Kinetic modelling of non-enzymatic browning of apple juice concentrates differing in water activity under isothermal and dynamic heating conditions

The kinetics of non-enzymatic browning in apple juice concentrates were investigated. The effect of a_w (in the range of 0.74–0.99) and/or reactant concentration on brown pigment formation was monitored under isothermal heat treatment at four temperatures (60, 70, 80 and 90 °C) in apple juice solutions having either the same or different concentrations of reactant solutes. The extent of the Maillard reaction was evaluated by spectrophotometric measurements at 420 nm (A₄₂₀). The absorbance–time curves were fitted to five different kinetic models (zero and first order, weibull, logistic and the parabolic model) and estimates of browning rate constants and other model parameters were obtained. Regression analysis revealed that the logistic model was the most appropriate for describing browning in apple juice. The initial reactant concentration, but not water activity, had a significant effect on the colour change of apple juice. The processing temperature also had a strong impact on browning kinetics. Secondary models, expressing the dependence of the best fitted primary model parameters on temperature and a_w, were further developed and validated by comparing the predicted model parameters with the values observed in independent isothermal experiments. Finally, the derived model was further evaluated against the observed browning responses of apple juice under dynamic heating conditions, underlining the applicability of the developed model as a practical prediction tool for the study of non-enzymatic browning.     

Antioxidant and tyrosinase inhibitory activities of different parts of guava (<Emphasis Type="Italic">Psidium guajava</Emphasis> L.)

The antioxidant and the tyrosinase inhibitory activities of 4 different solvents (acetone, ethanol, methanol, and water) for preparation of extracts from guava (branch, fruit, leaf, and seed) were evaluated by measuring total phenolic contents (TPC), DPPH radical scavenging activity, ABTS radical scavenging activity, reducing power (RP), and tyrosinase inhibitory activity. The extracts of branch and leaf showed relatively higher antioxidant properties than those of fruit and seed. The highest TPC (141.28 mg/g gallic acid equivalents), DPPH radical scavenging activity (IC₅₀=34.01 μg/mL), ABTS radical scavenging activity (IC₅₀=3.23 μg/mL), and RP (IC₅₀= 75.63 μg/mL) were found in acetone extract of leaf, while water extract of seed had the lowest antioxidant activity. The tyrosinase inhibitory activity of ethanol extract from guava leaf was 69.56%, which was the highest activity among the extracts. These results indicate that useful bioactive substances exist in the guava branch as well as leaf extracts.     

Dioscin: A synergistic tyrosinase inhibitor from the roots of Smilax china

In our study, we investigated the inhibition of mushroom tyrosinase in Smilax china. A methanol (MeOH) extract of S. china was partitioned into hexane, ethyl acetate (EtOAc) and water. Of the three fractions, EtOAc extract showed the strongest inhibition of tyrosinase activity with l-tyrosine or l-DOPA as a substrate. Two compounds were isolated from a final active fraction by activity-guided column chromatography. These compounds were identified as dioscin and oxyresveratrol by comparing their mass, ¹H- and ¹³C-NMR spectral data with those reported in the literature. Dioscin showed little inhibition activity of tyrosinase, whereas oxyresveratrol, a known tyrosinase inhibitor, showed a strong tyrosinase inhibitory activity. We discovered that a mixture of oxyresveratrol and dioscin (IC₅₀ = 5.1 and 5.7 μg/ml) highly increased the inhibition of tyrosinase activity with l-tyrosine or l-DOPA as the substrate as compared to either oxyresveratrol (IC₅₀ = 7.8 and 10.9 μg/ml) or dioscin (IC₅₀ > 100 and 100 μg/ml) alone.     

