Citrus phenylpropanoids and defence against pathogens. Part II: Gene expression and metabolite accumulation in the response of fruits to Penicillium digitatum infection

The effect of infection of Citrus sinensis (var. Navelina) fruits with Penicillium digitatum was studied at gene expression and metabolite levels. In this study, expression of genes involved in the phenylpropanoid pathway was studied in the flavedo (outer coloured part of the peel) and albedo (inner white part) in response to pathogen infection. Results of the time-course experiment showed that maximal expression of 10 out of 17 phenylpropanoid genes analysed occurred at 48 h post-inoculation, when decay symptoms started to appear, and mRNA levels either kept constant or decreased after 72 h post-inoculation. To further investigate the putative involvement of the phenylpropanoid pathway in the defence of citrus fruit, changes in the metabolic profile of both tissues infected with P. digitatum was studied by means of HPLC-PDA-FD. Metabolite accumulation levels along the time course suggest that flavanones, flavones, polymethoxylated flavones and scoparone are induced in citrus fruit in response to P. digitatum infection, although with different trends depending on the tissue.     

蜂胶提取物处理对柑橘诱导抗病性的影响

以柑橘为材料,对蜂胶提取物诱导柑橘抗青霉病的表达时间以及蜂胶提取物处理对柑橘果实抗病性相关物质及酶的影响进行研究。结果显示,蜂胶提取物处理后48h 人工接种意大利青霉,柑橘所表现出的抗病性最强。蜂胶提取物处理增加了柑橘果皮中酚类物质的含量,提高了柑橘果皮中苯丙氨酸解氨酶(PAL)、过氧化物酶(POD)、多酚氧化酶(PPO)、几丁质酶(CHT)与诱导抗病性密切相关的酶的活性。这表明蜂胶提取物可增强柑橘果实的防御系统,降低果实贮藏期间的发病率,对柑橘表现出良好的保鲜效果。     

Phenolics, betacyanins and antioxidant activity in Opuntia joconostle fruits

Sour prickly pears (xoconostles) are fruits from Opuntia joconostle cactus, which are cultivated in the central Mexico area. Phenolic and pigment content in various parts of O. joconostle fruits were analyzed. The antioxidant activity of a methanolic extraction and different semi-purified fractions were also evaluated by the DPPH⁺ method. Xoconostle fruits were obtained from a commercial orchard in Mexico State. Fruits were analyzed as whole fruit and each fruit part including pericarp, mesocarp and endocarp. Samples were homogenized and kept at 4 °C until sample preparation. Total phenolic content and total flavonoid content varied among the different parts of the fruit. The highest amount of phenolic compounds and total flavonoids content were found in pericarp 2.07 mg gallic acid equivalents (GAE)/g fresh weight (FW) and 0.46 mg(+)-catechin equivalents (CE)/g FW respectively. Seven phenolics were identified as protocatechuic, 4-hydroxybenzoic, caffeic, vanillic and syringic acids, rutin, and quercetin. The color of the fruit parts was mainly due to the presence of betacyanins. The betacyanin concentration was higher in the endocarp (23.03 mg betanin equivalents/100 g fresh weight) than in the pericarp and mesocarp. Betacyanins were identified by HPLC-PDA-MS as betanin, isobetanin, betanidin, isobetanidin, and phyllocactin. Methanolic extracts and semi-purified fractions A (phenolics and flavonols) and B (betacyanins) of xoconostle showed high antioxidant activity mainly in the pericarp. These results suggest that xoconostle is a rich source of antioxidant compounds such as phenolic compounds and betacyanins.     

