TTI-system equal to that of target index is crucial for the usefulness of a system to monitor the impact of thermal processes on foods. The proposed TTI, namely the heat-stable fraction of peroxidase covalently immobilized on porous glass beads in dodecane, can be used to indicate the intensity of a delivered pasteurization process when a z-value of 10°C is used for calculating the lethality. Lethalities read from the bio-indicator showed excellent agreement with those integrated from the measured time-temperature data.     

Phytochemical composition and antioxidant activity of peach as affected by pasteurization and storage duration

Fruit are very perishable and are often preserved as heat-processed foods. Clingstone peach [Prunus persica (L.) Batsch ‘Catherine’] fruit were heat-treated at 90 °C for 5 min and stored under aseptic conditions at room temperature (ca. 22 °C) for 90 days. Significant reductions in total carotenoids were observed immediately after pasteurization but total antioxidant activity and the concentration of total phenolics were unaffected. Pasteurization induced significant reductions in the concentration of protocatechuic acid (from 10.2 to 5.8 μg/g fw), zexanthin and β-cryptoxanthin. Significant reduction in antioxidant activity, expressed as ascorbic acid equivalents, from 0.52 to 0.25 mg/g fw, was observed during storage of pasteurized peach for 90 days. Total phenolics, expressed as gallic acid equivalents, decreased during storage from 0.57 to 0.28 mg/g fw and total carotenoids decreased from 4.0 to 1.3 μg/g fw. Procyanidin B1 increased from 15.8 to 26.8 μg/g fw and chlorogenic acid and neochlorogenic acid increased 35 and 43%, respectively. (?)-Epicatechin decreased during storage from 13.1 to 4.0 μg/g fw and quercetin-3-glucoside from 7.3 to 4.4 μg/g fw. All carotenoids decrease significantly with the exception of zeaxanthin, which increased during storage. Storage duration strongly affected the concentration of phenolics and carotenoids in pasteurized peach.     

Foliar catechol oxidase activity as a measure of copper nutrition of tomato plants

The diagnostic value of catechol oxidase assays as indices of copper nutritional status was investigated in tomato plants (Lycopersicon esculentum Mill) receiving graded copper treatment in sand culture. Foliar copper concentrations ranged from 0.79 to 5.16 μg g^?1 dry matter under various copper treatments but these results were misleading because copper-inadequate plants concentrated the element in older leaves. A colorimetric assay based on catechol oxidase-catalysed formation of measurable quinones in young tomato leaves discriminated sufficiently between the various copper treatments. The rates of invitro induction of this enzyme amounted to an expression of the plant growth response to copper supply and thus was indicative of the copper requirement of the plant. A paper strip-based modification of the enzyme assay simplified it further for diagnostic use in field situations.     

褐变抑制剂对苹果多酚氧化酶抑制机理研究

为研究不同褐变抑制剂对苹果多酚氧化酶(PPO)活性的抑制机理,采用磷酸缓冲液构建苹果汁模拟体系,选取苹果中含量较多的酚类物质绿原酸作为试验对象,以磷酸缓冲液为苹果汁模拟体系,选取4-己基间苯二酚(4-HR)、草酸、苯甲酸和对甲氧基苯甲酸为抑制剂,通过模拟试验研究抑制剂对绿原酸模拟苹果汁酶促褐变特性的影响,揭示抑制剂对苹果汁PPO的作用机理。结果表明,抑制剂对PPO的抑制机理差异较大,其中4-HR和草酸对PPO的抑制作用为竞争性抑制,植酸为混合性抑制,而苯甲酸为非竞争性抑制。该研究可为利用抑制剂控制苹果汁褐变提供理论依据。