Antibacterial activity of Melastoma candidum D. Don

Melastoma candidum D. Don is a plant of the Melastomataceae family that has been used as folk medicine in Taiwan. In this study, the antibacterial activity of M. candidum extracts was investigated. Water, acetone, ethanol (95 ml/100 ml), and ethyl acetate extracts of M. candidum exhibited antibacterial activity, especially the acetone and ethanol (95 ml/100 ml) extracts. Over one-third of MICs for those two extracts were close to or equal to that of amoxicillin. MICs and minimum bactericidal concentrations (MBCs) for the acetone extract were 0.02-0.64 mg/ml and 0.08-2.56 mg/ml, respectively; while for the ethanol (95 ml/100 ml) extract, corresponding values were 0.04-1.28 mg/ml and 0.16-5.12 mg/ml, respectively. The acetone M. candidum extract exhibited good thermal stability subsequent to heating from 70 to 121 °C for 15-60 min; further, no dramatic changes in the MICs in a range of pH 5-8 were noted. Overall, M. candidum acetone extract revealed a good bactericidal effect, good thermal stability (heating at 121 °C for 15 min), and broad antibacterial activity in the pH range of 5-8.     

Dessert and crab apple seeds as a promising and rich source of all four homologues of tocopherol (α, β, γ and δ)

Tocochromanols composition in apple seeds, obtained as a by-product during the fruit salad and juice production, of twelve varieties - seven crab apple (‘Kerr’, ‘Kuku’, ‘Quaker Beauty’, ‘Riku’, ‘Ritika’, ‘Ruti’ and K-8/9-24) and five dessert apples (‘Antej’, ‘Beforest’, ‘Kent’, ‘Sinap Orlovskij’ and ‘Zarja Alatau’) were studied. Tocopherols and tocotrienols were isolated using the micro-saponification method of high precision and accuracy and they were analysedanalysed by rapid RP-HPLC/FLD and RP-UPLC-ESI/MSⁿ. Four tocopherols, with predominance of homologues α and β, were detected in each tested sample. The seeds from two apple cultivars ‘Antej’ and ‘Beforest’ were characterized by unique and similar ratios of all four tocopherol homologues α:β:γ:δ (1.7:1.5:1.3:1.0 and 2.1:2.0:1.3:1.0, respectively). The concentration range of individual tocopherol homologues (α, β, γ and δ) in apple seeds were as follows: 17.22–25.79, 7.53–29.05, 0.61–13.82 and 0.16–10.79 mg/100 g dry weight basis (dwb), respectively. Moreover, three tocotrienols (α, β and γ) were identified in lesser amounts (0.02–0.74 mg/100 g dwb). Use of apple seeds to isolate tocopherol homologues can ensure better environmental sustainability and effective use of natural plant material.     

Free amino acid profiles from ‘Pinot noir’ grapes are influenced by vine N-status and sample preparation method

This study examined the impact of extraction method on ammonia, free amino acids, and yeast assimilable nitrogen (YAN) concentrations in ‘Pinot noir’ berries obtained from a vine nutrition study (altered supply of N, P, or K). Berries were either juiced or exhaustively extracted as whole berries prior to analysis. Extracts, compared to juice samples, had a significantly higher level of ammonia–N, assimilable amino acid–N, and YAN. For example, juice YAN values were approximately 50% of extract YAN values, when both were expressed in the same units. Free amino acid profiles and relative concentrations of individual amino acids were different in juice versus extracts, depending on how well the skin fraction was extracted prior to analysis. Lowering N supply reduced free amino acids, with arginine being reduced more than the other 20 free amino acids identified in ‘Pinot noir’ berries. This was true in both juice and extracts. Since berry skin contributed to actual YAN, wineries that determine YAN from mainly the pulp fraction (juice) may underestimate YAN and as a result add more (artificial) N supplement than is required for the healthy fermentation of red winemaking (whole berry fermentations). Extraction procedure should be taken into consideration when comparing grape YAN.     