Discrimination of citrus fruits using FT-IR fingerprinting by quantitative prediction of bioactive compounds

High throughput screening of citrus samples containing elevated concentrations of total carotenoids, flavonoids, and phenolic compounds was accomplished using ultraviolet–visible spectroscopy and Fourier transform infrared (FT-IR) spectroscopy, combined with multivariate analysis. Principal component analysis and partial least squares discriminant analysis using FT-IR spectra were able to differentiate seven citrus fruit groups into three distinct clusters corresponding to their taxonomic relationship. Quantitative prediction modeling of total carotenoids, flavonoids, and phenolic compounds in citrus fruit was established using a partial least squares regression algorithm from the FT-IR spectra. The regression coefficients (R ²) of predicted and estimated values of total carotenoids, flavonoids, and phenolic compounds were all 0.99. The results indicated that accurate quantitative predictions of total carotenoids, flavonoids, and phenolic compounds were possible from citrus fruit FT-IR spectra, and that the resulting quantitative prediction model might be useful as a rapid selection tool for citrus fruits containing elevated carotenoids, flavonoids, and phenolic compounds.     

Antioxidant capacity and hydrophilic phytochemicals in commercially grown native Australian fruits

Hydrophilic phytochemicals and antioxidant capacities of eight commercially grown native Australian fruits were determined. Kakadu plum (Terminalia ferdinandiana) contained a 6-fold higher level of total phenolic compounds and quandong (Santalum acuminatum) a 1.9-fold higher level of total phenolic compounds (TP, Folin–Ciocalteu assay) than blueberry (Vaccinum sp., cv. Biloxi). Both fruits displayed superior oxygen radical-scavenging capacity (ORAC-H assay) that was, respectively 4.1-fold and 6.5-fold of that of blueberry. The total reducing capacity (TRC; ferric reducing antioxidant power (FRAP) assay) of Kakadu plum and quandong exceeded the TRC of blueberry, respectively, 13.1- and 2.3-times. The primary sources of antioxidant capacities in the evaluated fruits were phenolic acids (benzoic and cinnamic) and flavonoids (flavonols, flavanones and anthocyanins) tentatively detected by liquid chromatography–mass spectrometry (LC–PDA–MS/MS). A high level of vitamin C was recorded for Kakadu plum and Australian citrus fruits. The major organic acids detected were citric and malic acid.     

Prevalence, concentration, spoilage, and mitigation of Alicyclobacillus spp. in tropical and subtropical fruit juice concentrates

The presence of Alicyclobacillus in fruit juices and concentrates poses a serious problem for the juice industry. This study was undertaken to determine the (i) prevalence, concentration, and species of Alicyclobacillus in tropical and subtropical concentrates; (ii) efficacy of aqueous chlorine dioxide in reducing Alicyclobacillus spp. spores on tropical and subtropical fruit surfaces; and (iii) fate of and off-flavor production by Alicyclobacillus acidoterrestris in mango and pineapple juices. One hundred and eighty tropical and subtropical juice concentrates were screened for the presence and concentration of Alicyclobacillus spp. If found, the species of Alicyclobacillus was determined by 16S rDNA sequencing and analysis with NCI BLAST. Of these samples, 6.1% were positive for Alicyclobacillus, and nine A. acidoterrestris strains and two Alicyclobacillus acidocaldarius strains were identified. A five-strain cocktail of Alicyclobacillus spp. was inoculated onto the surface of fruits (grapefruit, guava, limes, mangoes, oranges and pineapple), which were then washed with 0, 50, or 100 ppm aqueous chlorine dioxide. Significant reductions due to chlorine dioxide were only seen on citrus fruits. A five-strain cocktail of A. acidoterrestris was inoculated into mango and pineapple juices. Microbial populations were enumerated over a 16-day period. Aroma compounds in the juice were analyzed by GC-olfactometry (GC-O) and confirmed using GC-MS. GC-O of mango juice identified previously reported medicinal/antiseptic compounds. GC-O of pineapple juice revealed an unexpected “cheese” off-aroma associated with 2-methylbutyric acid and 3-methylbutyric acid.     