Increase of Antioxidant Activity of Tomato Juice Upon Functionalisation with Vegetable Byproduct Extracts

Phenolic-enriched extracts from blanched artichoke (BA), artichoke blanching waters (ABW), cauliflower (CA), carrot (CR), celery (CE) and onion (ON) byproducts were used to ‘functionalise’ tomato juice. The antioxidant activity of functional tomato juice significantly increased over control juice according to a set of in vitro antioxidant assays (i.e. inhibition of lipid peroxidation determined by the ferric thiocyanate method and scavenging of both ABTS^•+ and DPPH^• free radicals). A trained sensory evaluation panel determined the maximal allowed byproduct extract concentration in the functionalisation of tomato juice without modifying its natural sensory properties (mg extract/mL tomato juice): 2.5, 5, 10, 10, 10 and 20 for CA, ON, BA, ABW, CE and CR, respectively. The maximum antioxidant activity (within consumers' acceptance limits and measured by the ABTS^•+ method) was increased 5.4-, 3.4-, 2.5-, 1.7-, 1.5- and 0.6-fold over the control when functional tomato juice was assayed after modification with ABW, BA, CR, ON, CE and CA, respectively. A serving of functional tomato juice (250 mL) containing vegetable extracts (within consumers' acceptance limits) provides an additional intake of phenolic compounds which can range from 22 mg (when functionalised with CA extract) to 300 mg (with BA extract). In the light of the above investigations, the use of vegetable byproducts could be useful for developing a functional tomato juice with potentially increased health-promoting properties.     

氧化白藜芦醇对鲜切苹果及果汁褐变的影响

为研究氧化白藜芦醇(oxyresveratrol,OXY)对苹果褐变的抑制作用,采用不同浓度的OXY对鲜切苹果、苹果汁进行处理,探讨在不同储藏阶段切片色度和果汁褐变度变化情况及OXY对苹果汁内多酚氧化酶(polyphenol oxidase,PPO)和过氧化物酶(peroxidase,POD)活性的影响。结果表明:OXY可改善苹果切片的感官品质,显著延缓切片L*值的降低(P<0.05),抑制a*、b*、ΔE值的升高(P<0.05)。同时,OXY还能显著降低苹果汁褐变度(P<0.05),显著抑制苹果汁内PPO和POD活性(P<0.05)。综上,OXY能有效抑制鲜切苹果片及苹果汁褐变,其作用机制可能是通过抑制苹果内PPO和POD活性实现。     

Mechanism for the inhibition of apple juice enzymatic browning by Palo Fierro (desert ironweed) honey extract and other natural compounds

Inhibition of Red Delicious apple juice browning and apple polyphenoloxidase (PPO) activity by four natural anti-browning agents [palo fierro honey extract (PFH), caffeic acid phenethyl ester (CAPE), l-cysteine (Cys), and 4-hexylresorcinol (4HR)] has been studied. Browning of apple juice was markedly reduced by 4HR, Cys, and PFH, however, little effect was observed with CAPE. PFH, CAPE, and 4HR showed high inhibition of apple juice PPO. When the inhibition mechanism of these compounds over partially purified apple PPO was studied using chlorogenic acid as substrate, PFH acted as a noncompetitive inhibitor of apple PPO, with K_i = αK = 0.8 g/L, and IC₅₀ ranging 1.1-1.7 g/L. Cys showed an inhibitory pattern which could not be fitted to any type of reversible inhibition (IC₅₀ 0.02-0.03 g/L), while CAPE showed low inhibitory activity, which could be due to co-precipitation processes. PFH could be considered as an effective natural compound to reduce apple juice browning.     