数字图像处理技术结合偏最小二乘法定量分析柑橘质量

目的：构建柑橘质量模型,实现其计算机视觉法质量检测与在线分级。方法：以湖南湘中成熟中期涟红温州蜜柑为研究对象,对计算机视觉系统采集的各柑橘的4 幅图像进行图像裁切、图像去背景、图像二值化与取反操作后,提取柑橘区域像素,以柑橘区域像素与图像像素比为自变量,建立柑橘质量偏最小二乘回归(PLS)预测模型。结果：柑橘质量预测绝对误差为－ 14.9092～4.9981g,平均误差为－ 3.9278g,误差标准差4.5210g,± 10g 质量内的正确识别率为93.3333%,± 8g 质量内正确识别率76.6667%。结论：通过计算机视觉技术进行柑橘质量在线分级和生长期中挂果质量的监测是可行的。     

History,Global Distribution,and Nutritional Importance of Citrus Fruits

Abstract: Although the mysteries of its history and origin remain unsolved, worldwide cultivation and high‐demand production for citrus fruit (genus Citrus in family Rutaceae) make it stand high among fruit crops. Growth of the citrus industry, including rapid development of the processing technology of frozen concentrated orange juice after World War II, has greatly expanded with international trade and steadily increased consumption of citrus fruits and their products during the past several decades. Characterized by the distinct aroma and delicious taste, citrus fruits have been recognized as an important food and integrated as part of our daily diet, playing key roles in supplying energy and nutrients and in health promotion. With low protein and very little fat content, citrus fruits supply mainly carbohydrates, such as sucrose, glucose, and fructose. Fresh citrus fruits are also a good source of dietary fiber, which is associated with gastrointestinal disease prevention and lowered circulating cholesterol. In addition to vitamin C, which is the most abundant nutrient, the fruits are a source of B vitamins (thiamin, pyridoxine, niacin, riboflavin, pantothenic acid, and folate), and contribute phytochemicals such as carotenoids, flavonoids, and limonoids. These biological constituents are of vital importance in human health improvement due to their antioxidant properties, ability to be converted to vitamin A (for example, β‐cryptoxanthin), and purported protection from various chronic diseases.     

Variations in essential oil and fatty acid composition during Myrtus communis var. italica fruit maturation

The essential oil and fatty acid composition of Myrtus communis var. italica fruit during its ripening was determined. The effect of the harvesting time on some physical properties of Myrtus fruits, fruit weight and moisture content, were significant. The increase of fruit weight (from 2.54 to 8.79 g% fruits) during ripeness was correlated positively with that of moisture content (from 28% to 72%). Fruit essential oil yields varied from 0.003% to 0.01% and showed a remarkable increase at 60 days after flowering to reach a maximum of 0.11%. Forty-seven volatile compounds were identified in fruit essential oils; 1,8-cineole (7.31–40.99%), geranyl acetate (1.83–20.54%), linalool (0.74–18.92%) and α-pinene (1.24–12.64%) were the main monoterpene compounds. Total fatty acid contents varied from 0.81% to 3.10% during fruit maturation and the predominant fatty acids were linoleic (12.21–71.34%), palmitic (13.58–37.07%) and oleic (6.49–21.89%) acids. The linoleic acid proportions correlated inversely with palmitic and oleic acids during all the stages of ripening.     

Phytochemical and antioxidant characterization of mamey (Pouteria sapota Jacq. H.E. Moore & Stearn) fruit

Phytochemical compounds in fruits and vegetables have gained great importance in the last few years because of the increasing evidence suggesting their antioxidant and prevention of chronic diseases. Carotenoids, phenolics, flavonoids, and vitamins E and C, are among these phytochemicals. Several fruits have been characterized so far for their antioxidant and health properties but there is still limited information on fruits from the tropic. Therefore, the objective of this study was the characterization of mamey fruit (Pouteria sapota Jacq. H. E. Moore & Stearn) with regard to their antioxidant capacity and phytochemical profile. Phenolics, carotenoids and ??-tocopherol were quantified and identified by HPLC-DAD-Mass Spectrometry (LC-MS), and DPPH and FRAP assays were used to evaluate antioxidant capacity. Hydrophilic extracts of mamey fruit showed higher antioxidant capacity than the lipophilic portion. Total soluble phenols content was 28.5 mg GAE/100 g fw, being p-hydroxybenzoic acid as the main phenolic that was identified. Total carotenoid content was 1127.9 ??g ??-carotene/100 g fw with ??-carotene being the main contributor, in addition to lutein, and violoxanthin. Concentration of ??-tocopherol was 360.0 ??g/100 g fw. Results of this study suggest that mamey fruit is a good source of carotenoids and its inclusion in the diet is recommended.     

Electrical Properties of Garut Citrus Fruits at Low Alternating Current Signal and its Correlation with Physicochemical Properties During Maturation

In this research, local citrus fruits, namely Garut citrus, were analyzed for electrical properties related to physicochemical properties. Electrical measurement on fruit was done by using low alternating current with a frequency varying from 50 Hz to 1 MHz. The fruits are placed between two plate electrodes and treated as dielectric material. Electrical parameters per unit of weight were used in this study to compensate variations in weight. Electrical impedance, resistance, and reactance per weight of citrus fruits will decrease if the frequency is increased. Electrical circuit models have been constructed to describe the internal conditions of citrus fruits. To indicate the fruit maturity, the physicochemical properties were used, i.e., firmness, total soluble solids, pH, and hydrogen ion concentration. The value of resistance, impedance, and reactance per weight declined during citrus fruits maturation. The correlations between electrical and physicochemical properties are investigated too. The highest consistency of correlations happens at a frequency of 1 MHz. Based on the model of an electrical circuit, the highest value of electrical resistance is outer shell and the lowest is seed. And then, the highest value of electrical capacitance is albedo and the lowest is segment. Resistance values of the parts of citrus fruits, i.e., seed, segment, segment wall, and outer shell, were decreased during maturation. While capacitance value of segment, albedo, and flavedo were increased.     

Phytochemical and antioxidant characterization of the fruit of black sapote (Diospyros digyna Jacq.)

Consumption of fruits and vegetables has been associated with a healthy state which has been attributed, in part, to their antioxidant capacity. Characterization of the bioactive compounds with antioxidant activity found in fruits cultivated in the tropic is limited. Thus, the objective of the present work was the characterization of phytochemicals and antioxidants of the fruit of black sapote (Diospyros digyna Jacq.). HPLC-DAD-Mass Spectrometry (HPLC-MS) analyses were used to identify and quantify phenolics, carotenoids and tocopherols. Total soluble phenolic content was 247.8 mg GAE/100 g fw (fresh weight). Important phenolics identified were sinapic acid, myricetin, ferulic acid, and catechin. Total carotenoid content was 399.4 ??g of ??-carotene/100 g fw, and ??-carotene and lutein were the main carotenoids identified. ??-Tocopherol concentration was 672.0 ??g/100 g dry weight. Antioxidant capacity as measured by the DPPH and FRAP assays was higher in the hydrophilic than in the lipophilic extract, and it is thought to be due mainly to the phenolic content of this fruit. Results suggest that the fruit of black sapote has an antioxidant capacity comparable to other important fruits, and its inclusion in the diet is therefore recommended.     

Antiradical activity of different parts of Walnut (Juglans regia L.) fruit as a function of genotype

The objective of this work was to analyse phenolic compounds and antiradical capacity of different parts of walnut fruit among six genotypes of Juglans regia L. Therefore, total phenolic and flavonoid content were determined and methanolic extracts of walnut genotypes were considered by the reducing power, DPPH (2,2-diphenyl-1-picrylhydrazyl), superoxide anion and nitric oxide radical scavenging. Significant differences were found in phenolic content and radical scavenging capacity of different parts of fruits and among various genotypes. High correlation coefficient (R² = 0.81) was observed between phenol content and radical scavenging activity, but this was not always true (R² = 0.01). These results demonstrated that walnut genotypes have different phenolic compounds and phenolic compounds have different radical scavenging power. The differences of phenolic compounds were confirmed by using high performance liquid chromatography (HPLC).     