Antioxidant properties of chlorophyll-enriched and chlorophyll-depleted polyphenolic fractions from leaves of Vernonia amygdalina and Gongronema latifolium

This study investigated the optimum polyphenol extraction conditions for two Nigerian green leafy vegetables, Vernonia amygdalina (VA) and Gongronema latifolium (GL) that are widely used for food and medicinal purposes. Seven different solvents were used to extract the total phenolic contents of the leaves; 100% acetone, 80% acetone, 50% acetone, 100% ethanol, 70% ethanol, 100% methanol and 70% methanol and their total phenolic contents were determined. The results showed that the 80% acetone was significantly (p < 0.05) the most effective for polyphenol extraction from the leaves and generally the acetone-containing solvents were more effective than alcohol-containing solvents. The 80% acetone extract was fractionated on a silicic acid-packed column to give two main fractions: acetone eluted chlorophyll-enriched (flow-through) and ethanol eluted chlorophyll-depleted (column-bound). The ethanol fractions of VA and GL were significantly better (p < 0.05) DPPH radical scavengers than the acetone fractions. In contrast, the acetone fraction was a significantly better (p < 0.05) scavenger of hydroxyl radicals when compared to the ethanol fraction. Both acetone and ethanol fractions significantly (p < 0.05) and dose-dependently inhibited linoleic acid oxidation, though duration of inhibition was less at lower concentrations (10 and 25 ??g/ml) than at the highest concentration (50 ??g/ml).     

Odor and taste thresholds of potential carry-over/off-flavor compounds in orange and apple juice

The odor and taste threshold values of six aroma substances known to be constituents of fruit juices and other fruit products, i.e. limonene, α-terpineol, carvone, methyl 2-methylbutanoate, ethyl 2-methylbutanoate, and γ-decalactone, were determined in various matrices, i.e. model sugar/acid solution, apple and orange juice, as well as apple and orange substitute (made by dilution of fruit juice concentrate with water). Whereas for α-terpineol thresholds in the 1.2-11 mg/l area were defined, limonene and carvone were determined to be sensorially effective each at 0.5 mg/l. Very low thresholds were measured for γ-decalactone, methyl 2-methylbutanoate and ethyl 2-methylbutanoate that showed sensory activity in the area of 20, 1.5, and 0.5 μg/l, respectively. In relation to the aroma composition determined by high resolution gas chromatography-mass spectrometry (HRGC-MS), these results provide an objective possibility to evaluate the sensory efficacy and/or an ‘off-flavor’ potential of these compounds in fruit juices.     

Evaluation of Penicillium expansum isolates for aggressiveness, growth and patulin accumulation in usual and less common fruit hosts

Experiments were carried out in vivo and in vitro with four isolates of Penicillium expansum (I 1, E 11, C 28 and I 12) to evaluate their aggressiveness, growth and patulin accumulation in both usual (pears and apples) and less common hosts (apricots, peaches, strawberries and kiwifruits) of the pathogen. The 75% of isolates showed the ability to cause blue mould in all tested hosts. In particular, C 28 and I 1 were the most and the least aggressive isolates, respectively (52.9 and 10.6% infection and 20.7 and 15.4 mm lesion diameters). ‘Candonga’ strawberries and ‘Pinkcot’ apricots showed the largest lesion diameters (29.8 and 25.3 mm), followed by ‘Conference’ pears, ‘Spring Crest’ peaches and ‘Abate Fetel’ pears. With the exception of ‘Candonga’ strawberries, the formation of colonies and mycelial growth of P. expansum isolates on fruit puree agar media (PAMs) was stimulated in comparison to a standard growth medium (malt extract agar, MEA). Two of the most aggressive isolates in our assays (I 12 and C 28) showed the greatest accumulation of patulin both in vitro and in vivo, while the least aggressive isolate (I 1) produced patulin only in a few growth media and cvs. Patulin concentration on fruit PAMs was higher than patulin detected in infected fruit tissues. Apple PAMs were the more favorable substrates for patulin accumulation in vitro (maximum concentration 173.1 and 74.1 μg/mL in ‘Pink Lady and ‘Golden Delicious’ PAMs, respectively) and ‘Pink Lady’ apples inoculated with the isolate E 11 showed the greatest accumulation of patulin in the whole in vivo assay (33.9 μg/mL). However, infected tissue of cv Golden Delicious showed lower average accumulation of patulin (1.7 μg/mL) than that of cv Pink Lady (19.1 μg/mL), and no significant differences in patulin concentrations were found among ‘Golden Delicious’ apples and tested cvs of pears, kiwifruits and strawberries. Peaches were highly susceptible to patulin accumulation, showing average concentrations of 27.4 and 18.6 μg/mL in vitro and in vivo, respectively. Apricots were also consistently positive for patulin accumulation, both in vitro (average values of 20.1 μg/mL) and in vivo (average values of 9.4 μg/mL). Our study showed the potential of some less common hosts of P. expansum (in particular peaches and apricots) to support patulin production, indicating that a steady monitoring of patulin contamination should be carried out in fruit substrates other than apples and pears.     

Dual inhibitions of lemon balm (<Emphasis Type="Italic">Melissa officinalis</Emphasis>) ethanolic extract on melanogenesis in B16-F1 murine melanocytes: Inhibition of tyrosinase activity and its gene expression

The effects of wild type and UV-irradiated lemon balm (Melissa officinalis) ethanolic extracts (MOE and UMOE) on melanogenesis in vitro were examined. UMOE showed potent antioxidant activity and significantly inhibited the mushroom and melanocyte tyrosinase activity, and lowered cellular melanin content by 49% at 200 μg/mL in B16-F1 melanocytes. The key gene and protein expression of tyrosinase, tyrosinase-related protein (TRP)-1, and TRP-2 were reduced (−73% for TRP-1 protein at 200 μg/mL UMOE, p<0.05). MOE showed similar results to a slightly lesser degree. We found that myo-inositol, a major compound in lemon balm extracts, significantly reduced cellular melanin synthesis and its effect was greater than arbutin at 1 mM. These suggest that both MOE and UMOE have anti-melanogenic role by both direct inhibition of tyrosinase and down-regulation of gene expressions in melanogenesis. UV-irradiation slightly improved the anti-melanogenic activities. UMOE may be useful as natural anti-melanogenic biomaterials for functional foods and cosmetics.     

Factors affecting growth of foodborne pathogens on minimally processed apples

Escherichia coli O157:H7, Salmonella and Listeria innocua increased by more than 2 log₁₀ units over a 24 h period on fresh-cut ‘Golden Delicious’ apple plugs stored at 25 and 20 °C. L. innocua reached the same final population level at 10 °C meanwhile E. coli and Salmonella only increased 1.3 log₁₀ units after 6 days. Only L. innocua was able to grow at 5 °C. No significant differences were observed between the growth of foodborne pathogens on fresh-cut ‘Golden Delicious’, ‘Granny Smith’ and ‘Shampion’ apples stored at 25 and 5 °C. The treatment of ‘Golden Delicious’ and ‘Granny Smith’ apple plugs with the antioxidants, ascorbic acid (2%) and NatureSeal^® (6%), did not affect pathogen growth. The effect of passive modified atmosphere packaging (MAP) on the growth of E. coli, Salmonella and L. innocua on ‘Golden Delicious’ apple slices was also tested. There were no significant differences in growth of pathogens in MAP conditions compared with air packaging of ‘Golden Delicious’ apple plugs, but the growth of mesophilic and psychrotrophic microorganisms was inhibited. These results highlight the importance of avoiding contamination of fresh-cut fruit with foodborne pathogens and the maintenance of the cold chain during storage until consumption.     