ATP-regulation of antioxidant properties and phenolics in litchi fruit during browning and pathogen infection process

The impact of energy level on antioxidant properties in relation to pericarp browning and loss of disease resistance of litchi fruit was investigated. Litchi fruits were vacuum-infiltrated with distiled water (control), 1 mM adenosine triphosphate (ATP) and 0.5 mM 2,4-dinitrophenol (DNP) under 75 kPa for 3 min before being inoculated with Peronophythora litchi or not. ATP-treated fruits presented higher activities of antioxidant enzymes, including catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidase (APX). Higher activities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging, reducing power and contents of phenolic compounds were also observed in ATP-treated fruit during storage. In contrast, DNP treatment lowered the enzymes activities, scavenging ability and the contents of phenolic compounds. Higher levels of antioxidant enzymatic system and non-enzymatic system were observed in P. litchii-inoculated fruits than those in non-inoculated fruits. Application of ATP and DNP exhibited a similar change patterns and effects in inoculated fruits. When related to previously reported ATP levels, the results suggested that ATP levels could regulate the antioxidant system. Sufficient available energy is crucial for inhibiting browning and preventing the loss of disease resistance in harvested litchi fruit.     

Control of citrus green and blue molds by Chinese propolis

Green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, are economically important postharvest diseases of citrus fruits. In this study, Chinese propolis ethyl acetate extract (PEAE) was evaluated to control P. digitatum and P. italicum on postharvest citrus fruits. The results indicated PEAE strongly inhibited mycelia growth and induced hyphae prominent abnormal morphological alterations. Also, PEAE had strong detrimental effect on spore germination of the tested pathogens in a concentrationdependent manner. For in vivo tests, PEAE could both reduce decay caused by P. digitatum and P. italicum respectively in wound-inoculated fruit and naturally infected fruit; meanwhile, no negative influences on the overall quality of the citrus fruits were observed with PEAE treatment. Therefore, PEAE could be used as a natural antifungal agent to control citrus blue and green mold.     

Estimating volume and mass of citrus fruits by image processing technique

An image processing based technique was developed to measure volume and mass of citrus fruits such as lemons, limes, oranges, and tangerines. The technique uses two cameras to give perpendicular views of the fruit. An efficient algorithm was designed and implemented in Visual Basic (VB) language. The product volume was calculated by dividing the fruit image into a number of elementary elliptical frustums. The volume is calculated as the sum of the volumes of individual frustums using VB. The volumes computed showed good agreement with the actual volumes determined by water displacement method. The coefficient of determination (R²) for lemon, lime, orange, and tangerine were 0.962, 0.970, 0.985, and 0.959, respectively. The Bland–Altman 95% limits of agreement for comparison of volumes with the two methods were (−1.62; 1.74), (−7.20; 7.57), (−6.54; 6.84), and (−4.83; 6.15), respectively. The results indicated citrus fruit’s size has no effect on the accuracy of computed volume. The characterization results for various citrus fruits showed that the volume and mass are highly correlated. Hence, a simple procedure based on computed volume of assumed ellipsoidal shape was also proposed for estimating mass of citrus fruits. This information can be used to design and develop sizing systems.     

Identification of cytotoxic sesquiterpenes from Laurus nobilis L.

A new sesquiterpene, lauroxepine and six known sesquiterpene lactones, were obtained through bioactivity-directed isolation from a methanol extract of the fruits of Laurus nobilis. The hexane-soluble part of the methanol extract yielded lauroxepine, costunolide and gazaniolide, while the dichloromethane-soluble part of the methanol extract afforded costunolide and four other sesquiterpene lactones including santamarine, reynosin, 11,13-dehydrosantonin and spirafolide. The new sesquiterpene lauroxepine and spirafolide have a rare molecular structure carrying an oxepine ring. Structures of the compounds were determined through 1D and 2D NMR and mass (EI-MS) techniques. The extracts were investigated for both ovarian cytotoxic activity and DNA damaging properties against three yeasts. Among the three tested extracts prepared from flowers, leaves and fruits of L. nobilis, the most cytotoxic active extract against ovarian cancer cell line was found to be the fruit extract with 98% inhibition. Among all tested extracts, only the fruit extract showed marginal inhibition (63.2%) against one DNA repair-deficient yeast strain (pRAD52 Gal). Six known sesquiterpene lactones were found to be highly cytotoxic against the A2780 ovarian cancer cell line, however, lauroxepine was not found to be active in A2780.     

Modifications of taste-relevant compounds in strawberry fruit under NaCl salinity

Two strawberry (Fragaria × ananassa Duch.) cultivars differing in their sensitivity to NaCl stress, cv. Elsanta (sensitive) and cv. Korona (less sensitive), were cultivated under 0, 40 and 80 mmol NaCl/l for two months during flowering and fruiting until final fruit harvest. Modifications of sensory quality parameters and selected chemical properties of the non-climacteric fruit were evaluated. Generally, NaCl salinity decreased quality of strawberry fruit, especially in cv. Elsanta. Fruits of stressed plants contained lower amounts of sugars, organic acids and soluble solids, were less sweet and did not meet consumers’ requirements. Overall appearance of fruits decreased significantly. The reduced acceptance to consumers was closely correlated with the decline of sugar contents, especially sucrose content, as well as with the increase of organic acids, such as acetic acid. Sensory changes were revised on the basis of a dose to threshold relationship. Decreasing contributions of sugars to taste and a rising importance of sodium, acetic and citric acids as the most taste-relevant compounds were the main causes of the limited acceptance of salt-stressed fruits.     

Carotenoid content and expression of phytoene synthase and phytoene desaturase genes in bitter melon (Momordica charantia)

Momordica charantia, a tropical plant, produces a fruit that has a β-carotene concentration five times higher than that of carrot. To elucidate the molecular basis of β-carotene accumulation in M. charantia, the gene expression levels of phytoene synthase (McPSY) and phytoene desaturase (McPDS) were determined. These levels were particularly high in the flowers of M. charantia. During fruit maturation, the expression levels of McPSY and McPDS decreased during the mid-stages but increased in the fully mature fruit. In addition, carotenoids accumulated as the peel changed from green to orange. Thus, McPSY and McPDS expression correlated with carotenoid accumulation during fruit maturation. Principal component analysis (PCA) also was used to evaluate the differences among the profiles of seven carotenoids identified in the fruit at several maturation stages. Riper fruits had higher carotenoid concentrations than less ripe fruits.     

Biochemical monitoring of black raspberry (Rubus coreanus Miquel) fruits according to maturation stage by H NMR using multiple solvent systems

Nuclear magnetic resonance (NMR) techniques coupled with multivariate data analysis were used to conduct monitoring of biochemical changes of black raspberry fruits at different stages of maturation and under various extraction and NMR dissolution solvent conditions: extraction with 50% methanol and D₂O as an NMR dissolution solvent, extraction with 50% methanol and 50% methanol-d₄ as an NMR dissolution solvent, and extraction with 100% ethyl acetate and 100% methanol-d₄ as an NMR dissolution solvent. Partial least-squares discriminant analysis reliably distinguished black raspberry fruits according to the maturation stage, whereby the relative levels of various compounds such as amino acids, organic acids, sugars and phenolic compounds were compared using analysis of variance. Sucrose and most of the amino acids, and organic acids decreased, whereas fructose, glucose, and cyanidins increased in relative concentration according to maturation of black raspberry fruits. The total number and kinds of assigned compounds of the three solvent systems were also compared. This research demonstrates that the metabolic profile of black raspberry fruits changes during maturation, and provides objective criteria for determining the stage of black raspberry fruit maturation via a ¹H NMR-based metabolomics technique using multiple solvent systems.