Probiotic beverage from cashew apple juice fermented with Lactobacillus casei

This study optimized the conditions of Lactobacillus casei NRRL B-442 cultivation in cashew apple juice, as well as, determined the proper inoculum amount and fermentation time. Moreover, it was investigated the survivability ability of L. casei in cashew apple juice during refrigerated storage (4 °C) for 42 days. The optimum conditions for probiotic cashew apple juice production were initial pH 6.4, fermentation temperature of 30 °C, inoculation level of 7.48 Log CFU/mL (L. casei) and 16 h of fermentation process. It was observed that the L. casei grew during the refrigerated storage. Viable cell counts were higher than 8.00 Log CFU/mL throughout the storage period (42 days). The values of lightness, yellowness and total color change increased and the values of redness reduced along the fermentation and refrigerated storage periods. The fermented juice with L. casei is a good and healthy alternative functional food containing probiotics. Cashew apple juice showed to be as efficient as dairy products for L. casei growth.     

Inhibitory effects of chestnut inner skin extracts on melanogenesis

Antioxidant capacities (ABTS radical scavenging assay and ferric reducing/antioxidant power assay), mushroom tyrosinase inhibitory effect, and α-melanocyte stimulating hormone (α-MSH) induced melanogenesis inhibitory effect of 60% methanol extracts and ethylacetate fractions from chestnut inner skin in B16F10 cells were investigated to inspect whitening effect. Above research showed that 60% methanol extracts and ethylacetate fractions from chestnut inner skin resulted in a dose-dependent manner on in vitro antioxidant effects. Especially, the ethylacetate fractions inhibited enzyme activity of mushroom tyrosinases with an IC₅₀ value of 160 μg/mL. Ethylacetate fractions from chestnut inner skin also decreased cellular melanin synthesis in B16F10 melanoma cells. Expression of tyrosinase showed that ethylacetate fractions from chestnut inner skin significantly decreased cellular melanogenesis. Consequently, these results suggest that chestnut inner skin extracts can be considered for a whitening agent of human skin.     

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.     

Enzymatic Browning Inhibited in Fresh and Dried Apple Rings by Pineapple Juice

Sliced apple rings were treated with water (control), canned pineapple juice, frozen pineapple juice, ion-exchanged pineapple juice, frozen orange juice, ascorbic acid, a commercial antibrowning preparation or sodium bisulfite. The rings were either left exposed to air, vacuum packaged, or dehydrated. Browning was measured calorimetrically and by visual examination over extended periods of time. Pineapple juice was an effective browning inhibitor in both fresh and dried apples. Pineapple juice was fractionated using various size and charge separation procedures. All fractions inhibited enzymatic browning of crude apple extracts by at least 26%. Results indicate that the inhibitor is a neutral compound of low molecular weight.     

Rhubarb Juice as a Natural Antibrowning Agent

To search for natural antibrowning agents, rhubarb juice was tested on fresh‐cut apple slices and found to have a potent effect. Liberty apple slices were treated in various concentrations of rhubarb juice (5%–100%), and the rate of discoloration at room temperature was measured by a Hunter Colorimeter. Apple slices treated in the 5%– 10% solution showed browning activity with dL values of 2.3 – 2.5 at two hours. However, the concentrations of rhubarb juice above 20% inhibited apple browning effectively with no change in the L value for several hours. Analysis of oxalic acid in rhubarb juice showed that the 20% solution contained about 67 mg/100g.     

Prebiotic effect of fermented cashew apple (Anacardium occidentale L) juice

Leuconostc mesenteroides B-512F and L. mesenteroides B-742 were cultivated in clarified cashew apple juice to produce prebiotic oligosaccharides. Yeast extract (20 g/L); K₂HPO₄ (g/L) and sucrose (50 g/L) were added to the juice to promote the microbial growth and dextransucrase production. Initial pH was adjusted to 6.5 with H₃PO₄. Fermentations were carried out at 30 °C and 150 rpm for 24 h. The prebiotic effect of the fermented cashew apple juice, containing oligosaccharides, was evaluated through the Lactobacillus johnsonii B-2178 growth. L. johnsonii was incubated for 48 h using fermented cashew apple juice as substrate. Lactobacillus growth was compared to the microbial growth in non-fermented juice and in MRS broth. L. johnsonii growth in the fermented cashew apple juice was threefolds the observed growth in the non-fermented juice.